A study of seasonally delayed puberty in the male hare, Lepus Europaeus.

The brown hare, Lepus europaeus, has a mating season which extends from January to September. Adult males exhibit pronounced seasonal changes in the reproductive tract which are associated with changes in LH secretion. Maximum plasma levels of immunoreactive LH occur between March and June and minimal levels in the autumn non-mating period from September to December; this seasonal cycle in gonadotrophin output is reflected by the appropriate changes in the secretion of testosterone from the testes and in the activity of the accessory sex glands. Juvenile animals reach puberty only during the adult mating season, and the age of puberty thus varies with the date of birth. Males born before May reach puberty and become fertile at 3 months of age, while those born from May to July grow to a mature body size during the autumn non-mating season but puberty is delayed for several months. Since some animals experiencing delayed puberty were found to have elevated plasma levels of LH and testosterone, it is concluded that puberty is not completely suppresed by the environmental effects of the autumn, but that the developmental process is prolonged, resulting in the juveniles being synchronized with the adults in their reproductive activity.     

The role of endogenous gonadotropin-releasing hormone in the control of luteinizing hormone and testosterone secretion in the juvenile male monkey, Macaca fascicularis

To determine what changes occur in the activity of gonadotropin-releasing hormone (GnRH) neurons during pubertal development in primate species we tested the hypotheses that there are morphologic differences between GnRH-containing neurons in juvenile versus adult monkeys, and the low activity of the reproductive axis is governed by hypothalamic GnRH release in monkeys prior to puberty. We removed the brains from 5 juvenile and 5 adult male monkeys (Macaca fascicularis) and blocked, sectioned, and prepared each hypothalamus for light microscopic immunocytochemistry for GnRH-containing cells. The distribution and number of GnRH-containing neurons were similar in adult and juvenile brains; however, GnRH-containing perikarya in adult brains were significantly larger in total cross-sectional area (200 +/- 12 vs. 169 +/- 8 micron 2, P less than 0.05) and in cross-sectional area of the cytoplasm (139 +/- 2 vs. 88 +/- 6 micron 2, P less than 0.05) than in juvenile brains. In another group of 10 juvenile male macaques, we administered an antiserum to GnRH (Fraser #94; 2 ml/kg, i.v.) and monitored the effects on plasma luteinizing hormone (LH) and testosterone concentrations. The percentage of plasma samples with detectable LH levels decreased significantly (from 26.67 +/- 8.3% to 5.3 +/- 3.4%, P less than 0.05) after GnRH antiserum administration; however, plasma testosterone concentrations (0.08 +/- 0.02 ng/ml) remained unchanged. We conclude that during pubertal maturation in primate species there is increased synthesis and release of GnRH from a population of GnRH neurons that are active prior to puberty.     

Reduced growth hormone secretion prolongs puberty but does not delay the developmental increase in luteinizing hormone in the absence of gonadal negative feedback

Previous studies have shown that the growth hormone (GH) axis is important for timing the later stages of puberty in female monkeys. However, it is not clear whether these growth-related signals are important for the initiation of puberty and early pubertal events. The present study, using female rhesus monkeys, used two approaches to answer this question. Experiment 1 tested the hypothesis that reduced GH secretion would blunt the rise in nocturnal LH secretion in young (17 mo; n = 7) but not older adolescent ovariectomized females (29 mo; n = 6). Reduced GH secretion was induced by treating females with the sustained release somatostatin analogue formulation, Sandostatin LAR (625 microg/kg). Morning (0900-0930 h) and evening (2200-2230 h) concentrations of bioactive LH were higher in older adolescent compared to young adolescent females. However, diurnal concentrations were not affected by the inhibition of GH secretion in either age group when compared to the placebo-treated, control condition. Experiment 2 tested the hypothesis that reduced GH secretion induced in young juvenile females would delay the initial increase in nocturnal LH secretion and subsequent early signs of puberty. In order to examine this hypothesis, puberty in control females (n = 7) was compared to those in which puberty had been experimentally arrested until a late adolescent age (29 mo) by the use of a depot GnRH analogue, Lupron (750 microg kg(-1) mo(-1); n = 7). Once the analogue treatment was discontinued, the progression of puberty was compared to a group treated in a similar fashion but made GH deficient by continuous treatment with Sandostatin LAR (n = 6). Puberty occurred as expected in control females with the initial rise in evening LH at 21 mo, menarche at 22 mo, and first ovulation at 30 mo. As expected, Lupron arrested reproductive maturation, but elevations in morning and evening LH and menarche occurred within 2 mo of the cessation of Lupron in both Lupron and Lupron-GH-suppressed females. In contrast, first ovulation was delayed significantly in the Lupron-GH-suppressed females (41 mo) compared to the Lupron-only females (36 mo). These data indicate that within this experimental model, reduced GH secretion does not perturb the early stages of puberty but supports previous observations that the GH axis is important for timing the later stages of puberty and attainment of fertility. Taken together, the data indicate that factors that reduce GH secretion may have a deleterious effect on the completion of puberty.     

