Persistent Vaginal Cornification Research Articles

ERα in Tac2 Neurons Regulates Puberty Onset in Female Mice.

A variety of data suggest that estrogen action on kisspeptin (Kiss1)-containing arcuate nucleus neurons (which coexpress Kiss1, neurokinin B (the product of Tac2) and dynorphin (KNDy) neurons restrains reproductive onset and function, but roles for estrogen action in these Kiss1 neurons relative to a distinct population of rostral hypothalamic Kiss1 neurons (which does not express Tac2 or dynorphin) have not been directly tested. To test the role for estrogen receptor (ER)α in KNDy cells, we thus generated Tac2(Cre) and Kiss1(Cre) knock-in mice and bred them onto the Esr1(flox) background to ablate ERα specifically in Tac2-expressing cells (ERα(Tac2)KO mice) or all Kiss1 cells (ERα(Kiss1)KO mice), respectively. Most ERα-expressing Tac2 neurons represent KNDy cells. Arcuate nucleus Kiss1 expression was elevated in ERα(Tac2)KO and ERα(Kiss1)KO females independent of gonadal hormones, whereas rostral hypothalamic Kiss1 expression was normal in ERα(Tac2)KO but decreased in ERα(Kiss1)KO females; this suggests that ERα in rostral Kiss1 cells is crucial for control of Kiss1 expression in these cells. Both ERα(Kiss1)KO and ERα(Tac2)KO females displayed early vaginal opening, early and persistent vaginal cornification, increased gonadotropins, uterine hypertrophy, and other evidence of estrogen excess. Thus, deletion of ERα in Tac2 neurons suffices to drive precocious gonadal hyperstimulation, demonstrating that ERα in Tac2 neurons typically restrains pubertal onset and hypothalamic reproductive drive.

Hypothyroidism caused by phenobarbital affects patterns of estrous cyclicity in rats

We found that repeated treatment with phenobarbital (PB), a thyroid modulator, resulted in a persistent estrous stage in the present study. Although the effects of PB in blocking the surge release of luteinizing hormone (LH), inducing anovulation and prolonging the diestrous period has been well established, there is still no research describing the appearance of persistent estrous states in normal cycling rats dosed with PB. To further study this phenomenon, female rats exhibiting regular estrous cycle were administered an oral dose of PB for 14 consecutive days. Consecutively, vaginal smears were observed and rats from all the groups were sacrificed and serum hormone levels for prolactin, progesterone, estradiol, triiodothyronin (T3), thyroxine (T4) and thyroid stimulating hormone (TSH) were measured. Pituitary, thyroid, liver, uteri and ovaries were excised, weighed and further subjected to histological observations. We found that PB induced irregular estrous cycles, especially persistent estrus in rats. Histopathologically, the persistent estrous stages are characterized by persistent vaginal cornification in the vagina, cystic follicles and anovulation in the ovaries. Endocrinologically, serum T3 and T4 levels were significantly lower, and TSH was higher in treated-female rats compared to control females. The serum estradiol level and the estradiol/progesterone ratio tend to increase in treated-females. Furthermore, PB-treated animals with irregular estrous cycle were reduced by T4 replacement. Our data indicate that treatment with PB resulted in hypothyroidism and irregular estrous cycle, particularly a persistent estrous stage in normal cycling female rats.

Short-term implantation of oestrogen into the anterior amygdaloid area of immature rats delays the first pubertal ovulation.

Unilateral implants containing oestradiol benzoate (OB) and cholesterol at the ratio of 1 + 4 were placed for 48 h either in the region of the anterior amygdaloid area (AAA) and nucleus of the lateral olfactory tract (NLOT) or in the anterior or posterior part of the mediocortical amygdala of immature 26-day-old female rats, and the age at vaginal opening and the first ovulation was recorded. Whereas implants located in the mediocortical amygdala did not influence the occurrence of ovulation or advanced it distinctively, implantation of OB into the AAA/NLOT resulted in a highly significant delay of the first pubertal ovulation that was associated with postpubertal persistent vaginal cornification in part of the rats.

