Effects of acute stanozolol treatment on puberty in female rats

The effects of anabolic-androgenic steroid (AAS) abuse on the onset of puberty in female adolescents are largely unknown. This study assessed the acute effects of one AAS, stanozolol, on pubertal onset in the female rat. A single injection of stanozolol (5 mg/kg) on Postnatal Day (PN) 21 advanced vaginal opening but did not alter the onset of vaginal estrus. Higher doses of stanozolol treatment (10 and 25 mg/kg) also advanced vaginal opening but had no effect on vaginal estrus. The advancement of vaginal opening by stanozolol (5 mg/kg) was prevented by the concomitant administration of the pure antiestrogen ICI 182,780 (1 mg/kg) on PN20-22. Administration of the androgen receptor antagonist flutamide (10 mg/kg twice daily) on PN20-22 had no effect on the advancement of vaginal opening by stanozolol. Stanozolol treatment also advanced vaginal opening in ovariectomized rats. Perivaginal injections of a low dose of stanozolol (0.05 mg) on PN21 and PN23 also advanced vaginal opening. These results suggest that stanozolol is acting directly at estrogen receptors in the vaginal epithelium to advance vaginal opening and that prepubertal stanozolol treatment does not induce true precocious puberty.     

Anabolic-Androgenic Steroid Effects on Sexual Receptivity in Ovariectomized Rats

Anabolic-androgenic steroid (AAS) compounds are synthetic androgens taken by athletes to increase physical strength and endurance. Recent studies in our laboratory have demonstrated that AAS administration disrupts the estrous cycle of Long–Evans rats. The present experiments examined the effects of six commonly abused AAS compounds on sexual receptivity in ovariectomized rats. Adult female Long–Evans rats received estradiol benzoate (EB; 2.0 μg/day sc) for 6 consecutive days followed by 15 days of EB concurrent with daily sc injections of 7.5 mg/kg of one of the following AAS compounds: 17α-methyltestosterone, methandrostenolone, nandrolone decanoate, stanozolol, oxymetholone, testosterone cypionate, or the oil vehicle. On Day 15, all female rats received progesterone (1.0 mg/rat) 4 h before testing. Tests for sexual receptivity were conducted on Days 3, 6, 14, and 15 of AAS treatment. Although the time course of AAS effects on sexual receptivity varied, some overall effects were clear. For example, 17α-methyltestosterone, methandrostenolone, nandrolone decanoate, and stanozolol interfered with the display of sexual receptivity on Day 14, whereas oxymetholone and testosterone cypionate had no effect. Rats in all groups displayed high levels of sexual receptivity after receiving progesterone on Day 15. Our results show that AAS compounds vary in their degree of inhibition of female sexual behavior in ovariectomized rats.     

Inhibition of Estrogen-Induced Sexual Receptivity by Androgens: Role of the Androgen Receptor

Both naturally occurring and synthetic androgens have been shown to inhibit estrogen-induced sexual receptivity when administered to ovariectomized (OVX) rats. The mechanisms by which androgens exert these effects, however, remain unclear. Experiments were conducted to determine the role of the androgen receptor in the inhibition of estrogen-induced sexual receptivity in OVX rats by using flutamide, an androgen receptor antagonist. In each experiment, OVX Long–Evans rats received 6 consecutive days of estradiol benzoate (EB; 2.0 μg/day) followed by 15 days of EB concurrent with flutamide (10.0 mg/kg; twice daily) or the vehicle and one of the following androgens or the vehicle: dihydrotestosterone propionate (7.5 mg/kg), 3α-androstanediol (3.75 mg/kg), 17α-methyltestosterone (7.5 mg/kg), stanozolol (7.5 mg/kg), or nandrolone decanoate (7.5 mg/kg). On Day 15, all female rats received progesterone (P; 1.0 mg/rat) 4 h before testing. Tests for sexual receptivity were conducted on Days 3, 6, 14, and 15 of androgen/flutamide treatment. Each androgen inhibited sexual receptivity as expected, and concurrent treatment with flutamide reversed the inhibitory effects of all androgens on sexual receptivity on all test days. High levels of sexual receptivity were displayed in response to P on Day 15, regardless of experimental treatment. These results suggest that naturally occurring and synthetic androgens act at the androgen receptor to inhibit estrogen-induced sexual receptivity in OVX rats.     

