Control of adrenocorticotrophin secretion by catecholamines in the pregnant and foetal sheep.

The effect of adrenaline on the maternal and foetal plasma ACTH concentration of twelve pregnant sheep with chronically implanted vascular catheters has been studied. Adrenaline infused into the jugular vein of the ewe or foetus produced carotid arterial adrenaline concentrations of 1-9 ng/ml. The foetal plasma ACTH was 253 +/- 73 pg/ml and it showed a fivefold increase during adrenaline infusion; the ACTH concentration achieved was proportional to the plasma adrenaline. In the ewe plasma ACTH was 99 +/- 23 pg/ml. During adrenaline infusion to the ewe this rose by an amount dependent on the adrenaline concentration achieved and there was also a rise in foetal plasma ACTH but no consistent change in foetal plasma adrenaline. There was no reproducible change in plasma corticosteroid concentration during adrenaline infusion into the foetus but a rise in maternal plasma corticosteroid concentration during infusion into the ewes. Because the adrenaline concentrations achieved during the infusions were within the physiological range, the results indicate that circulating catecholamines may directly or indirectly influence the concentration of ACTH in the circulation. Also, physiological rises in plasma catecholamines in pregnant animals may stimulate the release of ACTH from the foetal pituitary.     

Developmental changes in the responses of the adrenal glands of foetal sheep to endogenous adrenocorticotrophin, as indicated by hormone responses to hypoxaemia.

The change in plasma ACTH and corticosteroid concentrations in response to a 60 min period of hypoxaemia were studied in foetal and adult sheep during the latter half of pregnancy. Hypoxaemia consistently caused large rises in the concentration of ACTH in foetal plasma, the magnitude of which did not change with gestational age but was related to the physiological state of the foetus. Before 139 days small and slow rises in corticosteroid (predominantly cortisol) concentration in foetal plasma were observed during hypoxaemia, and these may have been of maternal origin. After 139 days, hypoxaemia caused a rapid and large rise in the concentration of cortisol and corticosterone in foetal plasma, which was largely of foetal origin. Hypoxaemia caused no consistent change in maternal plasma ACTH concentration but was associated with progressive increases in plasma cortisol concentrations. The cortisol: corticosterone ratio in foetal plasma was 1-5 before 139 days and increased to 4-1 several days before term which was lower than the value of 9 in maternal plasma. Small concentrations of 11-deoxycortisol and cortisone were detected in maternal and foetal plasma, the changes of which were small during hypoxaemia. The results indicate that a maturational change in the sensitivity of the foetal adrenal to endogenous ACTH occurs several days before term.     

Adrenocorticotrophin and corticosteroid changes during dexamethasone infusion to intact and synacthen infusion to hypophysectomized foetuses.

Synacthen has been infused at 10 microgram/h into 4 hypophysectomized foetal sheep. This caused a rise in adrenocorticotrophin to a mean value of 512 pg/ml which remained fairly constant and did not show the large fluctuations seen on infusion into intact foetuses. The Synacthen half-life in the circulation had a mean value of 0.27 min. Hypophysectomy did not necessarily delay the foetal corticosteroid response to Synacthen infusion. The corticosteroid concentration achieved had a mean value of about 50 ng/ml which is substantially below that for intact foetuses and in one case it was maintained at only 20 ng/ml. Despite this delivery occurred within 5 days. Dexamethasone infusion reduced the plasma adrenocorticotrophin concentration by about 70% and the plasma cortisol concentration by about 60%.     

Protein binding of plasma cortisol in the foetal lamb near term.

Binding of cortisol to plasma proteins was studied in the foetal lamb by equilibrium dialysis at 37 degrees C. At 122 days of pregnancy the mean level of transcortin expressed as cortisol-binding capacity was 28 +/- 6 (S.D.) ng cortisol/ml plasma. During the last 14 days of pregnancy there was a progressive increase in transcortin-binding capacity to 85 +/- 14 ng cortisol/ml plasma. A sharp increase in the concentration of both protein-bound and unbound cortisol was observed over the same period. A rise in the concentration of total cortisol from around 3 to 42 ng/ml was associated with an increase in unbound cortisol from 0-2 to a maximum of 2-1 ng/ml. The concentration of albumin-bound cortisol was approximately equal to that of unbound cortisol. The mean value for the transcortin-cortisol affinity constant was 1-15 x 10(8) l/mol. It is concluded that an increase in transcortin-binding capacity is partly responsible for the prepartum increase of corticosteroid levels observed in normal foetal lambs.     

