Clinical correlates of environmental endocrine disruptors.

Endocrine disrupting chemicals (EDCs), such as environmental estrogens, are hypothesized to be associated with a global decrease in sperm counts, other male reproductive tract problems and increasing rates of female breast cancer. Results of human population studies do not support the association between certain organochlorine EDCs and female breast cancer. Moreover, there is minimal evidence linking EDCs or exposure to other environmental chemicals with male reproductive tract problems. With the exception of the increasing incidence of testicular cancer, it is also questionable whether male reproductive tract problems are increasing, decreasing or unchanged. However, several studies report large differences in sperm count and quality and other endocrine-related problems within countries and regions, but the environmental, dietary and/or lifestyle factors responsible remain unknown.     

Adverse effects of environmental toxicants, octylphenol and bisphenol A, on male reproductive functions in pubertal rats

It has been proposed that a global decline in sperm counts, semen quality, and several male reproductive disorders are associated with exposure to environmental chemicals. Thus, the present study examined the effects of two estrogenic chemicals, octylphenol (OP) and bisphenol A (BPA), on epididymal sperm counts and sperm motility, luteinizing hormone (LH)-releasing hormone (LHRH)-stimulated plasma LH and steroid hormones, insulin-like growth factor I (IGF-I), and accessory reproductive organs in pubertal male Wistar rats. Fifty-day-old rats in the OP group (n=11) and BPA group (n=11) received daily sc injections of the respective chemical at a dose of 3 mg/kg bw dissolved in 0.2 mL DMSO. Rats in the control group (DMSO group; n=10) received 0.2 mL DMSO alone. After 2 wk of treatment, a jugular blood sample was taken, and, on the next day, a second blood sample was taken 1 h after an sc injection of LHRH (250 ng). After 5 wk of treatment, rats were deeply anesthetized and heart blood was collected. Epididymal sperm motility and sperm head counts were determined. LHRH increased plasma LH to higher levels in all groups, but the increases were significant (p<0.01) in the BPA and OP groups. However, despite higher LH levels after LHRH injection, the incremental responses of testosterone and progesterone in the OP and BPA groups were small compared to those in the DMSO group, which showed a small LH response. After 5 wk of treatment, plasma testosterone levels were significantly (p<0.01) reduced in the OP and BPA groups and this was accompanied by reduced (p<0.05) epididymal sperm counts. However, the chemical-treated groups had high basal progesterone levels. No significant effects of chemicals on sperm motility parameters were noted. The chemical-induced increases (p<0.05) of the weight of ventral prostate gland were coincided with elevated plasma IGF-I levels in the BPA (p<0.05) and OP (p<0.01) groups. The present results demonstrated that OP and BPA can reduce sperm counts resulting from lowered plasma testosterone in male rats just after puberty. The enlarged ventral prostate gland may possibly be associated with increased plasma IGF-I, raising the possibility of a link between these chemicals and prostate diseases because IGF-I has been implicated in the pathogenesis of human prostate cancers.     

Prenatal exposure to low levels of androgen accelerates female puberty onset and reproductive senescence in mice

Sex steroid hormone production and feedback mechanisms are critical components of the hypothalamic-pituitary-gonadal (HPG) axis and regulate fetal development, puberty, fertility, and menopause. In female mammals, developmental exposure to excess androgens alters the development of the HPG axis and has pathophysiological effects on adult reproductive function. This study presents an in-depth reproductive analysis of a murine model of prenatal androgenization (PNA) in which females are exposed to a low dose of dihydrotestosterone during late prenatal development on embryonic d 16.5-18.5. We determined that PNA females had advanced pubertal onset and a delay in the time to first litter, compared with vehicle-treated controls. The PNA mice also had elevated testosterone, irregular estrous cyclicity, and advanced reproductive senescence. To assess the importance of the window of androgen exposure, dihydrotestosterone was administered to a separate cohort of female mice on postnatal d 21-23 [prepubertal androgenization (PPA)]. PPA significantly advanced the timing of pubertal onset, as observed by age of the vaginal opening, yet had no effects on testosterone or estrous cycling in adulthood. The absence of kisspeptin receptor in Kiss1r-null mice did not change the acceleration of puberty by the PNA and PPA paradigms, indicating that kisspeptin signaling is not required for androgens to advance puberty. Thus, prenatal, but not prepubertal, exposure to low levels of androgens disrupts normal reproductive function throughout life from puberty to reproductive senescence.     

