Changes in pituitary responses to synthetic ovine corticotrophin releasing factor in fetal sheep

The rise in cortisol in fetal sheep during late pregnancy has been related to increased responsiveness of the adrenal to ACTH. Most reports have suggested that plasma ACTH concentrations rise coincident with or after the prepartum increase in cortisol. To reexamine the relationship of cortisol with basal immunoreactive ACTH (IR-ACTH) throughout the last 40 days of pregnancy and to determine changes in fetal pituitary responsiveness during this time, we measured basal and synthetic ovine corticotrophin-releasing factor (oCRF) (10 ng-10 micrograms) induced rises in ACTH and cortisol in fetal sheep at days 110-115, 125-130, and 135-140 of pregnancy. The fetuses were catheterized on day 105-120 and entered spontaneous labour at greater than 140 days. Basal IR-ACTH (picograms per millilitre +/- SEM) rose from 16.7 +/- 2.9 pg/mL at day 110-115 to 34.8 +/- 8.7 pg/mL at day 141-145. There was a significant effect of time on basal ACTH concentrations with a mean increase of approximately 5 pg ACTH per millilitre of plasma per 5-day sampling interval. Plasma cortisol changed gradually between day 110 and 125 of gestation and then more rapidly to term. At day 110-115 of gestation there was no significant change in plasma ACTH after 10 or 100 ng oCRF, but there was a significant increase in ACTH after 1 microgram of oCRF. Plasma cortisol did not change after any CRF injection. The change in IR-ACTH after oCRF at day 125-130 of gestation was significantly greater than that at day 110-115. Plasma cortisol concentrations were elevated following 1- and 10-micrograms injections of oCRF.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effects of gestational age and intrafetal ACTH administration on the concentration of progesterone in the fetal membranes, endometrium, and myometrium of pregnant sheep

To examine the hypothesis that progesterone withdrawal from intrauterine tissues is a prerequisite to spontaneous labour or labour induced by administering ACTH to the ovine fetus, we measured the concentration of progesterone in amnion, chorion, endometrium, and myometrium of sheep at different stages of pregnancy and during ACTH-induced labour. There was no significant change in the concentration of progesterone nor in the progesterone:estradiol ratio in amnion or chorion in association with either spontaneous or ACTH-induced labour. The concentration of progesterone in endometrium rose significantly between days 50-60 and days 130-135 of gestation and decreased at term. There was also a fall in the progesterone:estradiol ratio in endometrium between days 130-135 and term. Neither the progesterone concentration not the progesterone:estradiol ratio changed in endometrium during ACTH-induced labour. In the myometrium the concentration of progesterone rose significantly between days 50-60 and day 100 of pregnancy and decreased between day 100 and days 130-135, with a further decline towards term. After intrafetal ACTH there was no change in the concentration of progesterone in the myometrium, although there was a fall in the progesterone:estradiol ratio. We conclude that labour occurring spontaneously at term is associated with a decrease in the progesterone concentration of maternal intrauterine tissues, the myometrium and endometrium. In contrast, there is no decline in the progesterone concentrations of the fetal membranes, the amnion and chorion.(ABSTRACT TRUNCATED AT 250 WORDS)     

Comparison of leucine enkephalin and adrenocorticotrophin effects on adrenal function in fetal and adult sheep

