Infusion of pregnant rats with calcitonin gene-related peptide (CGRP)(8-37), a CGRP receptor antagonist,increases blood pressure and fetal mortality and decreases fetal growth

Calcitonin gene-related peptide (CGRP) is the most potent endogenous vasodilatory peptide, and is involved in the regulation of blood flow to vital organs. We have previously shown that CGRP may be involved in vascular adaptations that occur during pregnancy, and that steroid hormones may be involved in these mechanisms. We hypothesized that endogenous CGRP is required for maintaining blood pressure and fetoplacental growth in pregnant rats, and that progesterone will enhance CGRP effects. The vasodilatory effects of CGRP are known to be inhibited by a competitive CGRP receptor antagonist, the C-terminal fragment CGRP(8-37). In the present study, we investigated whether continuous s.c. infusion of CGRP(8-37) to pregnant rats will reduce fetoplacental growth and increase systolic blood pressure. We also assessed whether progesterone will alter the effects of CGRP(8-37) on blood pressure during postpartum. Groups of five pregnant rats were s.c. infused with varying doses of CGRP(8-37) from Day 17 of pregnancy. Daily systolic blood pressures, pup weight, mortality at term delivery, and fetoplacental weights on Day 20 of gestation were measured. CGRP(8-37) at a dose of 0.083 mg day(-1) kg(-1) body weight (BW) showed no effects; however, doses of 0.33 and 1.33 mg day(-1) kg(-1) BW increased (P < 0.05) blood pressure during pregnancy, and these elevated blood pressures persisted during postpartum with the highest dose used. Progesterone (2 mg per injection, twice a day; s.c.) treatment significantly elevated blood pressure in rats infused with CGRP(8-37) during postpartum, suggesting that progesterone regulates CGRP-induced vascular effects. CGRP(8-37) infusion caused significant reductions in pup weight with an increase in mortality rate, and these effects were dose-dependent. Placental and fetal weights were also decreased prior to term on Day 20 of gestation, 72 h after CGRP(8-37) infusion, indicating effects on uteroplacental tissues. Therefore, we suggest that endogenous CGRP plays an important role in maintaining normal fetoplacental development, fetal survival, and vascular adaptations during pregnancy.     

Mesenteric arterial relaxation to calcitonin gene-related peptide is increased during pregnancy and by sex steroid hormones

The present study investigated whether pregnancy and circulatory ovarian hormones increase the sensitivity of the mesenteric artery to calcitonin gene-related peptide (CGRP)-induced relaxation and possible mechanisms involved in this process. Mesenteric arteries from young adult male rats or female rats (during estrous cycle, after ovariectomy, at Day 20 of gestation, or Postpartum Day 2) were isolated, and the responsiveness of the vessels to CGRP was examined with a small vessel myograph. The CGRP (10(-10) to 10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in mesenteric arteries of all groups. Arterial relaxation sensitivity to CGRP was significantly (P < 0.05) greater in female rats compared with male rats. Pregnancy increased the sensitivity to CGRP significantly (P < 0.05) compared to ovariectomized and Postpartum Day 2 rats. In pregnant rats, CGRP-receptor antagonist, CGRP(8-37), inhibited the relaxation responses produced by CGRP. The CGRP-induced relaxation was not affected by N(G)-nitro-l-arginine methyl ester (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by an inhibitor of guanylate cyclase (1H-[1 , 2 , 4 ]oxadizaolo[4 , 3 -a]quinoxalin-1-one, 10(-5) M). Relaxation responses of CGRP on mesenteric arteries were blocked (P < 0.05) by a cAMP-dependent protein kinase A inhibitor, Rp-cAMPs (10(-5) M). The CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by calcium-dependent (tetraethylammonium, 10(-3) M), but not ATP-sensitive (glybenclamide, 10(-5) M), potassium channel blocker. Therefore, the results of the present study suggest that mesenteric vascular sensitivity to CGRP is higher during pregnancy and that cAMP, cGMP, and calcium-dependent potassium channels appear to be involved. Therefore, we propose that CGRP-mediated vasodilation may be important to maintain vascular adaptations during pregnancy.     

