Evidence that cortisol inhibits basal adrenocorticotropin secretion in the sheep fetus by 0.70 gestation

To ascertain if reductions in fetal plasma cortisol cause increases in fetal plasma ACTH, we treated pregnant ewes or their fetuses with aminoglutethimide (10 mg/kg BW) and metyrapone (20 mg/kg BW) and measured the hormonal responses with RIAs. When given to fetuses (n = 9) at 0.90 +/- 0.01 gestation (term-145 days), the steroid synthesis inhibitors reduced fetal plasma cortisol from 35.1 +/- 11.9 to 18.5 +/- 6.2 ng/ml (P less than 0.01) and plasma ACTH increased from 37 +/- 7 to 189 +/- 74 pg/ml (P less than 0.02). Thus, late in gestation cortisol from the fetal adrenal suppresses basal fetal ACTH secretion. Blockade of steroid biosynthesis in pregnant ewes carrying intact fetuses at 0.76 +/- 0.02 gestation (n = 11) or adrenalectomized fetuses at 0.81 +/- 0.01 gestation (n = 6) also reduced cortisol and increased ACTH in fetal plasma. In intact fetuses cortisol declined from 9.4 +/- 2.0 to 3.6 +/- 0.9 ng/ml (P less than 0.05), and ACTH increased from 46 +/- 8 to 183 +/- 67 (P less than 0.01); cortisol declined in adrenalectomized fetuses from 2.1 +/- 0.4 to 1.1 +/- 0.3 ng/ml (P less than 0.01), and ACTH increased from 106 +/- 13 to 400 +/- 104 pg/ml (P less than 0.01). Cortisol infusions into intact and adrenalectomized fetuses prevented both the decline in steroid concentration caused by the biosynthesis inhibitors given to the ewe and the increase in fetal plasma ACTH concentration. These data indicate that reductions in plasma cortisol in adrenalectomized fetuses or intact fetuses at a time in development when the fetal adrenal produces little cortisol cause compensatory increases in fetal plasma ACTH concentration. The simplest explanation for these observations is that from approximately 0.70 gestation, basal fetal ACTH secretion is tonically inhibited by cortisol circulating in fetal plasma. This cortisol can originate from sources other than the fetal adrenal.     

Dissociation of pulsatile cortisol and adrenocorticotropin secretion in fetal sheep during late gestation.

In the fetal sheep, plasma cortisol concentrations gradually increase in the last weeks of gestation and abruptly rise during the final 48-72 h preceding birth. To determine if these changes in mean circulating cortisol concentrations result from increased pulsatile secretion and are driven by changes in ACTH pulses, blood samples from five chronically catheterized fetuses were collected every 5 min for 2 h at 133 days gestation and every 4 days thereafter until delivery at 146 +/- 2 days. Volume was replaced after each blood sample and erythrocytes were returned every 20 min. Plasma cortisol and ACTH secretion were pulsatile in fetuses at all ages. Cortisol pulse frequency increased significantly with gestation from a mean of 2.2 pulses/2 h at 133 days to 4.8 pulses/2 h at 146 days. The interpulse interval (mean +/- SE) decreased between 133 and 146 days from 54 +/- 11 min to 23 +/- 3 min, respectively. Cortisol pulse amplitude increased significantly from 10 +/- 2 ng/ml at 133 days to 44 +/- 13 ng/ml at 146 days. In contrast to cortisol, ACTH pulse frequency (3 +/- 0.6 pulses/2 h) and amplitude (21 +/- 3 pg/ml) were similar at 133 days and 146 days. The coincidence of cortisol and ACTH pulses did not change between 133 and 146 days. Furthermore, the number of coincident pulses failed to exceed random associations (hypergeometric probability analysis) and could have occurred by chance alone (P values ranged from 0.11-0.63). A point by point comparison of cortisol and ACTH concentrations in fetal circulation indicate that only 36% of the variance in cortisol concentrations could be explained by variance in ACTH (cross-correlation analysis). These data suggest that fetal cortisol and ACTH secretion are pulsatile and that, as gestation advances, increases in constitutive cortisol pulse amplitude and frequency may not be predominantly driven by pulsatile changes in ACTH in the ovine fetal circulation near term.     

Synergism between systemic corticotropin-releasing factor and arginine vasopressin on adrenocorticotropin release in vivo varies as a function of gestational age in the ovine fetus

In sheep, parturition is associated with maturation of fetal pituitary-adrenal function, and with rises in the concentrations of ACTH and cortisol (F) in fetal plasma. We examined the hypothesis that pituitary ACTH output in response to arginine vasopressin (AVP) and CRF separately and together might change during late pregnancy as a function of fetal age. Fetal sheep were chronically catheterized, and bolus iv injections of equimolar AVP, CRF, AVP plus CRF, or saline (controls) were given on days 110-115, 125-130, and 135-140 of gestation. AVP evoked significant rises in plasma ACTH on days 110-115 and 125-130, but not on days 135-140. After AVP, the peak plasma concentrations of ACTH were attained at 5-10 min, and basal (preinjection) values were reestablished by 30-60 min. After CRF treatment, plasma ACTH rose progressively throughout the 240 min of the study. Evidence was obtained in support of an increase in pituitary responsiveness to CRF between days 110-115 and 125-130 and a decrease in response on days 135-140, when basal F concentrations were higher. The ACTH response to AVP, relative to that to CRF, was greatest in the youngest fetuses. On days 110-115 only, CRF and AVP showed a synergistic response in ACTH output, especially during the first 30 min after agonist injection. Plasma F rose in response to the changes in endogenously released ACTH in a manner consistent with progressive fetal adrenal maturation between days 110-140 of pregnancy. We conclude that in vivo the ovine fetal pituitary responds separately and synergistically to AVP and CRF on days 110-115 of gestation, but the relative role of AVP in stimulating ACTH release decreases with progressive gestational age.     

