Catecholamines in hypothalamus, ovaries and uteri of rats with precocious puberty

The concentration of catecholamines in the hypothalamus and reproductive organs of rats with hypothalamic lesions placed on the day of birth was investigated. In an attempt to contribute to the discussion concerning the role of catecholamines in regulation of puberty, the aim of this study was to examine the content of hypothalamic, ovarian and uterine catecholamines in female rats with precocious vaginal opening. The animals were sacrificed on the day of precocious puberty, which occurred at the age of 25.71 +/- 0.98 days. The data obtained were compared with intact (pubertal) controls obtained on the day of vaginal opening (40.13 +/- 1.35 days) as well as in infantile intact controls of corresponding age of the lesioned animals. In the ovaries of both animals (i.e. lesioned and sacrificed on day of vaginal opening and the infantile controls of corresponding age), small and medium sized follicles were present. Ruptured follicles were evident only in the pubertal controls. The mass of ovaries and uteri from lesioned rats was also significantly lower than in the pubertal controls. Concentrations of norepinephrine in both ovaries and uteri on the day of vaginal opening of the animals with posterior hypothalamic lesions and of infantile controls, was significantly higher than in pubertal controls on the day of vaginal opening. Epinephrine was significantly higher in the uterine tissues of lesioned and infantile controls as compared to pubertal animals. The levels of dopamine and norepinephrine in the hypothalamus of lesioned and pubertal controls on the day of vaginal opening were significantly higher than in infantile controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Controlled neonatal exposure to estrogens: a suitable tool for reproductive aging studies in the female rat

The present study was designed to determine whether the modification of exposure time to large doses of estrogens provided a reliable model for early changes in reproductive aging. Silastic implants containing estradiol benzoate (EB) in solution were placed into 5-day-old female Wistar rats and removed 1 day (Ei1 group) or 5 days (Ei5) later. In addition, 100 micrograms [corrected] EB dissolved in 100 microliters corn oil was administered s.c. to another group (EI). Control rats received either vehicle implants or 100 microliters corn oil. Premature occurrence of vaginal opening was observed in all three estrogenized groups independently of EB exposure. However, females bearing implants for 24 h had first estrus at the same age as their controls and cycled regularly, and neither histological nor gonadal alterations could be observed at 75 days. Interestingly, they failed to cycle regularly at 5 mo whereas controls continued to cycle. On the other hand, the increase of EB exposure (Ei5, EI) resulted in a gradual and significant delay in the onset of first estrus and in a high number of estrous phases, as frequently observed during reproductive decline. At 75 days, the ovaries of these last two groups showed a reduced number of corpora lutea and an increased number of large follicles. According to this histological pattern, ovarian weight and progesterone (P) content gradually decreased whereas both groups showed higher estradiol (E2) content than controls. This resulted in a higher E2:P ratio, comparable to that observed in normal aging rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Germ cell deficient (gcd) mouse as a model of premature ovarian failure

Premature ovarian failure (POF) in women is characterized as menopause commencing before age 35. Although some cases of POF appear to be inherited, no experimental animal models of familial POF are available. Recently a mouse mutation has been identified that results in infertility due to a lack of primordial germ cells arising in early embryonic development. It was observed that shortly after puberty, females homozygous for this mutation entered reproductive senescence as defined by high levels of circulating gonadotropins, inability to respond either hormonally or functionally to superovulation, and a disrupted estrous cycle. Also, the ovaries completely lacked developing follicles and the endometrium was inactive. However, these mice had undergone complete sexual development as determined by age of vaginal opening, mammary gland histology, and sexual behavior. Thus, these animals closely mimic familial premature ovarian failure and may be useful models for study of the pathogenesis and treatment of this condition.