Collaborative work on evaluation of ovarian toxicity 2) Two- or four-week repeated dose studies and fertility study of mifepristone in female rats

In order to assess ovarian pathological changes and their relationship to changes in female fertility parameters, mifepristone, a progesterone receptor antagonist, was selected as the test article and was administered orally to female rats at dose levels of 0, 0.8, 4, 20 and 100 mg/kg for 2 or 4 weeks in repeated dose-toxicity studies and in a female fertility study at dose levels of 0, 0.8, 4 and 20 mg/kg from > 2 weeks before copulation to postcoital day 7. In the repeated dose toxicity studies, persistent estrus was seen in the vaginal smears, and multiple cysts in the ovaries at necropsy, increases in luteinized cysts and hypertrophy of previously formed corpora lutea were observed in the histopathological examination of ovaries in rats receiving 20 mg/kg or more for 2 or 4 weeks. In female fertility studies, persistent vaginal cornification was also observed at 20 mg/kg and the precoital interval was significantly shortened. All of the animals were completely infertile when dosed with 20 mg/kg during the post-coital period. An increase in pre-implantation losses was observed in the animals treated with 20 mg/kg during the pre-coital phase, while treatment with 4 mg/kg mifepristone during the post-coital phase induced an increase in post-implantation losses. These results suggested that a 2-week administration period would be sufficient to detect the ovarian toxicity of mifepristone in repeated dose toxicity study and the pathological findings in the ovaries would reflect the alterations in female reproductive endpoints in the female fertility study.

Kiss1 −/− Mice Exhibit More Variable Hypogonadism than Gpr54−/− Mice

The G protein-coupled receptor Gpr54 and its ligand metastin (derived from the Kiss1 gene product kisspeptin) are key gatekeepers of sexual maturation. Gpr54 knockout mice demonstrate hypogonadotropic hypogonadism, but until recently, the phenotype of Kiss1 knockout mice was unknown. This report describes the reproductive phenotypes of mice carrying targeted deletions of Kiss1 or Gpr54 on the same genetic background. Both Kiss1 and Gpr54 knockout mice are viable but infertile and have abnormal sexual maturation; the majority of males lack preputial separation, and females have delayed vaginal opening and absence of estrous cycling. Kiss1 and Gpr54 knockout males have significantly smaller testes compared with controls. Gpr54 knockout females have smaller ovaries and uteri than wild-type females. However, Kiss1 knockout females demonstrate two distinct phenotypes: half have markedly reduced gonadal weights similar to those of Gpr54 knockout mice, whereas half exhibit persistent vaginal cornification and have gonadal weights comparable with those of wild-type females. FSH levels in both Kiss1 and Gpr54 knockout males and females are significantly lower than in controls. When injected with mouse metastin 43-52, a Gpr54 agonist, Gpr54 knockout mice fail to increase gonadotropins, whereas Kiss1 knockout mice respond with increased gonadotropin levels. In summary, both Kiss1 and Gpr54 knockout mice have abnormal sexual maturation consistent with hypogonadotropic hypogonadism, although Kiss1 knockout mice appear to be less severely affected than their receptor counterparts. Kiss1 knockout females demonstrate a bimodal phenotypic variability, with some animals having higher gonadal weight, larger vaginal opening, and persistent vaginal cornification.

Changes in reproductive organs of female rats treated with bisphenol A during the neonatal period