At Day 120-125 of gestation equimolar amounts of ACTH and leu-enkephalin injected in vivo provoked similar rises in plasma cortisol concentrations in chronically catheterized fetuses. There was no concomitant change in plasma DHEA concentrations, or in maternal cortisol concentrations. At term (Days 135-140) 2 out of 5 animals responded similarly to both leu-enkephalin and ACTH injections with a rise in plasma cortisol concentrations, but the other 3 animals, in which basal cortisol concentrations had already risen, showed no response to either agonist. In adult sheep, ACTH provoked a significant increase in the plasma cortisol concentrations, but equimolar amounts of leu-enkephalin were without effect. There was a significant output of cortisol in response to ACTH administration by collagenase-dispersed adrenal cells from term sheep fetuses in vitro. Leu-enkephalin had no effect on cortisol output from dispersed adrenal cells when added by itself, or with ACTH. We conclude that leu-enkephalin is able to function as a stimulator of pituitary-adrenal function during fetal life. The lack of effect of leu-enkephalin on adrenal cells implies that its action is exerted not directly at the adrenal gland, but indirectly at the level of the hypothalamus or pituitary through stimulation of the release of other corticotrophic substances.     

Activation of adrenal function in fetal sheep by the infusion of adrenocorticotropin to the fetus in utero

We determined whether ACTH1-24, infused into fetal lambs at a rate that is known to cause premature labor, elicits changes in the responsiveness of the fetal adrenal glands, and alters the pattern of corticosteroid output. Plasma cortisol (F), corticosterone (B) and progesterone (P4) were measured during 72 h of infusion of saline or ACTH (10 micrograms/h) beginning on Day 127 of pregnancy. Adrenals were then dispersed into isolated cells, and the output of F, B and P4 after exogenous ACTH determined in vitro. Plasma concentrations of F and B were higher in ACTH-treated fetuses. The increment in F (5-to 7-fold) was greater than that in B (2-fold) such that the F:B ratio in plasma of ACTH-treated fetuses on Days 2 and 3 of infusion was 2.5 times higher than in controls. After 72 h of infusion, the adrenal weights in ACTH-treated fetuses (741 +/- 38 mg, +/- SEM; n = 4) were greater than in the control animals (349 +/- 11 mg). There was a significant effect of ACTH pretreatment in vivo on F output by isolated adrenal cells in vitro. Mean increments in F output after addition of ACTH1-24 (5000 pg/ml) in vitro rose from 368 +/- 235 pg/50,000 cells in controls, to 64,639 +/- 19,875 pg/50,000 cells after ACTH in vivo. There was no significant effect of ACTH in vivo on B output in vitro; the ratio of F:B output, either in the absence or presence of ACTH in vitro, was significantly higher in cells from ACTH-pretreated fetuses. There was a significant effect of in vivo ACTH on in vitro P4 output. After ACTH treatment in vivo there was an increase in the vitro output ratio of F:P4, but no change in the output ratio of B:P4. We conclude that ACTH treatment of the fetal lamb in vivo results in activation of fetal adrenal function, increased fetal adrenal responsiveness to ACTH, and directed corticosteroid biosynthesis towards cortisol. Our results are consistent with an increase in fetal adrenal 17 alpha-hydroxylase activity after ACTH treatment.     

Cortisol production in fetal adrenals of the silver fox

The present study was designed to examine cortisol production by the silver fox fetal adrenals and their response to ACTH at different periods of prenatal life. Serum levels of cortisol were determined on days 35, 40, 45 and 50 of gestation (term on day 52) in embryos of both sexes. Cortisol content in adrenal tissue homogenates and its in vitro adrenal production were also investigated at the same time points. Hormones were measured by RIA. The levels of cortisol changed slightly during embryonic life. The adrenal content and the in vitro production of cortisol increased sharply and progressively (by 4-10 times from days 35 to 50 of gestation). The rises in cortisol content and in vitro production were associated with a rapid growth of the fetal adrenals. There were no sex differences in cortisol level and its adrenal content. ACTH (50 mIU per sample) increased the in vitro cortisol production by the adrenals in the two sexes on all the studied days (by 3-4 times on day 35 and by 1.4-1.7 times on day 50). These results indicate that 1) silver fox fetal adrenals are capable of synthesising cortisol; 2) ACTH is a potent activator of the in vitro cortisol production during embryonic life in this species.     

Induction of labour in sheep by inhibition of 3-beta hydroxysteroid dehydrogenase: role of the fetal adrenal.

