Comparison of bioassay and radioimmunoassay data for study of changes in the pattern of LH secretion from birth to puberty in the heifer

To define gonadotrophin secretion rates in the prepubertal heifer, 12 Hereford x Friesian heifers were blood-sampled at 15-min intervals for periods of 24 h every 4 weeks from 3 weeks of age until puberty. Radioimmunoassay of plasma LH concentrations showed that, although LH episode frequency increased with age, overall mean LH concentrations and basal LH concentrations decreased between 3 and 15 weeks of age and then increased to 35 weeks of age. The validity of these trends in relation to biological activity of plasma LH was investigated using an in-vitro Leydig cell bioassay. Samples were selected from 24-h profile bleeds of 4 heifers at 3, 7, 11, 15, 19, 27 and 39 weeks of age. No significant differences were found in the patterns of change in overall mean LH concentrations, basal LH concentrations or LH episode amplitude when comparing the estimates obtained by radioimmunoassay with those by bioassay from birth over the prepubertal period. These results indicate that the changes with age observed by radioimmunoassay are representative of changes in biologically active hormone.     

In vitro binding of 125I-HCG to the rat ovary from birth to puberty

Summary Neither homogenates nor frozen ovarian sections of rats aged 1, 5 and 7 days demonstrated specific binding of ¹²⁵I-HCG. However, from day 10 to day 35, the homogenates could bind specifically, with an equilibrium association constant in the range of 0.9–2.7 × 10¹⁰ M^–1. The binding capacity increased from 5.8 fmol/mg tissue at day 10 to 15.7 fmol/mg tissue at day 35.As revealed by autoradiography, the frozen ovarian sections from 10-day-old rats showed ¹²⁵I-HCG binding localized over the interstitial and thecal tissues and, in the older age groups, also in the granulosa cells of follicles larger than 500 m in diameter.These results indicate that LH/HCG receptors appear in the rat ovary at the beginning of the second postnatal week, and that the interstitial cells are the main site of action of LH before puberty.     

Endocrine changes during onset of puberty in male spring Chinook salmon,Oncorhynchus tshawytscha

In male salmonids, the age of maturation varies from 1 to 6 years and is influenced by growth during critical periods of the life cycle. The endocrine mechanisms controlling spermatogenesis and how growth affects this process are poorly understood. Recent research has indicated that gonadotropins, 11-ketotestosterone, and insulin-like growth factor I play roles in spermatogenesis in fish. To expand our understanding of the roles of these endocrine factors in onset of puberty, male spring chinook salmon (Oncorhynchus tshawytscha) were sampled at monthly intervals 14 mo prior to spermiation. This sampling regime encompassed two hypothesized critical periods when growth influences the initiation and completion of puberty for this species. Approximately 80% of the males matured during the experimental period, at age 2 in September 1999. An initial decline in the ratio of primary A to transitional spermatogonia was observed from July to December 1998, and during this period plasma levels of 11-ketotestosterone and pituitary levels of FSH increased. From January 1999 onward, males with low plasma 11-ketotestosterone levels (<1 ng/ml) had low pituitary and plasma FSH levels and no advanced development of germ cells. Conversely, from January through September 1999, males with high plasma 11-ketotestosterone levels (>1 ng/ml) had testes with progressively more advanced germ cell stages along with elevated pituitary and plasma FSH. Plasma levels of insulin-like growth factor I increased during maturation. These data provide the first physiological evidence for activation of the pituitary-testis axis during the fall critical period when maturation is initiated for the following year.     

Variations in testicular androgen receptors and histology of the lamb testis from birth to puberty

Changes in testicular androgen receptor numbers were studied in lambs from 25 to 100 days of age. During this period, cytoplasmic receptors increased from 5 to 80 pmol/testis and nuclear receptors from 1 to 12 pmol/testis, while the total volume of Leydig cells increased 7-fold. The total number of Sertoli cells doubled between 25 and 40 days of age. From 40 days onward their number remained constant while their cellular and nuclear sizes increased by a factor of 3 and 1.5 respectively. Cytoplasmic receptor concentration was positively correlated with the number of Sertoli cells per section of seminiferous tubule, and negatively correlated with the number of germinal cells per cross section. One explanation for these results could be that Sertoli cells are the main androgen target cells in lamb seminiferous tubules.     