The effects of neonatal administration of estrogenic agents on rat reproductive organs were examined. Either bisphenol A (BPA; 0.25, 1, or 4 mg/pup) or 10 μg 17β-estradiol (E 2) was given subcutaneously to Sprague–Dawley female rats during the neonatal period from post-natal day (PND) 0 to 9. Animals ovariectomized at 80 days were given subcutaneous injections of 1 μg/kg E 2 for 3 days from PND 94 to 96. Clefts in the clitoris, early vaginal opening, irregular estrous cycles, a decrease in the area occupied by the corpora lutea (CL) in the ovary, and multiple cystic follicles in the ovary were found in the animals treated neonatally with 1 mg BPA. Uterine fluid weight measured after E 2 treatment on PND 94–96 was less than controls. In addition to these abnormalities, unusual body weight gains, persistent vaginal cornification, and lack of CL were observed in females treated neonatally with 4 mg BPA. The ovary weight on PND 80 and uterine fluid weight measured after E 2 treatment on PND 94–96 were less than controls for the 4 mg BPA group. Neonatal treatment with 10 μg E 2 induced similar abnormalities as found in the 4 mg BPA group. These results show that BPA when given during the neonatal period caused changes in female reproductive organs.

Estrogen Receptor-α Knockout Mice Exhibit Resistance to the Developmental Effects of Neonatal Diethylstilbestrol Exposure on the Female Reproductive Tract

Data indicate that estrogen-dependent and -independent pathways are involved in the teratogenic/carcinogenic syndrome that follows developmental exposure to 17β-estradiol or diethylstilbestrol (DES), a synthetic estrogen. However, the exact role and extent to which each pathway contributes to the resulting pathology remain unknown. We employed the αERKO mouse, which lacks estrogen receptor-α (ERα), to discern the role of ERα and estrogen signaling in mediating the effects of neonatal DES exposure. The αERKO provides the potential to expose DES actions mediated by the second known ER, ERβ, and those that are ER-independent. Wild-type and αERKO females were treated with vehicle or DES (2 μg/pup/day for Days 1–5) and terminated after 5 days and 2, 4, 8, 12, and 20 months for biochemical and histomorphological analyses. Assays for uterine expression of the genes Hoxa10, Hoxa11, and Wnt7a shortly after treatment indicated significant decreases in DES-treated wild-type but no effect in the αERKO. In contrast, the DES effect on uterine expression of Wnt4 and Wnt5a was preserved in both genotypes, suggesting a developmental role for ERβ. Adult αERKO mice exhibited complete resistance to the chronic effects of neonatal DES exposure exhibited in treated wild-type animals, including atrophy, decreased weight, smooth muscle disorganization, and epithelial squamous metaplasia in the uterus; proliferative lesions of the oviduct; and persistent vaginal cornification. Therefore, the lack of DES effects on gene expression and tissue differentiation in the αERKO provides unequivocal evidence of an obligatory role for ERα in mediating the detrimental actions of neonatal DES exposure in the murine reproductive tract.

Studying endocrine disrupter action and toxicology in ER knock‐out mice

Estrogen receptors (ER) are thought to play a crucial role in development, reproduction, carcinogenesis and normal physiology. Using gene targeting techniques, we have produced lines of transgenic mice homozygous for the disrupted ERα gene (αERKO) and ERβ genes (βERKO). Comparable levels of ER‐β mRNA were found in tissues of αERKO mice suggesting that ER‐β expression is not dependent on ERα. αERKO mice were totally unresponsive to uterotropic assays with estradiol, Genistein, hydroxy TAM, DES or EGF treatment. Progesterone receptor (PR) mRNA was detected in αERKO mice, but not stimulated by estrogen in the uterus, mammary gland and ovary. Pituitary hormones are elevated in αERKO females but same as WT in βERKO mice indicating that ERα plays a major role in peptide hormone regulation. Genistien was equally effective in αERKO as WT mice in suppressing serum LH levels suggesting its action in this estrogen target response involved a non‐ER mediated mechanism compared to the uterine genistein activity. Analysis of the mammary glands of adult αERKO mice, showed a primitive ductal rudiment while the βERKO had the fully developed ductal tree seen in WT siblings. The influence of ERα activity on mammary tumorgenicity was evaluated by crossing αERKO with an oncogenic WNT‐1 transgenic mouse line having an increased incidence of mammary tumors. Mice with WT ER levels and WNT‐1 transgene show 98% tumor incidence at 27 weeks of age. αERKO/WNT‐1 mice showed a delayed onset (54 weeks). These results indicate that mammary tumors can develop from ER negative tissues, but with a delayed onset. A second cross with erB2 (Neu) transgenics shows that WT and hetero Neu mice have a tumor incidence at 54 wks of age. αERKO/Neu have an extremely low incidence past 90 wks. Compared to the WNT/ERKO the ERKO/Neu have a poorer tumor rate suggesting that ERα plays a more prominent role in this oncogenic tumor induction. Since the initial description of DES carcinogenesis in both humans and mice, a major question was what aspect of the DES action was ER mediated or non‐receptor mediated. Perinatal DES treatment to WT mice showed numerous phenotypic toxicological and carcinogenic effects including, persistent vaginal cornification, uterine hyperplasia, oviductal hypertrophy in females. In similarly treated males, DES induced seminal vesicle atrophy and prostatic hyperplasia. αERKO treated males and females showed none of the observed toxic effects indicating that ERα was involved in mediating these DES effects and not ERβ. Further characterization of the mice and comparison of the DES effects in βERKO mice and double ER gene KO mice will be needed to more fully the specific roles of the two different forms of ER in estrogen hormone toxicology and hormonal carcinogenesis.

