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)     

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.     

High levels of corticotropin-releasing hormone immunoactivity in maternal and fetal plasma during pregnancy

Corticotropin-releasing hormone immunoactivity (CRHi) was measured in the plasma of 31 pregnant women and 6 nonpregnant women as well as in the umbilical cord plasma of 40 term fetuses. CRHi was not detectable (less than 44 pg/ml) in the plasma of 6 nonpregnant women or in 6 women in the first trimester of pregnancy. Mean plasma CRHi rose progressively to 58 +/- 18 and 270 +/- 68 pg/ml during the second and third trimesters, respectively, and again became undetectable within 24 h after delivery. Mean CRHi in 40 umbilical cord plasma samples was 136 +/- 16 pg/ml. Gel filtration of both fetal and maternal plasma showed that the majority of the CRHi eluted in the same position as synthetic human CRH. There was no significant correlation between CRHi and either beta-endorphin or ACTH in umbilical cord plasma, suggesting that this CRHi may not be primarily responsible for the release of beta-endorphin and ACTH into fetal plasma at delivery. A close correlation (r = 0.82) was found between simultaneously obtained maternal and umbilical cord plasma CRHi in 10 maternal-fetal pairs, supporting a common source for this peptide in maternal and fetal circulation. A placental source for fetal and maternal CRHi was suggested by the finding of a higher CRHi concentration in the umbilical vein than in the umbilical artery and by the disappearance of this peptide from maternal plasma after delivery. We conclude that a large amount of CRHi is secreted by the placenta into both the maternal and fetal circulation during pregnancy and suggest that this may be an important modulator of the maternal and fetal hypothalamic-pituitary-adrenal axis during gestation.     

Plasma corticotropin-releasing hormone concentrations during pregnancy and parturition

Plasma CRH was measured in maternal plasma throughout the third trimester of pregnancy, during labor, and postpartum. CRH levels were also measured in arterial and venous umbilical cord plasma samples. In normal pregnant women, plasma CRH increased from 50 +/- 15 (+/- SEM) pg/mL at 28 weeks gestation (n = 41) to 1462 +/- 182 pg/mL at 40 weeks (n = 55) and 1680 +/- 101 pg/mL (n = 65) in labor. Women with pregnancy-induced hypertension (n = 49) had plasma CRH levels significantly elevated above this normal range. Similarly, women who subsequently went into premature labor had raised levels several weeks before the onset of labor. After delivery, plasma CRH returned to normal within 15 h. Total plasma cortisol levels varied little throughout the third trimester, but increased during labor and remained elevated 2-3 days postpartum. There was, therefore, no correlation between plasma cortisol and CRH, implying that this placental CRH is not primarily involved in the control of the maternal hypothalamo-pituitary adrenal axis during pregnancy. The concentrations of CRH in umbilical cord plasma samples were considerably lower than those in the maternal circulation and were close to those in normal nonpregnant adults.     

First trimester placental growth factor and soluble fms-like tyrosine kinase 1 and risk for preeclampsia

An imbalance of pro- and antiangiogenic factors may lead to preeclampsia (PE). In this prospective nested case-control study, we investigated whether first trimester serum levels of placental growth factor (PlGF), a potent angiogenic factor, and its soluble inhibitor, soluble fms-like tyrosine kinase 1 (sFlt1), distinguished women who developed PE (n = 40) from those who developed gestational hypertension (n = 40), delivered a small for gestational age (SGA) newborn (n = 40), or completed a full term normal pregnancy (n = 80). Compared with controls, serum PlGF levels were lower among women who developed PE (23 +/- 24 pg/ml vs. 63 +/- 145 pg/ml; P < 0.01) or gestational hypertension (27 +/- 19 pg/ml; P = 0.03), or who delivered a SGA newborn (21 +/- 16 pg/ml; P < 0.01). In contrast, serum sFlt1 levels did not markedly differ between the groups: PE, 1048 +/- 657 pg/ml; gestational hypertension, 942 +/- 437 pg/ml; SGA newborns, 1011 +/- 479 pg/ml; and normal controls, 973 +/- 490 pg/ml. Multivariable analysis adjusting for potential confounders and serum sFlt1 levels demonstrated a 3.7-fold (95% confidence interval, 1.2-12.5) increase in risk for PE for every log unit decrease in serum levels of PlGF compared with controls. Analyses for gestational hypertension and SGA were not significant. Examined in tertiles, the risk for PE was increased 28.7-fold (95% confidence interval, 2.3-351.0) in the third (<12 pg/ml) compared with the first (>39 pg/ml) PlGF tertile. First trimester serum levels of PlGF and sFlt1 may identify women at high risk for PE.     