Mechanisms involved in calcitonin gene-related Peptide-induced relaxation in pregnant rat uterine artery

Human and rodent studies have demonstrated that calcitonin gene-related peptide (CGRP), a potent vasodilator, relaxes uterine tissue during pregnancy but not during labor. The vascular sensitivity to CGRP is enhanced during pregnancy, compared to nonpregnant human uterine arteries. In the present study, we hypothesized that uterine artery relaxation effects of CGRP are enhanced in pregnant rats compared to nonpregnant diestrus rats (NP-DE) and that several secondary messenger systems are involved in this process. We also hypothesized that the expression of CGRP-A receptor components, calcitonin receptor-like receptor (CRLR), receptor activity-modifying protein (RAMP1), and CGRP-B receptors are greater in pregnant rats. For vascular relaxation studies, uterine arteries from either NP-DE or Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP-A and CGRP-B receptor expressions were assessed by RT-PCR and Western immunoblotting, respectively. CGRP (10(-10)--10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in both NP-DE and Day 18 pregnant rat uterine arteries. Pregnancy increased the vasodilator sensitivity to CGRP significantly (P < 0.05) compared to NP-DE rats. CGRP receptor antagonist, CGRP8-37, inhibited CGRP-induced relaxation of pregnant uterine arteries. The CGRP-induced relaxation was not affected by NG-nitro-l-arginine methyl ester (L-NAME) (nitric oxide inhibitor, 10(-4) M) but was significantly (P < 0.05) attenuated by inhibitors of guanylate cyclase (ODQ, 10(-5) M) and adenylate cyclase (SQ 22536, 10(-5) M). CGRP-induced vasorelaxation was significantly (P < 0.05) attenuated by potassium channel blockers KATP (glybenclamide, 10(-5) M) and K(CA) (tetraethylammonium, 10(-3) M). The expression of CRLR and RAMP1 was significantly (P < 0.05) elevated during pregnancy compared to nonpregnant diestrus state (NP-DE). However, CGRP-B receptor proteins in uterine arteries were not altered with pregnancy compared to those of NP-DE. These studies suggest that CGRP-induced increases in uterine artery relaxation may play a role in regulating blood flow to the uterus during pregnancy and, therefore, in fetal growth and survival.     

Gestational changes in calcitonin gene-related peptide, nerve growth factor, and its receptors in rat dorsal root ganglia.

In dorsal root ganglia (DRG) cell cultures, levels of calcitonin gene-related peptide (CGRP) are increased in the presence of ovarian hormones and nerve growth factor (NGF). In addition, injection of ovariectomized rats with ovarian hormones led to an increase in levels of two NGF receptors, TrkA and p75(NTR), in DRG. Thus, we hypothesized that increased levels of ovarian hormones during pregnancy may elevate the synthesis of CGRP and NGF receptors in the DRG. DRG harvested from rats on specific days of pregnancy, on Day 2 postpartum, and after ovariectomy were subjected to radioimmunoassay, Western blot analysis, and NGF immunoassay to determine levels of CGRP, TrkA and p75(NTR), and NGF, respectively. CGRP levels in rat DRG were significantly higher during pregnancy than at Day 2 postpartum or in ovariectomized rats. Levels of both TrkA and p75(NTR) in DRG increased during pregnancy and remained elevated at Day 2 postpartum, but CGRP levels declined. Levels of NGF reached a statistically significant peak at Day 18 of gestation, and were not significantly reduced at Day 2 postpartum. Increased levels of ovarian steroid hormones during pregnancy may be involved in the synthesis of CGRP, however, the postpartum decreases in CGRP synthesis appear to be unrelated to NGF and its receptors.     

Female steroid hormones modulate receptors for nerve growth factor in rat dorsal root ganglia

