Influence of gonadal hormones on endocrine activity of gonadotroph cells in the adenohypophysis of male lambs during the postnatal transition to puberty

Using histomorphological and functional criteria we describe the feedback mechanisms which could play a role in the regulation of the gonadotrophic axis during the postnatal transition to puberty in male lambs. The working hypothesis was that the testicular factors change the peripheral levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) by influencing the synthesis rate and storage of LH and FSH in adenohypophyseal gonadotroph cells of weanling and weaned pubertal lambs. The examination was made in (i) 9-week-old infantiles, suckling lambs undergoing weaning, testis-intact (TEI) and orchidectomised (ORCHX) at the 6th week of age, and (ii) 16-week-old pubertal lambs TEI and ORCHX at the 12th week of age (n=5 per group). Changes in gonadotrophs were assayed with hybridohistochemistry, immunohistochemistry and radioimmunoassay. The percentage of the adenohypophyseal area (PA) occupied by cells containing LHβ-mRNA and FSHβ-mRNA and peripheral levels of both gonadotrophins were lower (P<0.01) in the 16-week-old TEI lambs in comparison with the 9-week-old ones. The PA occupied by cells immunoreactive for LHβ was lower (P<0.01), whereas in the case of FSH was greater (P<0.001) in the 16-week-old lambs. After orchidectomy the PA occupied by gonadotrophs stained for LHβ-mRNA was greater (P<0.01) in 16-week-old lambs. The PA occupied by LHβ-labelled cells was lower (P<0.05) in the 9-week-old ORCHX lambs, whereas in 16-week-old ones was higher (P<0.05) in comparison with the TEI lambs. The circulating LH was greater (P<0.01) in the ORCHX 9- and 16-week-old lambs compared to the TEI ones. The PA occupied by cells containing FSHβ-mRNA and the plasma FSH concentration were greater (P<0.001) after orchidectomy in lambs from both age stages. The PA occupied by FSHβ-labelled cells was greater (P<0.01) in the 9-week-old ORCHX lambs, whereas in 16-week-old ones was lower (P<0.05) compared to the lambs from TEI groups. In conclusion, in infantile lambs testicular factors may play inhibitory role in regulating FSH synthesis rate, storage and release in contrast to the stimulatory role in regulating LH storage reflected by the inhibitory role in regulating LH release. In lambs at the beginning of puberty, testicular factors may play inhibitory role in regulating LH synthesis rate, storage and release in contrast to the stimulatory role in regulating FSH storage reflected by the inhibitory role in regulating FSH synthesis rate and release. The effects of testicular hormones on the gonadotrophin storage, i.e. releasable pools in adenohypophyseal cells, are specific for both LH and FSH in lambs during the postnatal transition to puberty. Thus, the initiation of puberty in male sheep is a function of change of the inhibitory role of gonadal factors in regulating FSH storage to the stimulatory one and the stimulatory role of gonadal factors in regulating LH storage to the inhibitory one.     

The influence of ovarian factors on the somatostatin-growth hormone system during the postnatal growth and sexual development in lambs

The aim of the study was to elucidate the effects of ovarian hormones on somatostatin in the hypothalamic neurons and growth hormone (GH) secretion during the postnatal growth and development of sheep. The study was performed on 9-week-old (infantile) lambs that were ovary-intact (OVI) or ovariectomized (OVX) at 39 days of age, and on 16-week-old (juvenile) lambs that were OVI or OVX at 88 days of age. Hormones in neurons and somatotropic cells were assayed with immunohistochemistry and radioimmunoassay. Following ovariectomy, immunoreactive somatostatin was more abundant (p<0.05) in the hypothalamus of infantile lambs, whereas in juvenile lambs it was more abundant (p<0.05) in the periventricular nucleus but reduced (p<0.01) in the median eminence. In contrast to somatostatin in the hypothalamus, the content of immunoreactive GH in the hypophysis was less in OVX infantile lambs, but greater in OVX juvenile lambs (p<0.05). Basal blood serum concentrations of GH were greater (p<0.05) in OVX infantile lambs, whereas in OVX juvenile lambs, mean and basal concentrations of GH and amplitude of GH pulses were less than in OVI lambs (p<0.05). The postnatal increase in body weight was greatest in middle-late infancy (p<0.01). The body weight did not differ (p>0.05) between OVI and OVX lambs. In conclusion, ovarian factors may inhibit the GH secretion in infantile lambs but enhance the GH secretion in juvenile lambs. Transition to puberty, as related to the growth rate, appears to be due mainly to change in gonadal influence on the somatostatin neurosecretion. A stimulation of somatostatin output in the median eminence by gonadal factors in infancy is followed by a stimulation of somatostatin accumulation after infancy. Thus, ovarian factors modulate mechanisms within the somatotropic system of lambs to synchronize the somatic growth with sexual development.     