Responsivity of the baboon fetal pituitary to corticotropin-releasing hormone in utero at midgestation.

The present study was designed to determine whether the baboon fetal pituitary at midgestation was responsive in utero to a bolus injection of CRH. On day 100 of gestation (term = day 184), baboons were anesthetized with halothane/nitrous oxide, the fetus was exteriorized, and a cannula was inserted into a fetal carotid artery. Five minutes later (experimental time zero), a fetal carotid blood sample was obtained, and saline (0.5 ml) with (n = 6) or without (n = 3) ovine CRH (100 ng estimated to equal 500 ng/kg BW) was then infused via the fetal carotid over a 3-min period. Fetal blood samples were taken 5, 15, 30, 45, and 60 min post-CRH/saline treatment and assayed for ACTH. Mean (+/- SE) pretreatment fetal plasma ACTH concentrations were similar in animals that subsequently received saline (26 +/- 3 pg/ml) or CRH (29 +/- 6 pg/ml). Fetal plasma ACTH remained constant after the infusion of saline. In contrast, CRH increased (P less than 0.05) fetal plasma ACTH within 5 min in six of six baboons to a value (58 +/- 12 pg/ml) that exceeded (P less than 0.05) the zero time value and the respective mean value (27 +/- 5 pg/ml) in saline-treated fetuses. Fetal plasma ACTH concentrations continued to rise in four of six baboons 15 min after CRH injection to a level (68 +/- 15 pg/ml) which exceeded that in saline controls (27 +/- 2 pg/ml). In fetuses treated with CRH, overall mean fetal plasma ACTH concentrations from 0-60 min increased at a rate (1.47 pg/min) greater (P less than 0.05) than that in fetuses injected with saline (0.07 pg/min). In contrast to the effects of intracarotid CRH injection, fetal plasma ACTH was not increased after the infusion of 100 ng CRH into a fetal antecubital vein of three additional animals. Collectively, these findings indicate that intracarotid injection of a bolus of CRH into the baboon fetus rapidly increased fetal plasma ACTH concentrations. Moreover, the site of action of CRH was presumably the fetal pituitary. Therefore, we suggest that the baboon fetal hypothalamic-pituitary axis at midgestation has the capacity to secrete ACTH in response to a challenge of CRH.     

Androstenedione metabolism in the late gestation sheep fetus

We have determined metabolic parameters for androstenedione (A) in chronically catheterized late gestation (day 130) sheep fetuses. The MCR (MCRA) was 3210 +/- 229 (SEM, n = 12) ml/min, the fetal arterial whole blood concentration of A [A] was 65 +/- 5 pg/ml, and the blood production rate (PRA) was 204 +/- 20 ng/min. Pulsatile administration of ACTH in amounts that raised fetal arterial plasma cortisol concentrations by 5- to 7-fold increased [A] to 154 +/- 20 pg/ml and PRA to 471 +/- 31 ng/min with no change in MCRA. In the presence of metopirone to block fetal adrenal cortisol output, ACTH treatment still provoked elevations in [A] (to 198 +/- 23 pg/ml) and PRA (539 +/- 158 ng/min), without altering MCRA. The major radiolabeled product in blood of infused [3H]A was [3H]testosterone; smaller amounts of phenolic steroids were formed. Extensive metabolism of [3H]A occurred in whole blood in vitro. The major product was [3H]testosterone; the 17-oxidoreductase activity was associated with the red blood cells. Umbilical vein [A] was greater than umbilical artery [A]; ACTH treatment increased [A] in both vessels. Concomitant metopirone abolished the arteriovenous difference by eliminating the ACTH-induced increase in venous [A], although arterial [A] rose significantly. The venous [A] and the arteriovenous gradient were restored with exogenous glucocorticoid treatment to the fetus. Collagenase-dispersed fetal adrenal cells secreted A. Adrenal cells from fetuses pretreated with ACTH in vivo had higher basal and ACTH-induced output of A in vitro than cells from fetuses pretreated with saline in vivo. We conclude that the MCRA in fetal sheep is extremely high, in part due to conversion of A to testosterone in fetal blood. The elevated PRA after ACTH plus metopirone and the lack of an umbilical arteriovenous gradient of [A] in this, but not other groups of fetuses, suggests a source of A production independent of the cortisol-induced changes in the placenta. Direct evidence is provided for fetal adrenal secretion of A which is enhanced by ACTH pretreatment of the fetus in vivo and for the utilization of circulating A in the fetus as a precursor for estrogen in both fetal and maternal compartments.     

