Pulsatile output of prostaglandin F(2alpha) does not increase around the time of luteolysis in the pregnant goat.

Prostaglandin (PG) F(2alpha) secreted from the uterus is the luteolysin of the estrous cycle and is also believed to be responsible for luteolysis in the pregnant doe at term. We have reported that basal progesterone concentrations decrease before basal PGF(2alpha) concentrations increase, which is inconsistent with this view. In this study we investigated whether luteolysis is associated with increased frequency or amplitude of pulsatile PGF(2alpha) secretion in does over the last 2 wk of gestation. Progesterone concentrations decreased approximately 1 wk before parturition. There was no accompanying increase in PGF(2alpha) concentrations or pulse frequency, and those pulses that were observed were of lesser amplitude and duration than those that have been associated with luteolysis in cycling ewes. A small increase in PGF(2alpha) pulse frequency was identified during the 3 days before parturition, but this was not associated with any change in progesterone concentrations. The biological significance of these small changes in PGF(2alpha) pulse frequency is obscure, although the high concentration of this eicosanoid at labor may have been related to the final, precipitous decline in plasma progesterone concentrations. These findings do not support the notion that PGF(2alpha) is the principal luteolysin in the pregnant doe at term.

Effects of prostaglandin E2 on renal function and lung liquid dynamics in foetal sheep.

1. The aim of the present study was to determine the effects of prolonged prostaglandin E2 (PGE2) administration on the function of the foetal kidneys and lungs in order to gain a greater understanding of the role played by PGE2 in the control of foetal fluid balance. By studying the effects of PGE2 at two gestational ages, we have also been able to examine the influence of age. 2. We studied the effects of 26 h PGE2 infusion on foetal sheep at a mean (+/- SEM) of 120.0 +/- 0.6 (n = 6) and 139.0 +/- 0.8 (n = 4) days of gestation. In both groups, foetal urine production was significantly inhibited throughout the infusion period (P < 0.05). In younger, but not older foetuses, urine production returned to control values within 24 h of ending the infusion (P < 0.05). This PGE2-induced anti-diuresis was associated with foetal hypoxaemia and acidaemia, a reduction in free water clearance and an increase in foetal plasma arginine vasopressin concentrations (P < 0.05). 3. During PGE2 infusions, foetal breathing movements were inhibited, the effect being greater and more sustained in older foetuses (P < 0.05). 4. Infusions of PGE2 led to increased lung liquid production at both ages (P < 0.05); lung liquid volumes were reduced in older foetuses (P < 0.05), but were unchanged in younger foetuses. The reduction in lung liquid volume in older foetuses may have been due to inhibition of foetal breathing. 5. We conclude that increased circulating levels of PGE2 have profound effects on foetal renal and lung function which, if sustained, could compromise foetal lung development and perinatal well-being.

Studies on the role of ACTH in the regulation of adrenal responsiveness and the timing of parturition in the ovine fetus.