Lack of correlation of serum estradiol with growth velocity during male pubertal growth

The adolescent growth spurt in boys is under hormonal control. It is accepted that androgens and growth hormone contribute to male pubertal growth, but the role of estrogens is uncertain even though low-dose estradiol administration stimulates growth in prepubertal boys. In the present work, the correlation of serum testosterone and serum estradiol with growth velocity was studied in 16 pubertal normal boys. The study included correlations of growth velocity with serum nonsex hormone-binding globulin-bound testosterone and with serum nonsex hormone-binding globulin-bound estradiol, which are parameters of serum bioavailable sex hormones. A statistically significant positive correlation was found between serum testosterone and growth velocity but not between serum estradiol and growth velocity. These findings are against the hypothesis that estrogens play a growth promoting role during male puberty.     

Aneuploid sperm formation in rainbow trout exposed to the environmental estrogen 17α-ethynylestradiol

Environmental contaminants that mimic native estrogens (i.e., environmental estrogens) are known to significantly impact a wide range of vertebrate species and have been implicated as a source for increasing human male reproductive deficiencies and diseases. Despite the widespread occurrence of environmental estrogens and recognized detrimental effects on male vertebrate reproduction, no specific mechanism has been determined indicating how reduced fertility and/or fecundity is achieved. Previous studies show that male rainbow trout, Oncorhynchus mykiss, exposed to the environmental estrogen 17α-ethynylestradiol (EE2) before gamete formation and fertilization produce progeny with significantly reduced embryonic survival. To determine whether this observed decrease results from sperm chromosome alterations during spermatogenesis, male rainbow trout were exposed to 10 ng of EE2/l for 50 days. After exposure, semen was collected and sperm aneuploidy levels analyzed with two chromosome markers by fluorescent in situ hybridization. In vitro fertilizations were also conducted by using control and exposed sperm crossed to eggs from an unexposed female for offspring analysis. Evaluations for nucleolar organizer region number and karyotype were performed on developing embryos to determine whether sperm aneuploidy translated into embryonic aneuploidy. Results conclusively show increased aneuploid sperm formation due to EE2 exposure. Additionally, embryonic cells from propagated progeny of individuals possessing elevated sperm aneuploidy display high levels of embryonic aneuploidy. This study concludes that EE2 exposure in sexually developing male rainbow trout increases levels of aneuploid sperm, providing a mechanism for decreased embryonic survival and ultimately diminished reproductive success in EE2 exposed males.     

Neonatally administered tert-octylphenol affects onset of puberty and reproductive development in female rats