Negative feedback regulation of adrenocorticotropin secretion by cortisol in ovine fetuses

The purpose of this study was to test the hypothesis that physiological increases in the fetal plasma cortisol concentration inhibit fetal ACTH responses to stress. Fetal sheep, between 121 and 131 days gestation, were infused with cortisol (4 micrograms/min) or vehicle for 5 h. One hour after the end of the cortisol or vehicle infusion, fetuses were infused with sodium nitroprusside (100 micrograms/min) to stimulate fetal ACTH and adrenal corticosteroid secretion. Cortisol, but not vehicle, elevated fetal plasma cortisol and suppressed the fetal ACTH and cortisol responses to nitroprusside. Cortisol and 11-deoxycortisol concentrations were significantly correlated in fetal plasma samples drawn during experiments in which cortisol was not infused; however, the cortisol to 11-deoxycortisol ratio was significantly increased during the infusion of nitroprusside. Fetal heart rate increased during vehicle infusion and decreased during cortisol infusion. Fetal blood pressure was not altered by either cortisol or vehicle infusion. Cortisol infusion increased fetal blood hemoglobin concentration, decreased maternal blood hemoglobin concentration, and produced metabolic acidosis in both mother and fetus. Vehicle infusion did not alter either fetal or maternal hemoglobin or pH. The data do not suggest an obvious mechanism for the cortisol-induced changes in fetal and maternal pH and hemoglobin or in fetal heart rate. However, some of the changes might be attributable to changes in fetal sympathetic outflow or to fluid shifts. We conclude that physiological increases in fetal plasma cortisol concentration: 1) inhibit subsequent ACTH responses to stress and 2) alter fetal cardiovascular function.     

The effects of cortisol, vasopressin (AVP), and corticotropin-releasing factor administration on pulsatile adrenocorticotropin, alpha-melanocyte-stimulating hormone, and AVP secretion in the pituitary venous effluent of the horse

Plasma ACTH, arginine vasopressin (AVP), and alpha MSH were measured in pituitary venous effluent at 5-min intervals from five unanesthetized horses during cortisol infusion and after an iv bolus of AVP or ovine (o) CRF. In control experiments (no hormone) there was a significant overall correlation between the timing of concentration changes in ACTH and alpha MSH. Cortisol infusion increased jugular cortisol levels by 70% and was associated with a reduction in mean ACTH, AVP, and alpha MSH secretion rates and ACTH peak secretion rate, but did not alter the observed pulse frequencies of these hormones. Administration of AVP raised plasma concentrations to a level comparable to the spontaneous peaks in pituitary venous blood and resulted in an increase in the secretion of ACTH and alpha MSH in all horses. Furthermore, spontaneous AVP peaks occurred in pituitary venous blood between 90 and 180 min after AVP injection, indicating that the exogenous hormone did not suppress AVP secretion. oCRF administration led to a prolonged elevation in plasma CRF and an increase in secretion of ACTH and alpha MSH, but not AVP, in all horses. The pulsatile secretion of ACTH and alpha MSH was maintained despite plasma CRF levels in excess of 400 pmol/liter, and the timing of concentration changes in AVP and ACTH continued to be highly correlated. It is concluded that pulsatile ACTH secretion continues during cortisol, oCRF, or AVP administration. Like that of ACTH, alpha MSH secretion is stimulated by oCRF and AVP administration and suppressed by cortisol. Although the timing of concentration changes in ACTH and alpha MSH is highly correlated, the correlation of the actual concentrations of these two hormones varies considerably in different animals.     

The relationship of saline-induced changes in vasopressin secretion to basal and corticotropin-releasing hormone-stimulated adrenocorticotropin and cortisol secretion in man

To investigate the effect of endogenous arginine vasopressin (AVP) on ACTH secretion, normal subjects were given infusions of either hypertonic saline (HS) or isotonic saline (NS) combined with human corticotropin-releasing hormone (CRH) or placebo. Basal plasma AVP was 2.3 +/- 0.3 (+/- SE) pg/ml, did not change with NS treatment, and rose to 5.4 +/- 0.6 pg/ml during HS infusion (P less than 0.01). Both basal and CRH-stimulated plasma ACTH and cortisol concentrations increased during HS infusion. Peak plasma ACTH and cortisol levels were 11.4 +/- 1.5 pg/ml and 8.6 +/- 0.8 micrograms/dl, respectively, during the HS (plus placebo) infusion. During the NS (plus placebo) infusion, plasma ACTH and cortisol gradually declined to 6.8 +/- 0.5 pg/ml and 2.6 +/- 0.4 micrograms/dl. The timing of the rise in ACTH during the HS infusion paralleled the rise in AVP. When an iv dose of 1 microgram/kg CRH was administered during the saline infusions, peak plasma ACTH and cortisol levels were 27.7 +/- 6.3 pg/ml and 17.5 +/- 1.0 micrograms/dl, respectively, during the HS infusion and 15.6 +/- 1.7 pg/ml and 13.4 +/- 1.2 micrograms/dl during the NS infusion. When the areas under the hormone response curves were compared, CRH stimulated ACTH and cortisol secretion to a greater extent than did HS (P less than 0.05). The hormonal stimulation due to combined CRH and hypertonic saline was greater than that attributable to either factor alone (P less than 0.025), but was not different than the sum of the effects of the individual factors. These results indicate that increases in endogenous AVP produced by HS are associated with increases in both basal and CRH-stimulated ACTH and cortisol release. The effect of HS appears to be additive to but not consistently synergistic with the effect of CRH.     