A dramatic late-gestation increase in fetal plasma cortisol concentrations is critical for the timing of parturition in the sheep. This increase appears to depend upon an intact hypothalamo-pituitary unit and is characterised by increasing responsiveness of the fetal adrenal gland to ACTH. ACTH has been postulated as the critical determinant of the late-gestation cortisol increase; however, recent evidence has suggested that other factors, including the ACTH precursor, pro-opiomelanocortin, may also be involved. To further define the role of ACTH in determining the timing of parturition and the responsiveness of the fetal adrenal gland, intact (INT/ACTH) and hypophysectomised (HX/ACTH) fetuses received a continuous infusion of ACTH(1-24) from the time of surgery (approximately 115 days gestational age (GA)) at a rate we have previously shown to generate normal fetal cortisol concentrations and term parturition in HX fetuses. A third group of saline-infused intact fetuses (INT/SAL) served as the control group. Adrenal responsiveness was assessed by cortisol responses to ACTH(1-24) challenges at 120, 130 and 140 days GA. There were no differences between the three groups of fetuses in the timing of parturition, the late-gestation increase in cortisol concentrations or the size of the adrenal cortex. In both INT/SAL and INT/ACTH fetuses, there were significant increases in basal immunoreactive-ACTH concentrations with advancing GA, although no such increase was observed in HX/ACTH fetuses. The proportion of total ACTH immunoreactivity present in low molecular weight (LMW) forms in INT/ACTH fetuses was greater than that in INT/SAL fetuses, while the level of LMW ACTH in HX/ACTH fetuses was intermediate. Both ACTH(1-24)-infused groups of fetuses had dramatically enhanced adrenal responsiveness to ACTH(1-24) at all GAs tested when compared with INT/SAL fetuses and there was a correlation (in rank order) between the proportion of LMW ACTH immunoreactivity and adrenal responsiveness. From these observations it appears that there is a separate regulation of adrenal responsiveness from basal cortisol concentrations and that an increase in basal cortisol concentrations can occur in the absence of an increase in basal ACTH concentrations. Furthermore, an increase in adrenal responsiveness does not appear to predict the timing of parturition nor basal cortisol concentrations. Taken together with previous studies it appears that ACTH plays an essential role in maintaining the growth of the fetal adrenal and enhancing its responsiveness, but a late-gestation increase in ACTH concentrations is not required to regulate basal cortisol concentrations or the timing of parturition.

Angiotensin II infusion in vivo does not modulate cortisol secretion in the late-gestation ovine fetus.

Maturation of the fetal adrenal gland is critical for the onset of ovine parturition. It has long been proposed that the fetal adrenal gland may be under inhibitory influences during late gestation. In vitro evidence has suggested that angiotensin II may be such an inhibitory factor and may help to prevent a premature increase in cortisol concentrations. The aim of this study was to test the effect of angiotensin II infusion in vivo on basal cortisol concentrations and fetal adrenal responsiveness to an ACTH-(1-24) challenge. Fetuses received a continuous infusion of either angiotensin II (100 ng . min-1 . kg-1; n = 7) or saline (2 ml/h; n = 4), which commenced at 140 days of gestation (GA) and continued for a total of 50 h. Adrenal responsiveness to the administration of ACTH-(1-24) (5 microg/kg) was determined during angiotensin II or saline infusions at both 2 and 48 h after infusion onset. Angiotensin II had no significant effect on adrenal responsiveness after acute (2 h) or chronic (48 h) infusion. There was no effect of saline or angiotensin II infusion on basal immunoreactive ACTH or cortisol concentrations after 2 h, but there was a significant increase in basal cortisol concentrations in both treatment groups by 48 h, probably reflecting the normal rise in cortisol concentrations at this GA. Mean arterial blood pressure was significantly increased in angiotensin II-infused fetuses only. This study has therefore found no evidence to suggest that angiotensin II infusion in vivo modulates fetal basal cortisol concentrations or adrenal responsiveness in the last week of gestation, in contrast with previous in vitro studies. These results throw into question the proposed role of angiotensin II as a negative modulator of adrenal function in the ovine fetus.

Fetal and maternal endocrine changes approaching parturition in the goat: lack of evidence for prostaglandins E2 and F2alpha as signals for luteolysis.

We investigated the temporal relationship of fetal cortisol secretion to circulating concentrations of fetal ACTH1-39 and its high-molecular weight precursors in goats. We also measured the concentrations of progesterone, estradiol-17beta estrone sulfate, prostaglandin (PG) E, PGF2alpha, and PGF2alpha metabolite (PGFM) in maternal arterial plasma over the last month of gestation. Prostaglandin concentrations were also measured in utero-ovarian venous plasma. There was a positive association between ACTH1-39 in fetal plasma and the prepartum surge in fetal cortisol that commenced 8 days before labor. The fetal cortisol surge was followed by a simultaneous decrease in maternal progesterone and an increase in plasma estrogens commencing 3-4 days before labor. No change in basal prostaglandin concentration occurred before this time. There was a positive veno-arterial difference of PGE and PGF2alpha across the uterine vascular bed, confirming the uteroplacental unit as a major source of these eicosanoids in the plasma of the pregnant doe. We conclude that the fetal signal for parturition precedes luteolysis by some 5 days and find no evidence of changes in the basal concentrations of PGE and PGF2alpha in maternal plasma at the time of luteolysis.