Beta-endrophin immunoreactivity during human pregnancy.

The human placenta has been implicated as a source of numerous peptide hormones during pregnancy. Since the immunoassay detection of the proopiomelanocortin derived peptide beta-endorphin (beta E) in placental extracts in 1978, it has remained uncertain whether placental beta E immunoreactivity (IR) is 1) secreted into the maternal circulation and 2) opiate receptor active during pregnancy. To elucidate the nature of beta E IR in the placenta, both beta E IR and N-alpha-acetylated beta E (Ac beta E) IR were simultaneously measured in extracts of human pituitaries, placentas, and plasma by two homologous RIAs. Pituitary extracts (n = 6) contained 38 +/- 7 nmol beta E IR per g wet wt tissue (mean +/- SEM), of which only 20 +/- 4 pmol/g were Ac beta E IR. Term placental extracts (n = 19) had 201 +/- 30 fmol/g wet wt total beta E IR and 30 +/- 3 fmol/g wet wt total Ac beta E IR, which comprised 15% of total beta E IR in placental extracts. Total plasma beta E IR rose from 28 weeks gestation (8.5 +/- 0.3 fmol/mL, n = 159) to peak at labor (50 +/- 4 fmol/mL, n = 98; P < 0.01) but total Ac beta E IR was found in only four 28-week (1.7 +/- 0.9 fmol/mL) and 42 labor plasma samples (0.9 +/- 0.1 fmol/mL). Gel filtration chromatography of placental and pituitary extracts showed that while less than 1% of the beta E31-size material was acetylated in the pituitary, up to 60% of the beta E31-size material in placental extracts was acetylated. In pooled third trimester plasma extracts, however, only 4% of the beta E31-size material was acetylated. Furthermore, the ratio of beta E31:beta-lipotropin in pituitary extracts (n = 3) was 0.5; pooled plasma-0.5, and placental extracts (n = 5)-1.2. These data indicate that 1) the placenta extensively N-alpha-acetylates beta E31 destroying its opiate bioactivity while the pituitary does not; 2) beta E IR in pregnant women's plasma is similar to pituitary beta E IR, being mostly nonacetylated and similar in size to beta-lipotropin. These findings are consistent with a pituitary source for the elevated plasma beta E IR found during late pregnancy which may, in turn, be a consequence of elevated plasma concentrations of placentally secreted plasma corticotropin-releasing factor IR present during the third trimester.     

Serum immunoreactive erythropoietin during pregnancy and in the early postpartum

We studied 209 women during normal pregnancy, at delivery, or in the early postpartum, to determine whether erythropoietin (EPO) response was appropriate for the degree of anaemia. Serum immunoreactive EPO was measured in 74 nonpregnant women, including 33 normal subjects (16.4 +/- 4.1 mU/ml) and 41 women with hypoplastic, haemolytic, dyserythropoietic, or iron-deficient anaemia. An inverse linear relationship (R = -0.88, P less than 0.0001) between log(EPO) and Hct was observed. Predicted EPO values were derived for each Hct and an O/P ratio of observed/predicted log(EPO) was calculated for each sample (1.00 +/- 0.10, range 0.80-1.20). Serum EPO levels (mU/ml) were significantly higher during pregnancy (30 +/- 16, n = 142), at delivery (31 +/- 16, n = 41), and on day 7 postpartum (37 +/- 35, n = 26) than in normal women (P less than 0.001). EPO levels increased steadily from 18 +/- 6 mU/ml in the first, to 26 +/- 14 mU/ml in the second, and to 35 +/- 18 mU/ml in the third trimester (P less than 0.0001). The O/P ratio was normal on day 7 postpartum (1.01 +/- 0.16), at delivery (1.03 +/- 0.16), and in the third trimester (0.96 +/- 0.15), but was significantly reduced in the first two trimesters (0.88 +/- 0.15, P less than 0.001). A significant negative correlation between log(EPO) and Hct was lacking in the first two trimesters, was present but with a reduced slope during the third trimester and at delivery, and was normal postpartum. We conclude that EPO response to anaemia is impaired in early pregnancy, recovers in late pregnancy, and normalizes rapidly in the postpartum.     