Association of ghrelin and leptin with reproductive hormones in constitutional delay of growth and puberty

Background  

Constitutional delay of growth and puberty (CDGP) is a variation of the onset and timing of pubertal development without a defined endocrine abnormality. Recently published studies indicate that leptin and ghrelin play a role in puberty initiation and progress. They have been implicated in regulation of GnRH secretion, with ghrelin having inhibitory and leptin, facilitatory effects. We hypothesized that elevated ghrelin and reduced leptin concentrations could be implicated in altering the tempo of puberty in adolescents with CDGP. So in the current study we evaluate variations in leptin and ghrelin levels in adolescent boys with CDGP, the relationships between both hormones and reproductive hormones including LH, FSH and testosterone were also evaluated.     

Induction of precocious puberty in ewe lambs by pulsatile administration of GnRH

Circhoral administration (250 ng/h, i.v.) of GnRH induced a preovulatory-like surge of LH and subsequent luteal function in 4 of 4 ewe lambs 1 month before expected date of puberty. Within 12h of the start of pulsatile delivery of GnRH, mean concentrations of immunoactive and bioactive LH increased significantly (P less than 0.05) and the LH surge occurred by 1.8 +/- 0.6 days of treatment. Mean concentrations of serum progesterone were elevated significantly (P less than 0.001) 3 days after the surge. The biopotency of LH (bioactive LH/immunoactive LH) before the GnRH-induced surge of LH did not differ from LH biopotency in ewe lambs receiving circhoral delivery of saline (0.41 +/- 0.05 and 0.46 +/- 0.04, respectively). Biopotency of LH declined markedly at the GnRH-induced LH surge (0.25 +/- 0.04), but biopotency of serum LH was significantly augmented (P less than 0.05) during the period of luteal activity (0.70 +/- 0.07). Regular oestrous cycles were observed in 3 of 4 ewe lambs after the 10-day GnRH treatment period. These results indicate that pulsatile delivery of GnRH is effective in inducing precocious puberty in ewe lambs. Increase in LH biopotency does not appear to be required in the pubertal transition to reproductive cyclicity in this species. Augmented LH biopotency may be important in support of luteal function after first ovulation.     

Time-related neuroendocrine manifestations of puberty: a combined clinical and experimental approach extracted from the 4th Belgian Endocrine Society lecture

The neuroendocrine manifestations of puberty converge on changes in GnRH secretion. Their appraisal through the assay of GnRH-like material in 24-hour urine extracts shows an increased excretion of this material in the late prepubertal period. The most striking pubertal changes in GnRH secretion occur on a circadian and ultradian basis. In man, they can be evaluated only indirectly. The circadian variations in LH and FSH secretion characteristic of puberty may be observed in timed fractions of 24-hour urine with some delay when compared to the variations of plasma levels. Studies on the frequency of pulsatile LH secretion and during chronic intermittent administration of GnRH support the existence of an increased frequency of GnRH secretory episodes at puberty. LH response to synthetic GnRH is directly related to the frequency of stimulation by endogenous GnRH pulses and provides a very useful index of neuroendocrine maturation in patients with delayed or precocious puberty. A direct evaluation of pulsatile GnRH secretion is possible using the rat hypothalamus in vitro. In these experimental conditions, the frequency of pulsatile GnRH release increases during very early stages of sexual maturation in the male rat. GnRH itself and beta-endorphin are inhibitory regulators of GnRH secretion in vitro and may participate in the mechanisms restraining the pulse-generating machinery in the hypothalamus before puberty.     