The neuroendocrine events during the ovine growth-promoted maturation: the developmental importance of hypophysiotrophic action of somatostatin in ewes

The comparison of hypothalamic somatostatin (SRIH)-neuronal systems, hypophyseal somatotroph populations and growth hormone (GH) blood plasma patterns among developmental stages, from infancy until puberty, may help to describe the nature of the hypothalamo-hypophyseal mechanisms underlying the changes in GH on the systemic level leading to the somatic, that is growth and sexual maturity in sheep. The aim of this study was to elucidate (i) developmental importance of hypophysiotrophic action of SRIH, (ii) precise time of maturation of this action and (iii) photoperiodic regulation of the postnatal ontogeny in ewes. The central and peripheral activity of the SRIH-GH axis is described through a sequence of histomorphological and functional changes in Merino ewes born after the summer solstice. The actual time of puberty of these animals was delayed until the following breeding season, when the sheep were 14-month old. Histomorphometric examinations have been made in 21 infantile (preweanling, 12-week old), prepubertal (15- and 22-week old), peripubertal (30- and 52-week old) and pubertal (63-week old) ovary-intact sheep. Functional examinations of the GH plasma levels were determined every 1-2 weeks during the period from the 12th to 63rd week of age. The highest GH level was observed at the 13th week of age, on the beginning of the breeding season. The fluctuations in the GH level just after the winter and summer solstice were detected as the one and only deviation from a rule of uniformly low GH concentrations observed until puberty. The age of the fall in serum GH levels corresponded with the postweaning period and the beginning of the phase of the lower daily live-weight gains (growth rate). Thus, the development of GH secretion was finished before the 15th week of age, that is together with the ending of the transitional infantile/prepubertal period, whereas the maturational processing within the hypothalamo-hypophyseal unit prolonged after the 15th week of age until 22 weeks of age and concerned the role of SRIH as the hypophysiotrophic factor regulating somatic maturation, i.e. attenuating growth. Altogether, the pattern of GH secretion during weaning is important for the shift between infancy and prepuberty depended upon an intensive growth and defined as growth maturation. The maturation of the SRIH-GH axis is finished by 22 weeks of age, independently of photoperiodic influences, whereas the neuroendocrine mechanisms to integrate somatic, that is growth and sexual maturation, are seasonal in nature in the ewe. Our observations confirm the hypothesis of the inherent endogenous rhythm controlling somatic maturation in the sheep.     

Bioactive and immunoreactive FSH concentrations in ewe and ram lambs over the first year of life

Several studies suggest that the concentration of immunoreactive (I) FSH measured in peripheral plasma by radioimmunoassay does not always reflect the level of bioactive (B) hormone capable of eliciting a biological response (e.g. oestradiol synthesis by Sertoli cells in vitro). The aim of this study was to measure both B-FSH and I-FSH concentrations in male and female sheep during the first year of life, and to relate this to pubertal development. The hypothesis being tested was that B-FSH is present in both male and female sheep during the prepubertal period and that discrete changes in B-FSH are associated with the onset of puberty. Eight ewe lambs and eight ram lambs were blood sampled fortnightly from 2 to 52 weeks of age. All samples were assayed for B-FSH and I-FSH content. Pubertal development was monitored in ewe lambs from behavioural oestrus and from plasma progesterone concentrations, and in ram lambs from penile and testicular development and from plasma testosterone concentrations. Mean I-FSH concentrations varied significantly with time after birth, in both females and males (P<0.01). In contrast, B-FSH was found to vary with time in females only (P<0.01). Around the expected time of puberty in ram lambs (i.e. at 30–40 weeks of age), and thereafter, I-FSH concentrations were undetectable (<0.2 ng ml⁻¹), whereas the B-FSH concentrations were measurable at concentrations up to twice the assay detection limit (0.8 ng ml⁻¹) until 38 weeks of age. In ewe lambs, but not ram lambs, there was a significant linear relationship between B-FSH and I-FSH values (R=0.595; P<0.005). When standardised about the time of puberty, B-FSH (P<0.05) but not I-FSH was significantly higher in ewe lambs that failed to reach puberty. No differences for either B-FSH or I-FSH between pubertal and non-pubertal ram lambs were noted. In summary, B-FSH was often measurable in plasma throughout prepubertal development in sheep and the concentrations often differed from those of I-FSH, especially in ram lambs. However, there appeared to be no discrete changes in B-FSH that could be directly related to specific pubertal events. It is concluded that although FSH may be a prerequisite for prepubertal testicular development and/or ovarian follicular growth, it is not a critical factor in determining whether puberty is attained during the first year of life in this seasonally breeding species.     