Role of endogenous arginine vasopressin in potentiating corticotropin-releasing hormone-stimulated corticotropin secretion in man

Exogenously administered vasopressin (VP) augments ACTH secretion stimulated by CRH. This study was performed to elucidate the role of endogenous VP in potentiating CRH-induced ACTH secretion in man. Synthetic human CRH (100 micrograms) was injected iv into seven normal men after they had been water loaded (20 mL/kg; 60 and 30 min before CRH injection; WL-CRH test) and water deprived (water restriction for 18 h before CRH injection; WD-CRH test). Blood samples were obtained before and 5, 15, 30, 60, 90, and 120 min after CRH injection at 0900 h for determination of plasma ACTH, cortisol, arginine vasopressin (AVP), CRH, and catecholamine levels and osmolality. Urine was obtained immediately before and 120 min after CRH injection for determination of osmolality. The mean plasma AVP levels were significantly higher during the WD-CRH test [1.8 +/- 0.4 (+/- SE) to 1.9 +/- 0.4 pmol/L] than during the WL-CRH test (0.6 +/- 0.1 to 0.9 +/- 0.1 pmol/L). The mean plasma ACTH and cortisol levels rose significantly from basal (4.5 +/- 0.6 pmol/L and 320 +/- 20 nmol/L, respectively) to peak values of 14.0 +/- 2.1 pmol/L at 30 min and 700 +/- 50 nmol/L at 60 min, respectively, during the WD-CRH test. During the WL-CRH test, mean basal plasma ACTH and cortisol levels were 3.5 +/- 0.7 pmol/L and 420 +/- 50 nmol/L, respectively, and reached peak values of 7.7 +/- 1.1 pmol/L at 60 min and 550 +/- 40 nmol/L at 30 min, respectively. Both the mean peak levels and integrated ACTH and cortisol responses were significantly higher during the WD-CRH than during the WL-CRH test. There was no significant difference between the plasma CRH and catecholamine concentrations in both tests. These results suggest that endogenous AVP potentiates CRH-stimulated ACTH secretion and, thus, plays a physiologically significant role in regulating CRH-stimulated ACTH and cortisol secretion in man.     

In vivo adrenocorticotropin (1-24)-induced accumulation of cyclic adenosine monophosphate by ovine fetal adrenal cells is inhibited by concomitant infusion of metopirone

Activation of the ovine fetal adrenal gland after pulse ACTH (P-ACTH) administration is associated with an increase in plasma cortisol levels. We have investigated whether cortisol may play a role in this adrenal activation process. The ability of fetal adrenal cells to accumulate cAMP in response to ACTH in vitro was compared in fetuses (day 132 of gestation) that had received infusions (100 h) in utero of 1) saline or saline + tartrate (0.5 ml for 15 min/2 h) (n = 4); 2) P-ACTH (66.6 ng/min for 15 min/2 h) (n = 4); 3) P-ACTH + metopirone (31.3 mg/h) (n = 4), to inhibit 11 beta-hydroxylase activity. Control fetuses showed no significant increase in plasma cortisol levels throughout the infusion and there was no significant accumulation of cAMP by fetal adrenal cells in vitro in response to ACTH. There was a significant (P less than 0.05) increase in plasma cortisol concentrations from 2.21 +/- 0.47 (mean +/- SEM) ng/ml at 0 h to 35.7 +/- 11.6 ng/ml at 96 h in fetuses receiving P-ACTH in vivo. In these fetuses there was a significant (P less than 0.05) accumulation of cAMP after addition of ACTH by fetal adrenal cells in vitro (mean increment delta = 48 pmol). This rise in plasma cortisol was prevented in fetuses receiving P-ACTH + metopirone. Further, metopirone treatment prevented the increase in fetal adrenal weight and accumulation of cAMP after in vitro ACTH that normally followed ACTH treatment in vivo. This effect was not overcome by further addition of guanylylimido-diphosphate. These experiments raise the possibility that cortisol might mediate the increase in cAMP accumulation resultant upon in vivo P-ACTH treatment.     

Surgical disconnection of the hypothalamus from the fetal pituitary abolishes the corticotrophic response to intrauterine hypoglycemia or hypoxemia in the sheep during late gestation.

We have investigated the ACTH and cortisol responses to acute episodes of hypoxemia or hypoglycemia in fetal sheep in which the hypothalamus and pituitary were surgically disconnected at between 112 and 123 days gestation. Before 130 days gestation, basal plasma concentrations of ACTH were significantly greater in the hypothalamo-pituitary disconnected (HPD) fetuses than in the intact fetal sheep (126-130 days; 105.0 +/- 11.4 ng/liter, HPD group; 64.0 +/- 9.5 ng/liter, intact group). After 130 days, however, there was no difference between plasma ACTH concentrations in the HPD (136-140 days; 154.7 +/- 16.7 ng/liter HPD group; 113.6 +/- 19.1 ng/liter, intact group) and intact fetal sheep, and in both groups the mean ACTH concentrations were significantly greater after 136 days gestation than before 130 days. In the HPD group, however, while the plasma ACTH concentrations were elevated there was no prepartum increase in the plasma concentrations of cortisol. A decrease in the fetal arterial blood PO2 by approximately 50% for 30 min between 123 and 132 days, stimulated a significant increase in fetal ACTH and cortisol concentrations in the intact but not in the HPD fetuses. In the intact group, plasma ACTH concentrations were also significantly increased (P less than 0.001) above control values (98.2 +/- 21.2 ng/liter) at 120 min after the start of an iv infusion of insulin (1 IU/60 min) (517.2 +/- 160.5 ng/liter) and were still elevated at 60 min after the end of the infusion period (1248.1 +/- 643.2 ng/liter). In the HPD fetuses, however, there was no significant change in plasma ACTH concentrations during or after the insulin infusion. In both the HPD and intact groups, there was a significant increase in plasma ACTH concentrations above control values (62.5 +/- 8.5 ng/liter intact; 135.0 +/- 30.6 ng/liter, HPD) after intrafetal administration of CRF (+10 min; 117.5 +/- 8.1 ng/liter, intact; 225.3 +/- 33.1 ng/liter, HPD) indicating that the secretory capacity of the pituitary corticotrophs was not reduced by the HPD procedure. Our results demonstrate that an intact hypothalamic-pituitary connection is required to generate a normal prepartum increase in fetal cortisol concentrations and is essential for an appropriate fetal pituitary-adrenal response to intrauterine hypoxemia and hypoglycemia.     