In sheep parturition may be induced within 33 h in late gestation by inhibiting progesterone production with the 3 beta hydroxysteroid dehydrogenase inhibitor Epostane. Its effect has now been investigated in ewes carrying adrenalectomised (n = 5), hypophysectomised (n = 4) or intact (n = 5) fetuses to determine the role of the fetal adrenal during this type of maternally-induced delivery. Epostane was infused i.v. (1.5 mg/kg) into each group of ewes at 137-156 days gestation. Fetus and mother were sampled from the time of administration until delivery. Measurements of plasma ACTH, cortisol, progesterone and PGF2 alpha metabolite (PGFM) were made and intrauterine pressure was monitored. Epostane induced delivery significantly later in the adrenalectomised (44 h) and hypophysectomised (52 h) animals compared with the controls (33 h). The drop in maternal plasma progesterone was similar in all 3 groups, but the subsequent increases in arterial and uterine venous PGFM were smaller in the adrenalectomised and hypophysectomised ewes than in the controls. The large escalation in fetal plasma cortisol before birth in controls was absent in adrenalectomised and hypophysectomised fetuses. The slight rises in plasma cortisol observed in the latter from about 24 h after Epostane, were related to the concomitant increases in maternal plasma levels (r = 0.76, P less than 0.01). No fetuses became hypoxic or acidotic during the period of induction despite the prolonged labour of hypophysectomised and adrenalectomised fetuses.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biotransformation of pregnenolone - 7alpha-3H, progesterone - 7alpha-3H and dehydroepiandrosterone - 7alpha-3H by porcine fetal and maternal adrenal homogenate preparations.

The biotransformation of pregnenolone-7alpha-3H and of progesterone-7alpha-3H by porcine fetal and maternal adrenal homogenates at 56 and 112 days of pregnancy and of dehydroepiandrosterone-7alpha-3H by fetal adrenal homogenates has been investigated in vitro. Both pregnenolone-7alpha-3H and progesterone-7alpha-3H were metabolized extensively by maternal adrenal preparations, the principal radioactive metabolites isolated being cortisol, corticosterone, 11-deoxycortisol, deoxycorticosterone, 11beta-hydroxyprogesterone and androstenedione. In addition, 17alpha-hydroxyprogesterone, 20alpha-dihydroprogesterone and cortisone were formed from both substrates and 17alpha-hydroxypregnenolone and progesterone were formed from pregnenolone. Although essentially the same radioactive metabolites were isolated after incubation of fetal adrenal glands with pregnenolone-7alpha-3H or progesterone-7alpha-3H, a greater proportion of the radioactivity was associated with corticosteroids at 112 days of pregnancy than at 56 days. 11beta-Hydroxyandrostenedione and androstenedione were isolated and identified together with an unknown polar metabolite, after incubation of fetal adrenal tissue with dehydroepiandrosterone-7alpha-3H. These results are discussed in relation to feto-placental steroid biosynthesis and metabolism and the role of the fetal adrenal in the initiation of parturition in the pig.     

Steroid secretion by ACTH-stimulated human fetal adrenal tissue during the first week in organ culture

Fetal adrenal tissue has been reported to lose its in vivo secretory pattern by virtue of a loss of fetal zone cells after the first week in culture. Consequently, we studied the steroidogenic capacity and the responsiveness to ACTH of human fetal adrenal tissue during the first week in organ culture. The culture medium was removed daily and assayed for cortisol and dehydroisoandrosterone sulfate (DS). First, as the concentration of ACTH in the medium was increased from 0 to 1 micrograms/ml steroid secretion increased. When tissue fragments were maintained in the absence of ACTH for 3 to 4 days, there was a striking increase in steroid secretion upon addition of ACTH to the medium, with larger rates of secretion of cortisol than DS being observed. Second, the steroidogenic capacity of the separate zones of the fetal adrenal gland was assessed. Tissue from the fetal zone secreted large amounts of DS and small amounts of cortisol, whereas neocortex tissue secreted similar quantities of DS and cortisol. Third, fetal zone tissue was maintained the absence of ACTH for 4 days and thereafter ACTH was added to the media for an additional 6 days. In this experiment, there was a marked increase in DS secretion rate after the addition of ACTH and a smaller increase in cortisol secretion.     