Induction of true precocious puberty by neonatal treatment with danazol in female rats

Female rats at 5 days of age were given a single subcutaneous injection of varying doses of danazol or vehicle. Rats treated with 300 micrograms of danazol showed significant (P < 0.01, respectively) advancement in the day of vaginal opening (37.50 +/- 0.49 days vs. 25.20 +/- 0.19 days; mean +/- S.E.M.), first estrus (38.19 +/- 0.62 days vs. 29.10 +/- 0.26 days) and onset of estrous cycle (49.63 +/- 1.30 days vs. 37.07 +/- 1.50 days). All rats treated with danazol showed 4- or 5-day estrous cycle in the adulthood. Rats treated with 300 micrograms of danazol at 5 days of age discharged luteinizing hormone in the late stage of first proestrus. These results demonstrate that neonatally administered danazol produces the true precocious puberty in female rats, and this sexual precocity rat represents a unique model for analysis of the onset of puberty.

Correlations among three measures of puberty in mice and relationships with estradiol concentration and ovulation

Correlations among ages and weights at vaginal opening (AVO, WVO), positive vaginal smear (AVE, WVE), and copulatory plug (AVP, WVP) were determined using 623 mice. Two additional experiments were conducted to determine association of each with serum concentrations of estradiol and incidence of ovulation. Female mice were weaned at 21 days and 24 days of age were assigned randomly to mate with males. Mice were checked daily to determine AVO, AVE, and AVP. Mice were weighted weekly and WVO, WVE, and WVP were obtained by interpolation. Genetic correlations among ages and weights were small and mainly negative. Phenotypic correlations were small to moderate and mainly positive. Genetic correlations among the three measures of age and among the three measures of weight were moderate to high and positive; respective phenotypic correlations were somewhat smaller. In experiment 2, mice were checked daily for the three reproductive measures and bled at vaginal opening (n = 23), positive smear (n = 18), or copulatory plug (n = 19). Serum was assayed for estradiol via radioimmunoassay. No differences were found among the three indicators (p = 0.34). In experiment 3, mice were randomly assigned to be killed after detection of vaginal opening, positive smear, or copulatory plug. Oviducts were removed and flushed with saline to determine presence of ova. A greater (p < 0.05) proportion of mice had ovulated when killed after detection of copulatory plug (20/22) than after positive smear (4/27), and the proportion was greater after positive smear than after vaginal opening (0/14).(ABSTRACT TRUNCATED AT 250 WORDS)

Ex vivo determination of opiate antagonist binding at mu-opioid ([3H]-DAGO) receptors in hypothalamic micropunches from maturing female rats: comparison between SDZ 210-096 and nalmefene

We have previously shown that the duration of opioid receptor blockade is critical in determining the degree of opioid antagonist effect following peripheral injection of naloxone and naltrexone. In the present work, we have used this ex vivo technique to compare receptor occupancy of a new opiate antagonist, SDZ 210-096 (SDZ), to that of nalmefene (NLM) in maturing female rats. Two doses (SDZ, 5.6 and 50 mg/kg; NLM, 2.5 and 50 mg/kg) were injected subcutaneously into 3 groups of rats (infantile, juvenile and peripubertal). Micropunches from hypothalamic coronal slices (300 microns) were removed at various times post-injection for quantification of mu-opioid receptors with [3H]-DAGO. Acute administration of the lower dose of SDZ inhibited ligand binding almost completely by 3 h but 50% recovery was observed in all age groups by 12 h. In contrast, SDZ 50 mg/kg provided 80-100% antagonism for at least 24 h. Age-related differences in the ability of SDZ to inhibit [3H]-DAGO binding were observed in that hypothalamic mu-opioid receptors were blocked for longer periods in younger rats. Determination of receptor occupation following NLM injection confirmed that it too has prolonged duration of action but a 24 h blockade is not achieved with either dose of this antagonist. Age-related and dose-related changes in receptor occupancy were minimal compared to SDZ. These studies clarify the interaction of these antagonists at hypothalamic mu-opioid receptors and provide information which allows a clearer interpretation of results in experiments involving opioid blockade.