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.     

Correlation between plasma levels of ACTH and beta-endorphin in the first seven days of postnatal life

Plasma adrenocorticotropic hormone (ACTH) and beta-endorphin (beta-EP) concentrations were measured by radioimmunoassay in 122 newborns, born vaginally after spontaneous labor between the 38th and the 41st week of pregnancy. Blood samples were taken from umbilical cord in 10 newborns and from antecubital vein in the remaining 112 newborns, divided into 8 groups aged from 12 h to 7 days. The mean (+/- SE) ACTH concentrations in cord plasma were 81.87 +/- 10.16 pg/ml and decreased significantly (p less than 0.01) at the 24th h of life (49.09 +/- 6.93 pg/ml). Afterwards mean ACTH plasma concentrations fluctuated around the latter values. The mean (+/- SE) B-EP concentrations in cord plasma were 21.96 +/- 3.12 pmol/l and decreased significantly at the 24th h of life (13.43 +/- 2.08 pmol/l; p less than 0.01). From the 24th h to the 7th day the mean plasma concentrations of beta-EP were not significantly different. ACTH and beta-EP plasma levels were positively correlated (p less than 0.001) at delivery and during the first seven days of life.     

Induction of premature parturition in sheep: adrenocorticotrophin and corticosteroid changes during infusion of Synacthen into the foetus.

Synacthen (10 microgram/h) infused into foetal sheep at about day 125 of gestation caused premature delivery within 4 days. During the first 24 h of the infusion the secretion of adrenocorticotrophin was depressed and the assayable hormone concentration was within 500-1000 pg/ml. Subsequently, large fluctuations occurred in the adrenocorticotrophin concentration in the plasma of foetal sheep which were consistent with the stimulation of adrenocorticotrophin secretion. No transfer of Synachthen to non-infused twin foetuses was observed. The plasma corticosteroid concentration in the infused foetus also showed a small rise during the first 24 h of the infusion followed by large fluctuations in concentrations that coincided with the changes in adrenocorticotrophin. No consistent changes in the plasma corticosteroid concentration in the non-infused twin foetus were observed. These results are discussed in relation to the hormone changes occurring during normal delivery.     

Plasma corticotropin-releasing factor concentrations in the baboon during pregnancy.

We have studied the secretion of placental CRF during pregnancy in the baboon, an animal model with many similarities to human pregnancy. Plasma CRF was measured in two groups of animals. In group 1, studies were performed in six anesthetized animals beginning 8 days postconception. In group 2, studies were performed in five unanesthetized chronically catheterized maternal and five fetal animals in the latter third of pregnancy. In the first study beginning early in pregnancy, CRF was undetectable in all animals on days 8 and 15 postconception. Plasma CRF became detectable in two animals on day 24 and in the remaining four on day 30. Plasma CRF rose significantly to a mean of 810 +/- 160 pg/ml at 37 days gestation (F = 4.20; P < 0.001). Mean maternal plasma CRF was 2452 +/- 1120 pg/ml on day 44 and remained elevated, with a great deal of variability between subjects, until the end of the study period (128 days of gestation). Samples in this group were obtained after ketamine sedation. The effect of ketamine on CRF was studied in three chronically catheterized animals. Samples were obtained before and 2, 4, 6, and 24 h after ketamine administration (40 mg, iv). The baseline CRF concentration was 1168 +/- 131 pg/ml and did not change significantly over the time period studied. In the second study in the chronically catheterized animals, maternal plasma CRF was 1990 +/- 680 pg/ml at 131-140 days gestation and remained elevated until near term at 170 days (term = 175-180 days). Within 24 h after birth, plasma CRF became undetectable (< 60 pg/ml). CRF was also measured in chronically catheterized fetal baboons. The mean CRF concentration was 614 +/- 224 pg/ml at 131-140 days and remained in this range until the end of the period studied (151-160 days gestation). To characterize the CRF immunoactivity in maternal baboon plasma, Sephadex chromatography was performed on an 8.4-ml plasma sample obtained at 160 days gestation. The majority of the CRF immunoactivity eluted in the same position as synthetic human CRF. We conclude that high levels of placental CRF are present in the systemic circulation of the maternal and fetal baboon during pregnancy. In contrast to human pregnancy, which is characterized by an exponential rise in maternal CRF concentrations in the final weeks before delivery, an exponential rise in maternal baboon CRF concentrations occurs early in pregnancy.     