The influence of plasma lipoproteins on steroidogenesis of cultured ovine fetal and neonatal adrenal cells

The present study examined the effects of serum and lipoproteins on the function of cultured adrenal cells from 115-127-day-old ovine fetuses and from newborn lambs. On day 1 of culture, corticosteroid output was similar in medium containing 2% horse serum or in serum-free medium, both for fetal and neonatal cells. However, on day 5, cells cultured in the absence of serum produced smaller amounts of these steroids than cells maintained in medium containing serum; the difference was more marked under ACTH1-24 stimulation. Conversely, cAMP production was never lower in the absence than in the presence of serum. When stimulated by ACTH1-24 on day 2 of culture, fetal or neonatal adrenal cells incubated in the presence of a saturating concentration of ovine LDL produced more corticosteroids than cells incubated in serum-free medium; HDL also enhanced ACTH1-24-induced steroidogenesis, but to a lesser extent. VLDL was effective only with neonatal cells. In fetal and neonatal cells cultured for 6 days in ACTH-free medium, VLDL and LDL increased ACTH-induced steroidogenesis, but HDL did not. On the other hand, when cells were cultured in the presence of ACTH1-24, LDL and HDL were equipotent in supporting ACTH1-24-induced steroid output. Three major lipoprotein fractions were observed in serum of fetal and newborn lambs. The concentration of cholesterol was very low in the VLDL fraction of fetuses, but it was similar to that of newborns in LDL. Conversely, 4 times more cholesterol was present in HDL of newborns than in HDL of fetuses. These results suggest that: (i) after several days of cell culture, cholesterol availability is an important limiting factor for the steroidogenesis of cells maintained under serum-free conditions; (ii) both an "LDL pathway" and an "HDL pathway" are operating in adrenal cells from fetal as well as newborn sheep; (iii) LDL and HDL are important physiological sources of cholesterol to support steroidogenesis by fetal and neonatal adrenal cells.     

Conversion of progesterone to corticosteroids by the midterm fetal adrenal and kidney

Midterm fetal adrenal and kidney tissue homogenates were incubated with 3H-progesterone (1 microM) and its conversion to te 3H-corticosteroids metabolites studied. Cortisol (36.3%) and corticosterone (4.7%) were isolated from the adrenal, and 11-deoxycortisol (32.5%) and deoxycorticosterone (21.1%) from the kidney. The results of these incubations confirmed the presence of 17- and 21-hydroxylase activities in both fetal tissues, and that of 11 beta-hydroxylase activity only in fetal adrenal tissue. We conclude that during pregnancy when progesterone levels are high, biosynthesis by the fetal kidney of 11-deoxycortisol, the most abundant corticosteroid formed by this tissue in this investigation, might provide to the fetal adrenal an important precursor for cortisol biosynthesis within the fetal compartment.     

Induction of parturition by cortisol: effects on negative feedback sensitivity and plasma CRF.