Sertoli and Leydig cell numbers and gonadotropin receptors in rat testis from birth to puberty

Summary In testes of rats from 2 to 60 days of age, we examined the number of Sertoli cells (SC) and Leydig cells (LC) as well as the binding of radioiodinated gonadotropins to frozen sections and homogenates. The number of SC per testis increased only during the first 2 postnatal weeks, whereas that of LC was stable up to days 7–10 and increased thereafter. The uptake of ¹²⁵I-labelled human follicle-stimulating hormone (¹²⁵I-FSH) to frozen sections was confined to sex cords or seminiferous tubules, while that of ¹²⁵I-labelled human choriogonadotropin (¹²⁵I-hCG) matched the distribution of LC in the interstitium. High affinity receptors for FSH and hCG were found in homogenates at all stages studied. The number of FSH receptors per testis increased steadily, whereas that of hCG receptors was low until days 7–10 and rose afterwards. Thus, SC in rat testis appear to proliferate in the presence of fetal LC during the first 2 postnatal weeks and to differentiate concomitantly with the emergence of the adult LC generation after day 10. The complement of FSH receptors in SC remains constant as they proliferate and increases after day 21 as they differentiate. The hCG receptor number is relatively fixed in each LC generation, being higher in adult compared to fetal LC.     

Variation in hormonal feedback and reproductive performance in rams of different genotypes from birth through puberty

Comparative experiments were carried out for elucidate the mechanisms that establish and control sexual behaviour of rams. Fifty-four ram lambs 2 to 24 wk of age were used for each of two genotypes and their crosses. The genotypes examined were the highly fertile nonseasonal D'Man breed and the low fertile seasonal Timahdite breed as well as the crossbreed of these two genotypes. Morphological, spermatological, ethological and endocrine parameters were compared. There seems to be a breed-dependent difference in the luteinizing hormone (LH) releasing pattern after gonadotropin releasing hormone (GnRH) stimulation at a specific prepubertal time period. This in turn reflects a breed-dependent difference in behavioral response in similar stages of physical maturation. The difference in behaviour is much more marked than the difference in physical characteristics.     

Histological assessment of the mouse uterus from birth to puberty for the appearance of LGL-1+ natural killer cells.

The appearance of natural killer (NK) cells during growth and maturation of the murine uterus was studied by immunohistochemistry, using the monoclonal antibody LGL-1. To determine the contributions of microorganisms in the environment and of T-cell and B-cell regulation to the establishment of a uterine NK cell population, uteri from barrier-raised, flora-defined, random-bred CD-1 mice and from genetically T-cell- and B-cell-deficient SCID mice (genotype C.B-17 scid/scid) were compared to uteri from conventionally raised CD-1 mice. Uteri were studied from birth to the ages at which these mice are normally paired for mating (7-10 wk). Absolute uterine weight and the ratio of uterine weight to body weight increased remarkably between 3 and 5 wk of age in each group of animals. Growth continued beyond Week 5 of age, and in all groups the ratio of uterine weight to body weight was similar at puberty, although both the flora-defined CD-1 and SCID mice were significantly smaller than conventionally reared mice. LGL-1+ cells could not be detected in any of the neonatal uteri examined. LGL-1+ cells were first detected at 2 wk of age in uteri from the conventional and flora-defined CD-1 mice. A significant increase in the number of LGL-1+ NK cells occurred in the CD-1 uterus between Weeks 2 and 3 of age and again between Weeks 5 and 7 of age. Environmental conditions did not alter the frequency of LGL-1+ cells between the two groups of CD-1 mice at any age studied.(ABSTRACT TRUNCATED AT 250 WORDS)     