There now is evidence that many of the synthetic chemicals released into the environment can impact on the function of the endocrine system of many organisms. One group of chemicals, the alkylphenols, used in paints, pesticides, herbicides, detergents, and plastics, has been found to have the ability to bind estrogen receptors. This estrogenic property makes these compounds potentially hazardous to the developing reproductive system and neuroendocrine brain. In this study we determined the effects of exposure to the environmental toxins 4-nonylphenol (NP) and 4-tert-octylphenol (OP) and to synthetic estrogen diethylstilbesterol (DES) during the early postnatal period (d 0–10) on the development of reproductive function. The day of vaginal opening, ovulation, prepubertal LH levels, LH response to estradiol, estrous cyclicity, and ovarian histology were determined. In the OP- and DES-treated groups, the vaginal opening was observed to have occurred several days prior to that of the control group. The NP-treated group showed vaginal opening at ages similar to those of the control group. Treatment with OP prevented ovulation in a significant number of animals, as well as in all animals treated with DES, whereas the control and NP-treated animals ovulated normally. Animals treated with DES and OP had significantly lower ovarian weights and higher uterine weights than either control animals or NP-treated animals. Higher basal LH levels, as well as the absence of the prepubertal LH surge, were observed in both DES- and OP-treated animals. A significant number of OP-treated animals showed no LH response to the estradiol-17β challenge. NP-treated animals responded positively to the estradiol-17β challenge. Persistent estrus was also apparent in both OP- and DES-treated animals. Upon histological examination, the ovaries in OP-treated animals were found to have a decreased number of corpora lutea and an increased number of preantral and atretic follicles. These data suggest that exposure to OP during the critical period of sexual brain differentiation affects the onset of puberty and reproductive development.     

Spontaneous growth hormone and somatomedin-C/insulin-like growth factor-I secretion in obese subjects during puberty

It has been reported that adult obese subjects present a reduced growth hormone secretion. As no data are available in the pubertal period, which is characterized in lean subjects by an increased spontaneous growth hormone secretion, the growth hormone circadian concentration was studied in a group of 18 obese male subjects in different pubertal stages, and compared to 26 age-matched control subjects. The data observed evidenced no statistically relevant differences regarding LH and FSH circadian secretion and morning testosterone concentration. On the contrary a statistically significant (p less than 0.02) difference in growth hormone 24 h integrated concentration was evident, particularly in prepubertal subjects; the sleep-related peak was evident in 28% of obese subjects and in 85% of controls. Sm-C/IGF-I concentration was similar to the concentration observed in controls in the prepubertal stage, but did not show the expected increase in the late puberty. Auxological data, performed on a sample of 80 subjects, showed both advanced height and bone age at beginning of puberty, and a trend toward a reduction of percentile for height in parallel with the pubertal maturation, suggesting that pubertal growth spurt in obese subjects is at least less pronounced than in lean subjects. It is concluded that GH and Sm-C/IGF-I secretion is impaired during puberty in obese subjects, leading to a reduced growth rate, while in the prepubertal period factors other than GH may replace or even potentiate its action.     

Dynamics of gonadotropic hormones during ontogeny

The concentrations of gonadotropic hormones (luteinizing hormone--LH, and follicle-stimulating hormone--FSH) were studied in the blood plasma of 175 persons of both sexes beginning from birth up to the old age by means of specific radioimmunological methods. Evident change in the gonadotropic hormone level depending on age has been observed. Immediately after birth hormone concentrations are slightly higher and correspond to those of the pubertal period. A decrease in hormone concentration lasting up to the puberty is seen after marked hormone release into the blood of children 1 to 4 months of age. During the puberty the level of hormones rises exceeding their concentration in a mature age. Cyclic hormone secretion in females depending on the menstrual phase cycle and circadian secretion rhythm of males are peculiar to the pubertal period. Males of other age groups show the lack of the anterior pituitary lobe, corresponding in time to the lowest gonadotropin concentration in the blood of persons with circadian rhythm. The levels of gonadotropic hormones increase again following menopause and/or male climax commencement but their specific activity is reduced.     