Limbic seizures alter reproductive function in the female rat.

Reproductive dysfunction and endocrine disorders are common among women with temporal lobe epilepsy. This study used the kindled rat model to test the hypothesis that limbic seizures directly contribute to reproductive dysfunction. Kindling electrodes were implanted in the basolateral amygdala in adult female rats. Females were kindled by either brief, daily, suprathreshold stimulations with a bipolar electrode or sham-kindled (controls). Electrographic and behavioral seizures were monitored. Estrous cycles also were monitored with daily vaginal smears. Seizures arrested ovarian cyclicity in all (n = 42) kindled animals, the rats exhibiting persistent vaginal cornification (PVC). In these animals PVC was associated with high serum estradiol, increased pituitary weight, and polyfollicular ovaries consisting of many cystic follicles, as well as follicles in various stages of growth and atresia. In 93% of females, this effect occurred after the development of stage 5 motor seizures, when focal seizures had secondarily generalized. In contrast, only five (21%) of 24 sham-kindled controls exhibited PVC. A single injection of progesterone (P4) temporarily restored cyclicity in five (18%) of 28 kindled females exhibiting PVC. In contrast, P4 administration restored cyclicity in all five sham-kindled controls that had spontaneously stopped cycling. P4 treatment to kindled females in PVC resulted in a different endocrine profile than that in non-P4-treated, kindled rats in PVC. P4-treated rats had high serum estradiol, testosterone, and prolactin levels; they showed an increase in pituitary weight; and their ovaries contained numerous corpora lutea and cystic follicles surrounded by markedly overdeveloped thecal cell layers. Seizures initiated in the amygdala result in impairment of the hypothalamic-pituitary axis, resulting in loss of ovarian cyclicity.

Uterotrophic activity of bisphenol A in the immature rat.

Bisphenol A (BPA) is active in immature AP rat uterotrophic assays when evaluated using either the oral or the subcutaneous (sc) injection routes of exposure (three daily administrations of 400-800 mg/kg BPA). Premature vaginal opening was seen for 8 of 14 animals exposed to 600 and 800 mg/kg BPA by sc injection. Vaginal opening was not produced by BPA in the gavage studies. These results are consistent with those of Dodds and Lawson [Nature 137:96 (1936)] who found that BPA induces persistent vaginal cornification in ovariectomized rats exposed to three twice-daily injections of 85 mg/kg BPA (total daily dose 170 mg/kg), but they conflict with the reported inactivity of BPA in the immature mouse uterotrophic assay. The uterotrophic activity of diethylstilbestrol in the rat is also established (0.04 mg/kg/day for three days).