Effects of neonatal exposure to diethylstilbestrol on protein expression by vagina and uterus in mice

Neonatal treatment of female mice with diethylstilbestrol (DES) results in genital tract abnormalities including ovary-independent vaginal proliferation and cornification. Protein profiles were examined in vagina and uterus from 45-day-old, ovariectomized C57BL/Tw mice which had been given 5 daily injections of 2 micrograms DES or oil vehicle alone from the day of birth, and in those from 45-day-old, ovariectomized mice given 3 daily injections of 0.1 microgram DES from 42 days of age. Proteins extracted were analyzed by two-dimensional polyacrylamide gel electrophoresis. In the vagina, expression of 37 non-keratin proteins was altered by postpubertal injections of DES as compared with the controls. In the neonatally DES-exposed vagina, expression of 26 of 37 proteins was altered as compared with controls. In the uterus, expression of 22 proteins was altered in the postpubertally DES-exposed group as compared with that in the control; however, the protein expression pattern of the neonatally DES-exposed group closely resembled that of the control except for one protein (no. 23, pI = 6.1, MW = 39.5 kDa) which was specifically increased in the neonatally DES-exposed group. By immunoblot analysis, 6 keratin polypeptides (49.5, 50, 52, 53, 57 and 58 kDa) were identified in vaginae of ovariectomized mice exposed neonatally and postpubertally to DES and of the controls. These results indicate that neonatal DES exposure induces organ specific alterations in the synthesis of proteins in mouse vagina and uterus.

Prenatal ethanol exposure and opiatergic influence on puberty in the female rat

Fetal alcohol exposure (FAE) is associated with a variety of physiological and behavioral dysfunctions, including deficits to reproductive function. FAE has also been shown to increase brain beta-endorphin levels. This study sought to determine whether the common delay of the onset of puberty in fetal alcohol-exposed animals could be due to increased opiate inhibition of LH release. Prepubertal female rats were injected with an opiate antagonist, naltrexone, over days 26-29. This naltrexone treatment led to an acceleration of vaginal opening and first estrus in FAE animals; had no effect on chow-fed or pair-fed controls. The vaginal opening and first estrus advancement in FAE animals occurred at a lower body weight indicating independence from growth-promoting effects of the drug treatment. It is concluded that delays in puberty in FAE animals are not directly due to pituitary pathology, but are related, at least in part, to increased inhibition of the LHRH neuron and functional impairment of gonadotrophin secretion.

Neonatal exposure to substance P alters behavioral and substance P levels in the central nervous system of the adult rat

Substance P (SP) administered subcutaneously to male and female rats during a neonatal period (days 1-7 after birth), produced long-term effects. Thermal/pain perception and elements of both male and female copulatory behavior were altered. A significant increase in the SP level in the dorsal part of the spinal cord was demonstrated by radioimmunoassay and by micro-fluorescence. The present study indicates that exposure to SP during the neonatal period, when the role of SP in transmission is likely to be established, has biochemical and functional consequences for SP systems in the adult.

Ultrastructure of vagina and uterus in young mice after methoxychlor exposure

Ultrastructural effects of 17 beta-estradiol were compared with technical pesticide methoxychlor in uterus and vagina of young mice. Neonates received 14 daily ip injections of either sesame oil, 10.0 micrograms 17 beta-estradiol, or 0.05, 0.1, 0.5, or 1.0 mg methoxychlor. Estradiol accelerated vaginal opening to 11 days, increased reproductive tract weight gain, and induced vaginal cornification, the cells of which exhibited complex surface microridge patterns. The hypertrophied uterine cells were covered with dense, enlarged microvilli with bulbous expansions or clumps. The highest three methoxychlor doses were stimulatory. Exposure to 0.5 or 1.0 mg methoxychlor increased reproductive tract weights threefold due to excessive fluid accumulation, and induced vaginal cornification and opening by 10 days. The cornified cells lacked complex surface microridges, while uterine cells exhibited dense microvilli growth, atypical morphology, and separation. Although 0.5 and 1.0 mg methoxychlor were highly stimulatory, the surface alterations in uterus and vagina appeared different from estradiol.