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.     

Ewe lambs with higher breeding values for growth achieve higher reproductive performance when mated at age 8 months

We studied the relationships among growth, body composition and reproductive performance in ewe lambs with known phenotypic values for depth of eye muscle (EMD) and fat (FAT) and Australian Sheep Breeding Values for post-weaning live weight (PWT) and depth of eye muscle (PEMD) and fat (PFAT). To detect estrus, vasectomized rams were placed with 190 Merino ewe lambs when on average they were 157 days old. The vasectomized rams were replaced with entire rams when the ewe lambs were, on average, 226 days old. Lambs were weighed every week and blood was sampled on four occasions for assay of ghrelin, leptin and ß-hydroxybutyrate. Almost 90% of the lambs attained puberty during the experiment, at an average live weight of 41.4 kg and average age of 197 days. Ewe lambs with higher values for EMD (P < 0.001), FAT (P < 0.01), PWT (P < 0.001), PEMD (P < 0.05) and PFAT (P < 0.05) were more likely to achieve puberty by 251 days of age. Thirty-six percent of the lambs conceived and, at the estimated date of conception, the average live weight was 46.9 ± 0.6 kg and average age was 273 days. Fertility, fecundity and reproductive rate were positively related to PWT (P < 0.05) and thus live weight at the start of mating (P < 0.001). Reproductive performance was not correlated with blood concentrations of ghrelin, leptin or ß-hydroxybutyrate. Many ewe lambs attained puberty, as detected by vasectomized rams, but then failed to become pregnant after mating with entire rams. Nevertheless, we can conclude that in ewe lambs mated at 8 months of age, higher breeding values for growth, muscle and fat are positively correlated with reproductive performance, although the effects of breeding values and responses to live weight are highly variable.     

Influence of prostaglandins and thyrotropin releasing hormone (TRH) on hormone secretion and growth in wether lambs

A series of experiments were conducted in ewes and wether (castrate male) lambs to evaluate the influence of prostaglandins on secretion of anabolic hormones and to determine if repeated injections of prostaglandin (PG) F₂α would chronically influence the secretion of these hormones and perhaps growth rate as well.A single intravenous injection of PGA₁ and PGB₁ (100 μg/kg) exerted no significant (P > .10) influence on plasma concentrations of prolactin (PRL), growth hormone (GH) or thyrotropin (TSH) in ewes. PGA₁, but not PGB₁, stimulated an increase in the plasma concentration of insulin. Infusion of PGF₂α for 5.5 hr into ewes resulted in increased (P < .05) plasma concentrations of both GH and PRL while TSH and insulin were not significantly influenced. Prostaglandin F₂α, when injected subcutaneously into wether lambs (10 mg twice weekly) stimulated (P < .05) plasma GH concentrations after the first injection, but not after 3 weeks of treatment. Changes in plasma PRL or TSH were not observed consistently in the lambs treated chronically with PGF₂α or TRH.Prostaglandin F₂α, in the present studies, and PGE₁ in previously reported studies (1–3), has been demonstrated to be stimulatory to the secretion of PRL and GH. In contrast, PGA₁ and PGB₁, which lack an 11-hydroxyl group, failed to influence the secretion of either PRL or GH. It would, therefore, appear that the 11-hydroxyl group is a structural requirement for prostaglandins to influence the secretion of these two hormones in sheep.Treatment with thyrotropin releasing hormone (TRH), alone or in combination with PGF₂α, significantly (P < .05) increased growth rate (average daily gains) while PGF₂α did not, despite the fact that both compounds exerted similar effects on plasma GH.     

Serum luteinizing hormone, growth hormone and insulin-like growth factor-I after releasing hormone challenge in prepubertal ewe lambs selected for twinning