Effect of passive immunization against corticotropin-releasing factor (CRF) on the postadrenalectomy changes of CRF binding sites in the rat anterior pituitary gland

The concentration of corticotropin-releasing factor (CRF)-binding sites decreases in the rat anterior pituitary after adrenalectomy; this change may be related either to a direct effect of the circulating glucocorticoids at the pituitary level or to a desensitization of CRF receptors through an increased CRG release in hypophysial portal blood. In order to examine the latter possibility we have measured plasma adrenocorticotropin hormone (ACTH) levels and the number of anterior pituitary CRF binding sites in sham-operated and 24-hour adrenalectomized rats after blockade of endogenous CRF by passive immunization with an antiserum anti-rat CRF (CRF-AS), or after injection of normal rabbit serum (NRS). In NRS-injected rats, after sham operation, plasma ACTH concentration increased (227 +/- 34 vs. 118 +/- 19 pg/ml in controls) without change in CRF-binding sites capacity (20.7 +/- 2.6 vs. 24.6 +/- 3.5 fmol/mg protein in controls). Adrenalectomy induced a large rise in plasma ACTH (785 +/- 89 pg/ml) and a decrease in the number of CRF-binding sites (12.2 +/- 1.7 fmol/mg protein). After CRF-AS injection, plasma ACTH was normalized in sham-operated animals (149 +/- 24 pg/ml) and significantly reduced in adrenalectomized rats (472 +/- 76 pg/ml); the adrenalectomy-induced decrease in the number of CRF-binding sites was unaffected by the CRF-AS administration (12.2 +/- 1.7 fmol/mg protein). The administration of dexamethasone to adrenalectomized rats significantly reduced plasma ACTH concentrations (23.3 +/- 10.6 pg/ml) and prevented the loss in CRF-binding sites capacity (20.7 +/- 1.3 fmol/mg protein).(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of an antiserotoninergic drug, metergoline, on the ACTH and cortisol response to insulin hypoglycemia and lysine-vasopressin in man.

The effect of metergoline, a specific antiserotoninergic drug, on ACTH secretion was investigated in 29 normal volunteers and in 4 patients with increased ACTH production (3 with Addison's disease, 1 with Cushing's disease). In 15 normal subjects, a 4-day treatment with 10 mg daily of metergoline significantly blunted the ACTH response to insulin hypoglycemia. Mean peak ACTH values before and after treatment were, respectively, 333 +/- 39.2 (SE) and 235 +/- 38.8 pg/ml (P less than 0.05). The corresponding values of plasma cortisol were 29.6 +/- 2.96 and 20.5 +/- 2.67 mug/100 ml (P less than 0.05). In contrast, metergoline failed to affect the ACTH response to lysine-vasopressin (LVP) administered iv (8 subjects studied) and im (6 subjects studied). In 3 patients suffering from Addison's disease, an appreciable although not statistically significant lowering of the plasma ACTH levels was noted during metergoline administration. The mean pre- and post-treatment values of plasma ACTH in these patients were, respectively, 1116 +/- 192.2 and 666 +/- 100.8 pg/ml, 4240 +/- 50.0 and 3398 +/- 368.0 pg/ml, and 431 +/- 44.0 and 352 +/- 23.9 pg/ml. In one patient with Cushing's disease caused by a pituitary adenoma, metergoline did not appreciably modify plasma ACTH levels. Taken together, these results lend support to the concept of a physiological stimulating effect of serotonin on ACTH secretion. Moreover, they are compatible with the view that serotonin exerts its action chiefly at the hypothalamic level while LVP promotes ACTH release by a primary action on the pituitary.     

Immunoreactive alpha-MSH and ACTH levels in rat plasma and pituitary.