Calcitonin gene-related peptide (CGRP) is a vasodilatory peptide, and it is primarily synthesized in dorsal root ganglia (DRG). Plasma CGRP levels increase during pregnancy and with steroid hormones, and nerve growth factor (NGF) stimulates calcitonin/CGRP promoter and CGRP synthesis in DRG. We previously showed that CGRP levels in DRG were stimulated with steroid hormone treatments in vivo but not in vitro. Thus, the stimulation of CGRP by these hormones may be indirect through the upregulation of NGF effects. We hypothesized that the female sex steroid hormones upregulate NGF receptors, trkA and p75(NTR), in DRG. We examined the effects of 17 beta-estradiol (E(2)) and progesterone (P(4)) on NGF receptors in DRG obtained from ovariectomized (ovx) rats. Groups of 4 ovx rats were injected s.c. with 5 microg E(2), 4 mg P(4), or 5 microg E(2) + 4 mg P(4) in 0.2 ml sesame oil or injected with oil only and were killed at 6, 24, and 48 h. In addition, ovx rats were also injected s.c. with varying doses (0.2, 1.0, 5.0, 25 microg) of E(2) (0.5, 1.5, 4, 10 mg) P(4), and (5 microg) E(2) + (0.5, 1.5, 4.0, 10 mg) P(4) in 0.2 ml sesame oil, or vehicle, and killed at 6 (for E(2)) or 24 (for P(4) and E(2) + P(4)) h. Furthermore, groups of ovx rats were also killed at 12 and 24 h; 3 and 7 days; 2, 4, and 6 wk after ovariectomy. The DRGs were collected from all groups and then processed for Western immunoblotting to examine both trkA and p75(NTR) levels. Estradiol increased trkA at 6 h but not p75(NTR). Progesterone caused upregulation of trkA and p75(NTR) at 6 and 24 h. 17 beta-Estradiol + P(4) increased trkA at 6 and 24 h and p75(NTR) at all time points examined. One microgram of E(2) increased trkA but did not affect p75(NTR) levels. Progesterone at 4 and 10 mg upregulated trkA but only 10 mg P(4) increased p75(NTR). Five micrograms of E(2) coinjected with P(4) at 1.5 and 4 mg increased trkA, while p75(NTR) receptor was upregulated when coinjected with P(4) at 1.5 to 10 mg. The ovariectomy caused a decrease in trkA receptors compared to proestrus rats, and these decreases were significant by 6 wk, but surprisingly p75(NTR) increased at 2 wk after ovariectomy. 17 beta-Estradiol increased trkA but not p75(NTR) receptors in DRG, whereas P(4) caused increases in both trkA and p75(NTR) in DRG. In addition, the combination of these steroid hormones had more effect on both receptors than either hormone alone. Thus, we concluded that high levels of female steroid hormones such as those due to pregnancy or hormonal replacement therapy could increase NGF receptor expression in DRG that carry more NGF to elevate the CGRP synthesis in these groups. We suggested that the regulation of NGF receptors by ovarian steroids may underlie steroidal regulation of other factors such as CGRP.     

Effects of pregnancy and female sex steroid hormones on calcitonin gene-related peptide content of mesenteric artery in rats

Calcitonin gene-related peptide (CGRP) levels in plasma and the dorsal root ganglia (DRG) are increased during pregnancy and in ovariectomized rats injected with ovarian hormones. Vasodilatory responses to CGRP are also increased in these animals. In the present study, we hypothesized that pregnancy and ovarian hormones elevate the contents of CGRP in perivascular nerves. We assessed CGRP-dependent mesenteric vascular relaxation induced by electrical field stimulation (EFS) and arterial content of CGRP. Because the mesenteric artery represents resistance vessels, segments of mesenteric arteries collected from female rats at different stages of the estrous cycle, pregnancy, or postpartum and from male rats were used in this study. The EFS-induced relaxation in the presence and absence of CGRP(8-37), an antagonist of CGRP, was used to measure CGRP-dependent relaxation, and radioimmunoassay (RIA) of tissue homogenates was used to assess changes in CGRP content in mesenteric branch arteries. The results show that CGRP-dependent, EFS-induced relaxation response was lower in female rats at diestrus and proestrus than in male rats, and no statistically significant differences were observed between Gestational Day 20 and Postpartum Day 2. The RIA revealed significantly lower mesenteric artery CGRP levels in female rats at proestrus, gestation, and postpartum than in female rats at diestrus or in male rats. We conclude that no correlation exists between CGRP-dependent, EFS-induced relaxation and CGRP content in the mesenteric arteries of these animal groups. Because both CGRP levels in DRG and serum are reported to be elevated, the reduced CGRP content in the vasculature during pregnancy and proestrus implicate enhanced basal release of CGRP at the nerve terminal in these animals.     