Endocrine changes following partial hepatectomy

Subtotal hepatectomy and all the paraoperative actions induce a condition of stress characterized by the intensification of catabolic processes and overproduction of hormones with glycogenolytic and lypolytic action: catecholamines, T3, T4, ensuring the conditions required by some energy-dependent processes (mitoses and proteosyntheses) assuring the regeneration of the operated liver. The latter presents a depletion of dehydrogenases, of PAS + materials and fatty loading of the liver cells. In the conditions of liver distress, the muscles are those which supply the glucose, ensuring an as rapid as possible return of glycemia to normal values.     

Endocrine changes in the incubating and brooding turkey hen

Turkey hens were allowed to incubate eggs and to hatch and rear young. Plasma prolactin (Prl) levels increased prior to the start of continuous incubation and rose sharply as incubation progressed to reach a peak of 1178.2 +/- 221.8 ng/ml (mean +/- SEM) just before hatching. Prl levels then fell precipitously before the hens left the nest, and returned to preincubation levels (36.8 +/- 3.4 ng/ml) by the time the poults were 2 weeks old. These results show that the high plasma concentrations of Prl found during incubation are not initiated or maintained only by the stimulus of nesting. We suggest that the decline in Prl levels at the end of incubation could be related to the pipping and hatching of eggs, and the consequent shift to maternal behavior. Plasma growth hormone (GH) levels were significantly increased in hens which were brooding poults, but not in hens incubating eggs. An elevenfold, 1-day increase in plasma GH was observed immediately after the hens left the nests. Mean plasma GH levels rose from 12.0 +/- 4.7 ng/ml on the day that the hens left the nests to 133.0 +/- 32.0 ng/ml on the following day, and then declined to 23.1 +/- 9.6 ng/ml after an additional day. There were no significant changes in plasma thyroxine levels during laying, incubation and brooding. Plasma glucose concentration was significantly depressed during incubation.     

Plasma thyrotropin concentration in the male pig: profile from birth to puberty and the effect of season and social environment in the young adult

Plasma thyrotropin (TSH) secretion was studied in crossbred (Landrace x Large White) immature and young adult Landrace male pigs. Levels of TSH were low over the first 9 wk post-natally and were maximal at 12 wk of age. Thereafter, hormone levels declined and by 16 wk returned to values similar to those at 7 wk. In addition, a transient increase in TSH was noted at 22 wk. A second experiment involved 2 groups of young adult boars housed either in a socially non-restrictive environment (adjacent to estrual females) or a socially restrictive environment (not in direct physical contact with females). TRH stimulated secretion of TSH and the magnitude of this response was affected by month; minimum and maximum responses were found in May and August respectively. There was an effect of social environment on TRH-induced TSH secretion; during February and August, the magnitude of the TSH response to TRH was lower in socially restricted than in socially non-restricted boars.     

Serum profiles of androstenedione, testosterone and LH from birth through puberty in buffalo bull calves

Blood samples were taken once per week for 4-7 weeks from 59 buffalo calves in 14 age groups, 1-2 months apart. Hormones were quantified by validated radioimmunoassays. Values of androstenedione and testosterone were low at birth (141.3 +/- 33.5 pg/ml and 18.0 +/- 2.9 pg/ml, respectively; mean +/- s.d.). Serum androstenedione concentrations gradually increased from birth until 8 months of age and declined (P less than 0.05) thereafter, whereas mean testosterone values were low up to 8 months and then significantly (P less than 0.05) increased as age advanced. LH concentrations averaged 2.12 +/- 0.47 ng/ml at birth. Thereafter, a decline in LH values was followed by an increase between 6 and 15 months of age. We conclude that, in buffalo bull calves, the pubertal period occurs from about 8 to 15 months of age. For pubertal buffalo bulls 15-17 months of age, serum concentrations of androstenedione, testosterone and LH were 156.9 +/- 54.6 pg/ml, 208.4 +/- 93.8 pg/ml and 2.10 +/- 0.70 ng/ml, respectively.     