Uterotrophic Activity of Bisphenol A in the Immature Rat

Bisphenol A (BPA) is active in immature AP rat uterotrophic assays when evaluated using either the oral or the subcutaneous (sc) injection routes of exposure (three daily administrations of 400-800 mg/kg BPA). Premature vaginal opening was seen for 8 of 14 animals exposed to 600 and 800 mg/kg BPA by sc injection. Vaginal opening was not produced by BPA in the gavage studies. These results are consistent with those of Dodds and Lawson [Nature 137:96 (1936)] who found that BPA induces persistent vaginal cornification in ovariectomized rats exposed to three twice-daily injections of 85 mg/kg BPA (total daily dose 170 mg/kg), but they conflict with the reported inactivity of BPA in the immature mouse uterotrophic assay. The uterotrophic activity of diethylstilbestrol in the rat is also established (0.04 mg/kg/day for three days).

Purified methoxychlor stimulates the reproductive tract in immature female mice

Methoxychlor is an estrogenic pesticide currently used as a substitute for DDT. The estrogenic effects of 98% pure methoxychlor or base-washed pure methoxychlor were examined on reproductive organs of immature mice and compared to control and estradiol-treated mice. Within 24 hours of birth, neonatal mice received 14 daily intraperitoneal injections of one of the following chemicals: sesame oil only, 10.0 μg of 17-β estradiol, or 0.05 mg, 0.5 mg, or 1.0 mg of 98% pure methoxychlor, or 1.0 mg base-washed 98% pure methoxychlor. Equal doses (1.0 mg) of 98% pure or base-washed methoxychlor stimulated the reproductive organs of immature females such that the effects closely resembled those seen after estradiol treatments. In comparison to control mice, these pesticide treatments also induced precocious vaginal opening, persistent vaginal cornification, increased reproductive tract weights, and epithelial hypertrophy in both the vagina and uterus. However, only estradiol treatments significantly elevated albumin levels in the uterine fluid of the immature mice while the highest methoxychlor doses significantly increased the uterine cell heights when compared to all other groups.

Endocrine and morphological features of cystic ovarian condition in antiprogesterone RU486-treated rats.

Four-day cyclic Wistar rats (200 g body wt) were injected (sc) with the antiprogestagen RU486 (4 mg RU486/0.2 ml oil) on estrus, metestrus, diestrus and proestrus. Groups of rats (12-15) were decapitated on days 1 (day of expected ovulation), 5, 9, 13, 17 and 21 after the 4 days of RU486 treatment. Oil-injected rats decapitated on proestrus (day 0) and estrus (day 1) served as controls. In both controls and RU486-treated rats, the following parameters were noted: ovulation, vaginal smears and luteinizing hormone (LH), follicle-stimulating hormone (FSH), prolactin, testosterone and estradiol-17 beta serum concentrations. Also, pituitary, adrenal, uterus and ovary weight were recorded. RU486 induced ovulation blockade, persistent vaginal cornification, uterine ballooning and increased serum levels of LH, FSH, prolactin, testosterone and estradiol. Furthermore, the LH/FSH and testosterone/estradiol ratios in serum increased. Pituitary and ovary weights also increased. The enlarged ovaries showed follicular cysts undergoing atresia and/or different degrees of luteinization of granulosa cells resembling, in some cases, genuine corpus luteum containing the ovocyte. The small follicles showed extensive atresia and stimulated thecal cells. These effects are reversible and remain in a stationary state for about 9-13 days after RU486 treatment. While the endocrinological alterations found in rats treated with RU486 are similar to those exhibited in polycystic ovarian disease, the morphological alterations found in the ovaries seem to be more closely related to the multicystic ovarian condition.(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive abnormalities in the prepubertal jaundiced Gunn rat.

The female, jaundiced Gunn rat has been previously reported to be infertile. This study describes some abnormalities in the reproductive system of the prepubertal jaundiced female rat. Vaginal opening occurred at the time of weaning, which was approximately 7 days earlier when compared to the nonjaundiced female littermates. Following vaginal opening, the jaundiced rat showed persistent vaginal cornification. The estimated age at first ovulation in the jaundiced rat was 52 days. The uteri of jaundiced rats were significantly larger than those of nonjaundiced rats by 17 days after birth. The accelerated uterine growth and the precocious vaginal opening in the jaundiced rat suggest hyperestrogenism. Feeding activated charcoal to jaundiced rats significantly reduced the uterine weight. These results show that the reproductive abnormalities in the jaundiced female rat appear in the prepubertal life and continue during adult life resulting in infertility.