Nutritional influences on sexual maturation in the rat

The effect of altered nutrition on sexual maturation may depend in part on the nature and timing of the dietary change. The data are conflicting as to whether rats undernourished before weaning but normally fed after weaning have delayed puberty, but such undernourished rats clearly weigh less at vaginal opening than do normally fed animals. Altered nutrition after weaning can change the timing of puberty, and in such cases the body weight at puberty of the animals given the modified diet is frequently abnormal. The factors regulating the age and weight at puberty of rats fed altered diets seem to include the degree of underfeeding, as reflected in the growth rate, and the composition of the diet. Undernourished immature male rats have low serum testosterone secondary to gonadotropin deficiency. Basal luteinizing hormone (LH) in these animals is either low or "inappropriately normal" relative to their hypoandrogenic state (low serum testosterone and sexual accessory gland weights), and serum LH increases after luteinizing hormone-releasing hormone (LHRH) or castration are normal or minimally reduced. Serum follicle-stimulating hormone (FSH) in undernourished rats is subnormal basally and after administration of LHRH, but not after castration, which suggests that the low basal serum FSH is due to inhibition of FSH output by a testicular factor. Spermatogenesis may be unaltered by dietary changes severe enough to cause hypoandrogenism, although very severe under-nutrition will impair sperm production.     

Prenatal androgens and the timing of seasonal reproductive transitions in sheep.

Both the onset of puberty in the lamb and the annual resumption of reproductive activity in adult male and female sheep are characterized by increased secretion of LH due to reduced responsiveness to steroid inhibition. However, the timing of puberty is sexually differentiated, for males undergo a reduction in sensitivity to steroid feedback at 10 wk of age, whereas females remain highly responsive to steroid inhibition until 30 wk. This sex difference is determined by androgens in utero. The present study was conducted to determine whether a sex difference exists in the timing of seasonal transitions in adult males and females. We compared serum LH in gonadectomized, estradiol-treated males (n = 7), females (n = 6), and androgenized females (n = 5) from blood samples collected twice weekly for one year. As determined by changes in the pattern of LH secretion, the onset and termination of the autumn breeding season were not different between males, females, and androgenized females (termination: 1 February +/- 4 days, mean +/- SE all groups; onset: males, 22 August +/- 4 days; females, 5 September +/- 18 days; androgenized females, 16 September +/- 10.5 days). However, there was a transient increase in LH (20 May to 23 June) in males, but not in females or androgenized females. Although no effects of prenatal testosterone were evident in the control of LH secretion in adult androgenized females, LH secretion in androgenized males was elevated throughout the nonbreeding season in 3 of 5 animals, indicating that exogenous testosterone may reduce seasonal increases in responsiveness to steroid inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)     

A longitudinal study of leptin during development in the male rhesus monkey: the effect of body composition and season on circulating leptin levels