Proestrous hormonal changes preceding the onset of ovulatory failure in lightly androgenized female rats

Proestrous hormonal profiles were characterized in lightly androgenized female rats prior to the onset of the delayed anovulatory syndrome (DAS). In these females, ovulatory failure and persistent vaginal estrus (PVE) occur at a very early age. Female Sprague-Dawley rats were injected with 10 micrograms testosterone propionate (TP) on postnatal Day 5. Control rats were untreated. All animals were weaned at 21 days of age, and following the onset of puberty, estrous cyclicity was monitored by vaginal smear. Rats showing regular 4-day cycles were used. Between 50-70 days of age, intra-atrial cannulae were implanted on a morning of proestrus (0700-0900 h) and blood was sampled at 2-h intervals from 1000 to 2000 h. Additional samples were taken at 0.5-h intervals from 1600 to 1800 h. Plasma was assayed for luteinizing hormone (LH), follicle-stimulating hormone (FSH) and progesterone (P) by radioimmunoassay (RIA). All animals were monitored for the onset of PVE or other alterations in estrous cyclicity. Females treated neonatally with TP that subsequently showed PVE by 150 days of age (PRE DAS) displayed a reduced peak amplitude (P less than 0.01) and delay in onset (1600 vs. 1400 h) of LH but not FSH secretion, when compared to controls. Females treated neonatally with TP that did not enter PVE by 150 days of age (No DAS) also showed a delayed rise in LH when compared to controls. However, the amplitude of LH secretion was not different from controls or PRE DAS females.(ABSTRACT TRUNCATED AT 250 WORDS)     

Opiate antagonist treatment reinstates estrous cycles in middle-aged persistent-estrous rats

Middle-aged female rats display luteinizing hormone (LH) surge deficits and cycle irregularity followed by the onset of persistent estrus (PE). The central nervous system has been identified as a primary locus of failure in PE rats, but the particular neural elements involved have not been determined. The goal of the present study was to identify a role for endogenous opioid peptides (EOP) in age-related acyclicity by evaluating the effect of opiate antagonist treatment on vaginal cytology in PE rats. PE rats were administered, s.c., saline (SAL), naloxone (NAL) or naltrexone (NTX) once daily for 20 days, or repetitively on Day 1 and on successive proestrus days if cyclicity was resumed. Single NTX (50 mg/kg), but not NAL (2 mg/kg), treatment interrupted the PE state in almost half of treated animals. Daily or repetitive proestrus NTX (10 mg/kg) treatment interrupted PE more frequently, and many animals displayed repeated estrous cycles and ovulation. Afternoon LH surges were observed after initial NTX treatment in animals displaying PE interruption. This demonstration that LH surges and ovulatory cycles can be reinitiated in PE rats with NTX suggests that dysfunction in the 'brake' on EOP secretion during proestrus may be one of the neuroendocrine impairments mediating acyclicity in aging female rats.     

Reproductive toxicity assessment of lasofoxifene, a selective estrogen receptor modulator (SERM), in female rats

BACKGROUND: Lasofoxifene is a nonsteroidal selective estrogen receptor modulator (SERM). With high affinity to the alpha and beta human estrogen receptors and greater potency than other SERMs, lasofoxifene is potentially a superior treatment for postmenopausal osteoporosis. In light of the known effects of estrogen-modulating compounds on female reproductive indices, two studies were conducted to evaluate the effects of lasofoxifene on female rat cyclicity, reproduction, and parturition. METHODS: One study evaluated effects of lasofoxifene on estrous cyclicity, and the second study assessed effects on implantation and parturition. In the cyclicity study, lasofoxifene was administered to female rats at doses of 0.1, 0.3, and 1.0 mg/kg/day for 14 consecutive days. After treatment, there was a 3-week reversibility phase followed by a mating phase. In the implantation study, lasofoxifene was administered to pregnant female rats at doses of 0.01, 0.03, and 0.1 mg/kg/day for 7 consecutive days (gestation day [GD] 0-6). Some animals were euthanized on GD 21, and the remainder of the group was allowed to deliver the F1 generation. Several developmental indices were evaluated in the F1 pups through post-natal day (PND) 21. RESULTS: In the cyclicity study, all lasofoxifene-treated females were anestrous by Study Day 7 (1.0 mg/kg) or 9 (0.3 and 0.1 mg/kg). The reversibility phase resulted in restoration of normal estrous cycles by the end of 1 (0.1 mg/kg) or 2 weeks (0.3 and 1.0 mg/kg). During the mating phase, no adverse effects occurred in pregnancy success or reproductive parameters. In the implantation study, all doses of lasofoxifene increased pre- and post-implantation losses, increased gestation length, and reduced litter size. None of the developmental parameters measured on the F1 generation was adversely affected. CONCLUSION: Lasofoxifene reversibly altered the estrous cycle and inhibited implantation, consistent with what would be expected from a member of the SERM class.     