Regulation of sex hormone-binding globulin production by growth factors

Sex hormone-binding globulin (SHBG) is a glycoprotein whose production has been demonstrated to be regulated by both sex steroids, as well as by thyroid hormone and peptide hormones such as insulin. However, none of these regulatory factors would explain the marked decrease in serum SHBG seen throughout the prepubertal and pubertal time period in both boys and girls. Furthermore, current in vitro data show that both androgens and estrogens can stimulate SHBG production by the human hepatoblastoma cell line Hep G2; yet, in vivo androgens appear to suppress SHBG levels, while estrogens are associated with elevated levels. This study was undertaken to determine possible mechanisms to explain this phenomenon. Hep G2 cell cultures were incubated with insulin-like growth factor I (IGF-I), epidermal growth factor (EGF), transforming growth factor alpha (TGF-alpha), or dehydroepiandrosterone (DHEA). Significant decreases in the level of SHBG in the culture medium relative to control cultures occurred for each of the growth factors (P less than .01), whereas an increase in SHBG levels was observed in the medium of DHEA-treated cells. When cells were coincubated with IGF-I and thyroxine (T4), which alone stimulates SHBG production both in vivo and in vitro, the SHBG response to T4 was blunted. These results suggest that growth factors, as well as insulin, may be important determinants in SHBG production.     

Reversal of Ethanol-Induced Testosterone Suppression in Peripubertal Male Rats by Opiate Blockade

Teenage drinking is a major problem in the United States, as well as abroad. Besides psychosocial implications, ethanol (EtOH) has detrimental effects on the reproductive system. Clinical problems associated with reduced reproductive hormones include osteoporosis, decreased muscle function, anemia, altered immune function, prostate involution, and decreased reproductive abilities. Education coupled with strategies aimed at preventing these deleterious consequences even in the face of continued EtOH intake is extremely important. We have tested the possibility that naltrexone, a drug currently used in patients to decrease alcohol craving, might also prevent the fall in the male hormone, testosterone, caused by EtOH exposure. Rats aged 35 days old (prepubertal), 45 days old (midpubertal), and 55 days old (late pubertal) were injected (intraperitoneally) with either saline, EtOH, naltrexone, or EtOH plus nabexone. In the two older age groups, EtOH significantly suppressed testosterone, which was prevented by administration of naltrexone. In the youngest animals, there was no treatment effect presumably due to low basal levels of testosterone. EtOH similarly reduced luteinizing hormone (LH), but this suppression was not prevented by naltrexone. There was no consistent effect of any treatment on hypothalamic concentration of pro-LH releasing hormone (RH) (LHRH), LHRH, or on steady-state levels of LHRH mRNA. We conclude that, as animals progress through puberty, EtOH suppresses LH and testosterone. The testosterone decline can be prevented by opiate blockade with naltrexone, an effect primarily seen at gonadal level. Thus, naltrexone, a drug already used clinically to reduce EtOH intake, also has protective physiological effects on the endocrine system.     

Strengths and weaknesses of in vitro assays for estrogenic and androgenic activity

The endocrine and reproductive effects of xenobiotics are believed to be due to (1) their mimicking the effects of endogenous hormones; (2) their antagonizing the effects of endogenous hormones; (3) their altering the pattern of synthesis and metabolism of natural hormones; and (4) their modifying hormone receptor levels. It has been suggested that endocrine disruptors may play a role in the decrease in human semen quantity and quality, an increase in the anomalies of male genital tract, and an increase in the testicular and breast cancer incidence during the last 50 years. Testing these hypotheses will require: (1) identifying estrogen and androgen agonists and antagonists among the chemicals present in the environment; (2) assessing the interactions among the endocrine disruptors to which humans are exposed; and (3) finding markers of estrogen (and androgen) exposure. The development of fast and sensitive bioassays is central to the achievement of these three goals.     

Increase of anteroventral periventricular kisspeptin neurons and generation of E2-induced LH-surge system in male rats exposed perinatally to environmental dose of bisphenol-A