Controls of corticotrophin-releasing factor output by hypothalamic tissue from fetal sheep in vitro

Corticotrophin-releasing factor (CRF) is thought to be an important physiological regulator of the pituitary-adrenal axis in fetal sheep and, as such, plays a fundamental role in the initiation of parturition in this species. However, little is known of the controls of CRF secretion from the fetal hypothalamus. We looked for the presence of CRF in fetal hypothalami, and examined whether the hypothalamic CRF concentration or molecular species changed in relation to gestational age. We established an in-vitro perifusion system to examine the release of CRF from perifused hypothalami taken from fetuses at day 100 and day 140 of pregnancy, under basal conditions and in response to potassium depolarization and/or dexamethasone administration. Immunoreactive CRF was present in fetal hypothalami as early as day 100 (2.42 +/- 0.99 (S.E.M.) micrograms/g protein, n = 9) and in similar concentrations at day 140 (2.31 +/- 0.69 micrograms/g protein, n = 9). There was a significant (P less than 0.05) increase in hypothalamic CRF content to 14.79 +/- 4.09 micrograms/g protein (n = 16) between day 122 and day 135 of gestation. Using Sephadex G-75 chromatography, hypothalamic extracts at day 100, days 122-135 and day 140 eluted with a single peak of immunoreactivity which corresponded to synthetic ovine CRF(1-41). The basal release of CRF from perifused hypothalami at day 140 (76.6 +/- 10.4 pg/fraction, n = 8) was significantly (P less than 0.05) greater than at day 100 (50.1 +/- 10.2 pg/fraction, n = 11). Dexamethasone significantly inhibited basal CRF release at day 140 of gestation but not at day 100.(ABSTRACT TRUNCATED AT 250 WORDS)     

Corticotropin-releasing factor secretion increases in rat hypophysial portal blood during insulin-induced hypoglycemia

To study the possible involvement of hypothalamic corticotropin-releasing factor (CRF) in the stimulation of adrenocorticotropic hormone (ACTH) release caused by insulin-induced hypoglycemia (IIH), we measured CRF secretion in hypophysial portal blood (HPB) in rats anesthetized with sodium thiopental after injection of insulin. Before treatment, systemic ACTH levels (952 +/- SE 143 pg/ml; n = 12) were well above normal values, probably reflecting the anesthetic and surgical stress consecutive to the preparation for portal blood collection. Insulin injection induced a significant increase of ACTH release within 15 min (1,588 +/- 168 vs. 741 +/- 144 pg/ml; n = 6, in vehicle-injected rats) which lasted for at least 1 h. CRF levels in HPB were 857 +/- SE 168 pg/ml (n = 13) during the first-hour pretreatment collection. Vehicle injection did not modify CRF secretion (759 +/- 142 pg/ml; n = 6). Insulin injection provoked a significant increase in CRF release (1,449 +/- 257 pg/ml; n = 7). These data suggest that an increased hypothalamic CRF secretion is responsible for the stimulation of pituitary ACTH release following IIH. The possible involvement of central neuromediators in the IIH-induced CRF production is discussed.     

Free-to-total leptin ratio in maternal plasma is constant throughout human pregnancy

To clarify the mechanism of leptin resistance during pregnancy, we measured plasma leptin concentrations, free to total leptin ratio (percent free leptin) and soluble leptin receptor concentrations in pregnant women, and compared the results with those in non-pregnant women. We collected plasma samples from 23 non-pregnant and 31 pregnant women in the third trimester. Plasma samples from 5 pregnant women were collected longitudinally in each trimester. Plasma leptin concentrations in pregnant women in the second trimester (17.4 +/- 3.2 ng/ml) were higher than those in the first trimester of pregnancy (11.0 +/- 2.8 ng/ml, n = 5), as previously reported. However, percent free leptin did not change significantly throughout pregnancy. Percent free leptin correlated with total leptin concentrations (ng/ml) in non-pregnant women (r = 0.727, P < 0.0001), but not in women in the third trimester of pregnancy (r = 0.006). Constant percent free leptin during pregnancy despite increased leptin concentrations indicates increased leptin binding capacity in pregnant women, that might partly contribute to the establishment of leptin resistance. On the other hand, soluble leptin receptor concentrations showed significant negative correlation with BMI and plasma leptin concentrations in pregnant women (r = -0.470, P < 0.01 and r = -0.493, P < 0.01, respectively) but not in non-pregnant women. These data suggest the possibility that soluble leptin receptor is a minor component of leptin binding capacity in the plasma of pregnant women.     