In fetal sheep, plasma concentrations of both adrenocorticotropic hormone (ACTH) and cortisol increase at the end of gestation. The increase in fetal plasma cortisol concentration induces placental 17 alpha-hydroxylase and 17, 20 lyase activities and therefore stimulates the placenta to secrete relatively more estrogen and relatively less progesterone. The resultant increase in the estrogen-to-progesterone ratio is thought to increase uterine contractility and initiate labour. We had previously demonstrated that the efficacy of cortisol-induced suppression of ACTH secretion at the end of gestation was reduced. We hypothesized that cortisol-induced stimulation of placental steroidogenesis promoted the secretion of a steroid hormone which reduced negative feedback efficacy, and therefore allowed both ACTH and cortisol secretion to increase simultaneously. Others had proposed that cortisol stimulates the placental secretion of corticotrophin releasing factor, which might also stimulate fetal ACTH secretion. This study was designed to test the hypotheses that cortisol reduces its own feedback efficacy or stimulates CRF secretion. Five pregnant ewes with twin pregnancies were studied after chronic catheterization. One fetus was subjected to infusion of hydrocortisone sodium succinate (10 micrograms/min, iv) and the other to infusion of saline. After 5 and 53 h of infusion, each fetus was subjected to a period of hypotension produced by infusion of sodium nitroprusside. The infusion of hydrocortisone sodium succinate decreased plasma progesterone concentrations in the fetal circulation into which the steroid was infused, and in the maternal circulation. Fetal plasma CRF concentrations were increased on the third day of infusion, the day in which the fetuses went into labour.(ABSTRACT TRUNCATED AT 250 WORDS)     

Modulation of the responses of fetal sheep to adrenergic stimulation by adrenal demedullation and chemical sympathectomy

The responses to sympathetic stimulation of fetal sheep adrenal-demedullated or sympathectomised by infusion of guanethidine sulphate have been studied. Sympathetic responses in such denervated or sympathectomised fetuses was studied by intravenous infusion of adrenaline or noradrenaline at about 0.4 micrograms/min per kg. This infusion increased plasma concentration 100-200 fold and there was no significant difference between the control fetuses and those in the vasrious treatment groups. Catecholamine infusions at these rates normally have little effect upon fetal blood gas and pH values, but in adrenal-demedullated fetuses adrenaline infusion drepressed fetal arterial PO2 by 4-6 mmHg (P less than 0.05). The heart rate and blood pressure responses to catecholamine infusion in sympathectomised fetuses was, as expected, much increased. Similar observations were made on adrenal-demedullated fetuses, an unexpected finding, and this is taken to illustrate loss of the adrenal medulla is associated with enhanced responsiveness to adrenergic stimulation in peripheral tissues. The majority of the endocrine and metabolic responses, as reflected in fetal plasma concentrations of ACTH, cortisol, insulin, glucose, lactate and fatty acids, to catecholamine infusion were similarly much enhanced by adrenal-demedullation and chemical sympathectomy. Of particular note was a substantial increase in the responsiveness of the fetal adrenal, as reflected in plasma cortisol, to stimulation by ACTH, a change that usually induces labour, but not so in the present sheep. The results on increased sensitivity in adrenal-demedullated fetuses are discussed in relation to likely tissue mechanisms mediating the changes.     

Testosterone receptor blockade after trauma and hemorrhage attenuates depressed adrenal function

Although the testosterone receptor antagonist flutamide restores the depressed immune function in males after trauma and hemorrhage, it remains unknown whether this agent has any salutary effects on adrenal function. To study this, male rats underwent laparotomy and were bled to and maintained at a blood pressure of 40 mmHg until 40% of the shed blood volume was returned in the form of Ringer lactate. Animals were then resuscitated and flutamide (25 mg/kg body wt) was administered subcutaneously. Plasma adrenocorticotropic hormone (ACTH) and corticosterone, as well as adrenal corticosterone and cAMP were measured 20 h after resuscitation. In additional animals, ACTH was administered and ACTH-induced corticosterone release and adrenal cAMP were determined. The results indicate that adrenal contents of corticosterone and cAMP were significantly decreased and morphology was altered after hemorrhage. Administration of flutamide improved corticosterone content, restored cAMP content, and attenuated adrenal morphological alterations. Flutamide also improved the diminished ACTH-induced corticosterone release and adrenal cAMP response at 20 h after hemorrhage and resuscitation. Furthermore, the diminished corticosterone response to ACTH stimulation in the isolated adrenal preparation was improved with flutamide. These results suggest that flutamide is a useful adjunct for improving adrenal function in males following trauma and hemorrhage.     