Goblet-like cells in atrophic vaginal smears and their histologic correlation. Possible confusion with endocervical cells

The occurrence and origin of goblet-like cells seen between clusters of parabasal cells in atrophic vaginal smears were investigated. The goblet-like cells were cytologically identified in the vaginal smears from 23 (19.2%) of 120 patients whose smears showed an atrophic pattern, but without any inflammatory, dysplastic or malignant changes. Histologically, these cells were found in sections from 6 (18.8%) of 32 elderly women with atrophic vaginal epithelium. The goblet-like cells were situated among the squamous cells of the upper layer of the atrophic squamous epithelium from the vagina to the portio. These goblet-like cells in atrophic smears were initially misinterpreted as endocervical cells, which are regarded as a marker of smear adequacy in the cytologic screening for cancer of the uterine cervix. The correct interpretation of these goblet-like cells in smears from postmenopausal and elderly women is thus obviously important in assessing the adequacy of the sample for the detection of abnormal cells.

The timing of gonadal refractoriness in the female Turkish hamster (Mesocricetus brandti) is not dependent on the timing of gonadal regression

When prepubertal female Turkish hamsters are reared on 12L:12D, individuals respond reproductively in two ways; the majority exhibit a delay in the onset of regular vaginal estrous cyclicity (first vaginal estrus; FVE), and some individuals exhibit FVE at a time not different from females reared on 16L:8D. Soon, however, these females also become reproductively quiescent. This study addresses the following questions: (1) At what age do these two subpopulations become refractory to 12L:12D? (2) Is the onset of refractoriness in adults reared on 12L:12D dependent on the time when they become anovulatory? All females reared on 12L:12D become refractory at a similar age (169.1 +/- 4.4 days in those that exhibit delayed FVE vs. 165.3 +/- 6.8 days in those that exhibited an early FVE and then became anovulatory; p much greater than 0.05). Also, there is no correlation between the age at which vaginal cycles ceased and the age at which those individuals became refractory (r2 = 0.12; slope not different from 0). On the basis of these data, we propose that in the female Turkish hamster the onset of photorefractoriness is timed, not by the interval of reproductive quiescence, but by a preceding event, perhaps the initiation of short photoperiod exposure or the onset of photosensitivity.

Developmental pattern of estrogen receptor expression in female mouse genital tracts

The distribution of the estrogen receptor (ER) was investigated in neonatal female genital tracts (uterus, oviduct, cervix, and vagina) from days 1-22 after birth, using immunohistochemistry employing an anti-ER monoclonal antibody. In uteri, the ER in epithelial cells began to be observed by day 4. The number of positive epithelial cells and the staining intensity gradually increased until day 22 of age. On the other hand, uterine stroma cells gave a strong ER immunostaining even on day 1. The staining intensity reached a maximum by days 4-7 and then slightly decreased with age. In the oviduct, cervix, and vagina, epithelial cells showed positive ER immunostaining on day 1, and the intensity increased gradually until day 22. ER immunostaining in stroma cells was almost constant during the development period. The ER in both epithelial and stroma cells from these younger animals showed similar biochemical properties, i.e. an increased affinity for nuclei and resistance to extraction with PBS. Thus, during neonatal development of the female reproductive tract, ER is present not only in stroma cells but also in epithelial cells. This ER protein exhibits properties and characteristics similar to those of adult mice. The presence of ER suggests that some of the estrogen actions of cell proliferation, differentiation, and tissue abnormalities resulting from prenatal and postnatal estrogen administration may be mediated by receptor interactions.

Scanning microscopy of the developing vagina in postnatal gerbils

Scanning electron microscopy of postnatally developing gerbil vagina (birth to maturity) shows that longitudinal folds form prior to transverse folds; the process of fold formation is initiated on the dorsal wall and proceeds ventrally. From days 1 to 7 postnatally, the vaginal epithelium is composed of either flat or bulging cells, depending on the vaginal region. The luminal cell surface is covered with uniform stubby microvilli and solitary cilia. Between days 9 and 20, the flat cells with distinct cell boundaries spread toward more proximal areas, leading to the formation of mixed patches of cells with flat or rounded apices. Individual elongated microvilli or tufts of forked microvilli may sprout from their surfaces. Solitary cilia gradually disappear. The transition from immature to mature vaginal epithelium starts around day 20, when individual cells recess below the level of neighboring cells. This process spreads throughout the vagina during the following days, reflecting local changes in the subsurface layers of the epithelium preparatory to exfoliation. Around day 40 the actual exfoliation of the luminal cell layer starts. By this time the surface characteristics of many of the desquamating cells have changed. In addition to microvilli, microridges are being formed. The process of exfoliation is finished by about day 60. The newly appearing cell layers now transform into typical cornified cells of the cycling vaginal epithelium.