Changes in the concentration of 17 alpha,20 alpha-dihydroxypregn-4-en-3-one during pregnancy, labor, and delivery and the effect of dexamethasone treatment during the third trimester of pregnancy

To study whether an alteration of placental steroid metabolism occurs during human pregnancy similar to that in the ewe, we measured the concentration of 17 alpha,20 alpha-dihydroxypregn-4-en-3-one (17,20 alpha-OHP) in peripheral plasma. As the pregnant ewe nears term, the utero-ovarian venous concentrations of 17,20 alpha-OHP increase, suggesting induction of placental 17 alpha-hydroxylase. The mean plasma concentration of 17,20 alpha-OHP measured by RIA in normal menstruating women was 1.1 +/- 0.12 (+/- SE) ng/ml. Similar values were found in plasma from ovariectomized women. In the first and second trimesters of pregnancy, the plasma values of 17,20 alpha-OHP were not significantly different from those in the nonpregnant women, while in the third trimester, the mean plasma concentration was significantly increased (mean +/- SE, 2.6 +/- 0.3 ng/ml). The plasma concentration of 17,20 alpha-OHP was studied in 15 women in late pregnancy, during labor, at delivery, and postpartum. The concentration increased during labor as delivery approached and reached a maximum at the time of delivery, ranging from 4.1-11.2 ng/ml, followed by a significant decrease within 1-4 h postpartum. The mean (+/- SE) 17,20 alpha-OHP concentrations in the venous and arterial cord blood were 8.7 +/- 1.6 and 5.8 +/- 2.0 ng/ml, respectively. To study the effect of increased circulating level of corticosteroids on the serum concentration of progestins, 74 women with premature labor with or without premature rupture of membranes were treated with either placebo or 4 im injections of dexamethasone phosphate (5 mg each) at 12-h intervals. Blood samples were drawn at 0, 14, 26, and 46 h, approximately 2 h after each dexamethasone dose. Plasma progesterone, 17 alpha-hydroxyprogesterone (17-OHP), and 17,20 alpha-OHP values at zero time were 140 +/- 15.8 (+/- SE; n = 21), 7.8 +/- 1.5 ng/ml (n = 16), and 2.3 +/- 0.3 ng/ml (n = 20), respectively. In patients treated with dexamethasone, the plasma progesterone values tended to increase at 14, 20, and 46 h, but 17-OHP and 17,20 alpha-OHP values decreased significantly compared to levels in placebo-treated patients. In conclusion, the concentration of plasma 17,20 alpha-OHP increased during the third trimester of pregnancy, and the increment continued through labor and delivery. During antenatal dexamethasone administration, progesterone in the maternal circulation tended to increase, while 17-OHP and 17,20 alpha-OHP decreased significantly. In the human, in contrast to the ewe, dexamethasone treatment in the third trimester does not appear to stimulate placental 17 alpha-hydroxylase activity.     

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)     

Tissue plasminogen activator levels change with plasma fibrinogen concentrations during pregnancy

To investigate the relationship between coagulation activities and the fibrinolytic system during normal pregnancy, we measured the plasma concentrations of coagulation factors, antithrombin III (AT III), D-dimer, tissue plasminogen activator (tPA), total protein S (TPS), and plasminogen activator inhibitor type 1 (PAI-1) in 436 apparently healthy pregnant, postpartum, and nonpregnant women. There were no significant changes in AT III, TPS, and factor XI concentrations during pregnancy and puerperium. However, factor VII, VIII, IX, and XII activities increased gradually as pregnancy progressed, reached maximum values in the third trimester, and returned to nonpregnant levels by 5-8 weeks postpartum. Plasma D-dimer levels in the third trimester of pregnancy were 1.23+/-0.42 micro g/ml, significantly higher than for the first trimester (0.34+/-0.16 micro g/ml, P<0.01). The tPA antigen levels averaged 1.8-fold higher in the late third trimester than in the first trimester; the plasma fibrinogen concentrations averaged 1.6-fold higher in the late third trimester than in the first trimester. Compared to the peak values during pregnancy, tPA levels averaged 39.8% lower and plasma fibrinogen concentrations averaged 40.0% lower at 5-8 weeks postpartum. The tPA levels correlated strongly with the plasma fibrinogen concentrations ( r=0.52, P<0.01). In short, this study shows that tPA levels change in parallel with plasma fibrinogen concentrations during and after normal pregnancy.     