Age-related changes in ovarian morphology from birth to menopause in the Japanese monkey,Macaca fuscata fuscata

Age-related changes in ovarian morphology were studied in female Japanese monkeys,Macaca fuscata fuscata. A total of 47 nonlactating females of various ages ranging from new-born to >28 yr old were used. Ovarian size increased during the first decade of life, reached a plateau at around 10 yr. This was followed by a gradual decline throughout the remaining life span. The ovarian cortex of new-born animals consisted of numerous clusters of mitotic primordial germ cells. Such mitotic germ cells were observed even in the ovary of 28-day-old animal, but were not found in any animal after 1.5 yr of age. Numbers of primordial follicles decreased exponentially with the advance of age, and only a few primordial follicles were observed after about 16 yr of age. The numbers of primary and tertiary follicles increased from ages 4 to 16 yr, with a peak at 8 to 10 yr, and then decreased gradually. Developing tertiary follicles were observed as early as 1.5 yr of age. About 40% of tertiary follicles were atretic follicles throughout life, and their size was similar to that of developing tertiary follicles. Corpora lutea or corpora albicantia were found in ovaries more than 4 yr old. Remnants of corpora lutea and corpora albicantia, together with thick-walled blood vessels and fibrosis, became apparent in ovaries after 16 yr, and were observed characteristically in ovaries over 26 yr of age. There was no significant difference in the number or in the size of tertiary follicles between the breeding and nonbreeding seasons.     

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.     

Quantitative changes in alkaline phosphatase in epithelial cells of rat small intestine from birth to weaning

Synopsis Alkaline phosphatase activity has been measured in mucosal scrapings of rat small intestine from birth to weaning. The levels of activity were then compared with those found in brush border fractions and cell residues over the same period. The amount of activity found in the residues was too high and variable to be accounted for in terms of diffusion, and it was concluded that during the developmental period considerable quantities of enzyme were present in the cytoplasm.The duodenal changes were similar, in form, in both mucosal scrapings and brush border, but the changes in the ileal brush borders were markedly different from those found in the ileal mucosal scrapings. A peak in the activity measured in the brush border fraction was observed during the weaning period. A partial explanation for the observed changes is suggested but a detailed analysis was not possible at the present stage in the work.     

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.     

Endocrine mechanisms of puberty in heifers: estradiol negative feedback regulation of luteinizing hormone secretion

The hypothesis that luteinizing hormone (LH) secretion in prepubertal females is responsive to estradiol negative feedback and that decreased feedback occurs as puberty approaches was tested in heifers. In the first experiment, seven heifers were maintained prepubertal by dietary energy restriction until 508 days of age (Day 0). All heifers were placed on a high-energy diet on Day 0 at which time they received no additional treatment (CONT), were ovariectomized (OVX) or were ovariectomized and subcutaneously implanted with estradiol-17 beta (OVX-E2). This feeding regimen was used to synchronize reproductive state in all heifers. A second experiment was performed with 16 prepubertal heifers using the same treatments at 266 days (Day 0) of age (CONT, OVX and OVX-E2) but no dietary intake manipulation. In both experiments, LH secretion increased rapidly following ovariectomy in OVX heifers. In the initial experiment, LH secretion was maintained at a low level in OVX-E2 heifers until a synchronous rapid increase was noted coincidental with puberty in the CONT heifer. In the second experiment, LH secretion increased gradually in OVX-E2 heifers and attained castrate levels coincidental with puberty in CONT heifers. A gradual increase in LH secretion occurred as puberty approached in CONT heifers. These results indicate that: a) LH secretion in prepubertal heifers is responsive to estradiol negative feedback; and b) estradiol negative feedback decreases during the prepubertal period in beef heifers.