Effect of alteration of maternal plasma progesterone concentrations on fetal behavioural state during late gestation.

Placental progesterone synthesis exposes the fetus to high levels of progesterone and progesterone metabolites during late gestation which may influence fetal behaviour. To determine the role of maternal progesterone synthesis in the control of fetal arousal state and fetal breathing movements (FBM), the effect of raising and lowering maternal progesterone concentrations was examined in chronically catheterised fetal sheep. Fetal and maternal vascular catheters, fetal tracheal and amniotic fluid catheters as well as electrodes for recording fetal electrocortical (ECoG), electro-ocular (EOG) and nuchal muscle electromyographic (EMG) activity were implanted between 118 and 122 days gestational age (GA). Progesterone, 100 mg, administered twice daily i.m. for 3 days (130-133 days GA) resulted in a marked elevation in maternal plasma progesterone concentrations (370 +/- 121%, n = 5, P < 0.05), but had no effect on fetal plasma concentrations. Fetal EOG episodes and the duration of fetal behavioural arousal were significantly suppressed throughout the progesterone treatment period (74.4-81.1% and 58-65% respectively, P < 0.05, n = 5). Four ewes received Trilostane (25 mg i.v.), a 3 beta-hydroxysteroid dehydrogenase inhibitor, between 136 and 140 days GA. Maternal and fetal progesterone concentrations were significantly lowered by 60 min after treatment (19.8 +/- 8.0% and 39.5 +/- 24.3% respectively, P < 0.05). The incidence of fetal EOG activity increased from a pretreatment level of 26.8 +/- 1.5 min/h to 30.3 +/- 2.8 min/h at 1-6 h and to 35.0 +/- 1.7 min/h (P < 0.05) during the 7-12 h after Trilostane treatment. The duration of FBM episodes was significantly higher at 1-6 h and 7-12 h after Trilostane treatment (19.5 +/- 3.0 and 23.6 +/- 5.5 min/h respectively, P < 0.05) compared with pretreatment levels (11.2 +/- 1.2 min/h). We conclude that increasing maternal progesterone levels suppresses fetal EOG activity and behavioural arousal, whereas reducing maternal progesterone synthesis leads to an elevation of EOG activity and FBM.

Suppression of arousal by progesterone in fetal sheep.

The high rate of progesterone synthesis by the placenta in late gestation exposes the ovine fetus to high concentrations of progesterone and its metabolites that may affect activity of the fetal brain. The aim of this study was to determine the effect of inhibiting maternal progesterone synthesis on sleep-wake activity in fetal sheep. Fetal and maternal vascular catheters, a fetal tracheal catheter, and electrodes for recording fetal electrocortical (ECoG), electro-ocular (EOG) and nuchal muscle electromyographic (EMG) activity were implanted. At 128-131 days gestation, progesterone production was inhibited by an injection of trilostane (50 mg), a 3beta-hydroxysteroid dehydrogenase inhibitor. Vehicle solution or progesterone (3 mg h(-1)) was then infused into the ewe between 6 and 12 h after the trilostane treatment. Maternal progesterone concentrations were significantly reduced from 1-24 h after trilostane treatment (P < 0.05) when followed by vehicle infusion. Fetal breathing movements (FBM), EOG, nuchal muscle EMG, and behavioural arousal increased 12 h after trilostane treatment (P < 0.05). In contrast, there was no change in fetal arousal, EOG, EMG or FBM activities when progesterone was infused after the trilostane treatment. These findings show that progesterone can influence fetal behaviour, and indicates that normal progesterone production tonically suppresses arousal, or wakefulness in the fetus.