Regulation of calcitonin gene-related peptide expression in dorsal root ganglia of rats by female sex steroid hormones

Calcitonin gene-related peptide (CGRP), a potent vasodilator primarily synthesized in dorsal root ganglia (DRG) neurons, has been shown to decrease vascular resistance and thus regulate blood flow to a variety of organs in rats. Serum CGRP levels in the human have been reported to increase with pregnancy and decrease postpartum. It has been suggested that female sex steroid hormones play a role in cardiovascular function, but the mechanisms are unknown. In this study, we examined the effects of estradiol-17beta (E(2)) and progesterone (P(4)) on the expression of CGRP in DRG in adult rats both in vivo and in vitro. Ovariectomized (ovx) animals were injected s.c. with 5 microg E(2), 4 mg P(4), or 5.0 microg E(2) + 4 mg P(4) in 0.5 ml sesame oil or with oil only, and groups of 4 rats were killed at 0, 24, or 48 h. DRGs were then removed and analyzed for CGRP mRNA and immunoreactive (i-)CGRP content by Northern blotting and RIA, respectively. Primary cultures of DRG neurons from adult female rats were used to assess the effects of varying doses of E(2) (1, 10, 100 nM), P(4) (10, 100, 1000 nM), or E(2) (10 nM) + P(4) (100 nM) in the absence or presence of nerve growth factor (NGF; 20 ng/ml); and CGRP mRNA content in the cells and i-CGRP in the medium were quantitated at 24 or 48 h after incubation. Results of in vivo studies showed that E(2) caused a significant increase in CGRP mRNA at 24 h (1.8-fold) and in i-CGRP levels both at 24 h (2. 8-fold) and at 48 h (3.4-fold) in DRG of ovx rats. P(4) also stimulated expression of both CGRP mRNA and i-CGRP. In the in vitro studies, either E(2) or P(4) alone or the two in combination were without effect on CGRP expression in cultured DRG neurons at all the doses tested. However, in the presence of NGF, both CGRP mRNA and peptide levels were significantly enhanced by E(2), P(4), and E(2)+P(4) in a time-dependent (2.0- to 2.8-fold at 24 h, 3.0- to 5. 0-fold at 48 h) and dose-dependent manner, with maximal effects achieved at 1.0 nM (E(2)) and 100 nM (P(4)) at 24 h of incubation. In summary, both E(2) and P(4), either alone or in combination, stimulate CGRP peptide synthesis in DRG neurons through increasing CGRP mRNA. The effects of these steroid hormones are mediated through amplifying the NGF-induced synthesis of CGRP in these neurons. Thus, we propose that the cardiovascular functions of female sex steroid hormones may be mediated, at least in part, by the up-regulation of neuronal CGRP synthesis, via NGF-mediated mechanisms.     

Effects of estradiol and progesterone on vertebral collagen, glycosaminoglycans and phosphatases in ovariectomized adult rats.

Vertebral collagen, glycosaminoglycans (GAGs), tartrate-resistant acid phosphatase (TRAP) and alkaline phosphatase (ALP) were measured in ovariectomized (ovx) adult Wistar rats treated with estradiol (E 2 ) (10 micro g/kg BW for 35 days on alternate days, and progesterone (P 4 ) (140 micro g/kg BW for 35 days on alternate days) in E 2 + P 4 treated rats. P 4 given alone or in combination with E 2 significantly increased the levels of collagen in the vertebral bone. Neither ovx nor E 2 treatment altered the concentration of collagen in these rats. Administration of E 2 or P 4 significantly decreased the concentration of hyaluronic acid (HA), but remaining unaffected when a combination of these steroids was given. In contrast to their effect on HA, E 2 and P 4 each significantly increased the levels of chondroitin sulfate (CS) in the vertebral bone. The specific activity of ALP was decreased after ovx. E 2 and P 4 alone or in combination also registered a significant decrease in the activities of ALP and TRAP. The results suggest that E 2 and P 4 each exert definite effects on vertebral bone turnover in ovariectomized rats.     