Cortisol in fetal fluids and the fetal adrenal at parturition in the tammar wallaby (Macropus eugenii)

Glucocorticoid hormones may play a critical role in initiating parturition in tammar wallabies. In this study, we investigated the concentration of cortisol in fetal fluids and cortisol production by fetal adrenals over the last 3 days of the 26-day pregnancy and within 24 h postpartum. The fetal adrenals almost doubled in size between Days 24 and 26 of pregnancy, and their cortisol content increased over 10-fold during this period, from 10 pg to over 100 pg per adrenal pair. After birth, neonatal adrenals continued to grow, but cortisol content fell dramatically to 20 pg. The prepartum increase in adrenal cortisol was reflected by a substantial rise in cortisol concentrations in yolk sac fluid, allantoic fluid, and fetal blood, which were below 10 ng/ml on Day 24 and rose to over 40 ng/ml by Day 26. Cortisol concentrations in neonatal blood decreased postpartum, mirroring decreased cortisol content in neonatal adrenals. Cortisol production by the fetal adrenal was stimulated in vitro by ACTH and prostaglandin E2, suggesting that the in vivo increase may be stimulated by release of ACTH from the fetal hypothalamic-pituitary axis and prostaglandin E2 from the placenta. These results indicate that increasing cortisol production by the fetal adrenal is a characteristic of late pregnancy in the tammar wallaby and support the suggestion that fetal cortisol may trigger the initiation of parturition in this marsupial species.     

Altered fetal pituitary-adrenal function in the ovine fetus treated with RU486 and meloxicam, an inhibitor of prostaglandin synthase-II

Term and preterm labor are associated with increased fetal hypothalamic-pituitary-adrenal (HPA) activation and synthesis of prostaglandins (PGs) generated through the increased expression of prostaglandin H synthase-II (PGHS-II) in the placenta. Inhibition of PGHS-II has been advocated as a means of producing uterine tocolysis, but the effects of such treatment on fetal endocrine functions have not been thoroughly examined. Because PGE(2) is known to activate the fetal HPA axis, we hypothesized that administration of meloxicam, a PGHS-II inhibitor, to sheep in induced labor would suppress fetal HPA function. Chronically catheterized pregnant ewes were treated with RU486, a progesterone receptor antagonist, to produce active labor, and then treated with either high-maintenance-dose meloxicam, graded-maintenance-dose meloxicam, or a saline infusion. Maternal uterine contraction frequency increased 24 h after the RU486 injection and the animals were in active labor by 48 +/- 4 h. RU486 injection led to increased concentrations of PGE(2), ACTH, and cortisol in the fetal circulation, and increased concentrations of 13,14 dihydro 15-ketoprostaglandin F(2 alpha) (PGFM) in the maternal circulation. Uterine activity was inhibited within 12 h of beginning meloxicam infusion at both infusion regimes. During meloxicam infusion there were significant decreases in fetal plasma PGE(2), ACTH, and cortisol concentrations, and PGFM concentrations in maternal plasma. In control animals, frequency of uterine contractions, maternal plasma PGFM, fetal plasma PGE(2), ACTH, and cortisol concentrations increased after RU486 administration, and continued to rise during saline infusion until delivery occurred. We conclude that RU486-provoked labor in sheep is associated with activation of fetal HPA function, and that this is attenuated during meloxicam treatment to a level considered compatible with pregnancy maintenance.     