Continuous intrafetal infusion of prostaglandin E2 prematurely activates the hypothalamo-pituitary-adrenal axis and induces parturition in sheep.

This study has investigated the effect of continuous intrafetal infusion of PGE2 or saline on hormone concentrations and the length of gestation in sheep. Fetal and maternal vascular catheters were surgically implanted at 112.3 +/- 1.3 days (n = 10), and the infusions were started at 121 +/- 1.2 days of gestation (term = 147). Fetuses were infused with either PGE2 (n = 5; 2 micrograms/min for 48 h and then increased to 4 micrograms/min for the remainder of the experiment) or the vehicle solution (n = 5; sterile isotonic saline) via the fetal carotid artery. In the PGE2-infused group, fetal and maternal plasma PGE2 concentrations increased (P < 0.001) after the change to the higher dose rate (4 micrograms/min) and remained elevated, fetal plasma immunoreactive ACTH (ir-ACTH) concentrations dramatically increased after the start of the infusion being maximal at 11 h before decreasing to match concentrations exhibited by the saline-infused group. Fetal plasma cortisol concentrations increased after the start of the PGE2 infusion (P = 0.05) and increased further after the change to the higher dose rate of 4 micrograms/min (P < 0.001). Concentrations of PGE2, ir-ACTH, and cortisol in the saline-infused group did not change until labor. Plasma concentrations of PGE2 (P < 0.001) and ir-ACTH (P < 0.005) increased on the day of labor in both treatment groups, and fetal cortisol concentrations increased (P < 0.001) in both groups in the last few days before labor. The proportion of low molecular weight ir-ACTH in the plasma of PGE2-infused fetuses was significantly higher than that of saline-infused fetuses (P < 0.001) during the first 15 days of infusion. In the saline-infused group, the proportion of low molecular weight ir-ACTH increased in the last few days before labour (P = 0.001), whereas no change was seen in PGE2-infused fetuses at this time. Maternal plasma progesterone concentrations decreased in both groups in the last few days before labor (P < 0.001). Fetuses infused with PGE2 delivered at 138.4 +/- 2.1 days, whereas control fetuses infused with saline delivered at 148.2 +/- 0.5 days (P < 0.001). The spontaneous increase in PGE2 preceding normal labor may thus play an important role in activation and maturation of the hypothalamic-pituitary-adrenal axis in fetal sheep.

Locations and molecular forms of gastrin-releasing peptide-like immunoreactive entities in ovine pregnancy.

Large quantities of gastrin-releasing peptide-like immunoreactivity (GRP-LI) are present in ovine pregnancy fluids (allantoic fluid > fetal plasma > esophageal fluid = amniotic fluid = urine > maternal plasma) and in term endometrium (60 +/- 29 pmol.g-1) and myometrium (4.5 +/- 1.2 pmol.g-1). The larger molecular size [greater than GRP (1-27)] of this GRP-LI entity is not due to a GRP binding protein nor to a C-terminal extension of GRP. In contrast, ovine fetal colon extracts appear to contain the usual GRP (1-27) and GRP (18-27) forms. Hence, the uterus, not the fetus, is the probable source of this novel GRP-like peptide. It apparently acts as a hormone in ovine pregnancy and may play an important role in fetal-placental development.

Development of adrenocorticotropin-(1-39) and precursor peptide secretory responses in the fetal sheep during the last third of gestation.