Influence of the immature testis on sexual differentiation in the tammar wallaby, Macropus eugenii (Macropodidae: Marsupialia)

Reproduction in the tammar wallaby, Macropus eugenii (Desmarest), is highly seasonal in the females but not the males. This study was designed to determine whether the difference is established during early life as a result of exposure to the developing testes. At day 10 after birth, when the sex can be distinguished externally, testes were removed from males and placed under the flank skin of females, while other groups of males and females were subjected to surgery without interfering with the gonads. The testis grafts remained palpable for 3-6 months. Sex-chromosome constitution was confirmed by karyotyping. At 3 years of age, the body weights and dimensions of the grafted females were not significantly different from those of the sham-operated females, whereas those of the castrated males were significantly larger and were equal to those of the sham-operated males, indicating that there is genetical control of growth independent of the testis in this species of marsupial. During 5 years of observations, none of the grafted females ever produced young, whereas all of the sham-operated females produced young each year from the second year. The grafted females had a mixture of male and female reproductive structures. The pouch and mammary glands developed normally, as did the Mullerian duct derivatives, the vaginal complex, the uteri and the oviducts. The ovaries were either devoid of oocytes and follicles or had reduced numbers, the Wolffian ducts were retained to varying degrees, the urogenital strand had developed into a prostate indistinguishable in size and structure from that of intact males, and the genital tubercle had developed into a normal-sized penis with a crus penis and Cowper's glands. In the castrated males, the scrotum developed normally and contained the gubernaculum and vas deferens. There was no evidence of Mullerian duct derivatives, and the urogenital strand was a simple canal, as in females. There were no Cowper's glands and no penis or erectile tissue. In one hemicastrated male, there was no development of the penis, although the remaining testis occupied the scrotum and showed compensatory hypertrophy. These findings indicate that the testis, at day 10, has a profound influence on the early differentiation of the Wolffian ducts, prostate and penis but cannot influence the differentiation of the Mullerian duct derivatives. The testis does not have any effect on the development of the pouch, mammary glands or scrotum or on somatic growth, all of which are apparently under independent genetical control.

Neonatal melatonin administration advances rat vaginal opening and disrupts estrous cyclicity and estrogen-dependent regulatory mechanisms of luteinizing hormone and prolactin

Melatonin (100 micrograms/rat) was administered to female rats on day 5 of life, 3 hours prior to the onset of darkness or at 12:00 hours. Melatonin administration induced precocious puberty in both cases, as indicated by the advance of the time of the vaginal opening and the appearance of the first estrous smear as compared with controls (P less than 0.01), together with an increase in the number of estrous smears (P less than 0.05) and a reduction in the number of diestrous smears (P less than 0.05). Decreased serum prolactin levels were observed on day 21 of age (P less than 0.05) in melatonin-treated rats with both of the melatonin injection times as compared with controls. No differences were apparent in basal luteinizing hormone (LH) levels either at 30 or at 60 days of age comparing melatonin- and vehicle-treated rats with either of the scheduled melatonin injection times. As to serum follicle-stimulating levels (FSH) levels, there was a marked decrease in circulating FSH levels in melatonin-treated rats in both cases on days 21, 30, and 45 (P less than 0.05) as compared with controls. A marked increase of serum prolactin at both 48 and 55 hours after estradiol benzoate (EB) administration was detected in 30-day-old melatonin-treated rats as compared with controls (P less than 0.05 for both points). Also, an increased responsiveness of prolactin to EB was found on the first day post-administration. At 60 days of age, an increase in prolactin responses to EB was observed on the first day post-administration (31 and 48 hours after, (P less than 0.01), whereas no differences were detected at any other studied time. The LH burst that occurs 31 hours after EB administration in 30-day-old rats was decreased in melatonin-treated animals as compared with controls (P less than 0.05). In 60-day-old melatonin-treated rats, a marked increase in the LH response to EB administration, 31 hours after injection (P less than 0.01), was observed. These data suggest that neonatal melatonin administration in pharmacological amounts induces precocious puberty as measured by vaginal opening and, furthermore, it advances the appearance of the first estrous smear with age-dependent modifications of estrous cyclicity and prolactin and LH responses to EB.