Differential actions of metyrapone on the fetal pituitary-adrenal axis in the sheep fetus in late gestation

It is not clear if an increase in intra-adrenal cortisol is required to mediate the actions of adrenocorticotropic hormone (ACTH) on adrenal growth and steroidogenesis during the prepartum stimulation of the fetal pituitary-adrenal axis. We infused metyrapone, a competitive inhibitor of cortisol biosynthesis, into fetal sheep between 125 and 140 days of gestation (term = 147 +/- 3 days) and measured fetal plasma cortisol, 11-desoxycortisol, and ACTH; pituitary pro-opiomelanocortin mRNA and adrenal expression of ACTH receptor (melanocortin type 2 receptor), steroidogenic acute regulatory protein (StAR), 11beta-hydroxysteroid dehydrogenase type 2 (11betaHSD2), cytochrome P450 cholesterol side-chain cleavage (CYP11A1), cytochrome P450 17-hydroxylase (CYP17), 3beta-hydroxysteroid dehydrogenase, and cytochrome P450 21-hydroxylase mRNA; and StAR protein in the fetal adrenal gland. Plasma ACTH and 11-desoxycortisol concentrations were higher (P < 0.05), whereas plasma cortisol concentrations were not significantly different in metyrapone- compared with vehicle-infused fetuses. The ratio of plasma cortisol to ACTH concentrations was higher (P < 0.0001) between 136 and 140 days than between 120 and 135 days of gestation in both metyrapone- and vehicle-infused fetuses. The combined adrenal weight and adrenocortical thickness were greater (P < 0.001), and cell density was lower (P < 0.01), in the zona fasciculata of adrenals from the metyrapone-infused group. Adrenal StAR mRNA expression was lower (P < 0.05), whereas the levels of mature StAR protein (30 kDa) were higher (P < 0.05), in the metyrapone-infused fetuses. In addition, adrenal mRNA expression of 11betaHSD2, CYP11A1, and CYP17 were higher (P < 0.05) in the metyrapone-infused fetuses. Thus, metyrapone administration may represent a unique model that allows the investigation of dissociation of the relative actions of ACTH and cortisol on fetal adrenal steroidogenesis and growth during late gestation.     

Cortisol inhibits ACTH but not the AVP response to hypoxaemia in fetal lambs at days 123-128 of gestation

During acute hypoxemia in fetal sheep the elevation in ACTH concentration in the fetal circulation at days 125-129 is greater than that at term, but similar rises in AVP occur at both times. To examine whether the diminished ACTH response is due to elevated endogenous cortisol, and if there is differential control of ACTH and AVP release in hypoxemia, we infused either vehicle or cortisol (5 micrograms/min) into fetal sheep at days 123-128 for 5 h before and then during a 2-h period of acute hypoxemia (mean PaO2 decrease 8.2 mmHg) without acidemia. During cortisol infusion, plasma cortisol rose to 40-50 ng/ml, similar to values in term fetuses. In vehicle-infused fetuses, cortisol rose from 2.1 to 7.0 ng/ml at +1 to +2 h of hypoxemia. ACTH rose significantly during hypoxemia in the vehicle-infused fetuses, and this response was attenuated by cortisol infusion. In contrast, fetal AVP rose significantly during hypoxemia both in the presence and absence of cortisol infusion. Fetal breathing movements, and electroocular activity decreased during hypoxemia, and these responses were not altered by cortisol. We conclude that cortisol exerts differential negative feedback on ACTH but not on AVP release during hypoxemia. The maintained AVP response may facilitate cardiovascular adjustments of the fetus to hypoxemia even when endogenous cortisol is elevated, such as near term.     