Although it is known that concentrations of immunoreactive ACTH increase during late gestation in fetal sheep plasma, the nature of the ACTH has not been well characterized. We used two-site immunoradiometric assays to separately measure high mol wt ACTH precursors (POMC and pro-ACTH) and ACTH-(1-39) in plasma of fetal sheep with chronic arterial and venous catheters. We compared the ratio of these peptides as a function of gestational age under basal conditions and in response to exogenous vasopressin and/or corticotropin-releasing hormone. Under basal conditions, the concentration of precursors was not changed throughout the last third of gestation; however, ACTH-(1-39) increased significantly approaching term. The molar ratio of precursors to ACTH-(1-39), therefore, decreased from 15.8 +/- 1.0 at 110 days to 7.9 +/- 0.6 at 140 days gestation. At all gestational ages, vasopressin and corticotropin-releasing hormone increased ACTH-(1-39) and precursors, albeit with different time courses. At 120 days gestation, arginine vasopressin plus CRH produced synergistic increases in ACTH-(1-39) and precursors, whereas the response was only additive at other ages. The present results indicate that the elevation in the resting plasma immunoreactive ACTH concentration that occurs near term is constituted by an increase in the concentration of ACTH-(1-39) relative to those of POMC and pro-ACTH, which may have further physiological significance. Also, CRH and AVP are potent stimulators of both ACTH-(1-39) and ACTH precursors.

Biological activity of adrenocorticotropic hormone precursors on ovine adrenal cells.

Adrenocorticotropic hormone (ACTH) is synthesized in the corticotrophs as a precursor, pro-opiomelanocortin (POMC), which is processed via proACTH to ACTH. Both precursors and ACTH are secreted. Although the steroidogenic activity of ACTH is well characterized, that of the precursors is not. This study assessed the capacity of POMC and proACTH to alter cortisol synthesis. POMC and proACTH were prepared by subjecting medium, conditioned by exposure to DMS-79 cells, to Sephadex chromatography, and the bioactivity was assessed in cultured-dissociated ovine adrenal cells. Alone neither POMC (< or = 2.6 nM) nor proACTH (< or = 0.7 nM) showed any consistent acute (6 h) stimulatory or inhibitory action on cortisol in either fetal or adult cells. In contrast, in fetal cells the precursors inhibited steroidogenic response to ACTH-(1-24). POMC at 2.6 nM, but not lower concentrations, decreased the cortisol responses to 0.01, 0.1, and 1 nM ACTH by at least 50%. ProACTH (0.70 and 0.23 nM) decreased the responses to ACTH at 0.01 nM by 89 and 67%, respectively, and at 0.1 nM by 49 and 34%, respectively. At 1 nM ACTH only 0.7 nM proACTH decreased the response to ACTH (by 69%). In contrast, in adult adrenal cells, the precursors did not significantly reduce the response to ACTH (range 0.01-1 nM). Therefore, these data indicate that POMC and proACTH can inhibit the cortisol response to ACTH in fetal adrenal cells, an effect that is concentration dependent. The data suggest that precursors may play a physiological role, possibly regulating fetal plasma cortisol concentrations.

Prostaglandin E2 administered to fetal sheep increases the plasma concentration of adrenocorticotropin (ACTH) and the proportion of ACTH in low molecular weight forms.

This study investigated the effects of repeated short term (2-h) intrafetal infusions of prostaglandin E2 (PGE2) on ACTH and cortisol release in fetal sheep during late gestation (119-144 days). We compared the effects of administration of PGE2 (2 micrograms/min) into the fetal carotid artery or jugular vein. PGE2 infusion significantly (P < 0.001) increased fetal plasma immunoreactive (ir-) ACTH and cortisol concentrations regardless of the vessel used for administration. Saline infusion did not alter the concentrations of ir-ACTH or cortisol for the duration of the experiment. To compare the responses of fetal ir-ACTH and cortisol to repeated intracarotid infusions of PGE2, the hormone data were grouped into five gestational age ranges (119-125, 126-130, 131-135, 136-140, and 141-145 days). Fetal ir-ACTH was stimulated by PGE2 infusion at all gestational ages studied; the greatest response was achieved at the earliest gestational age range, 119-125 days. PGE2 infusion preferentially stimulated the release of low mol wt ACTH [ACTH-(1-39); 60 min from the start of infusion] at all gestational ages (P < 0.01), but basal low mol wt ACTH did not increase with gestational age until after 140 days. Cortisol concentrations were increased within 30 min of infusion at all gestational ages studied. These results suggest that PGE2 may play a role in maintaining elevated ir-ACTH concentrations in the face of high levels of cortisol in fetal sheep before parturition.