Changes in the uterus and vagina of mice treated neonatally with antiestrogens

Adenosis-like lesions (ADL) were found in the upper vagina including the cervical region of ICR mice as early as 1 day after 5 daily injections of 200 micrograms tamoxifen (Tx) starting on the day of birth (200-micrograms Tx mice). ADL developed progressively from 5 to 30 days of age. Involution of the musculature and suppression of the gland genesis occurred in the uterus of 5- to 30-day-old, 200-micrograms Tx mice. The uterine abnormality resulted in a loss of type III collagen and laminin, and in an increase in fibronectin and type I collagen in the mesenchymal stroma of 15-day-old, 200-microgram Tx mice. Vaginal ADL and uterine myometrial involution were also encountered in 35-day-old mice given neonatal injections of 2-200 micrograms Tx, 200 micrograms clomiphene (Clm) and 200 micrograms nafoxidine (Naf), respectively. These changes were never observed in control and 0.2-microgram Tx mice. Ovariectomy performed at 10 days resulted in a reduction in the weight of uteri and the extent of ADL occupancy in Tx, Clm and Naf mice. Five daily injections of 0.1 microgram 17 beta-estradiol (E2) beginning at 30 days of age increased uterine weight and ADL occupancy extent in Tx (2-200 micrograms), Clm and Naf mice. The present findings suggest, therefore, that the antiestrogens act as an estrogen agonist to mouse uterus and vagina and that the induced ADL develops progressively depending on ovarian estrogen.

Vaginal abnormalities in ovariectomized BALB/cCrgl mice after neonatal exposure to different doses of diethylstilbestrol

Newborn BALB/cCrgl female mice received five daily injections of various doses of diethylstilbestrol (DES), 0.0001-10 micrograms. Mice were killed at 6 days of age or at 4 months after ovariectomy at 40-42 days. Subepithelial nodules of polygonal cells in the upper (Mullerian) vagina during early postnatal life were associated with the later occurrence of ovary-independent persistent stratification with or without cornification in mice treated neonatally with 0.1-10 micrograms DES and thus are a possible predictor of this phenomenon. The thresholds for the induction of ovary-independent epithelial pegs, downgrowths and adenosis (glandular formations) were 0.1 microgram and 0.5 microgram DES/day, respectively.

Growth-promoting effects of relaxin and related compositional changes in the uterus, cervix, and vagina of the rat

Although the precise role of relaxin has yet to be elucidated, it has been implicated in the regulation of physiological and biochemical processes in the reproductive tract during pregnancy and parturition. In this study, the growth-promoting effects of relaxin and related compositional changes in the uterus, cervix, and vagina of immature ovariectomized estrogen-primed rats were examined. Relaxin increased the wet weight of the uterus, cervix, and vagina in a significant and linear manner over the log of the dose range (1-30 micrograms; 6 h). The increase in uterine weight was due to increases in both dry weight and water content at all doses. A dose of 1 microgram relaxin induced maximal increases in dry weights in the cervix and vagina over control values; higher doses increased wet weight, but these changes were due solely to increases in water content. Thirty micrograms of relaxin were found to increase total soluble protein and glycogen content of the vagina above control values after 6 h. Relaxin did not alter the total collagen levels of the uterus or cervix, and collagen concentrations were significantly reduced in these organs 6 and 24 h after treatment. Total glycosaminoglycan levels were elevated by relaxin in the uterus (6 h) and cervix (24 h). Total vaginal collagen was increased 24 h after relaxin injection, but the collagen concentration was decreased over the time interval studied, and glycosaminoglycan levels in the vagina were unaltered. In summary, relaxin stimulates growth of the uterus, cervix, and vagina by increasing water content and tissue mass. The increases in distensibility that relaxin induces in these organs appear to be related to changes in the fluid matrix and proteoglycan metabolism rather than alterations in collagen concentration, at least 6-24 h after a single injection. These results support the hypothesis that relaxin plays a significant role in the maintenance of pregnancy through its contribution to fetal accommodation and in the facilitation of parturition through expansion of the entire birth canal.