The objective of this study was to examine longitudinal changes in serum leptin concentrations during development and to correlate those changes with sexual development in male rhesus monkeys housed under natural environmental conditions. Blood samples were drawn from 8 control animals approximately every other month from 10 to 30 mo of age and thereafter monthly through 80 mo of age. Leptin levels declined through the juvenile period until the onset of puberty and were negatively correlated with body weight. Seven of the eight animals became sexually mature during the breeding season of their fourth year of life. Puberty was delayed in the other animal until the subsequent breeding season. There were no significant fluctuations in leptin levels prior to or in association with the pubertal rise in LH and testosterone (T) secretion. During the peripubertal period, levels of leptin varied between 2 and 3 ng/ml. The animal that exhibited delayed puberty had the lowest body weight and highest leptin levels during this period. With the achievement of sexual maturity, leptin levels varied seasonally, with peak levels in the late winter (Jan-Mar) and a nadir in the late summer (Aug-Sept). A late winter rise in leptin was also evident in most of the animals during Years 2 and 3, but not during Year 4. In the fall of Years 5 and 6, the seasonal rise in leptin concentrations lagged 3-4 mo behind the seasonal increase in LH and T. In the fall of Year 5, but not thereafter, leptin levels were positively related to percent body fat and negatively correlated with lean body mass. The data do not support the hypothesis that increasing leptin concentrations trigger the onset of puberty in the male rhesus monkey. During the juvenile period and after sexual maturation, but not during the peripubertal period, leptin secretion varied with season in the animals; but the environmental factors that cue or drive this rhythm remain to be determined.     

Luteinizing hormone and testosterone secretory profiles of boars: Effects of stage of sexual maturation

Two short term studies of LH and testosterone secretory profiles were carried out to evaluate the effects of stage of sexual maturity on the patterns of secretion of these hormones in Large White x Landrace boars. Four pubertal and three post-pubertal boars were subjected to plasma sampling every twenty minutes for 24 hours. During puberty, plasma profiles of LH varied in a manner indicative of a highly pulsatile mode of secretion. Likewise, large fluctuations in plasma testosterone levels were noted at this age, but they were not as frequent as those of LH. In contrast, plasma LH and testosterone profiles of post-pubertal boars showed fewer and smaller fluctuations in hormone concentrations. The overall mean levels of LH and testosterone were 0.82 and 1.04 ng/ml in pubertal boars, and 0.39 and 0.81 ng/ml in post-pubertal animals. At neither age was there any evidence of diurnal variations in plasma hormone concentrations.     

Inhibin B,follicle stimulating hormone,luteinizing hormone and testosterone during childhood and puberty in males: changes in serum concentrations in relation to age and stage of puberty

Inhibin B is a gonadal dimeric polypeptide hormone that regulates synthesis and secretion of follicle stimulating hormone (FSH) in a negative feedback loop. The aim of the present study was to determine changes in serum inhibin B, gonadotropins and testosterone concentrations during childhood and puberty in males. We studied the relationship between circulating inhibin B, gonadotropins and testosterone in serum of healthy boys during the first two years of life and then in pubertal development. Using a recently developed two-side enzyme-linked immunosorbent assay (ELISA), inhibin B levels were measured in the serum of 78 healthy boys divided into eleven age groups from birth to the end of pubertal development. In addition, serum levels of gonadotropins and testosterone were measured. Serum inhibin B, gonadotropins and testosterone increased during the first months of postnatal life. A peak in serum inhibin B and gonadotropins concentrations was observed around 3-4 months of age. There was a significant positive correlation between serum inhibin B and gonadotropins and testosterone levels during the first 2 years of life. After this early increase, serum inhibin B, gonadotropins and testosterone levels decreased significantly and remained low until puberty followed by an increase beginning with the onset of puberty. Serum levels of inhibin B reached a peak at stage G3 of puberty. Around midpuberty, inhibin B lost its positive correlation with luteinizing hormone (LH) and testosterone from early puberty, and developed a strong negative correlation with FSH, which persisted into adulthood. We conclude that inhibin B plays a key role in the regulation of the hypothalamic-pituitary-gonadal hormonal axis during male childhood and pubertal development. Inhibin B is a direct marker of the presence and function of Sertoli cells and appears to reflect testicular function in boys.     