Effects of incremental infusions of arginine vasopressin on adrenocorticotropin and cortisol secretion in man

Arginine vasopressin (AVP) regulates ACTH release under certain conditions, and exogenously administered AVP is used clinically to stimulate ACTH secretion. We attempted to determine at what plasma concentration AVP can stimulate ACTH release. Six normal men were given infusions of AVP (Ferring) or vehicle between 1600 and 1700 h on five occasions: 1) saline (30 mL/h); 2) 10 ng AVP/min; 3) 30 ng AVP/min; 4) 100 ng AVP/min; and 5) 300 ng AVP/min. Plasma AVP, ACTH, and cortisol concentrations were measured every 10 min during the infusions. Basal plasma AVP levels were less than 1 ng/L (less than 0.92 pmol/L). The lowest AVP dose raised plasma AVP into the range found in fluid-deprived subjects (7-8 ng/L;6.5-7.3 pmol/L), but had no effect on plasma ACTH concentrations. AVP in a dose of 30 ng/min also had no effect. The 100 ng AVP/min dose raised plasma AVP concentrations to 51.4-65.5 ng/L (46-60 pmol/L). This increase led to a transient insignificant increase in plasma ACTH from 13.9 +/- 1.2 (+/- SEM) ng/L (3.1 +/- 0.3 pmol/L) to 20.0 +/- 1.4 ng/L (4.4 +/- 0.3 pmol/L), while plasma cortisol rose significantly from 146 +/- 10 to 209 +/- 19 nmol/L (P less than 0.01) after 60 min of infusion. The 300 ng AVP/min dose raised plasma AVP levels to about 260 ng/L (239 pmol/L); the maximal plasma ACTH and cortisol levels were 39.5 +/- 5.0 ng/L (8.7 +/- 1.1 pmol/L; P less than 0.01) and 348 nmol/L (P less than 0.01), respectively. Thus, peripheral plasma AVP levels have to be raised high above the physiological range before ACTH release is stimulated. We conclude that any AVP reaching the adenohypophysis through the peripheral circulation is of much less importance for the regulation of ACTH secretion than is AVP derived from the pituitary portal circulation.     

Plasma adrenocorticotropin and cortisol concentrations during acute hypoxemia after a reversible period of adverse intrauterine conditions in the ovine fetus during late gestation

The present study determined the pituitary-adrenal responses to acute hypoxemia after a period of reversible adverse intrauterine conditions produced by partial compression of the umbilical cord for 3 days in the sheep fetus during late gestation. At 118 +/- 2 days gestation (term is approximately 145 days), 12 sheep fetuses were instrumented under halothane anesthesia with an occluder cuff around the umbilical cord, amniotic and vascular catheters, and a transit-time flow probe around an umbilical artery. In 6 of the fetuses at 125 days, umbilical blood flow was reduced by about 30% from baseline for 3 days (UCC), after which the occluder was deflated. The remaining 6 fetuses acted as sham-operated controls in which the occluder was not inflated. All fetuses were then subsequently subjected to 2 periods of acute hypoxemia, elicited by reducing the maternal inspired fraction of oxygen (FiO(2)) at 2 +/- 1 and 5 +/- 2 days after the end of cord compression or sham compression. In addition, 4 fetuses from each group were subjected to an ACTH challenge 1-2 days after the final episode of acute hypoxemia. Maternal and fetal arterial blood samples were taken at appropriate intervals during cord compression, acute hypoxemia, and ACTH challenge for analyses of blood gases, pH, and plasma ACTH and cortisol concentrations. Partial compression of the umbilical cord produced reversible mild fetal asphyxia, a transient increase in fetal plasma ACTH, and a progressive increase in fetal plasma cortisol. At 5 +/- 2 days after the end of compression, despite similar blood gas status between the groups, basal plasma cortisol, but not ACTH, concentrations were significantly greater in compressed fetuses relative to sham controls. However, this dissociation did not affect a similar increment in fetal plasma ACTH and cortisol concentrations during acute hypoxemia or in the fetal plasma cortisol response to the ACTH challenge in either group. An increase in adrenocortical mass occurred in fetuses preexposed to partial compression of the umbilical cord relative to sham controls. The data suggest that fetal exposure to a reversible period of adverse intrauterine conditions produced by partial compression of the umbilical cord does not affect the magnitude of the fetal hypothalamic-pituitary-adrenal axis response to subsequent acute hypoxemia, but it leads to resetting of basal hypothalamic-pituitary-adrenal axis function in the fetus. The mechanism for this resetting may include an increase in adrenocortical steroidogenic synthetic capacity, but it is not due to a change in adrenocortical sensitivity to ACTH. Inappropriate fetal glucocorticoid exposure after reversible periods of adverse intrauterine conditions has important implications for fetal and postnatal development.     