Vitamin E protects hypothalamic beta-endorphin neurons from estradiol neurotoxicity.

Estradiol valerate (EV) treatment has been shown to result in the destruction of 60% of beta-endorphin neurons in the hypothalamic arcuate nucleus. Evidence suggests that the mechanism of EV-induced neurotoxicity involves the conversion of estradiol to catechol estrogen and subsequent oxidation to free radicals in local peroxidase-positive astrocytes. In this study, we examined whether treatment with the antioxidant, vitamin E, protects beta-endorphin neurons from the neurotoxic action of estradiol. Our results demonstrate that chronic vitamin E treatment prevents the decrement in hypothalamic beta-endorphin concentrations resulting from arcuate beta-endorphin cell loss, suggesting that the latter is mediated by free radicals. Vitamin E treatment also prevented the onset of persistent vaginal cornification and polycystic ovarian condition which have been shown to result from the EV-induced hypothalamic pathology.

Vitamin E protects hypothalamic beta-endorphin neurons from estradiol neurotoxicity

Estradiol valerate (EV) treatment has been shown to result in the destruction of 60% of beta-endorphin neurons in the hypothalamic arcuate nucleus. Evidence suggests that the mechanism of EV-induced neurotoxicity involves the conversion of estradiol to catechol estrogen and subsequent oxidation to free radicals in local peroxidase-positive astrocytes. In this study, we examined whether treatment with the antioxidant, vitamin E, protects beta-endorphin neurons from the neurotoxic action of estradiol. Our results demonstrate that chronic vitamin E treatment prevents the decrement in hypothalamic beta-endorphin concentrations resulting from arcuate beta-endorphin cell loss, suggesting that the latter is mediated by free radicals. Vitamin E treatment also prevented the onset of persistent vaginal cornification and polycystic ovarian condition which have been shown to result from the EV-induced hypothalamic pathology.

Reproductive abnormalities in female mice exposed neonatally to various doses of coumestrol

Female C57BL/Crgl mice were neonatally exposed to various doses of coumestrol to determine the threshold doses required for the occurrence of reproductive tract abnormalities. Newborn mice received daily subcutaneous injections of 10(-3), 10(-2), 8 X 10(-2), 10(-1), 1, 5, 25, 50, and 100 micrograms coumestrol in 0.005 ml dimethyl sulfoxide (DMSO) or DMSO alone, or received no treatment for the first 5 d of life. Some of the animals were ovariectomized at 40 d of age. Mice were killed at 20-22 mo of age. All neonatal doses of coumestrol advanced vaginal opening before that of controls. At 2 and 20-22 mo of age, doses greater than or equal to 25 micrograms consistently resulted in ovary-independent persistent vaginal cornification as judged by vaginal smears. Intact untreated and DMSO-treated control mice exhibited aging changes in the genital tract, some cervical adenosis and early cervicovaginal pegs and downgrowths, uterine cystic glandular hyperplasia, corpora lutea, and scattered areas of ovarian ceroid deposition. Intact mice receiving neonatal coumestrol exhibited cervicovaginal pegs and downgrowths (at all doses with the exception of 25 and 50 micrograms), cervical adenosis (at doses greater than or equal to 8 X 10(-2) micrograms), uterine squamous metaplasia (significant at doses greater than or equal to 50 micrograms), and a decrease in uterine cystic glandular hyperplasia (significant at doses greater than or equal to 25 micrograms). The levels of 10(-1), 5, and 100 micrograms neonatal coumestrol daily resulted in hemorrhagic follicles. An increase in ovarian ceroid deposition (significant at doses greater than or equal to 5 micrograms) was observed. At 40 d and 20-22 mo of age, corpora lutea were consistently absent from the 100-micrograms-treated animals. Most of the ovariectomized untreated and DMSO-treated control animals showed typical castrate-like morphology of the genital tract, with the majority of the control mice exhibiting uterine cystic glandular hyperplasia. Ovariectomized mice receiving coumestrol neonatally exhibited various degrees of cervicovaginal alterations: pegs and downgrowths (significant at all doses with the exception of 10(-1) micrograms), endometrial collagen deposition (significant at greater than or equal to 25 micrograms), and reduced or absent uterine glands (significant at 10(-3), and 10(-11), and at all doses greater than or equal to 5 micrograms).