Hypothalamic-pituitary disconnection in fetal sheep blocks the peripartum increases in adrenal responsiveness and adrenal ACTH receptor expression

Although it has been recognized for over a decade that hypothalamic-pituitary disconnection (HPD) in fetal sheep prevents the late gestation rise in plasma cortisol concentrations, the underlying mechanisms remain unclear. We hypothesized that reductions in adrenal responsiveness and ACTH receptor (ACTH-R) expression may be mediating factors. HPD or sham surgery was performed at 120 days of gestation, and catheters were placed for blood sampling. At approximately 138 days of gestation, fetuses were killed, and adrenals were removed for cell culture and analyses of ACTH-R mRNA and protein. After 48 h, adrenocortical cells were stimulated with ACTH for 2 h, and the medium was collected for cortisol measurement. The same cells were incubated overnight with medium or medium containing ACTH or forskolin (FSK), followed by ACTH stimulation (as above) and cortisol and cellular ACTH-R mRNA analyses. HPD prevented the late gestation increase in plasma cortisol and bioactive ACTH and reduced adrenal ACTH-R mRNA and protein levels by over 35%. HPD cells secreted significantly less cortisol than sham cells (3.2 +/- 1.2 vs. 47.3 +/- 11.1 ng.ml(-1).2 h(-1)) after the initial ACTH stimulation. Overnight incubation of HPD cells with ACTH or FSK restored cortisol responses to acute stimulation to levels seen in sham cells initially. ACTH-R mRNA levels in cells isolated from HPD fetuses were decreased by over 60%, whereas overnight incubation with ACTH or FSK increased levels by approximately twofold. Our findings indicate that the absence of the cortisol surge in HPD fetuses is a consequence, at least in part, of decreased ACTH-R expression and adrenal responsiveness.     

Corticoid formation by the monkey fetal adrenal: Evaluation of 17-, 21- and 11-hydroxylase activities

There is indirect evidence that cortisol synthesis in the fetal rhesus monkey adrenal gland is limited at Day 135 of gestation but increases thereafter. This study was conducted to ascertain whether a reduced synthetic capacity is caused by a deficiency in 17-, 21- or 11-hydroxylase activity. For the sake of comparison 11- and 21-hydroxylases were also estimated in adult adrenals. 11-, 21-Hydroxylases were measured in the entire adrenal by the oxidation of NADPH by mitochondria and microsomes, respectively. 17-Hydroxylase was evaluated in outer and inner regions of the fetal gland by the formation of [³H]17-hydroxyprogesterone, -11-deoxycortisol, -cortisol and -androstenedione from [³H]progesterone. The maximum velocity of both the 11- and 21-hydroxylase was similar in fetal and adult glands indicating that corticoid formation in the fetus is not constrained by levels of these enzymes.[³H]Progesterone was extensively metabolized to -17-hydroxyprogesterone, -androstenedione, -11-deoxycortisol and -cortisol by homogenates from both regions of the fetal adrenal. The ratio of [³H]-cortisol to [³H]11-deoxycortisol was consistently higher in incubations of the inner glandular area. Together, these findings indicate that 17-hydroxylase is also active at Day 135 and that the 11-hydroxylase may be more concentrated in the fetal cortex. These data suggest in addition that the restriction in cortisol formation occurs at a step prior to the metabolism of progesterone to cortisol.     

Effect of prenatal stress on the pituitary-adrenal axis in blue foxes

Handling is a source of stress for farm bred blue foxes. The influence of handling during the late gestation period on the pituitary--adrenal axis was studied in 10-day old male and female blue foxes. Cortisol and progesterone were measured by radioimmunoassay in the plasma, adrenal homogenates, and in vitro incubates from animals of both sexes. Adrenals were incubated in vitro in the absence or presence of ACTH. In addition, the adrenal weight and plasma concentration of ACTH were assessed. In cubs of both sexes, the adrenal weight was decreased after prenatal stress. The plasma concentration of progesterone and the adrenal cortisol in vitro production were elevated in the prenatally stressed female cubs, as compared to the control, along with the adrenal progesterone in vitro production in prenatally stressed male cubs. The adrenal cortisol and progesterone content and plasma ACTH and cortisol concentrations were not affected by prenatal stress. In conclusion, the results of this study suggest that the prenatal stress induced by handling pregnant vixens can affect the pituitary--adrenal axis in neonatal offspring, this effect being more pronounced in female cubs.