The effects of adrenocorticotropin and prolactin on adrenal dehydroepiandrosterone secretion in the baboon fetus

The present study was designed to determine whether PRL, in addition to ACTH, stimulates adrenal secretion of dehydroepiandrosterone (DHA) in vivo at midgestation in the baboon fetus (Papio anubis). On day 100 of gestation (term = day 184), fetuses were exteriorized, and a constant infusion of saline (0.1 ml/min) was initiated via a fetal femoral vein. Forty minutes later, a bolus injection of 30 nmol ACTH/ml saline (n = 5), 40 nmol ovine PRL/ml saline (n = 4), or 1 ml saline (n = 5) was administered via the fetal femoral venous catheter. ACTH (0.15 nmol/min.0.1 ml saline), PRL (0.20 nmol/min.0.1 ml saline), or saline (0.1 ml/min) was then infused for an additional 25 min. Blood samples were obtained from the contralateral fetal femoral vein and the maternal saphenous vein immediately before and after peptide infusion and from the umbilical vein and artery at the end of the infusion. Fetal serum DHA concentrations (range, 9-11 micrograms/100 ml) were significantly increased (P less than 0.05) by PRL and ACTH, but not by saline. In contrast, fetal concentrations of cortisol (15-20 micrograms/100 ml) and DHA sulfate (DHAS; 13-18 micrograms/100 ml) were not altered by infusion of test substances into the fetus. The maternal concentrations of F (49-61 micrograms/100 ml) and DHAS (19-22 micrograms/100 ml) exceeded (P less than 0.05) respective values in the fetus, whereas DHA concentrations (2-3 micrograms/100 ml) in the mother were lower (P less than 0.05) than those in fetal serum. The serum concentrations of DHA, DHAS, and cortisol in the mother were not altered by PRL or ACTH. Regardless of the treatment, concentrations of DHA and DHAS in umbilical vein were lower (P less than 0.05) than those in the umbilical artery. These findings indicate that PRL as well as ACTH are effective in vivo in stimulating serum DHA concentrations in fetal baboons at midgestation. The greater concentration of DHA in umbilical artery vs. umbilical vein as well as the lack of response in maternal DHA concentrations indicate that the site of action of PRL and ACTH is the fetal adrenal. Therefore, we conclude that at midgestation, there is the potential for multifactorial regulation of baboon fetal adrenal androgen production and that PRL, in addition to ACTH, can function as a fetal adrenocorticotropic factor in vivo.     

Handling during pregnancy in the blue fox (Alopex lagopus): the influence on the fetal pituitary-adrenal axis

Previous studies revealed that handling is a stressor for farmed blue foxes. The present study was designed to examine the effects of a 1-min daily handling stress applied to pregnant blue fox vixens on the function of the fetal pituitary-adrenal system. Plasma concentrations of adrenocorticotropin hormone (ACTH), cortisol, and progesterone, adrenal content of cortisol and progesterone, in vitro adrenal production of these steroids and response to ACTH, and adrenal weights were measured in control (C; n = 73) and stressed (S; n = 58) fetuses. The ACTH levels were lower in stressed fetuses than in the controls (C: males, 128.6 +/- 6.1 pg/ml; females, 165.9 +/- 6.1 pg/ml; S: males, 122.3 +/- 5.4 pg/ml; females, 145.0 +/- 8.1 pg/ml; P < 0.05). In contrast, increased plasma cortisol concentrations in both sexes were demonstrated in stressed compared with control fetuses (C: males, 9.2 +/- 0.4 ng/ml; females, 9.2 +/- 0.4 ng/ml; S: males, 11.8 +/- 0.7 ng/ml; females, 13.2 +/- 0.7 ng/ml; P < 0.00001). The same difference was observed in plasma progesterone concentrations (C: males, 1.54 +/- 0.07 ng/ml; females, 1.49 +/- 0.10 ng/ml; S: males, 1.86 +/- 0.11 ng/ml; females, 1.74 +/- 0.10 ng/ml; P < 0.01). Prenatal stress did not change the baseline adrenal production of cortisol but prevented the cortisol response to ACTH in female fetuses and decreased the progesterone production in both sexes. Additionally, prenatally stressed fetuses of both sexes had significantly lower adrenal weights than controls (C: males, 9.4 +/- 0.3 mg; females, 9.5 +/- 0.4 mg; S: males, 8.1 +/- 0.3 mg; females, 8.2 +/- 0.4 mg; P < 0.001). These results indicate that prenatal handling stress induces a dysregulation of the pituitary-adrenal axis in the fetus and suggest that increased plasma glucocorticoids in the stressed dam can cross the placenta and influence the fetal hypothalamicpituitary-adrenal axis.     