Physiological pineal effects on female reproductive function of laboratory rats: prenatal development of pups, litter size and estrous cycle in middle age

The present study investigates whether and how the pineal or its hormone melatonin influences female reproductive functions, namely the litter size, prenatal development of offsprings, and estrous cyclicity, especially its age-related cessation in a non-seasonal breeder, the laboratory rat. Wistar rats were maintained under a 24 h light-dark (12Lratio12D) cycle. Female rats were divided into 3 groups: non-operated (NO), sham-operated (SX), and pinealectomized (PX). Surgeries were performed in 35-40 day-old females. Starting at an age between 70 days and 7 months, female rats of all 3 groups were repeatedly mated with intact males. PX mothers more frequently delivered pups with malformations (e.g., taillessness, hydronephrosis, 7 out of 1263 pups) than control rats (0/1323; p<0.007). In the first delivery at 3 months of age, but not at later ages, PX mothers delivered more pups of lower body weight than control animals (p<0.001). Examination of vaginal smears showed that almost all female rats of the NO, SX, and PX groups had 4-day estrous cyclicity when they were young-between 60 days and 5 months of age. At an age of 17 to 18 months, most female rats of the NO and SX groups showed irregular, continuously diestrous or pseudopregnancy-like patterns, and 4-day estrous cyclicity was found in only 10% of the NO or SX animals. In contrast, about 50% of the PX rats showed 4-day estrous cyclicity at this older age (p< 0.001). Melatonin, when added to drinking water (0.4 mg/L) for 16 days during the dark phase increased the frequency of diestrous phase, except in continuously diestrous rats and very few others. This melatonin effect was strong in PX rats but relatively weak in SX rats. In conclusion, the pineal hormone appears to influence various reproductive functions and developmental processes, especially pregnancy and the timing of reproductive aging in rats. The effects of pinealectomy are more prominent at an age of 60 to 80 days (i.e., shortly after puberty) and at the beginning of the cessation of cycles in middle-aged females.     

Effect of bromocriptine and progesterone on the length of the ovarian cycle in 4- and 5-day estrous cyclic rats

To study the effect of prolactin and progesterone on the length of the reproductive cycle in the rat, rats of different estrous cycle length (four and five days, respectively) were injected daily (09.00 h) with either bromocriptine (1 mg/rat) or 70% ethanol vehicle (0.25 ml) from the day of estrus onward, up to the appearance of the next ovulation. Each group of rats was then (16.00, metestrus) also injected with either progesterone (4 mg/rat) or 0.2 ml of olive oil. The effects of these treatments on the length of the estrous cycle was studied by both the recording of vaginal smears daily and by direct visualization of oocyte-cumulus complexes on the ensuing day of estrus (10.00 h-12.00 h). Bromocriptine treatment shortened the length of the cycle by one day in 5-day but not in 4-day cyclic rats, while progesterone treatment lengthened estrous cycles by one day in both groups of rats. Treatment with both bromocriptine and progesterone had no effect on the estrous cycle length of 5-day cyclic rats, but did prolong in one day the cycle of 4-day cyclic rats. These facts suggest that prolactin regulates the length of the ovarian reproductive cycle in the rat through its action on the secretion of progesterone by the corpus luteum.     