Autonomic nervous system mediation of the pancreatic polypeptide response to insulin-induced hypoglycemia in conscious rats.

To investigate the neural regulation of pancreatic polypeptide (PP) secretion during hypoglycemia in the rat, insulin was administered to chronically cannulated rats, and plasma PP responses were compared between saline-treated animals and animals pretreated with a ganglionic blocking agent (hexamethonium), a muscarinic antagonist (atropine), combined alpha- and beta-adrenergic receptor blockade (propranolol + tolazoline), or combined adrenergic blockade + atropine. PP was measured using a new RIA which selectively detects PP in rat plasma. In control rats (n = 10), plasma PP increased from a baseline level of 30 +/- 3 pg/ml to 271 +/- 41 pg/ml during hypoglycemia (plasma glucose = 29 +/- 2 mg/dl) (delta PP = +241 +/- 42 pg/ml, P less than 0.0005), demonstrating that in rats, as in other species, insulin-induced hypoglycemia is a potent stimulus for PP release. PP only increased by 31 +/- 10 pg/ml during similar hypoglycemia in 7 hexamethonium-treated rats (P less than 0.01 vs. control animals). Thus, at least 90% of the PP response to hypoglycemia is neurally mediated. The plasma PP response to hypoglycemia was +85 +/- 24 pg/ml in atropine-treated rats (P 0.01 vs. control rats), suggesting that approximately 65% of the PP response is mediated via muscarinic acetylcholine receptors on the islet F cell. The PP response to hypoglycemia in rats with combined adrenergic blockade (delta = +168 +/- 32 pg/ml) was slightly, but not significantly smaller than that in control rats. The combination of combined blockade + atropine resulted in a PP response (delta = +26 +/- 7 pg/ml) to hypoglycemia that was similar to that in hexamethonium-treated rats (P less than 0.01 vs. control rats). These results suggest: 1) The PP response to hypoglycemia is predominantly the result of muscarinic, cholinergic activation. 2) There is a minor adrenergic contribution to the response. 3) The plasma PP response may be useful as an index of autonomic neural input to the islet during hypoglycemia.     

Immunoreactive corticotropin-releasing factor in rat plasma

Immunoreactive ACTH (I-ACTH) levels in the rat anterior pituitary and plasma, and immunoreactive corticotropin-releasing factor (I-CRF) concentrations in the median eminence (ME) and plasma were determined after adrenalectomy and in insulin-induced hypoglycemia. I-CRF was detected in plasma from normal rats (mean +/- SD, 5.6 +/- 0.9 pg/ml; n = 6). Gel filtration chromatography of I-CRF from pooled plasma of these rats revealed a single peak which eluted in the position of authentic rat CRF. I-CRF levels in ME and I-ACTH levels in anterior pituitary decreased immediately after adrenalectomy, then gradually increased to high levels 14 days after surgery. Plasma I-CRF and I-ACTH concentrations increased immediately after surgery, slightly decreased to near the control levels at 24 h, and then increased to high concentrations 14 days after surgery. Plasma and ME I-CRF levels 14 days after adrenalectomy, followed by daily dexamethasone replacement, were almost the same as control levels. In insulin-induced hypoglycemia, plasma I-ACTH and I-CRF concentrations increased and ME I-CRF content decreased at 30 and 60 min. These results suggest that plasma I-CRF levels reflect changes in hypothalamic CRF levels.     