Prenatal Exposure to Androgen Excess Increases LH Pulse Amplitude During Postnatal Life in Male Sheep

Prenatal exposure to excess testosterone has a profound impact on reproductive and metabolic functions in young and adult female sheep. Nevertheless, few studies have addressed the impact of prenatal exposure to an excess of androgens on reproductive and metabolic functions in males. The aim of the present study was to assess the impact of prenatal exposure to an excess of testosterone or dihydrotestosterone on the luteinizing hormone (LH) pulse characteristics during sexual development in male sheep. Control male sheep (C-males) and males born to mothers exposed to twice weekly injections of 30 mg testosterone or dihydrotestosterone from day 30-90 and 40 mg from day 90-120 of gestation (T-males, DHT-males) were studied at 5, 10, and 20 weeks of age, ages that represent infancy, early prepubertal, and late prepubertal stages of sexual development in this species, respectively. Patterns of LH pulsatility showed that T- and DHT-males exhibited a higher secretion of LH during the 6-h study and a higher amplitude of the LH pulses compared with C-males. Moreover, nadir of the pulses was higher in T- and DHT-males compared with C-males. Frequency of LH pulses, however, was not different within ages or between groups. These results show that males can be responsive to prenatal androgenization and suggest that treatment transiently alters the amplitude of LH pulses probably as the result of defects in the pituitary responsiveness pattern or in the gonadotropin-releasing hormone (GnRH) release pattern.     

Short-term pulsatile administration of luteinizing hormone releasing hormone in male adolescents with multiple idiopathic pituitary hormone deficiencies

In order to define both level and severity of defect in patients with idiopathic multiple pituitary hormone deficiencies (MPHD) and to find out which patient might benefit from pulsatile LHRH substitution therapy, the effect of short-term pulsatile LHRH infusion in 6 affected male adolescents was studied. Controls were 9 boys with constitutional delay of puberty (CD). During a spontaneous nocturnal plasma profile LH and FSH levels were prepubertal with little evidence of pulsatile secretory LH activity in all MPHD patients. During short-term pulsatile LHRH stimulation (36 h), however, all showed a significant rise in mean LH and FSH levels (p less than 0.0001). Linear regression analysis revealed significant continuous increases of FSH (p less than 0.001) in all patients and of LH (p less than 0.01) in all but one patient. These changes were not accompanied by an increase of testosterone, androstenedione and DHAS levels. Since all MPHD patients showed steadily increasing gonadotropin levels if stimulated in a pulsatile manner, we conclude that the defect might only in part be located at the pituitary level. Long-term pulsatile substitution therapy with LHRH is likely to be successful in these patients as has been demonstrated in patients with known hypothalamic defect.     

Adolescent TBI‐induced hypopituitarism causes sexual dysfunction in adult male rats

Adolescents are at greatest risk for traumatic brain injury (TBI) and repeat TBI (RTBI). TBI‐induced hypopituitarism has been documented in both adults and juveniles and despite the necessity of pituitary function for normal physical and brain development, it is still unrecognized and untreated in adolescents following TBI. TBI induced hormonal dysfunction during a critical developmental window has the potential to cause long‐term cognitive and behavioral deficits and the topic currently remains unaddressed. The purpose of this study was to determine if four mild TBIs delivered to adolescent male rats disrupts testosterone production and adult behavioral outcomes. Plasma testosterone was quantified from 72 hrs preinjury to 3 months postinjury and pubertal onset, reproductive organ growth, erectile function and reproductive behaviors were assessed at 1 and 2 months postinjury. RTBI resulted in both acute and chronic decreases in testosterone production and delayed onset of puberty. Significant deficits were observed in reproductive organ growth, erectile function and reproductive behaviors in adult rats at both 1 and 2 months postinjury. These data suggest adolescent RTBI‐induced hypopituitarism underlies abnormal behavioral changes observed during adulthood. The impact of undiagnosed hypopituitarism following RTBI in adolescence has significance not only for growth and puberty, but also for brain development and neurobehavioral function as adults. © 2014 Wiley Periodicals, Inc. Develop Neurobiol 75: 193–202, 2015     

Age-related changes in urinary testosterone levels suggest differences in puberty onset and divergent life history strategies in bonobos and chimpanzees