Ovarian follicular and corpus luteum changes, progesterone concentrations, estrus and ovulation following estradiol benzoate/progesterone based treatment protocol in cross-bred cows

The objectives of the present study were to investigate the effects of the stage of the estrous cycle at the start of an estradiol benzoate (EB) and progesterone (P) based treatment protocol on new follicular wave emergence, subsequent estrus and ovulation. The experiment was conducted using a crossover design with each cow (five cross-bred cows) being assigned to one of three groups at 3-month intervals within a 1-year period. Estrous cycle stage in individual cows was initially synchronized with prostaglandin F(2)alpha. After detection of estrus, each cow was injected intramuscularly (i.m.) with 2 mg EB and 200 mg P (EB/P) on day 5, 12 or 17 of the estrous cycle (estrus=day 0), followed by 1 mg EB i.m. 12 days after the EB/P treatment. Ovarian ultrasonographic examinations showed that the emergence of a new follicular wave occurred after EB/P treatment in all groups and the mean interval from EB/P treatment to wave emergence did not differ among the groups (3.2-3.8 days). All cows in each group exhibited behavioral estrus and ovulated the newly formed dominant follicle. However, cows in the day-17 group exhibited estrus 1-3 days before the second EB injection. The concentrations of progesterone showed faster reduction, during the treatment period, in the day-12 and -17 groups compared to the day-5 group. These results indicate that the EB/P treatment induces an emergence of a new follicular wave, irrespective of the estrous cycle stage at the start of treatment, but the effect of EB/P protocol on estrous/ovulation synchronization is influenced by the stage of the estrous cycle.     

Effects of androgens on serum concentrations of gonadotropins and ovarian steroids in gilts

To examine how androgens affect endocrine events associated with increased ovulation rate, gilts were injected with androgen receptor agonists, an antagonist, or a combination of both. Blood samples were collected hourly from Day 13 to estrus (Day 0 = onset of estrus) coincident with gilts (n = 6 per treatment) receiving daily treatments of vehicle (corn oil), 10 mg of testosterone, 10 mg of 5 alpha-dihydrotestosterone (dihydrotestosterone), 1.5 g of flutamide (an androgen receptor antagonist), testosterone plus flutamide, or dihydrotestosterone plus flutamide. Treatment of gilts with testosterone or dihydrotestosterone alone increased (P < 0.05) concentrations of FSH in serum, and these effects were blocked by cotreatment with flutamide. Estradiol-17beta and androstenedione concentrations in serum were increased (P < 0.05) at 2 h after injection of testosterone or testosterone plus flutamide but not after dihydrotestosterone treatment, probably because of the role of testosterone as a substrate for estradiol-17beta and androstenedione synthesis. There were no effects of the six treatments on serum concentrations of progesterone during luteolysis, but treating gilts with testosterone shortened (P < 0.05) the proestrous period. Total embryonic loss by Day 11 in gilts treated with dihydrotestosterone was reversed when gilts were cotreated with dihydrotestosterone plus flutamide. Results of this experiment indicated that androgen actions both increased FSH secretion and reduced embryonic survival by a mechanism(s) dependent on the androgen receptor.     

Ovarian endocrine disruption underlies premature reproductive senescence following environmentally relevant chronic exposure to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin

The aryl hydrocarbon receptor (AHR) mediates the effects of many endocrine disruptors and contributes to the loss of fertility in polluted environments. While previous work has focused on mechanisms of short-term endocrine disruption and ovotoxicity in response to AHR ligands, we have shown recently that chronic exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces premature reproductive senescence in female rats without depletion of ovarian follicular reserves. In the current study, premature reproductive senescence was induced using a range of low-dose exposure to TCDD (0, 1, 5, 50, and 200 ng kg(-1) wk(-1)) beginning in utero and continuing until the transition to reproductive senescence. Doses of 50 and 200 ng TCDD kg(-1) wk(-1) delayed the age at vaginal opening and accelerated the loss of normal reproductive cyclicity with age without depletion of follicular reserves. Serum estradiol concentrations were decreased in a dose-dependent fashion (>/=5 ng kg(-1) wk(-1)) across the estrous cycle in perisenescent rats still displaying normal cyclic vaginal cytology. Serum FSH, LH, and progesterone profiles were unchanged by TCDD. The loss of reproductive cyclicity following chronic exposure to TCDD was not accompanied by decreased responsiveness to GnRH. Ovarian endocrine disruption is the predominant functional change preceding the premature reproductive senescence induced by chronic exposure to low doses of the AHR-specific ligand TCDD.     