Adrenomedullin production is increased in normal human pregnancy

OBJECTIVE: Adrenomedullin, a recently discovered vasoactive peptide originally identified in pheochromocytoma, has been found to be increased in the plasma of pregnant women at term. This study was designed to elucidate whether adrenomedullin secretion is dependent on gestational age and the possible source and function of this peptide in human pregnancy. STUDY DESIGN: Adrenomedullin concentrations were determined by RIA in amniotic fluid and maternal plasma obtained from 110 pregnant women between 8 and 40 weeks of gestation. Subjects were stratified into five groups according to gestational age. In term patients (n = 15), adrenomedullin was also measured in the umbilical artery and vein separately. RESULTS: High concentrations of adrenomedullin were present in plasma and amniotic fluid samples from patients in the first, second and third trimester. There was no significant difference in mean maternal plasma concentration of adrenomedullin between the five patient groupings. Amniotic fluid adrenomedullin concentrations decreased from 81.2 +/- 11.7 pg/ml at 8-12 weeks of gestation to 63.7 +/- 6.0 pg/ml at 13-20 weeks of gestation and then increased at 21-28 weeks of gestation to 99.1 +/- 10.4 pg/ml. A further increase was found in samples collected after 37 weeks of gestation (132.6 +/- 10.1 pg/ml). In the umbilical vein, adrenomedullin concentration was higher (P < 0.05) than in the artery (65.7 +/- 6.1 pg/ml and 48.5 +/- 5.2 pg/ml respectively), suggesting that adrenomedullin in the fetal circulation derives from the placenta. CONCLUSIONS: Our results demonstrate the presence of adrenomedullin in maternal plasma and amniotic fluid throughout gestation, and show that its production starts very early in gestation, suggesting that this hormone may have an important role in human reproduction, from implantation to delivery.     

A central mechanism is involved in the secretion of ACTH in response to IL-6 in rats: comparison to and interaction with IL-1 beta.

The cytokines interleukin-1 beta (IL-1 beta), interleukin-6 (IL-6) and tumor necrosis factor-alpha are known to be potent effectors of ACTH secretion. Some of the peripheral effects of IL-1 beta appear to be related to the secretion of IL-6 induced by IL-1 beta. Thus, we evaluated the effect of IL-6 on ACTH secretion and its interaction with IL-1 beta. Rats received recombinant human (rhIL-6) or murine (rmIL-6) IL-6 through indwelling jugular cannulae. rhIL-6 (200 ng or 2 micrograms/rat) produced peak plasma ACTH levels which were 3- to 4-fold greater than basal levels. rmIL-6 produced similar responses. Neither species of IL-6 affected plasma prolactin levels. Comparison of rhIL-1 beta (200 ng) to rhIL-6 (200, 100 or 50 ng) showed that IL-6 elevated ACTH in a dose-dependent manner and that IL-1 beta was significantly more effective. IL-1 beta was also administered concomitantly with or 10 min after IL-6. Delivered together, IL-1 beta (100, 30 or 10 ng) and IL-6 (100 ng) produced significantly higher ACTH levels than when given alone. This additivity was also evident when IL-6 was given 10 min prior to IL-1 beta. The coadministration of IL-6 (2 micrograms) with corticotropin-releasing factor (CRF, 1 micrograms/kg, b.w.) also had an additive effect on ACTH secretion (at 20 min: 300 +/- 40 pg/ml for CRF; 320 +/- 83 pg/ml for IL-6; and 540 +/- 44 pg/ml for CRF + IL-6), whereas a higher dose of CRF (10 micrograms/kg b.w.) yielded ACTH levels of 1,000 +/- 107 pg/ml at 20 min, with no further enhancement by IL-6. Incubation of pituitary cells with IL-6 alone (0.1, 1.0 or 3.0 nM) produced a slight but significant stimulation of ACTH secretion within 2 h in response to the higher doses of IL-6 only (p < 0.05), but did not modify the effect of CRF in vitro. To determine if the action of IL-6 was at a site(s) within the brain, IL-6 (30 or 100 ng/0.5 microliters) was injected into the third cerebroventricle of alert rats. 100 ng IL-6 elicited peak plasma ACTH levels (300 +/- 65 pg/ml) within 30 min; these were significantly higher than the buffer responses (90 +/- 25 pg/ml, p < 0.01), and lower than the responses to 30 ng IL-1 beta (530 +/- 50 pg/ml, p < 0.001). 30 ng IL-6 was ineffective.(ABSTRACT TRUNCATED AT 400 WORDS)     

Elevated serum acylated (biologically active) ghrelin and resistin levels associate with pregnancy-induced weight gain and insulin resistance