Prostaglandin E2, fetal maturation and ovine parturition.

The major source of PGE2 in ovine pregnancy is the placenta, with secretion occurring bidirectionally into fetal and maternal circulations. The placental output of PGE2 appears to increase when demand on placental function is increased, suggesting that the normally observed increase in its concentration towards term is driven by the growing demands of the fetus. The fetal pituitary is also involved in the control of PGE2 synthesis. PGE2 has potent stimulatory actions on the fetal pituitary to increase both the absolute concentration and the bioactive fraction of ACTH-containing peptides in the fetal circulation. It also directly stimulates glucocorticoid secretion from the fetal adrenal gland. We propose that PGE2 provides a tonic stimulation of the fetal HPA axis in late gestation, contributing to phenomena such as the apparent insensitivity of the pituitary to cortisol feedback and the increasing sensitivity of the fetal adrenal. Because of its apparent responsiveness to placental workload, it may transduce stimuli from the placenta and transmit them to the fetal HPA axis, giving a possible biochemical basis to the empirically observed correlation between fetal metabolic demand and gestation length.

Chronic administration of low doses of adrenocorticotropin to hypophysectomized fetal sheep leads to normal term labor.

Parturition in the sheep is preceded by an increase in the plasma concentration of fetal ACTH and an increase in the plasma cortisol concentration. The role and importance of the increase in fetal ACTH in stimulating fetal glucocorticoid synthesis and the subsequent onset of labor require closer examination, as it has been demonstrated that the fetal adrenal becomes more responsive to ACTH in late gestation. This study sets out to determine whether the increase in plasma ACTH in the late gestation fetal sheep is essential for maturation of the fetal adrenal gland and normal delivery. Fetal sheep were either hypophysectomized (HX) and cannulated or cannulated only (intact) at 125 days gestation. Immediately after surgery, HX fetuses were infused with a constant dose of ACTH-(1-24) (ACTH/HX; 100 ng/h.kg, i.v.) or saline (SAL/HX) until uterine electromyography indicated the onset of labor or 161 days gestation was reached (term = 147 +/- 2.6 days). The mean gestational age at labor of the ACTH/HX group was 147 +/- 2.9 days, whereas none of the animals in the SAL/HX entered labor, and they were killed at 161 days gestation. The concentration of ACTH in both ACTH/HX and SAL/HX fetal plasma was less than 2.2 pg/ml throughout the study. The concentration of cortisol in ACTH/HX fetuses mimicked that in intact fetuses in late gestation, reaching 80 ng/ml at term. The concentration of cortisol in SAL/HX fetuses remained less than 5 ng/ml. This study supports the hypothesis that the ovine fetal adrenal becomes increasingly responsive to ACTH in late gestation and indicates that ACTH may only be permissive in the activation of adrenal function. In intact fetal sheep there may be endogenous inhibition of the fetal adrenal, requiring relatively high plasma concentrations of ACTH [100-250 pg/ml ACTH-(1-39)] in late gestation.

Effect of late hypothalamo-pituitary disconnection on the development of the HPA axis in the ovine fetus and the initiation of parturition.