A radioimmunoassay is described for the measurement of alpha-melanocyte-stimulating hormone (alpha-MSH). The antibody was produced in rabbits by immunization with alpha-MSH coupled to bovine serum albumin with carbodiimide. The antibody did not react significantly with ACTH, beta-MSH, or 6 fragments of ACTH. The sensitivity and reliability of the assay were improved by employing a simple plasma extraction procedure. When applied to a 2 ml plasma sample, the detection limit of the radioimmunoassay was 6 pg/ml. ACTH was measured with a sensitive and specific radioimmunoassay previously described for humans and adapted for the rat. The anti-ACTH serum cross-reacted with the biologically active portion of alpha-p ACTH and not with alpha-MSH, beta-MSH or the alpha-p 17-39 and alpha-p 25-39 fragments of ACTH. The detection limit was 20 pg/ml. Plasma and pituitary alpha-MSH and ACTH had the same immunoreactivity as synthetic alpha-MSH and ACTH. alpha-MSH and ACTH contents of the rat neurointermediate lobe were 1398 +/- 360 (SE) ng and 28.2 +/- 2.9 ng, respectively, while in the anterior lobe they were 102 +/- 31 ng and 551 +/- 36 ng, respectively. The plasma alpha-MSH concentration at 8 AM in male rats was 64 +/- 8 pg/ml when the plasma ACTH concentration was 92 +/- 15 pg/ml. Over a 24-hour period two peaks of plasma alpha-MSH were observed, one at 4 AM (142 +/- 35 pg/ml) and the other at 4 PM (139 +/- 26 pg/ml). Plasma ACTH was higher at noon (151 +/- 43 pg/ml) and 4 PM (130 +/- 48 pg/ml). Short-term exposure to ether induced a transient increase in alpha-MSH level 5 min later and a rapid return to normal levels. Plasma ACTH increased significantly 2.5 min after the onset of ether stress and remained high for 30 min. Two hours' exposure to ether did not change plasma alpha-MSH, although a 3-fold increase in plasma ACTH was observed. Haloperidol injection was followed by a large increase in plasma alpha-MSH, whereas ACTH levels increased similarly after saline and Haloperidol injection. Corticoid administration reduced ACTH, but not alpha-MSH. Three weeks after adrenalectomy, alpha-MSH levels had not changed but ACTH levels had increased ten-fold. These data indicate that alpha-MSH is secreted in the rat, and that the regulation of its secretion is different from that of ACTH.     

The responses of plasma adrenocorticotropin and cortisol to corticotropin-releasing hormone (CRH) and cerebrospinal fluid immunoreactive CRH in anorexia nervosa patients

Pituitary-adrenocortical responses to the iv injection of 100 micrograms synthetic ovine corticotropin-releasing hormone (CRH) were studied in 13 patients with anorexia nervosa, and the concentrations of immunoreactive CRH in cerebrospinal fluid were measured in 7 of them. Mean basal levels of plasma ACTH and cortisol were 32 +/- 5 pg/ml (+/- SEM) and 21.1 +/- 1.5 micrograms/dl, respectively. The latter value was significantly higher than that in age-matched normal women (P less than 0.005). The mean increments of plasma ACTH and cortisol in response to CRH injection in those 13 patients were 21 +/- 5 pg/ml and 5.3 +/- 1.7 micrograms/dl, respectively, significantly lower than those in normal women (58 +/- 6 pg/ml and 15.3 +/- 7.7 micrograms/dl, respectively; P less than 0.005). When 4 patients were reexamined after weight gains of between 3 and 22 kg, their responses to the CRH injection increased. The mean concentration of immunoreactive CRH in the cerebrospinal fluid of seven patients was 30.8 +/- 3.9 pg/ml (+/- SEM), which was higher than the value of 18.4 +/- 1.1 pg/ml (P less than 0.005) in control subjects with cervical spondylosis. These findings suggest the possibility that hypersecretion of CRH may occur in patients with anorexia nervosa.     

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.     

Inhibition of ACTH response to oral and intravenous metyrapone by antiserotoninergic treatment in man.

Plasma ACTH levels after oral and iv metyrapone administration were studied in 7 and 5 healthy women respectively both under basal conditions and after a 4-day treatment with metergoline, a specific antiserotoninergic agent. In 3 additional women, the effects of methysergide, another antiserotoninergic drug, on the plasma ACTH rise induced by oral metyrapone, were evaluated. A significant lowering of the plasma ACTH levels attained after either oral or iv metyrapone was observed following metergoline administration: 149+/-64.3 vs 239+/-49.1 pg/ml (mean peak values), P less than 0.05 in the oral test and 331+/-19.7 vs 221+/-19.5 pg/ml, P less than 0.02 in the iv test. The fall of plasma cortisol caused by metyrapone was comparable before and after the antiserotoninergic treatment. An interference of metergoline in the ACTH radioimmunoassay was also excluded. After metergoline administration, a slight reduction in the baseline plasma ACTH values was noted: 79+/-7.7 vs 67+/-7.7 pg/ml (NS). A decrease, however not statistically significant, of the metyrapone-induced plasma ACTH elevation occured after methysergide administration: 421+/-150.7 vs 344+/-135.1 pg/ml. These results can be interpreted as indicating that antiserotoninergic treatment caused an inhibition of hypophysial ACTH release in response to metyrapone. Caution is recommended, however, before concluding, on the basis of these findings, that serotonin as such plays a physiological stimulating role on ACTH secretion.     