Effect of estrogen on pituitary peptide-induced dehydroepiandrosterone secretion in the baboon fetus at midgestation

We have previously shown that ACTH and PRL stimulate baboon fetal adrenal dehydroepiandrosterone (DHA) production both in vitro and in vivo and that estrogen diminishes the responsivity of the adrenal to tropic peptides in vitro. In the present study we determined the effects of increasing placental estrogen production by the administration of androstenedione at midgestation on DHA production by the baboon fetus in vivo. Pregnant baboons were untreated (n = 8) or treated (n = 9) with increasing numbers of androstenedione implants inserted in the mother at 8-day intervals between days 70-100 of gestation (term = day 184). On day 100, the fetuses were exteriorized, and a constant infusion of saline (0.1 ml/min) was initiated via a catheter inserted into a femoral vein of the fetus. At 40 min, a bolus injection of either 30 nmol ACTH or 40 nmol ovine PRL was administered to fetuses. ACTH or PRL (0.2 nmol/min.0.1 ml saline) were then infused for an additional 25 min. The concentrations of serum estradiol (E2) in the uterine vein (20.2 +/- 1.5 ng/ml; mean +/- SE) and estrone (E1) in umbilical vein (11.9 +/- 3.1 ng/ml) of androstenedione-treated baboons were 2-fold greater (P less than 0.05) than respective values in untreated baboons. Baseline concentrations of DHA in the femoral vein of the fetus were similar in all treatment groups (overall mean, 120 +/- 20 ng/ml) and greater (P less than 0.05) than values (27 +/- 3) in the mother. In untreated control baboons, basal DHA concentrations in the fetus were increased (P less than 0.05) by 69 +/- 17% and 94 +/- 29% after fetal injection of ACTH (n = 4) or PRL (n = 4), respectively. In contrast, neither PRL (n = 5) nor ACTH (n = 4) had any effect on serum DHA when injected into androstenedione-treated baboons. Regardless of treatment, injection of ACTH or PRL into the fetus had no effect on DHA concentrations in the mother. Collectively, these findings indicate that the ability of the fetal adrenal to increase DHA production in response to an acute infusion of ACTH or PRL was abolished in baboons in which placental estrogen production was increased prematurely at midgestation. Therefore, we suggest that during the second half of gestation in the baboon a regulatory system may exist in utero, in which there is feedback control of the placental product estrogen on the formation of the fetal adrenal precursor DHA.     

The role of calcitonin gene-related Peptide in the in vivo pituitary-adrenocortical response to acute hypoxemia in the late-gestation sheep fetus

This study tested the hypothesis that calcitonin gene-related peptide (CGRP) has a role in mediating the in vivo fetal adrenal glucocorticoid response to acute stress. The hypothesis was tested by investigating the effects of fetal treatment with a selective CGRP antagonist on plasma ACTH and cortisol responses to acute hypoxemia in the late-gestation sheep fetus. Under anesthesia, six fetuses at 0.8 of gestation were surgically instrumented with vascular catheters. Five days later, fetuses were subjected to 0.5-h hypoxemia during treatment with either iv saline or a CGRP antagonist, in randomized order, on different days. Treatment started 30 min before hypoxemia and ran continuously until the end of the challenge. Arterial blood samples were collected for plasma ACTH and cortisol measurements (RIA) and blood gas monitoring. CGRP antagonism did not alter basal arterial blood gas or endocrine status. During hypoxemia, similar falls in arterial partial pressure of oxygen occurred in all fetuses. During saline infusion, acute hypoxemia induced significant increases in fetal ACTH and cortisol concentrations. During CGRP antagonism, the pituitary-adrenal responses were markedly attenuated. Correlation of paired plasma ACTH and cortisol values from all individual fetuses during normoxia and hypoxemia showed positive linear relationships; however, neither the slope nor the intercept of the peptide-steroid relationship was affected by CGRP antagonism. These data support the hypothesis that CGRP is involved in the in vivo regulation of fetal adrenocortical steroidogenesis during acute hypoxemia. In addition, the data reveal that CGRP may have a role in the control of other components of the hypothalamo-pituitary-adrenal axis during stimulated conditions in fetal life.     

Vasopressin mediates the interleukin-1 alpha-induced decrease in luteinizing hormone secretion in the ovariectomized rhesus monkey.

Arginine vasopressin (AVP) has previously been shown to participate in the neuroendocrine control of the adrenal axis. In this study we investigated the role of AVP in the mechanisms linking stress and decreased gonadotropin secretion and evaluated the action of an AVP antagonist on interleukin-1 alpha (IL-1 alpha)-induced changes in gonadotropin and cortisol release in the primate. Adult ovariectomized rhesus monkeys were given a 30-min intracerebroventricular infusion of IL-1 alpha (2.1 micrograms/30 min; n = 5) or IL-1 alpha plus an AVP antagonist (240 micrograms/120 min; [deamino-Pen1,O-Me-Tyr2,Arg8] vasopressin; n = 7); the AVP antagonist infusion was started 30 min before IL-1 alpha and continued for 2 h. Controls included intracerebroventricular infusions of physiological saline (n = 5) or AVP antagonist alone (n = 3). LH concentrations were measured at 15-min intervals during a 3-h preinfusion morning baseline control period and a 5-h postinfusion period. Cortisol concentrations were determined at 45-min intervals. Pulsatile LH release remained unchanged after a control saline or AVP antagonist infusion. Overall LH concentrations decreased significantly after IL-1 alpha infusion, from a morning control baseline of 109.9 +/- 8.8 to 53.7 +/- 3.2 ng/ml after the infusion (P less than 0.05). Concomitant infusion of the AVP antagonist prevented the IL-1 alpha-induced LH inhibition (morning control baseline, 144.5 +/- 6.8; postinfusion, 132.3 +/- 5.8; P = NS vs. saline; P less than 0.0001 vs. IL-1 alpha). While cortisol concentrations decreased throughout the experimental period in the animals receiving saline, they increased after IL-1 alpha infusion: mean +/- SE postinfusion cortisol concentrations were 29.6 +/- 1.9 micrograms/dl (saline) vs. 44.0 +/- 1.7 micrograms/dl (IL-1 alpha; P less than 0.0001). Coinfusion of AVP antagonist and IL-1 alpha did not block the IL-induced cortisol increase (46.8 +/- 1.5 micrograms/dl; P less than 0.0001 vs. morning). After the infusion of AVP antagonist alone, cortisol concentrations significantly decreased from a morning control value of 40.2 +/- 1.6 to 34.9 +/- 1.6 micrograms/dl (P less than 0.05). The results confirm our previous demonstration of an inhibitory effect of IL-1 alpha on gonadotropin secretion in the ovariectomized rhesus monkey and indicate for the first time an important inhibitory role for AVP in the control of gonadotropin secretion during stress. The data also suggest that in this species, the adrenocortical response to IL-1 does not require AVP.     