The studies of Liggins et al. (1) in which fetuses stalk-sectioned from day 116 onwards delivered at or near term, suggested that a connection between the fetal hypothalamus and pituitary is not essential for parturition to occur. The objective of this study was to repeat these experiments on the effects of pituitary stalk sections at different gestational ages and include information on the plasma concentrations of key fetal hormones. We have used the more sophisticated technique of hypothalamo-pituitary disconnection (HPD) at either of two gestational age ranges (123-127 days or 133-135 days). Completeness of the procedure was assessed by demonstrating an attenuated prolactin response to chlorpromazine challenge. Following HPD, gestation was prolonged for at least eight days beyond term (146.2 +/- 1.5 days) in 9 of the 10 fetuses operated. Fetal plasma ACTH1-39 concentrations were not different between the HPD and control fetuses, increasing in all groups with increasing gestation. Fetal plasma cortisol concentrations increased (P < 0.01) in control fetuses over gestation. Cortisol concentrations did not change significantly in the day 125 HPD group following HPD but increased in the day 135 HPD group (P < 0.05) with advancing gestation. These latter concentrations, however were markedly less (P < 0.001) than those for control fetuses prior to parturition. Fetal and maternal plasma PGE2 concentrations increased (P < 0.01) in the control group over gestation but did not change following HPD. Maternal plasma progesterone concentrations decreased (P < 0.05) after day 143 in the control group but did not change in the HPD group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of inhibition of prostaglandin synthesis on flow and composition of fetal urine, lung liquid, and swallowed fluid in sheep.

OBJECTIVE: Our aim was to determine the effects of blocking prostaglandin synthesis, by infusion of indomethacin into the fetal circulation, on factors regulating amniotic fluid volume and on plasma composition in the mother and fetus. STUDY DESIGN: Indomethacin was administered to fetal sheep during 8 hours at 124.0 +/- 1.2 days of gestation (n = 7) and at 134.7 +/- 0.8 days of gestation (n = 7) (term approximately 147 days). Vehicle infusions were performed at 128.8 +/- 1.4 days of gestation (n = 5). RESULTS: Fetal urine production was significantly reduced and both fetal urine osmolality and plasma arginine vasopressin concentrations were significantly elevated in response to indomethacin infusions at both gestational ages. Fetal blood and urine lactate concentrations were elevated in response to indomethacin. Later in gestation, fetal lung liquid flow was significantly changed from a net efflux to a net influx. There was no significant effect of indomethacin on the volume of fluid swallowed by the fetus. CONCLUSION: Inhibition of fetal prostaglandin synthesis profoundly reduces the production of the two major fetal fluids contributing to amniotic fluid, namely, urine and lung liquid. These findings may explain why indomethacin reduces amniotic fluid volume.

Early hypophysectomy of sheep fetuses: effects on growth, placental steroidogenesis and prostaglandin production.

The factors involved in the control of steroid secretion from the ovine placenta and in fetal growth are as yet unclear. We hypothesized that factors derived from the fetal pituitary may play a role in the production and release of placental steroids and in growth of the fetus, and have investigated the effects of fetal hypophysectomy performed between day 70 and day 79 of gestation (term = 147 days) on systemic concentrations of hormones derived from the placenta, and on fetal growth. Maternal peripheral progesterone, placental lactogen and uterine vein progesterone increased significantly from day 90 in all ewes. Peripheral concentrations of prostaglandin E2 and peripheral and uterine vein oestrone sulfate increased significantly in the control group but not in the fetal hypophysectomy group. Uterine vein prostaglandin E2 increased significantly after day 95 in the control group and after day 105 in the fetal hypophysectomy group. Early fetal hypophysectomy caused marked growth retardation. The weights of the brain, kidneys and liver of hypophysectomized fetuses were the same as those of controls suggesting that their growth is not under pituitary control. In contrast, the weights of heart and lungs were reduced in proportion to body weight, suggesting that heart, lung and carcass growth were under pituitary control. Our data indicate that the fetal pituitary influences the control of placental steroid and prostaglandin E2 biosynthesis after day 90 of gestation in sheep, but that output of other hormones such as placental lactogen is independent of pituitary control, and may determine organ-specific growth parameters that are unaffected by removal of the fetal pituitary.