Studies on the effects of the N-terminal domain antibodies of calcitonin receptor-like receptor and receptor activity-modifying protein 1 on calcitonin gene-related peptide-induced vasorelaxation in rat uterine artery

The vascular relaxation sensitivity to calcitonin gene-related peptide (CGRP) is enhanced during pregnancy, compared with nonpregnant human and rat uterine arteries. In the rat uterine artery, two types of CGRP receptors have been shown to coexist, CGRP-A receptor, which is a complex of calcitonin receptor-like receptor (CRLR), and receptor activity-modifying protein (RAMP(1)) and CGRP-B receptor, which is different from CRLR. In the present study, we hypothesized that: 1) CGRP-induced vasorelaxation in rat uterine artery is mediated through CGRP-A receptor and 2) N-terminal (Nt) domain of CRLR (Nt-CRLR) has a major contribution in ligand binding and mediating CGRP- induced relaxation effects in rat uterine artery. Polyclonal antibodies against Nt-domain of CRLR and RAMP(1) (Nt-RAMP(1)) were raised in rabbits and characterized for their specificity and were used to inhibit CGRP-induced vasorelaxation in rat uterine artery. For vascular relaxation studies, uterine arteries from Day 18 pregnant rats were isolated, and responsiveness of the vessels to CGRP was examined with a small vessel myograph. CGRP (10(-10) to 10(-7) M) produced a concentration-dependent relaxation of norepinephrine-induced contractions in Day 18 pregnant rat uterine arteries. These effects were significantly (P < 0.05) inhibited when uterine arteries were incubated with the antibody raised against Nt-CRLR (PD(2) = 6.75 +/- 0.20) and were totally abolished in presence of antibodies for both Nt-CRLR and Nt-RAMP(1) (PD(2) = 6.14 +/- 0.35). In contrast, a monoclonal antibody for CGRP-B receptor had no effect on CGRP-induced rat uterine artery relaxation. These studies suggest that CGRP effects in rat uterine artery are mediated through CGRP-A receptor and that Nt-domain of CRLR may play a predominant role in CGRP binding and thus in causing CGRP-induced uterine artery relaxation.     

Vascular hyperresponsiveness to adrenomedullin during pregnancy is associated with increased generation of cyclic nucleotides in rat mesenteric artery

Cardiovascular adaptation is a hallmark of pregnancy. Here we report on vascular hyperresponsiveness to an endogenous vasodilator, adrenomedullin (ADM), during pregnancy. Intravenous administration of ADM dose dependently decreased the mean arterial pressure, and the decrease was significantly greater in pregnant compared with nonpregnant rats without affecting the heart rate. In endothelium-intact mesenteric artery precontracted by ED70 concentration of norepinephrine, the potency and efficacy of ADM in causing the vasodilation of mesenteric arterial rings from pregnant rats are significantly higher compared with nonpregnant females at diestrus. The magnitude of inhibition of concentration-dependent response to ADM by the inhibition of either soluble guanylate cyclase or adenylate cyclase was greater in pregnant rats. Moreover, ADM-induced cyclic nucleotide generation, both cGMP and cAMP, in the mesenteric artery was elevated during pregnancy and was sensitive to the receptor antagonist, ADM22-52. These findings suggest that during pregnancy the vasodilatory effects of ADM are greater and are associated with increased generation of cyclic nucleotides in resistance vessels, and these changes may be part of the cardiovascular adaptations that occur during pregnancy.     

Sex steroid hormones enhance hypotensive effects of calcitonin gene-related Peptide in aged female rats

The aim of the present study is to investigate whether vascular protective effects of steroid hormones in aged female rats are mediated through calcitonin gene-related peptide (CGRP), a known potent vasodilator. This rat model reflects the postmenopausal state in humans. We examined whether blood pressure lowering effects of CGRP are enhanced in aged female rats when steroid hormone treatments are administered. We observed that 1) continuous infusion of CGRP lowered blood pressures in rats treated with estradiol-17beta and progesterone (P < 0.05), 2) acute hypotensive effects of CGRP were significantly (P < 0.05) greater in the presence of steroid hormones than in vehicle-treated groups, 3) blood pressure decreases in response to CGRP are lower in aged female rats than they are in young adult ovariectomized rats, and 4) age-related differences in the hypotensive effects of CGRP were nullified when animals were treated with steroid hormones. These data suggest that female sex steroid hormones may modulate arterial blood pressure by regulating the CGRP effector system in female rats regardless of age.     

