Effect of androstenedione administration on the maternal hypothalamo-pituitary-adreno-placental axis in the pregnant rhesus monkey

11β-HSD1 in Human Fetal Membranes as a Potential Therapeutic Target for Preterm Birth

Human parturition is a complex process involving interactions between the myometrium and signals derived from the placenta, fetal membranes, and fetus. Signals originating from fetal membranes are crucial components that trigger parturition, which is clearly illustrated by the labor-initiating consequence of membrane rupture. It has been recognized for a long time that among fetal tissues in late gestation the fetal membranes possess the highest capacity for cortisol regeneration by 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1). However, the exact role of this unique feature remains a mystery. Accumulating evidence indicates that this extra-adrenal source of cortisol may serve as an upstream signal for critical events in human parturition, including enhanced prostaglandin and estrogen synthesis as well as extracellular matrix remodeling. This may explain why such high capacity for cortisol regeneration develops in human fetal membranes at late gestation. Therefore, inhibition of 11β-HSD1 may provide a potential therapeutic target for prevention of preterm birth. This review summarizes the current understanding of the functional role of cortisol regeneration by 11β-HSD1 in human fetal membranes.

The anti-androgen combination, flutamide plus finasteride, paradoxically suppressed LH and androgen concentrations in pregnant spotted hyenas, but not in males

The androgen receptor blocker flutamide and the 5α-reductase inhibitor finasteride have been used in a variety of species to investigate the ontogeny of sexual dimorphisms by treating pregnant females or neonates at critical periods of sexual differentiation. Likewise, we have used these drugs to study the profound masculinization of the external genitalia in female spotted hyenas. However, a potential pitfall of administering flutamide, either alone or in combination with finasteride, is that it maintains or even raises plasma concentrations of luteinizing hormone (LH) and testosterone (T), because negative feedback of the hypothalamic-pituitary-gonadal axis is disrupted. Contrary to expectations, when pregnant spotted hyenas were treated with flutamide and finasteride (F&F), the concentrations of T during late gestation were suppressed relative to values in untreated dams. Herein, we further investigate the paradoxical effects of F&F treatment on a battery of sex hormones in spotted hyenas. Beyond the effects on T, we found plasma concentrations of LH, estradiol, progesterone and androstenedione (A4) were also significantly lower in F&F-treated pregnant hyenas than in controls. Flutamide and finasteride did not have similar effects on LH, T, and A4 concentrations in male hyenas. The paradoxical effect of F&F treatment on LH and T concentrations in the maternal circulation suggests that negative feedback control of gonadotropin and androgen secretion may be modified in spotted hyenas during pregnancy.

Placental corticotrophin-releasing hormone, local effects and fetomaternal endocrinology

The human placenta produces corticotrophin-releasing hormone (CRH) in exponentially increasing amounts during pregnancy with peak levels during labour. CRH in human pregnancy appears to be involved in many aspects of pregnancy including placental bloodflow, placental prostaglandin production, myornetrial function, fetal pituitary and adrenal function and the maternal stress axis. Since fetal cortisol levels are associated with pulmonary development and maturity, placental CRH may have an indirect role in fetal development.Although the precise role of placental CRH in the regulation of gestational length and timing of parturition is unclear it appears to be involved in a placental clock. While glucocorticoids inhibit hypothalamic CRH production they stimulate CRH gene expression in the placenta.This difference may allow the fetal and maternal stress axes to influence this placental clock.Maternal CRH levels are elevated in many pathological conditions of pregnancy where fetal well-being is compromised, and in these situations it may act to maintain a stable intrauterine environment. Therefore, CRH appears to link placental function, maternal well-being, fetal well-being and fetal development to the duration of gestation and the timing of parturition.