Research on age-related changes in morphology, social behavior, and cognition suggests that the development of bonobos (Pan paniscus) is delayed in comparison to chimpanzees (Pan troglodytes). However, there is also evidence for earlier reproductive maturation in bonobos. Since developmental changes such as reproductive maturation are induced by a number of endocrine processes, changes in hormone levels are indicators of different developmental stages. Age-related changes in testosterone excretion are an indirect marker for the onset of puberty in human and non-human primates. In this study we investigated patterns of urinary testosterone levels in male and female bonobos and chimpanzees to determine the onset of puberty. In contrast to other studies, we found that both species experience age-related changes in urinary testosterone levels. Older individuals of both sexes had significantly higher urinary testosterone levels than younger individuals, indicating that bonobos and chimpanzees experience juvenile pause. The males of both species showed a similar pattern of age-related changes in urinary testosterone levels, with a sharp increase in levels around the age of eight years. This suggests that species-differences in aggression and male mate competition evolved independently of developmental changes in testosterone levels. Females showed a similar pattern of age-related urinary testosterone increase. However, in female bonobos the onset was about three years earlier than in female chimpanzees. The earlier rise of urinary testosterone levels in female bonobos is in line with reports of their younger age of dispersal, and suggests that female bonobos experience puberty at a younger age than female chimpanzees.     

The neuroendocrinology of human puberty revisited

The fundamental aspects of the hypothalamic luteinizing hormone-releasing hormone (LHRH)(1) [1]pulse generator-pituitary gonadotrophin-gonadal apparatus in mammals have striking commonalities. There are, however, critical, substantive differences in the neuroendocrinology of puberty among species. The onset of puberty in the human is marked by an increase in the amplitude of LH pulses, an indirect indicator of the increase in amplitude of LHRH pulses. The hypothalamic LHRH-pituitary gonadotrophin complex is functional by at least 0.3 gestation in the human foetus; the sex difference in the fetal and neonatal pattern of LH and FSH secretion is an apparent consequence of imprinting of the fetal hypothalamus-pituitary-gonadotropin apparatus by fetal testosterone. Until about 6 months of age in boys and 12-24 months in girls, the testes and ovaries respond to the increased LH in boys and follicle-stimulating hormone (FSH) in girls by secreting testosterone and oestradiol, respectively, reaching levels that are not again achieved before the onset of puberty. Striking features of the ontogeny of the human hypothalamic pulse generator are: (1) its development and function in the foetus; (2) the continued function of the hypothalamic LHRH pulse generator-pituitary gonadotrophin-gonadal axis in infancy; (3) the gradual damping of hypothalamic LHRH oscillator activity during late infancy; (4) its quiescence during childhood - the so-called juvenile pause; (5) during late childhood the gradual disinhibition and reactivation of the LHRH pulse generator, mainly at night; (6) the increasing amplitude of the LHRH pulses, which are reflected in the progressively increased and changing pattern of circulating LH pulses, with the approach of and during puberty. The intrinsic central nervous system (CNS) mechanisms responsible for the inhibition of the LHRH pulse generator during childhood (the juvenile phase) involve the major role of an inhibitory neuronal system - the CNS inhibitory neurotransmitter gamma-aminobutyric acid (GABA) and GABAergic neurons, as revealed by studies in the rhesus monkey by Terasawa and her associates. With the onset of puberty, the disinhibition and reactivation of the LHRH pulse generator is associated with a fall in GABAergic neurotransmission and a concomitant increase in the input of excitatory amino acid neurotransmitters (including glutamate) and possibly astroglial-derived growth factors. Despite remarkable progress over the past three decades, large gaps remain in our understanding of the neurobiological, genetic and environmental mechanisms involved in the control of the onset of puberty. The role of leptin in the control of the onset of puberty is reviewed. Severe leptin deficiency is associated with hypogonadotrophic hypogonadism; it appears that a critical level of leptin and a leptin signal is required to achieve puberty. The weight of evidence supports the hypothesis that leptin acts as one of several permissive factors and not a trigger in the onset of human puberty. The application of these advances provides a framework for the described classification of sexual precocity and delayed puberty.1 GnRH is synonymous with LHRH.     