Growth hormone is secreted by ectopic pituitary grafts and stimulates maternal behavior in rats

The onset of maternal behavior at parturition in rats is hormonally regulated. Recently, we reported that treatment of behaviorally inexperienced, hypophysectomized (hypox), ovariectomized (ovx) rats with a sequential steroid treatment of progesterone (P) and estradiol (E2), and either ectopic anterior pituitary grafts or prolactin (PRL), stimulated maternal responsiveness toward foster young. That growth hormone (GH) has a number of PRL-like activities led us to ask whether the actions of PRL on maternal behavior were specific to PRL or might be shared by other PRL-like protein hormone, i.e., GH. In Experiment 1 we quantified plasma concentrations of GH and PRL by RIA in groups of hypox female rats that were ovariectomized and treated with a combination of ectopic pituitary grafts (Days 1-23) and Silastic capsules filled with P (Days 1-11) and E2 (Days 11-23). Blood samples were collected from Days 1 to 23 of treatment. Both plasma PRL and GH levels increased after grafting, initially rising 10- to 60-fold by Day 4 and gradually declining throughout the remainder of the 23-day sampling period. Throughout the 3-week period after grafting plasma GH levels were as high or higher than those of PRL. In Experiment 2 the behavioral effects of exogenously administered ovine (o)-GH were measured in groups of hypox, ovx rats that were treated with P and E2 as in Experiment 1. Experimental rats were injected twice daily with 0.25 mg oGH beginning on Day 1. Testing for maternal behavior toward foster young was conducted daily from Day 12 to Day 22. In steroid-treated rats, GH treatment stimulated a more rapid onset of maternal behavior (latencies of 3 vs greater than 10 days for vehicle-injected controls). These data indicate that GH, like PRL, is secreted by ectopic pituitary grafts and is capable of stimulating maternal behavior.     

Length of prolactin priming differentially affects maternal behavior in female rats

Prolonged exposure to prolactin (Prl) or to ectopic pituitary grafts that secrete Prl has been shown to stimulate maternal behavior in steroid-treated, hypophysectomized female rats. Since Prl levels in the blood of pregnant rats increase beginning 2-3 days prepartum, it was of interest to determine whether acute Prl priming prior to exposure to rat young would also stimulate full maternal behavior. Hypophysectomized, ovariectomized nulliparous rats were assigned to one of three treatments: Group 1, prolonged Prl; Group 2, acute Prl; or Group 3, controls/no Prl. All groups were implanted with 3 X 30 mm progesterone (P)-filled Silastic capsules s.c. at the time of ovariectomy (ovx) on Treatment Day 1. After ovx, Group 1 rats (prolonged Prl) were injected twice daily with 0.5 mg Ovine (o) Prl throughout the course of the study. Group 2 (acute Prl) and 3 (controls/no Prl) females were injected with vehicle alone or noninjected from Day 1-10. On Day 11 of Treatment, P implants were removed from all rats and each female was given a 2 mm estradiol-17 beta (E2)-filled Silastic implant. Starting on Day 11, Group 2 females were injected twice daily with oPrl. Group 3 rats continued to receive vehicle only. Behavioral testing began on Day 12 and was conducted daily through Day 22. Prolonged Prl priming (Group 1) stimulated a rapid onset of all aspects of maternal behavior (latencies less than 1 day, all p less than 0.05-0.001 vs. Group 3 controls). Control latencies ranged from 4-10 days.(ABSTRACT TRUNCATED AT 250 WORDS)     

Attenuated hypotensive response to proadrenomedullin N-terminal 20 peptide in pregnant rats: modulation by steroid hormones

The hypotensive effect of proadrenomedullin N-terminal 20 peptide (PAMP) was examined in conscious pregnant (8, 14, and 20 days of pregnancy) and nonpregnant rats. Intravenous administration of PAMP (3–60 nmol/kg) produced a dose-dependent depressor response in both pregnant and nonpregnant rats. However, the maximum decrease in blood pressure was significantly attenuated in pregnant rats in mid- and late-gestation (14 and 20 days), but not in early gestation (8 days), than in nonpregnant rats. In ovariectomized rats, the depressor responses in 17β-estradiol (E2)-treated, progesterone (P)-treated, and E2+P-treated rats were significantly attenuated compared with the control rats. We also demonstrated that treatment of sex hormones reduces the depressor response to PAMP in 8-day pregnant rats. In addition, we showed that treatment of sex hormone receptor antagonists partially prevents the attenuation of the depressor response to PAMP in 20 day pregnant rats. These findings suggested that the hypotensive response to PAMP was more attenuated in pregnant rats in mid- and late-gestation than in nonpregnant rats, and that the changes in depressor response that occur at term in pregnant rats may be mediated by sex hormones. PAMP may play some important role in cardiovascular regulation during pregnancy.     