Perinatal exposure to environmental levels of bisphenol-A (BPA) impairs sexually dimorphic behaviors in rodents. Kisspeptin neurons in anteroventral periventricular nucleus (AVPV), which plays an important role in the activation of GnRH neurons and the initiation of LH-surge, have been suggested to be sexual dimorphism in rats. This study focused on exploring the influence of a perinatal exposure to an environmental dose of BPA on the development and maturation of male AVPV kisspeptin neurons and hypothalamus-pituitary-gonadal axis. Female rats were injected sc with 2 μg BPA/kg·d from gestation d 10 through lactation d 7. Anatomical and functional changes in AVPV kisspeptin neurons and hypothalamus-pituitary-gonadal axis were examined in prepubertal, pubertal, and adult male rats exposed perinatally to BPA (BPA-rats). Here, we show that in postnatal d (PND)30/50/90 BPA-rats, the number of AVPV kisspeptin-immunoreactive cells was persistently increased in comparison with age-matched control male rats. The number of GnRH-immunoreactive cells in PND30 BPA-rats declined approximately 40% compared with control male rats, whereas that in PND50/90 BPA-rats was increased in a G protein-coupled receptor 54-dependent manner. Estradiol could induce a stable LH-surge in PND90 BPA-rats and control female rats, which was sensitive to the G protein-coupled receptor 54 inhibitor. In PND30/50 BPA-rats, plasma level of LH was higher, but the level of testosterone was lower than control male rats. These findings provide evidence that perinatal exposure to an environmental dose of BPA causes a sustained increase in AVPV kisspeptin neurons in male rats, leading to the generation of estradiol-induced LH-surge system.     

The effect of medroxyprogesterone acetate on gonadotropin secretion in girls with precocious puberty.

Plasma luteinizing hormone (LH) and follicle stimulating hormone (FSH) as detected by radioimmunoassay have been found to be present in prepubertal children and show a gradual rise until the onset of puberty. Children with idiopathic true precocious puberty have plasma gonadotropin levels which are appropriate for their advanced degree of sexual development. A potent progestational agent, 6-methyl-17-hydroxyprogesterone acetate or medroxyprogesterone has been used in the treatment of precocious puberty and will suppress its physical manifestations. In this study the effect of medroxyprogesterone on gonadotropin levels was investigated in seven girls with true precocious puberty. Plasma LH values were found to be significant lower in patients receiving this agent than in a group of normal prepubertal girls. FSH values did not differ from the control group. One patient was evaluated prior to treatment and showed decreasing levels of LH after therapy was begun. These data suggest that medroxyprogesterone may act on the pituitary-hypothalamic axis to suppress the pubertal levels of LH.     

Basic fibroblast growth factor (bFGF) gene expression and protein production during pubertal development of the seminiferous tubule: follicle-stimulating hormone-induced Sertoli cell bFGF expression.

The potential role of basic fibroblast growth factor (bFGF) as a mediator of cell-cell interactions in the growth and development of the testis was examined. Nuclease protection analysis was used to evaluate bFGF gene expression in the testis and other male reproductive tract tissues. bFGF expression was evident in seminal vesicle, prostate, epididymis, and, at low levels, testis of 20-day-old rats. The developmental expression of bFGF in whole testis and isolated somatic cells types was determined. Mesenchymal-derived peritubular cells and epithelial-like Sertoli cells were isolated from prepubertal, midpubertal, and late pubertal rat testes. In whole testis, bFGF expression is predominant early in prepubertal testicular development and decreases with sexual maturity. Both freshly isolated peritubular and Sertoli cells express bFGF at relatively constant levels during pubertal development, with a slight suppression at the late pubertal stages. Freshly isolated mature Leydig cells also expressed low levels of bFGF. Cultured Sertoli and peritubular cells produced bFGF-like proteins, including 18- and 24-kilodalton forms. Interestingly, FSH increased Sertoli cell bFGF gene expression and protein production. Previously, FSH and bFGF have been shown to stimulate immature Sertoli cell growth. The results of the current study suggest that the ability of FSH to regulate testis and Sertoli cell proliferation may in part be indirectly mediated through the local production and action of bFGF. bFGF has also previously been shown to localize in developing germinal cells. Therefore, FSH-induced Sertoli cell bFGF expression may mediate Sertoli-germinal cell interactions involved in the control of the spermatogenic process. Observations demonstrate the presence of bFGF at a time coinciding with active growth of the somatic cell populations of the seminiferous tubule. Potential roles for bFGF in the seminiferous tubule to consider include angiogenesis of the tubule, prepubertal Sertoli cell proliferation, and mediating Sertoli-germinal cell interactions.     