Fetectomy alters maternal pituitary-adrenal function in pregnant rhesus macaques

The interplay between the fetus and mother may play a key role in the regulation of primate pregnancy and parturition. This study was designed to test the hypothesis that fetectomy alters maternal pituitary-adrenal function. Between 117 and 122 days of gestation (term = 167 days), six rhesus macaques underwent surgery for catheter implantation. At surgery the fetuses were removed while the membranes and placenta were left in situ. Six additional intact catheterized pregnant animals served as controls. Animals were maintained under a 12L:12D cycle with lights-on from 0700 to 1900 h. Beginning at least 1 wk after surgery, maternal arterial blood samples were collected at 3-h intervals for 24 h for hormone and catecholamine analysis. This sampling protocol was repeated at weekly intervals until cesarean delivery at 151-157 days of gestation. Following fetectomy, plasma ACTH, dehydroepiandrosterone sulfate (DHEAS), and cortisol levels were significantly lower (36%, 35%, and 44%, respectively) compared with control animals (P;lt 0.05). Despite a significant reduction in overall levels, the rhythm in maternal plasma cortisol was maintained following fetectomy. Plasma dopamine and norepinephrine were also depressed (P;lt 0.05), whereas epinephrine remained unaffected. Our data clearly demonstrate the role of the fetus in the regulation of the maternal pituitary-adrenal axis during gestation. This interaction plays a significant role in the regulation of maternal endocrine function that may influence the initiation of labor.

Androstenedione treatment of pregnant baboons at 0.7-0.8 of gestation promotes a premature forward shift in the nocturnal maternal plasma estradiol surge relative to progesterone and increases myometrial contraction activity

Androstenedione treatment of pregnant monkeys at 0.8 of gestation reproduces endocrine, biophysical, and biochemical changes similar to those measured during spontaneous, term labor in the pregnant monkey. In the pregnant baboon, the spontaneous onset of labor at term has been attributed to a forward shift in the nocturnal estradiol surge relative to that of progesterone in maternal plasma. This study investigated whether androstenedione treatment of the pregnant baboon at 0.7-0.8 of gestation promotes a premature forward shift in the nocturnal surge of maternal plasma estradiol relative to progesterone and whether this shift is associated with premature increases in nocturnal myometrial activity. Eight pregnant baboons were prepared surgically under general anesthesia with vascular catheters and myometrial electromyogram electrodes between 121 and 139 days of gestation (term is ca. 185 days). Catheters were maintained patent by continuous infusion of heparinized saline from the time of surgery until one of two treatments began following at least 9 days of postoperative recovery. In four baboons (Group I), the saline administration was replaced by a continuous infusion of 10% intralipid vehicle during Day 1 of the experimental protocol. During Day 2 and Day 3, the intralipid infusion was switched for a continuous infusion of androstenedione dissolved in intralipid set at a low (0.8 mg x kg(-1) x h(-1)) and at a high (1.6 mg x kg(-1) x h(-1)) dose, each delivered for 24 h. The other four pregnant baboons (Group II) received 10% intralipid vehicle for Days 1, 2, and 3 of the experimental protocol. One baboon from Group I received an additional dose of 0.4 mg x kg(-1) x h(-1) for 24 h before the low and the high dose of androstenedione. In each baboon, during each experimental day, maternal arterial blood samples (1 ml) were taken at 1 h intervals for 12 h, starting 3 h before the onset of darkness in the animal's environment, for measurement of maternal plasma estradiol and progesterone concentrations via RIA. Myometrial contractions were counted during each night-time period of the experimental protocol. All pregnant baboons demonstrated increases in maternal plasma estradiol and progesterone concentrations at night-time. Androstenedione had a dose-dependent effect in elevating day-time maternal plasma estradiol concentrations and in promoting a forward shift in the nocturnal surge of maternal plasma estradiol without affecting the nocturnal progesterone profile in maternal plasma. Maternal treatment with androstenedione also led to an increase in nocturnal myometrial contraction activity. We conclude that androstenedione treatment of the pregnant baboon at 0.7-0.8 of gestation promotes a premature forward shift in the nocturnal estradiol surge relative to that of progesterone in maternal plasma and that this shift is associated with an increase in nocturnal myometrial contraction activity, in a similar way to that measured during spontaneous onset of labor at term in this species.