Prolactin receptors in the rat mammary gland. Change during the estrous cycle

Ovine prolactin (o-PRL) binding to mammary gland membranes was studied during the estrous cycle in the rat. Groups of rats were decapitated throughout the 4-day estrous cycle at 10 h00 on the days of diestrus I, diestrus II and estrus and at 10 h00, 12 h00, 16 h00 during the day of proestrus. Daily vaginal smears were taken to determine the stage of the estrous cycle which was also controlled by PRL and LH serum levels. Prolactin receptors were quantified in the 100 000 g pellet. For one Scatchard analysis, mammary gland membranes from 5 animals were pooled. Results given are the mean of 4 or 5 pools. Results obtained showed that the apparent affinity constant (KA) remained unchanged during the days of diestrus II and at all the times studied of proestrus and showed a slight but significant decrease on the days of estrus and diestrus I (or metestrus). The binding capacity did not vary from the day of diestrus II to the proestrus 16h00 (11.3 +/- 2.8 fmoles/mg protein) but sharply increased on the day of estrus (190.4 +/- 35.9 fmoles/mg protein). Binding capacity remained elevated on the day of diestrus I. This increase of PRL receptors on the day of estrous would appear to be an important step in preparing mammary gland for pregnancy and lactation.     

Puberty and ovulatory release of gonadotropins in spontaneously hypertensive rats

The age at vaginal opening, estrous cyclicity, serum levels of luteinizing hormone (LH), follicle stimulating hormone (FSH) and prolactin (PRL) on the day of proestrus, and number of ova and ovarian weight as measured on the day of estrus in spontaneously hypertensive (SH) and genetically matched normotensive Wistar Kyoto (WKY) female rats were compared. In SH rats, there was a significant delay in the vaginal opening, but the regular 4-day estrous cycle followed afterwards. No significant changes were observed in the afternoon increase in serum LH, FSH and PRL on the day of proestrus in SH and WKY rats, although the basal levels of LH and PRL in the morning (11:00 h) were lower in SH rats than in WKY rats. The mean number of ova in SH rats was also less than in WKY rats, whereas the ovarian relative weight was similar in both species of rats. It can be said that SH rats undergo certain, but not critical, endocrine and/or neuroendocrine changes related to reproduction.     

Glucoprivic regulation of estrous cycles in the rat

Previous research has shown that glucoprivation induced by chronic 2-deoxy-D-glucose (2DG) treatment extends estrous cycle length and disrupts reproductive behaviors in female hamsters, similar to food deprivation. Such treatment also suppresses food intake, which is reversed in male rats by reducing brain histamine levels prior to 2DG treatment. We, therefore, determined if 2DG extends estrous cycles in the female rat and if this is due to elevated brain histamine levels. We measured estrous cycle length during 2DG-induced glucoprivation, in the presence and absence of alpha-fluoromethylhistidine (FMH), a treatment that reduces brain histamine levels. Adult female rats were treated for 72 h with either saline (n = 8), 2DG (200 mg/kg S.C. every 6 h; n = 9), or FMH (100 mg/kg i.p. daily) + 2DG (200 mg/kg; n = 7). An additional group was treated with FMH (100 mg/kg i.p.; n = 5) alone. To determine if 2DG extends estrous cycles due to glucoprivation or to decreased caloric intake, a group of rats (n = 7) received a reduced diet equal to the mean daily food intake of rats receiving 2DG alone. 2DG induced more long estrous cycles compared to rats receiving saline, FMH + 2DG, or FMH alone. In rats treated with FMH + 2DG, the percentage of 4-5-day cycles was similar to that of saline-treated rats, and a high percentage of 4-5-day cycles was also observed in rats receiving a reduced diet. These data suggest that 2DG does not suppress estrous cycles through a decrease in total calorie intake, but rather by inducing glucoprivation. In addition, during 2DG-induced glucoprivation, elevated brain histamine levels contribute to the mechanism that suppresses reproductive function.     