Environmental-like exposure to low levels of estrogen affects sexual behavior and physiology of female rats

Xenoestrogens are endocrine-disrupting chemicals that mimic the action of endogenous estrogen hormones. Effects of xenoestrogen on aquatic wildlife are well documented, whereas the experimental evidence for impairment of reproductive behavior and physiology in mammals after exposure to xenoestrogens has been debated. The strongest arguments against such studies have been that the route, time course, and intensity of exposure did not simulate environmental exposure and that the chemicals tested have additional nonestrogenic toxic effects, hindering generalization of actual xenoestrogenic effects. Here we show that environmental-like exposure to the pure estrogen 17alpha-ethinylestradiol during development alters reproductive behavior and physiology in adult female Sprague-Dawley rats. We simulated environmental exposure by giving low doses (0.4 and 0.004 microg/kg.d) of 17alpha-ethinylestradiol orally to pregnant females from conception to weaning of the pups, which continued to receive the treatment until puberty. We studied the sexual behavior, estrous cycle, and estradiol plasma levels of intact female rats when they reached 3 months of age. Exposure to the higher dose strongly affected female sexual behavior and physiology, with suppression of lordosis and the estrous cycle and enhanced aggression toward males. The lower dose disrupted appetitive components of sexual behavior that influence the rate of copulation. Estradiol plasma levels were not affected by the treatment. Our study revealed that exposure to low oral doses of a pure estrogen during development alters female sexual behavior and physiology. These results suggest potential risks of reproductive failure from xenoestrogen exposure in realistic ecological conditions.     

Exposure of newborn male and female rats to environmental estrogens: delayed and sustained hyperprolactinemia and alterations in estrogen receptor expression

Environmental estrogens (xenoestrogens) are synthetic compounds that are abundant in the environment and mimic natural estrogens. The estrogenicity of two such compounds, bisphenol A (BPA) and octylphenol (OP), during development of the neuroendocrine system was investigated. The objective was to compare the effects of neonatal exposure to BPA, OP, and diethylstilbestrol (DES), a potent synthetic estrogen, on prepubertal serum PRL levels and estrogen receptor (ER) expression in the anterior pituitary and medial basal hypothalamus. Receptor expression in the uterus and prostate, two peripheral estrogen-responsive tissues, was also examined. Newborn male and female Fischer 344 rats were s.c. injected on days 1-5 after birth with corn oil (control), BPA and OP (100 or 500 microg/day), or DES (5 microg/day). Rats were bled on days 15, 20, and 25 and on the day of death (day 30), and serum PRL was analyzed by RIA. Relative expressions of ERalpha and ERbeta were determined by RT-PCR. BPA and OP induced delayed, but progressive, increases in serum PRL levels, up to 3-fold above control levels, in both males and females. The low dose of either compound was equally or more effective as the high dose in eliciting and sustaining elevated serum PRL levels, namely hyperprolactinemia. In contrast, the DES treatment resulted in a transient rise in serum PRL levels. BPA, OP, and, to a lesser extent, DES increased the expression of both ERalpha and ERbeta in the anterior pituitary of males, but not females, whereas the hypothalamic ERs were less responsive to these compounds. DES treatment caused down-regulation of ERalpha expression in the uterus and up-regulation of ERbeta in the prostate, whereas BPA or OP was without effect. In conclusion, exposure of newborn rats of either sex to environmental estrogens results in delayed and sustained hyperprolactinemia and differential alterations in ER expression in the hypothalamus and pituitary. DES appears to target the lower reproductive tract more effectively than the neuroendocrine system.     

Adrenomedullary response to caffeine in prepubertal and pubertal obese subjects.