Opposing effects of androgen and estrogen on pituitary-adrenal function in nonpregnant primates

Maternal administration of androstenedione produces a sustained fall in maternal plasma adrenocorticotropic hormone (ACTH) concentrations in the pregnant nonhuman primate. We hypothesize a negative feedback influence on the maternal hypothalamo-pituitary-adrenal (HPA) axis by androgens in primates. This may reflect an important maternal adaptation during pregnancy in primates preventing premature induction of labor by maternal stress. However, androstenedione is precursor for placental estradiol-17beta synthesis, and infusion of androstenedione into pregnant primates elevates maternal plasma estradiol-17beta to term concentrations. Thus, it could be argued that 1) the effects attributed to androstenedione on the maternal HPA axis are mediated by estrogen rather than by androgen and 2) the negative influence of androgens may be on placental ACTH rather than, or in addition to, pituitary ACTH. To discriminate between androgenic and estrogenic effects of androstenedione on pituitary and/or placental ACTH function in primates we measured plasma ACTH, cortisol, and dehydroepiandrosterone sulfate (DHEAS) concentrations in nonpregnant baboons after treatment with either androstenedione or estradiol-17beta. Nine female baboons were studied between 14 and 22 days postpartum prior to estrous cycling. After 2 days of baseline, a continuous i.v. infusion of androstenedione (1.5 mg/kg per h in 10% intralipid, IL) was started at 0900 h and maintained for 9 days in 3 baboons. A similar protocol was carried out in another 3 baboons that received a continuous i.v. infusion of estradiol-17beta (10 microg/kg per h in 10% IL) instead of androstenedione. Three additional baboons received continuous i.v. IL vehicle alone and served as controls. Arterial blood samples (0.5 ml) for measurement of plasma hormones were taken during baseline and after 1, 3, 5, 7, and 9 days of infusion. Baseline plasma ACTH, DHEAS, and cortisol concentrations were similar among all groups. Plasma ACTH did not change during IL, increased following estradiol-17beta, and fell during androstenedione treatment. Accordingly, plasma cortisol and DHEAS concentrations were also unaltered by IL, and both steroids increased during estradiol-17beta treatment. In contrast, plasma cortisol and DHEAS remained unaltered from baseline during androstenedione treatment, despite the fall in plasma ACTH measured at this time. These data in the nonpregnant baboon 1) are consistent with negative feedback on pituitary ACTH by androgens and 2) demonstrate a positive influence on pituitary-adrenal function by estrogen in primates.

Level of postoperative analgesia is a critical factor in regulation of myometrial contractility after laparotomy in the pregnant baboon: implications for human fetal surgery

OBJECTIVES

We used 2 dosage levels of postoperative opioid administration to determine whether the degree of postoperative analgesia after laparotomy during the last third of baboon pregnancy alters maternal pituitary-adrenal function, androgen secretion, and placental estrogen production. We also determined the relationship of estrogen production to surgery-induced increase in myometrial contraction activity.

STUDY DESIGN

After laparotomy under halothane general anesthesia at 0.75 gestation, 10 pregnant baboons were administered intra-arterially either a normal dose or a double dose of the opioid analgesic buprenorphine for 48 hours. Maternal plasma samples for steroid hormone and oxytocin analyses were obtained at circadian time 1000 hours and at circadian time 1800 hours, 4 hours before and 4 hours after the lights went off, respectively. Myometrial electromyographic contraction activity was quantified for the 6 hours from circadian time 1100 hours to circadian time 1700 hours.

RESULTS

Maternal plasma cortisol and dehydroepiandrosterone sulfate concentrations were lower in the dark period (at circadian time 1800 hours) than during daylight (at circadian time 1000 hours) in the double-dose group but not the normal dose group. In contrast, maternal plasma estradiol level was higher at circadian time 1800 hours than at circadian time 1000 hours in the normal dose group but not in the double-dose group. Maternal plasma estrogen level was higher during the hours of darkness in the normal dose group than in the double-dose group. Furthermore the number of myometrial contractions around the onset of darkness was greater in the normal dose group than in the double-dose group.

CONCLUSIONS

The double dose of analgesia results in lower maternal nighttime plasma estradiol concentrations and significantly less nocturnal contraction activity. These observations further confirm an association between increased maternal plasma estrogen concentrations and increased myometrial contractility in the nonhuman primate. In addition, they suggest that adjustment of the level of postoperative analgesia may be of importance in preventing premature labor after chuman intrauterine fetal surgery.