Effect of antalarmin,a novel corticotropin-releasing hormone antagonist,on the dynamic function of the preterm ovine fetal hypothalamo-pituitary-adrenal axis

This study describes the effect of antalarmin on basal and stimulated activity of the hypothalamo-pituitary-adrenal (HPA) axis function in the late gestation ovine fetus. Fetuses received antalarmin (15 mg/h i.v.) or vehicle (cremophor El 50% in ethanol) from day 130 gestational age. Antalarmin infusion did not significantly affect immunoreactive corticotropin (ir-ACTH) concentrations, although there was a tendency for ir-ACTH to be lower and cortisol concentrations were lower in the antalarmin-treated fetuses (p < 0.01). The ir-ACTH response to corticotropin-releasing hormone (CRH) challenge was attenuated (p < 0.05) in the antalarmin-treated fetuses, but neither antalarmin- nor vehicle-treated fetuses had significant cortisol responses to CRH. The ir-ACTH response to hypoxia was diminished (p < 0.05) in the antalarmin-treated fetuses while the cortisol responses of antalarmin- and vehicle-treated fetuses were indistinguishable. Deconvolution analysis revealed no effect of antalarmin treatment on ir-ACTH secretory dynamics. In contrast, antalarmin decreased (p < 0.05) basal, mean and integrated cortisol. The plasma cortisol responses of antalarmin- and vehicle-treated fetuses to exogenous ACTH(1-24) were indistinguishable. These data indicate that, while antalarmin inhibits CRH- and stress-induced ir-ACTH secretion, basal ir-ACTH secretion may be less affected by antalarmin treatment. Paradoxically, cortisol secretion is impaired by antalarmin infusion, although adrenal responsiveness to ACTH is not impaired. These results confirm a role for CRH in stress-induced ACTH secretion in the ovine fetus, though its role in the regulation of basal ACTH and cortisol secretion is unclear.     

Hormone ontogeny in the ovine fetus: XIV. The effect of 17 beta-estradiol infusion on fetal plasma gonadotropins and prolactin and the maturation of sex steroid-dependent negative feedback

17 beta-Estradiol (E2; 100 micrograms/kg X day) was infused iv for 6 days into three chronically catheterized ovine fetuses beginning at 105-106 days of gestation (term, 147 days) and into four younger fetuses for 3 days commencing at 87-92 days. Control studies were performed on three fetuses at each age. At 90 days, E2 had no effect on the basal concentration of either LH or FSH. In both control and E2-infused fetuses, repeated LHRH testing was associated with a decreased LH response, but the decrease was not greater in the E2-infused fetuses. The FSH response was unaffected in either group. At 105 days, E2 caused suppression of the mean basal concentration of plasma LH from 1.2 +/- 0.1 to 0.1 +/- 0.1 ng/ml (P less than 0.01) and of basal FSH from 5.6 +/- 0.5 to 3.3 +/- 0.6 ng/ml (P less than 0.05). The LH response to LHRH administration (50-micrograms iv bolus) also was suppressed by E2. The maximal incremental LH response fell from 7.1 +/- 0.4 to 3.3 +/- 0.5 ng/ml (P less than 0.01); the integrated response decreased from 5.8 +/- 0.2 to 1.8 +/- 0.2 ng/ml X h (P less than 0.01). However, no effect was observed on the rise in FSH concentration evoked by LHRH. In control studies at 105 days, basal and LHRH-stimulated gonadotropin concentrations remained constant during the experiment. These results indicate that the capacity for exogenous E2 to suppress fetal pituitary gonadotropin secretion in the ovine fetus develops between 90 and 105 days of gestation, before the normal ontogenic decrease both in the basal concentration of fetal pituitary gonadotropins and in LHRH-stimulated FSH and LH secretion, which occur later in gestation. We suggest that the development of the E2-sensitive negative feedback mechanism in the fetal hypothalamic-pituitary unit is a major factor in this decrease. At 90 days gestational age, the mean fetal plasma concentration of PRL was not affected by the infusion of E2 into the fetus (5.9 +/- 1.5 ng/ml before E2 infusion 8.1 +/- 3.2 ng/ml during E2 infusion). However, at 105 days, the mean PRL concentration rose from 49.3 +/- 18.2 to 101.6 +/- 26.1 ng/ml (P less than 0.01) after the infusion of E2. The capacity for E2 to stimulate PRL release develops in parallel with the rise in fetal plasma PRL and estrogen concentrations. The results provide evidence that circulating estrogens are a determinant of fetal PRL concentrations in late gestation.