OBJECTIVE: To investigate whether blunted adrenomedullary responsiveness to stimuli is a primary feature of human obesity in childhood and adolescence DESIGN: Comparison of plasma catecholamine response to caffeine in obese and lean subjects before and after puberty onset. SUBJECTS: Twelve lean prepubertal subjects (six males and six females), 15 prepubertal obese subjects (seven males and eight females), 12 pubertal lean subjects (six males and six females) and 24 pubertal obese subjects (12 males and 12 females) MEASUREMENTS: Plasma levels of Luteinizing hormone (LH), follicle-stimulating hormone (FSH), 17beta-estradiol and testosterone were used to validate Tanner score. Systolic and diastolic blood pressure, pulse rate and plasma catecholamines before and after caffeine administration (4 mg/kg of ideal body weight). RESULTS: Caffeine administration significantly stimulated adrenaline release in all subjects studied. The incremental area of adrenaline response to caffeine, analysed by multiple comparison test, was lower in pubertal obese subjects with respect to other groups. CONCLUSIONS: At variance with what is observed in adulthood obesity, prepubertal obese subjects show an intact adrenomedullary response to caffeine.     

Effects of chronic hyperghrelinemia on puberty onset and pregnancy outcome in the rat

Ghrelin, the endogenous ligand of the GH secretagogue receptor, has been recently involved in a wide array of biological functions, including signaling of energy insufficiency and energy homeostasis. On the basis of the proven reproductive effects of other regulators of energy balance, such as the adipocyte-derived hormone leptin, we hypothesized that systemic ghrelin may participate in the control of key aspects of reproductive function. To test this hypothesis, the effects of daily treatment with ghrelin were assessed in rats, pair-fed with control animals, in two relevant reproductive states, puberty and gestation, which are highly dependent on proper energy stores. Daily sc injection of ghrelin (0.5 nmol/12 h; between postnatal d 33 and 43) significantly decreased serum LH and testosterone levels and partially prevented balano-preputial separation (as an external index of puberty onset) in pubertal male rats. On the contrary, chronic administration of ghrelin to prepubertal females, between postnatal d 23 and 33, failed to induce major changes in serum levels of gonadotropins and estradiol, nor did it modify the timing of puberty, as estimated by the ages at vaginal opening and first estrus. Moreover, females treated with ghrelin at puberty subsequently displayed normal estrous cyclicity and were fertile. Conversely, ghrelin administration (0.5 nmol/12 h) during the first half of pregnancy (d 1-11) resulted in a significant decrease in pregnancy outcome, as estimated by the number of pups born per litter, without changes in the number of successful pregnancies at term or gestational length. Overall, our data indicate that persistently elevated ghrelin levels, as a putative signal for energy insufficiency, may operate as a negative modifier of key reproductive states, such as pregnancy and (male) puberty onset.     

Effects of melatonin on PRL secretion during different photoperiods of the day in prepubertal and pubertal healthy subjects

The effect of melatonin on PRL secretion has not been established yet. In an attempt to establish whether PRL response to melatonin changes in relation to the photoperiods of the day and pubertal maturation, we evaluated PRL plasma levels after melatonin administration in 19 prepubertal and pubertal healthy subjects of both sexes in two different periods of the day: in the morning, when the sensitivity to melatonin is low, and in the afternoon, when the responsiveness to melatonin is higher. Melatonin was given im at a dose of 0.2 mg/kg BW PRL plasma levels were determined with double antibody RIA method. When melatonin was administered in the morning, all pubertal subjects and 7 of 9 prepubertal ones showed no significant variation of PRL levels; a significant decrease was observed in the other 2 prepubertal subjects. On the contrary, when melatonin was given in the afternoon, a significant increase in PRL plasma levels was seen in all pubertal subjects; no significant changes were found in 6 prepubertal ones, while in the other 3 a marked decrease could be observed. The results reveal that the response of PRL to melatonin depends upon the times of day of administration and on pubertal development.