Serum prolactin concentrations and the initiation of maternal behavior in the rat

Maternal behavior and serum prolactin were measured in pregnant and virgin female rats. Pregnant rats were either ovariectomized or shamovariectomized on Day 17 of pregnancy, while virgin females were ovariectomized at the same age. Two days after surgery nests were rated and the three treatment groups were tested for responsiveness to rat pups. Both pregnant treatment groups built superior nests compared to the virgin group and also responded more frequently to rat pups within a 1 hr test period than the virgin controls. In addition, significantly more ovariectomized pregnant subjects responded to pups than did intact pregnant females. Serum prolactin levels did not differ among the three treatments nor did exposure to pups affect serum prolactin levels. In each treatment group serum prolactin was less than 15 ng/ml, well below the 139.7 ng/ml mean found on Day 23 of pregnancy. These data suggest that high levels of serum prolactin during late pregnancy are not essential for the initiation of maternal behavior in the rat.     

Implantation delay and anti-deciduogenic activity in the rat by the anti-androgen, hydroxyflutamide

Studies were undertaken to determine whether the anti-androgen, hydroxyflutamide, has anti-progestagenic activity by using implantation, maintenance of pregnancy, and decidualization as end points. Prepubertal rats were induced to ovulate with the injection of 4 IU pregnant mare's serum gonadotropin and allowed to mate. Mated females were assigned randomly to various treatment groups. Beginning at 0800 h on Day 4 of pregnancy and at 12-h intervals thereafter, rats received a series of 6 s.c. injections of 5 mg hydroxyflutamide in oil, or oil only. Localized changes in endometrial vascular permeability, indicative of implantation, were assessed on Days 6 and 8 of pregnancy, after an injection of Evans blue dye. By Day 6, implantation has been initiated in the vehicle-treated rats, but not in hydroxyflutamide-treated rats. Hydroxyflutamide treatment was terminated on Day 6, and implantation was initiated by Day 8. The weights of uterine dye sites in hydroxyflutamide-treated rats on Day 8 were similar to those in vehicle-treated rats on Day 6. The number of fetuses and placentae were similar in all groups on Day 19. The weights of fetuses in both hydroxyflutamide-treated and hydroxyflutamide + progesterone-treated rats were similar and significantly lower than those in control rats. Although there were no significant differences between vehicle-treated or hydroxyflutamide-treated rats in the proportion of rats delivering and litter size, the hydroxyflutamide-treated rats delivered pups a mean of one day later than did the controls. Endometrial decidualization in ovariectomized, steroid-treated rats, following artificial stimuli, was significantly suppressed in hydroxyflutamide-treated rats compared with controls.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of estradiol and progesterone on early embryonic development in aging rats

Regularly cyclic, middle-aged female rats exhibit a decreased incidence of fertility, and those females that are fertile produce small litters. These decreases in fertility and litter size are associated with reduced numbers of normal blastocysts formed and implanted, suggesting that pre- and/or peri-implantation failures may be the causes for these aging-related reproductive declines. The present study examined the relationships and influence of circulating estradiol (E2) and progesterone (P) levels on early embryonic development and implantation in middle-aged rats. Serial blood samples obtained from cannulated, middle-aged pregnant rats revealed minor decreases in plasma P and increases in E2 levels during Days 2-4 of pregnancy, compared to young pregnant rats, resulting in significantly (p less than 0.001) decreased plasma P/E2 ratios. These alterations in endogenous hormone secretion in middle-aged pregnant rats were associated with fewer normal blastocysts on Day 5 of pregnancy and reduced numbers of normally implanting embryos. Correlation analysis further revealed a significant (p less than 0.05) inverse relationship between mean circulating E2 levels and numbers of normal conceptuses on Day 12 of gestation. Moreover, s.c. administration of P implants (in Silastic) to middle-aged pregnant rats increased serum P levels by about 34-40 ng/ml, and significantly (p less than 0.05) reduced the incidence of abnormal embryos before implantation. In contrast, treatment with E2 minipumps produced a sustained rise in serum E2 (by about 7-15 pg/ml) and resulted in the complete absence of embryos in the reproductive tracts by Day 5 of pregnancy.(ABSTRACT TRUNCATED AT 250 WORDS)