AIM: To study fasting biologically active serum ghrelin (RIA) and resistin (ELISA) levels in different trimesters of pregnancy (HP, n=45, 15 in each) and in gestational diabetes mellitus (GDM, n=30) compared to non-pregnant healthy women (NP, n=40) in correlation with TNF-alpha, soluble (s)TNF-receptor (R)-1, -2, leptin (ELISA), C-peptide (Cp, RIA) and Cp/blood glucose ratio (bg). STUDY DESIGN: Cross-sectional case control study. RESULTS: Acylated ghrelin levels were significantly increased (p<0.0001) in the 2nd (377+/-38pg/ml, X+/-S.D.) and decreased in the 3rd trimester (252+/-36) and in GDM (226+/-21) compared to NP controls (309+/-20) and HP women in the 1st trimester (314+/-41). Serum resistin levels were higher in the 1st (8.5+/-2.6ng/ml), 2nd (10.2+/-2.1) and 3rd (13.1+/-3.6) trimesters of pregnancy and in GDM (15.7+/-3.5) than in NP controls (6.5+/-2.3). Significant (p<0.01) negative linear correlations were found among fasting serum ghrelin and body mass index (BMI), the fasting C-peptide (Cp) level, C-peptide/blood glucose (Cp/bg) ratio, TNF-alpha, soluble (s)TNFR-2, leptin and resistin concentrations in both, HP and GDM groups. Significant positive correlations were observed between serum acylated ghrelin and adiponectin, and between BMI and fasting Cp, Cp/bg, TNF-alpha, sTNFR-1, -2 and leptin levels in both pregnant groups. CONCLUSION: Increased fasting serum acylated ghrelin concentrations in the 2nd trimester may associate with weight gain during pregnancy. Hyperresistinemia may also be associated with the pregnancy-induced insulin resistance. A negative regulatory feed-back mechanism between resistin, TNF-alpha and ghrelin may be hypothesized.     

Serum folate binding capacity in leukemias, liver diseases and pregnancy.

Total and unsaturated folate binding capacity (TFBC, UFBC) have been measured in sera of selective groups of patients to study the role of cell turnover, cell necrosis and the effect of pregnancy in determining their concentrations in blood. The mean value of TFBC in 35 normal sera was 151 +/- (SD) 53 pg/ml with a saturation of 88%. The TFBC was raised in chronic granulocytic leukemia (CGL), in acute hepatitis, in cirrhosis, and in pregnancy (third trimester). The normal mean value of TFBC was found in chronic lymphocytic leukemia (CLL) and inthe first trimester of pregnancy. The mean UFBC in the normal sera was 19 +/- 18 pg/ml. In all the pathological conditions studied the mean UFBC was significantly greater than normal and it was particularly high in CGL (85 +/- 78 pg/ml).     

Tumor necrosis factor-alpha is a potent ACTH secretagogue: comparison to interleukin-1 beta

Tumor necrosis factor-alpha (TNF) and interleukin-1 beta (IL-1) are secreted by activated monocytes and other immune cells. Since IL-1 has been shown to elevate rat plasma ACTH and both of these cytokines induce similar acute-phase responses, the present studies of TNF were undertaken to characterize the ACTH response to this immune cell product. Human rTNF, administered iv at doses (100-1000 ng) which failed to affect blood pressure, food consumption or prolactin levels, resulted in significant peak elevations of rat plasma ACTH within 20 min (mean +/- SE 304 +/- 94 and 958 +/- 128 pg/ml for 100 and 1000 ng, respectively, compared to 53 +/- 16 pg/ml for vehicle). rTNF from two different sources produced similar elevations of ACTH as an equivalent amount of rIL-1. TNF failed to affect cultured anterior pituicytes, and it did not modify the response to CRF. When administered into the upper third cerebroventricle, TNF 20 ng failed to affect ACTH levels whereas IL-1 30 ng raised ACTH to 638 +/- 79 pg/ml compared to 177 +/- 24 pg/ml for vehicle (p less than .001). Furthermore, intraparenchymal injection of IL-1, directly above the median eminence, elevated ACTH to 484 +/- 93 pg/ml; again, TNF was completely ineffective. Thus, TNF-alpha and IL-1 beta are both potent ACTH secretagogues with complementary modes of action; however, the proximate target of TNF action appears to be peripheral to the CNS and pituitary whereas that of IL-1 appears to be the median eminence.