Seasonal changes in plasma concentrations of immunoreactive inhibin and testicular activity in male Japanese monkeys

Seasonal changes in plasma immunoreactive (ir-) inhibin, testosterone, LH, and FSH concentrations were examined in five sexually mature male Japanese monkeys (Macaca fuscata fuscata) housed indoors individually, to explore the reproductive cyclicity in the male. Blood samples were collected monthly throughout one year, and testicular size, semen volume, and number of sperm in the semen were ascertained at the same time in the same animals. Semen samples were obtained by penile electrostimulation. The results showed a clear seasonal increase in all parameters: plasma ir-inhibin, testosterone, testicular size, semen volume, and total number of sperm in the liquid portion of the semen during the autumn and winter months in synchrony with the natural breeding season. In contrast, plasma LH and FSH remained unchanged throughout the year, although plasma FSH tended to increase during the breeding season concomitant with an increase in plasma ir-inhibin. A significant positive correlation between FSH and ir-inhibin was observed in two of five monkeys. The positive correlations between plasma ir-inhibin and testicular activities during both the developing and regressing phases of the testicular cycle indicate that plasma ir-inhibin is a useful indicator of testicular activity as well as an indicator of Sertoli cell function in the Japanese monkey.     

Secretory patterns of leptin and luteinizing hormone in food-restricted young female sheep

Leptin, the product of the ob gene, has been proposed as a metabolic signal that regulates the secretion of GnRH/LH. This may be critical during prepubertal development to synchronize information about energy stores and the secretion of GnRH/LH. This study aimed to assess the effect of food restriction on the episodic secretion of leptin and LH in young female sheep. Five 20-week-old prepubertal females were fed a low-level diet for 10 weeks to maintain the body weight. Control females of the same age received food ad libitum. Blood samples were collected at 10-min intervals for six hours at 20, 26, and 30 weeks of age, and plasma leptin, LH, insulin and cortisol concentrations were measured. In the control group, no changes were found in pulsatile LH secretion characteristics. Mean LH concentrations and LH amplitude were lower in the food-restricted group than in the control group at 26 and 30 weeks of age. In the control group, pulsatile leptin secretion did not change. When compared to control lambs of the same age, the food-restricted group showed lower mean plasma leptin concentrations, pulse amplitude and plasma insulin levels, after 6 weeks of restriction (week 26), although by week 30, plasma leptin concentrations and plasma insulin rose to those of the control group. Leptin pulse frequency did not change, nor did mean plasma levels of insulin in the control group at any age studied. Mean plasma concentration of cortisol did not change within or between groups. These data suggest that plasma leptin concentrations may not be associated with the onset of puberty under regular feeding and natural photoperiod in lambs. Prolonged food restriction, however, induces metabolic adaptations that allow an increase of leptin during the final period, probably related to the development of some degree of insulin resistance.     

Hormonal and behavioral changes at puberty in the squirrel monkey

Developmental changes in the reproductive behavior and physiology of 9 male and 15 female juvenile squirrel monkeys were evaluated in a 20-month study. Plasma levels of gonadal steroids remained relatively low for this species until most animals reached puberty between 2.5 and 3 years of age. Longitudinal assessment of plasma progesterone levels indicated that the onset of ovarian cycles tended to be synchronized between females although the 5 heaviest females began to cycle earlier than the rest. The heavier females reached puberty at a time which was appropriate to their birth in the wild, whereas most of the remaining females conceived 6 months later during a second period of reproductive activity that coincided with the laboratory mating season. Pubescent males underwent their first seasonal elevation in plasma testosterone levels during the second period and its onset was synchronized across all males. Thus, even in the absence of adults, pubertal processes in the squirrel monkey were strongly influenced by the seasonal breeding pattern. In addition, behavioral observations revealed that social maturation closely parallels reproductive ability in females, whereas males enter a protracted subadult stage after puberty.