Shifts in gonadotropin and steroid levels that precede anestrus in female golden hamsters exposed to a short photoperiod

Female golden hamsters exposed to short photoperiods become anestrous and exhibit daily surges of gonadotropins and progesterone. Since little is known about the transition between the cycling and anovulatory states, the following experiments were done to determine whether there are hormonal changes that precede cessation of estrous cyclicity. Females killed on the morning of estrus, up to the tenth estrous cycle in short days, showed no hormonal or ovarian morphologic evidence of changes in reproductive function. When assessed on the afternoon of estrus, however, serum levels of luteinizing hormone and progesterone increased significantly before vaginal and ovarian cyclicity ceased. Females sampled in both the morning and afternoon at increasing durations since their last vaginal estrus revealed that maximal daily surges of both gonadotropins and progesterone were not consistently manifested until the vaginal cycle had been absent for 2 weeks. By then, estrogen levels and uterine weights were low and ovaries showed hypertrophied interstitia and arrested follicular growth. We have demonstrated that there are hormonal changes in females before the loss of the vaginal cycle and onset of major daily hormonal surges. Our results suggest that alterations in feedback relationships between steroid hormones and gonadotropins may precede photoperiod-induced anestrus.     

Physiological Pineal Effects on Female Reproductive Function of Laboratory Rats: Prenatal Development of Pups,Litter Size and Estrous Cycle in Middle Age

The present study investigates whether and how the pineal or its hormone melatonin influences female reproductive functions, namely the litter size, prenatal development of offsprings, and estrous cyclicity, especially its age‐related cessation in a non‐seasonal breeder, the laboratory rat. Wistar rats were maintained under a 24 h light‐dark (12L∶12D) cycle. Female rats were divided into 3 groups: non‐operated (NO), sham‐operated (SX), and pinealectomized (PX). Surgeries were performed in 35–40 day‐old females. Starting at an age between 70 days and 7 months, female rats of all 3 groups were repeatedly mated with intact males. PX mothers more frequently delivered pups with malformations (e.g., taillessness, hydronephrosis, 7 out of 1263 pups) than control rats (0/1323; p<0.007). In the first delivery at 3 months of age, but not at later ages, PX mothers delivered more pups of lower body weight than control animals (p<0.001). Examination of vaginal smears showed that almost all female rats of the NO, SX, and PX groups had 4‐day estrous cyclicity when they were young–between 60 days and 5 months of age. At an age of 17 to 18 months, most female rats of the NO and SX groups showed irregular, continuously diestrous or pseudopregnancy‐like patterns, and 4‐day estrous cyclicity was found in only 10% of the NO or SX animals. In contrast, about 50% of the PX rats showed 4‐day estrous cyclicity at this older age (p< 0.001). Melatonin, when added to drinking water (0.4 mg/L) for 16 days during the dark phase increased the frequency of diestrous phase, except in continuously diestrous rats and very few others. This melatonin effect was strong in PX rats but relatively weak in SX rats. In conclusion, the pineal hormone appears to influence various reproductive functions and developmental processes, especially pregnancy and the timing of reproductive aging in rats. The effects of pinealectomy are more prominent at an age of 60 to 80 days (i.e., shortly after puberty) and at the beginning of the cessation of cycles in middle‐aged females.     

Involvement of 5-HT1A receptors in passive avoidance learning in intact and ovariectomized female rats

The influence of chronic administration of 5-HT1A receptor agonist 8-OH-DPAT (0.05 mg/kg, s.c.) and 5-HT1A receptor antagonist NAN-190 (0.1 mg/kg, i.p.) injected for 14 days alone or in combination with 17beta-estradiol (0.5 microg i.m./rat/day) was studied on passive avoidance performance (PAR) and on behavior in the open field test in adult intact and ovariectomized (OVX) female rats. Administration of 5-HT1A receptor antagonist NAN-190 alone significantly improved PAR (p<0.05) in intact females with proestrus and estrus and in OVX females. Administration of 5-HT1A receptor agonist 8-OH-DPAT alone or in combination with 17beta-estradiol significantly (p<0.05) improved PAR in OVX rats and failed to normalize PAR in intact rats with proestrus and estrus. Results of the work specify the involvement of 5-HT1A receptors in the mechanisms of passive avoidance learning in OVX female rats.     