Immunoreactive corticotropin-releasing hormone in human plasma during pregnancy, labor, and delivery

We previously reported that immunoreactive corticotropin-releasing hormone (CRH) is present in human placenta and third trimester maternal plasma, and that such material is very similar to rat CRH and the predicted structure of human CRH. We suggested that maternal plasma immunoreactive CRH may be of placental origin. To further investigate this possibility, we measured plasma immunoreactive CRH in women during pregnancy, labor, and delivery and 1 and 2 h postpartum, and in nonpregnant women. Umbilical cord plasma and placental CRH concentrations were also measured. In the first trimester of pregnancy, the mean maternal plasma level was 5.9 +/- 1.0 pg (+/- SEM)/ml (n = 24), not significantly different from that in 10 nonpregnant women (5.8 +/- 0.8 pg/ml). Plasma CRH concentrations progressively increased during pregnancy (second trimester, 35.4 +/- 5.9 pg/ml (n = 39); early third trimester (28-34 weeks), 263 +/- 41 pg/ml (n = 14); late third trimester (35-40 weeks), 800 +/- 163 pg/ml (n = 20)]. There was a significant correlation between maternal plasma CRH levels and weeks of pregnancy. Plasma CRH concentrations were further elevated (2215 +/- 329 pg/ml; n = 9). During early labor, peaked at delivery (4409 +/- 591 pg/ml; n = 28), and declined rapidly after delivery [1 h postpartum, 1042 +/- (353 pg/ml (n = 13); 2 h postpartum, 346 +/- 91 pg/ml (n = 13)]. There was a significant correlation (r = 0.562; P less than 0.01) between matched maternal plasma and placental CRH concentrations. The mean umbilical cord plasma CRH level (50.6 +/- 6.1 pg/ml; n = 28) was much lower than that in the mother at the time of delivery. Umbilical venous plasma CRH levels were significantly greater than those in simultaneously obtained umbilical arterial plasma (70.8 +/- 11.3 and 41.8 +/- 4.9 pg/ml, respectively; n = 11). There was a significant correlation (r = 0.384; P less than 0.05) between maternal and fetal CRH concentrations. Gel filtration of plasma obtained from women during the third trimester, at delivery, and early postpartum and placental extracts revealed two major peaks of immunoreactive CRH: a high mol wt peak and one at the elution position of rat CRH. In contrast, only rat CRH-sized material was detected in plasma from nonpregnant women and umbilical cord plasma. Maternal plasma immunoreactive CRH-sized material stimulated ACTH release from anterior pituitary tissue in a dose-dependent manner and was equipotent with rat CRH.(ABSTRACT TRUNCATED AT 400 WORDS)     

Substantial rise of plasma beta-endorphin levels after insulin-induced hypoglycemia in human subjects.

To elucidate whether insulin-induced hypoglycemia enhances the release of beta-endorphin in man, plasma extracts obtained from healthy subjects and patients with Graves' disease before and 45 min after insulin injection were subjected to gel chromatography, and the fractions obtained were measured by RIA for beta-endorphin. In four healthy subjects, basal plasma beta-endorphin levels were less than 3 to 3.1 pg/ml, and the levels rose substantially to 47.5 +/- 12.4 pg/ml (mean +/- SE) 45 min after insulin injection. Basal plasma beta-endorphin levels in three hyperthyroid patinets (less than 3 to 3.8 pg/ml) did not seem to be different from those in healthy subjects; however, the rise after insulin injection tended to be higher in cases of hyperthyroidism, with a peak value of 68.5 +/- 9.7 pg/ml. Plasma beta-lipotropin and ACTH levels also rose in parallel with beta-endorphin in response to insulin-induced hypoglycemia in both healthy subjects and hyperthyroid patients. It would thus appear that beta-endorphin, like ACTH or beta-lipotropin, is released in human subjects by hypoglycemic stress.     

Is the plasma ACTH concentration a reliable parameter in the insulin tolerance test?