Corticotropin-releasing hormone directly and preferentially stimulates dehydroepiandrosterone sulfate secretion by human fetal adrenal cortical cells

Estrogens produced by the placenta play a pivotal role in the endocrine control of pregnancy and induce many of the key changes involved in parturition. The placentae of humans and higher primates use the C19 androgen dehydroepiandrosterone sulfate (DHEA-S) supplied by the fetal adrenals as the principal substrate for estrogen synthesis. Thus, secretion of androgens by the fetal adrenals may be central to the process of primate parturition. The timing of human parturition also is correlated with placental CRH concentrations in the maternal circulation. Because the mechanisms that regulate DHEA-S production by the fetal adrenals are incompletely understood, we examined whether there is a functional relationship between CRH and steroid production by human fetal adrenal cortical cells. Using Northern blot analysis, we detected messenger RNA transcripts (2.7 kb) encoding the type-1 CRH receptor in total RNA extracted from midgestation human fetal adrenals, suggesting that the fetal adrenal cortex may be directly responsive to CRH. To test this, primary cultures of human fetal adrenal cortical cells were exposed to human CRH. Human CRH increased DHEA-S production by cultured human fetal adrenal cortical cells in a dose-dependent fashion, with an ED50 of 10-100 pmol/L. Human CRH was as effective as ACTH at stimulating DHEA-S production; however, it was 70% less potent than ACTH at stimulating cortisol production, indicating that its actions were preferentially directed toward increasing DHEA-S synthesis. Consistent with this thesis, we found that CRH increased abundance of messenger RNA encoding cytochrome P450 cholesterol side-chain cleavage and 17alpha-hydroxylase/17,20 lyase but not 3beta-hydroxysteroid dehydrogenase in adrenal cells. CRH did not alter cell number, indicating that it is not mitogenic for fetal adrenal cortical cells. These data demonstrate a direct functional interaction between CRH and the fetal adrenal. Therefore, placental CRH production, which rises exponentially during human pregnancy, may play a key role in promoting DHEA-S production by the fetal adrenals, which could lead to increasing placental estrogen synthesis and contribute to the process of parturition in humans.

Maternal adrenalectomy eliminates a surge of plasma dehydroepiandrosterone in the mother and attenuates the prenatal testosterone surge in the male fetus

Previous work has established a number of sex-related deficits in immune function, behavior, and endocrine responses to stress in the offspring of dams exposed to ethanol. To examine the potential role of maternal glucocorticoids as a mediator of these sexually dimorphic effects in the fetus, we examined the influence of prenatal alcohol exposure in the presence or absence of maternal glucocorticoids on fetal plasma corticosterone (CORT) production. An additional question to be addressed by these studies was whether maternal adrenalectomy could eliminate the known inhibition by ethanol of the prenatal surge of plasma testosterone in male fetuses. Pregnant dams were adrenalectomized (ADX) or sham-adrenalectomized on gestational day (G) 7 and placed on a liquid diet containing 35% ethanol-derived calories or pair-fed an isocaloric control diet throughout the experiment. On G18, G19, and G21, plasma levels of CORT, testosterone, and dehydroepiandrosterone (DHEA) were measured in male and female fetuses and their mothers. Ethanol administration consistently increased maternal plasma CORT levels but did not significantly alter CORT levels in the fetus. Maternal ADX resulted in compensatory increases in fetal CORT levels that were lower in fetuses of ADX dams on alcohol, suggesting a direct effect of ethanol on fetal pituitary-adrenal activity. There were no significant sex differences in fetal plasma CORT levels in response to any of these manipulations. A novel surge of maternal plasma DHEA was found on G19 that was absent in plasma from ADX dams. In spite of the absence of a surge on G19, plasma DHEA levels of ADX dams rose from very low levels at G18 to levels on G21 that were significantly higher than in Sham dams. A normal testosterone surge was observed in male fetuses on G18 and G19 from sham-adrenalectomized dams administered the pair-fed diet. However, this surge was greatly attenuated in males administered ethanol and also in male fetuses from ADX dams. These results reveal a direct inhibitory influence of ethanol on fetal CORT secretion as well as on the prenatal testosterone surge in males. Furthermore, these studies demonstrate the presence of a surge of DHEA in the pregnant rat. Overall, these data suggest that there is a critical adrenal factor in the rat that regulates the maternal surge of DHEA on G19 and the prenatal testosterone surge of male fetuses on G18-19.