Puberty in female rats: relative effect of exercise and food restriction

Reproductive development in relation to growth and fat deposition was compared in three groups of female rats: a group that was allowed to grow only slowly by requiring them to work hard on a running wheel for their food; a group in which the same slow rate of growth was imposed by restricting their food intake, but without an exercise requirement; and a normally growing, nonexercising, ad libitum-fed, control group. Animals forced to run for their food experienced vaginal opening at a significantly lower body weight than either of the other two groups. The same trend was apparent for the first ovulation, but not significant. Thus the present results suggest that, under some conditions, intense exercise may actually accelerate rather than decelerate reproductive development, at least relative to body weight. With the possible exception of body weight, none of the whole-body parameters measured in this experiment (body weight, growth rate, or amount of fat) were found to be critically related to the first ovulation when all three groups of females were considered as a unit. Thus the present results also argue against some of the current hypotheses, all developed using dietary manipulation, that the onset of fertility is somehow dependent on one of these factors.

The complexity of anti-estrogen responses

The actions and biological responses of anti-estrogens are a function of: the experimental conditions, the parameters, the organ and the animal species considered. Target tissues for estrogens in the guinea-pig during the perinatal period are interesting models to explore the action of anti-estrogens. The summary of the data indicates: (1) In the fetal uterus of guinea-pig in in vivo experiments (after injection to the maternal compartment) tamoxifen acts as a real agonist concerning growth, as a partial agonist concerning the stimulation of the progesterone receptor. (2) In in vitro experiments (in organ culture of fetal uterus or in isolated cells) anti-estrogens (tamoxifen or 4-hydroxy-tamoxifen) act as antagonists and also inhibit the effects provoked by estrogens. (3) In the uterus and vagina of newborn guinea-pigs, tamoxifen and its derivatives: 4-hydroxytamoxifen and N-desmethyltamoxifen act as real agonists concerning the uterotrophic and vaginotrophic effects, and also stimulate the amount of DNA per organ, but concerning the progesterone receptor in the uterus, in the short treatment anti-estrogens act as partial agonists but they have no effect in the long treatment. In the vagina in the short treatment anti-estrogens provoke no significant effects, but in the long treatment they are full agonists. In neither of the two biological responses studied (growth and progesterone receptor) does tamoxifen and its derivatives block the action of estradiol. (4) The use of a monoclonal antibody to the estrogen receptor revealed quantitative differences in the activation of the estrogen receptor when bound to estradiol or tamoxifen. This observation was in agreement with the lesser extent of binding to DNA-cellulose of the tamoxifen-estrogen receptor complex as compared with the estradiol-estrogen receptor complex. This fact suggests an impaired activation of the estrogen receptor induced by tamoxifen which might be related to the different biological responses provoked by estrogens and anti-estrogens.

Effect of neonatal melatonin administration on sexual development in the rat

In order to study the mechanisms by which melatonin modulates sexual development, 5-day-old female Wistar rats have been treated with a single s.c. injection of melatonin, 3 h before the darkness onset. Criteria for sexual development were the age of vaginal opening and the circulating levels of prolactin, LH, FSH and estradiol. Also, pineal melatonin content was measured. There was a precocious puberty (P less than 0.01) in melatonin-treated rats measured by the age of the vaginal opening. An increase in the number of estrous smears over the whole period studied was observed in melatonin-treated animals as compared to controls. Along with these modifications, there was decrease in pineal melatonin content and serum prolactin levels, on day 21 of life (P less than 0.05), with an increase in both parameters on day 30 of age, in melatonin-treated rats as compared to controls, with no modifications at any other time studied. No differences were detected for serum LH levels considering the whole period studied for both groups. There was a faster decrease in plasma FSH levels with age in melatonin-treated animals than in controls. Serum estradiol levels were decreased in the peripubertal period in melatonin-treated rats as compared to controls. All these data suggest that the modifications induced by neonatal melatonin administration on prolactin, FSH and estradiol could be responsible for the precocious puberty shown in this study.