Long-term genital tract changes in female mice treated neonatally with coumestrol

The neonatal mouse model has proven to be an effective system to examine long-term reproductive tract abnormalities resulting from early exposure to estrogens. Newborn C57BL/Crgl mice received 8 × 10 −2 μg diethylstilbestrol (DES) or 100 μg coumestrol (a plant estrogen) in 0.005 mL dimethyl sulfoxide (DMSO) or DMSO alone or received no treatment for the first 5 days of life. Half of the animals wedre ovariectomized at 40 days of age. Vaginal lavages were examined for 15 consecutive days before termination at 13 months of age, at which time genital tracts and mammary glands were removed for histological examination. Diethylstilbestrol- and coumestrol-treated animals exhibited ovary-independent persistent vaginal cornification as well as cervico-vaginal pegs and downgrowths, uterine squamous metaplasia, and an enhancement of age-related changes in the ovary including hemorrhagic follicles. In general, neonatal exposure to the naturally occurring plant estrogen, coumestrol, has long-term effects similar to those seen following exposure to natural and synthetic estrogens.

Longitudinal studies of estrous cyclicity in C57BL/6J mice: III. Dietary modulation declines during aging

Dietary modulation of estrouos cyclicity was studied throughout the reproductive lifespan to assess the stability of age-related changes in cyclicity and to probe underlying mechanisms. Animals were fed a standard diet or an isocaloric breeder diet that differed in nutrient composition to promote fecundity. In young mice, the breeder diet more than doubled the frequency of short (4-day) cycles, and, as a result, increase the total number of cycles during the cycling lifespan by 10%. Dietary potentiation of short cycles disappeared between 7 and 9 months of age, and most subsequent age-related changes in cyclicity were resistant to dietary influence. The breeder diet had no effect on the transition from 4- to 5-day cycles, the onset of acyclicity, or on the incidence or duration of persistent vaginal cornification. It only delayed the increased of very long (> 5-day) cycles by 1 month. These results show that most age-related changes in cyclicity are not influenced by dietary differences that affect cyclicity in young mice, and that diminished responsiveness to dietary variation is among the earliest age-related changes in the reproductive system. In addition, the results suggest that differences in cycle frequency and, presumably, in cumulative exposure to pre-ovulatory elevations of ovarian steroids do not influence the cycling lifespan in this strain of mouse.

Effect of neonatal androgenization on positive feedback in female mice.

Exposure of female mice to androgens within 5 days of birth impairs fertility. Such treatment in rats results in a post-pubertal acyclic state of persistent vaginal cornification and in an inability, when ovariectomized, to show normal positive feedback on luteinizing hormone (LH) release in response to steroid challenge. In the present study, we explored whether neonatally androgenized mice demonstrate positive feedback. Female mice were administered 100 micrograms of testosterone propionate (TP) on either Day 1 (TP1) or Day 5 (TP5) after birth, or vehicle on Day 1 (SO1). Androgen-treated mice had a statistically significant advance in onset of vaginal opening as compared with vehicle-treated mice. All mice that received TP entered constant vaginal estrus, whereas those given vehicle showed variable cytology. All mice were ovariectomized at 7 wk of age and received Silastic capsules containing a priming dose of 17 beta-estradiol. When all mice were challenged 1 wk later with sequential administration of estradiol benzoate and progesterone, a significant increase in plasma LH level was present only in the vehicle-treated mice. We conclude that neonatal androgenization defeminizes the neuroendocrine mechanisms controlling gonadotropin release.