Effects of chronic exposure to estradiol on ovarian cyclicity in C57BL/6J mice: potentiation at low doses and only partial suppression at high doses

Long-term exposure to ovarian hormones contributes to age-related changes in estrous cyclicity in rodents. Estrogens are implicated in this process, but the concentration of estrogen required to exert these effects is not well established. Also, although estrogens are presumed to alter vaginal cyclicity by affecting the hypothalamic-pituitary axis, they may also impair the ability of the vaginal epithelium to cornify. To address these issues, young and middle-aged ovariectomized (ovx) C57BL/6J mice were exposed for 7-10 wk to plasma levels of estradiol (E2) at one of three ranges (30-40, 50-80, or 120-160 pg/ml). Ovaries from young mice were then transplanted under the renal capsule, and vaginal cyclicity was monitored for 4 mo. Mice exposed to the lowest level of E2 not only failed to stop cycling, but had a higher monthly frequency of estrous cycles than did controls (nearly 1 extra cycle/mo). Mice exposed to the intermediate level of E2 showed no impairment in cyclicity. Although mice exposed to the highest concentrations of E2 showed no vaginal cyclicity, they continued to ovulate as evidenced by fresh, albeit reduced, numbers of corpora lutea. These results indicate that, in ovx mice, (1) chronic exposure to relatively low concentrations of E2 potentiates cyclicity, (2) very high levels of E2 are required to induce acyclicity, and (3) this acyclicity reflects vaginal as well as neuroendocrine alterations. The results also indicate that vaginal acylicity may be a poor indicator of ovulatory acyclicity in mice that have been chronically exposed to E2.     

Doses of prostaglandin F(2)alpha effective for induction of estrus in goats

A total of 11 cycling does weighing between 24 and 50 kg were injected with varying dosages of prostaglandin F(2)alpha (PGF(2)alpha) between 7 and 10 days into each estrous cycle. Five injections each of 1.25, 2.5, 5.0, or 7.5 mg PGF(2)alpha were alternated with five injections of 1.0 ml saline. Saline treated does served as controls. All does were teased twice daily with a buck and observed for signs of estrus for 5 days post-injection. Daily systemic concentrations of progesterone (P(4)) were determined by radioimmunoassay. The mean (+/- S.E.) hours from injection to estrus was 47 +/- 3.3, 42 +/- 4.3, 44 +/- 8.5, and 43 +/- 5.5 for does receiving 1.25, 2.5, 5.0, and 7.5 mg PGF(2)alpha, respectively. None of the does receiving saline exhibited estrus in the 5-day post-injection observation period. Mean (+/- S.E.) concentrations of systemic P(4) in all does on the day of injection was 4.22 +/- 0.45 ng/ml. Concentrations 24 hours post-injection were 0.21 +/- 0.02, 0.15 +/- 0.05, 0.17 +/- 0.04, 0.16 +/- 0.04, and 4.5 +/- 1.36 ng/ml for does receiving 1.25, 2.5, 5.0, and 7.5 mg PGF(2)alpha, and 1.0 ml saline, respectively. The results suggested that 1.25 mg PGF(2)alpha was effective for induction of estrus in the cycling goat.     

Conditions for establishment of reflex ovulation in light estrous rats.

Continual anovulatory state associating with persistent vaginal cornification (light estrus) was induced by placing 4-day cycling rats under continuous lighting (LL). Uterine cervical stimulation was applied at arbitrary solar hours to light estrous rats showing continual vaginal estrus for more than 2 weeks. The ovulation was induced between 14 and 16 hr after the stimulation dissociating entirely with solar hours. Injection of anti-LHRH serum 5 min after the stimulation but not later than 20 min blocked this ovulation. Ovulation thus induced was always followed by pseudopregnancy with continual leucocytic vaginal smear lasting 10.70 days. The change in concentrations of peripheral serum progesterone during this period was almost similar to that of normal pseudopregnancy except extremely low levels observed at the start and end. Effectiveness of the cervical stimulation for induction of ovulation in light estrous rats was related to not only the duration of light estrus but also the time after transfer to LL, suggesting that the neural mechanism of ovulation in light estrous rats shifted from that of the spontaneous to reflex ovulators due to the extinction of environmental photic cue.