OBJECTIVE: The insulin tolerance test (ITT) is an established standardized test for the evaluation of the hypothalamic-pituitary-adrenal axis. While a peak cortisol value of >18 microg/dl is usually interpreted as a sufficient response to the ITT, the plasma ACTH response has not yet been standardized. METHODS: We evaluated retrospectively the peak plasma ACTH concentrations during 140 ITTs in 125 patients with suspected pituitary insufficiency and prospectively in 15 healthy subjects. RESULTS: All healthy subjects had a peak cortisol concentration >/=18 microg/dl; 32 of 125 tests in the patients showed an insufficient cortisol response (peak cortisol concentration <18 microg/dl). The peak stimulated ACTH concentration in patients with secondary adrenal insufficiency (SAI) was 49.2+/-37.2 pg/ml (mean+/-s.d.) vs 130.9+/-89.3 pg/ml in patients without SAI, and 110.9+/-55.4 pg/ml in normal subjects (P<0.001). There was a weak, but significantly positive correlation between the peak ACTH and peak cortisol concentrations (rho=0.446, P<0.001), but there was also a very wide spread of the values. Defining a cut-off value for the peak plasma ACTH concentration with a sufficient sensitivity and specificity to identify patients with an impaired hypothalamic-pituitary-adrenal (HPA) axis was not possible. A peak plasma ACTH <20 pg/ml as a cut-off value had a sensitivity of 25% and a specificity of 98% for SAI. A cut-off value of a peak plasma ACTH <140 pg/ml had a sensitivity of 97% but a low specificity of 39%. CONCLUSIONS: Although there is a significant positive correlation between the peak ACTH and the peak cortisol concentrations, we conclude that there is no additional benefit in determining the ACTH concentrations during an ITT. Because of the strong variations of the values, the peak ACTH concentration is a poor parameter for the evaluation of the HPA axis.     

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.     

LOPERAMIDE, AN OPIATE ANALOGUE, INHIBITS PLASMA ACTH LEVELS IN PATIENTS WITH ADDISON''S DISEASE

The effects of loperamide, an opiate analogue of the piperidine class on pituitary hormone secretion were evaluated in eight patients with Addison's disease. In all patients loperamide administration (16 mg orally) induced a marked fall in plasma ACTH levels (P less than 0.01), without affecting GH, PRL and LH levels. Plasma ACTH concentration fell significantly from 854 +/- 167 pg/ml (mean +/- SEM) to 460 +/- 123 pg/ml at 60 min (P less than 0.01). The inhibition persisted throughout the whole test period, the nadir being reached at 300 min. Low dose naloxone infusion 180 min after loperamide administration caused plasma ACTH to rise from 181 +/- 61 pg/ml to 539 +/- 99 pg/ml (P less than 0.01). The present data suggest that the opiate analogue loperamide is a potent inhibitor of ACTH secretion in patients with Addison's disease, which may be acting on mu receptors, since its effect is blocked by low doses of naloxone.     

Evaluation of a radioimmunoassay for plasma adrenocorticotrophin.

A radioimmunoassay for plasma ACTH has been described and evaluated. Rabbit antiserum produced by immunization with [Asp25, Ala26, Gly27,]-alphah-corticotrophin-(1--28)-octacosa-peptide (a sequence analogue of alphah1--28-ACTH) bovine gamma globulin conjugate was used. The antiserum is specific for the NH2-terminal portion of the ACTH molecule and cross-reactivity of human, porcine and rat ACTH in the system has been demonstrated. Reasonable agreement was found between estimates obtained by bioassay and radio-immunoassay of the ACTH content of rat pituitary gland incubation media, indicating a close relationship between the sequence of ACTH recognized by the antibodies and the sequence possessing the steroidogenic activity. Measurement of the amount of ACTH in the plasma required the preliminary extraction and concentration of the hormone. Over a range of concentrations between 3.5 and 3600 pg/ml, extraction recovery was independent of the initial concentration of ACTH in the plasma. Extraction gave rise to no changes in the immunological properties of standard ACTH. The concentration of immunoreactive ACTH in rat plasma was 48 +/- 3.6 (S.E.M.) pg/ml in the morning and 106 +/- 9.9 pg/ml in the afternoon. Exposure to either for 5 min and subsequent laparotomy gave rise to a significant increase in the concentration of immunoreactive ACTH in the plasma. The resting level of ACTH and the ACTH response to stress were both significantly higher 1 and 7 days after adrenalectomy. Intravenous injection of a hypothalamic extract elicited a considerable rise in the concentration of immunoreactive ACTH in the plasma, but no response was seen after oral administration of this partially purified extract. The sensitivity, precision and specificity of this ACTH radioimmunoassay make it a useful tool for studying pituitary--adrenal physiology.