Two studies evaluated hormonal markers as indicators of the onset of puberty in Debouillet sheep selected for twinning. In Trial 1, 29 ewe lambs (50 +/- 0.5 kg, 159 to 187 d of age) were given 10 microg GnRH (i.v.) on September 15 and blood was collected at 30 min intervals after the injection for 2 h. Additional samples were taken twice weekly and progesterone (P4) was measured. The day that serum P4 was greater than 1 ng/mL for 2 consecutive sampling days was classified as the day of puberty. Average day of puberty was October 12 (average age at puberty was 199 d) and ewes with values less or greater than the average were classified as early or late, respectively. Average weight at GnRH challenge was 50 kg and ewes weighing less or more were classified as light or heavy, respectively. Early ewes weighed more (P = 0.01) and reached puberty sooner (P = 0.01) than late ewes. Heavy lambs reached puberty earlier, weighed more at GnRH challenge, and had more LH area under the curve (AUC, P < 0.05) than light ewes. In Trial 2, we gave 27 ewe lambs (54 +/- 0.9 kg, 173 to 189 d of age) a single i.v. injection of 10 microg GnRH and 10 microg GHRH on September 17. Average day of puberty was October 13, average weight was 54 kg, and average age at puberty was 208 d. Categories were designated as described for Trial 1. Early lambs reached puberty sooner (P = 0.01) and weighed more (P = 0.01) than late lambs, but the puberty groups had similar LH AUC (P = 0.64) and GH AUC (P = 0.75), whereas IGF-I was greater (P = 0.01) in early puberty ewes than in late puberty ewes. Heavy lambs reached puberty earlier (P = 0.06), weighed more (P = 0.01), and tended (P = 0.11) to have more GH AUC than light ewes. No difference was observed in LH AUC or IGF-I between weight groups (P > 0.15). Results suggest that serum LH after GnRH is not a reliable indicator of the onset of puberty in ewe lambs selected for twinning, but heavier ewes tended to produce more GH after a GHRH challenge and reach puberty earlier than lighter ewe lambs.     

Family physician and endocrinologist coordination as the basis for diabetes care in clinical practice

Background

The role of estrogens in male physiology has become evident. However, clinically useful normative data for estradiol secretion in boys has not previously been established due to the insensitivity of current methods used in clinical routine. By use of a validated ultra-sensitive extraction RIA, our aim was to establish normative data from a group consisting of healthy boys in prepuberty and during pubertal development.

Methods

Sixty-two 24-hours serum profiles (6 samples/24 hours) were obtained from 44 healthy boys (ages; 7.2–18.6 years) during their pubertal development, classified into five stages: prepuberty (testis, 1–2 mL), early (testis, 3–6 mL), mid (testis, 8–12 mL), late-1 (testis,15–25 mL, not reached final height) and late-2 (testis,15–25 mL, reached final height). Serum estradiol was determined by an ultra- sensitive extraction radioimmunoassay with detection limit 4 pmol/L and functional sensitivity 6 pmol/L.

Results

Mean estradiol concentrations during 24-hours secretion increased from prepuberty (median: <4 (5–95 percentiles: <4 – 7) pmol/L) to early puberty (6 (<4 – 12 pmol/L) but then remained relatively constant until a marked increase between mid-puberty (8 (4 – 17) pmol/L) and late-1 (21 (12 – 37) pmol/L) puberty, followed by a slower increase until late-2 puberty (32 (20 – 47) pmol/L). The diurnal rhythm of serum estradiol was non-measurable in pre- and early puberty, but discerned in mid-puberty, and become evident in late pubertal stages with peak values at 0600 to 1000 h.

Conclusion

With the use of an ultra-sensitive extraction RIA, we have provided clinically useful normative data for estradiol secretion in boys.     

The capacity to increase GH secretion at puberty reflects the severity of GH deficiency.

This study evaluates the effect of the spontaneous pubertal increase in sex steroids on GH secretion in GH-deficient patients. Fifteen patients (10 boys, 5 girls) with idiopathic isolated GH deficiency diagnosed before puberty (GH peak < 8 micrograms/l after 2 arginine insulin stimulation tests) were reevaluated for their GH secretion using the same test after completion of their hGH therapy and puberty. Their ages at diagnosis and at the last evaluation were 8.2 +/- 0.7 (SE) (range 4.9-14.9) and 17.8 +/- 0.3 years (15-23), respectively. The data at diagnosis and at last evaluation showed that (1) the mean height increased from -4 +/- 0.3 to -2.5 +/- 0.3 SD (p < 0.01), (2) the mean GH peak increased from 4.4 +/- 0.3 (1.6-8) to 7.6 +/- 0.8 micrograms/l (2-13.2, p < 0.01); at the last evaluation, 8/15 patients had GH peak > 8 micrograms/l and (3) the mean plasma insulin-like growth factor I increased from 0.28 +/- 0.05 to 0.42 +/- 0.03 U/ml (n = 6, p < 0.05). The mean increase in the GH peak was 3.2 micrograms/l (-3 to 10.6). It was negatively correlated with the degree of growth retardation at diagnosis (r = -0.74, p < 0.005). We conclude that the increase in the GH peak at puberty in patients with GH deficiency reflects the severity of GH deficiency and that a corrective factor of the cutoff number is necessary for the diagnosis of GH deficiency in puberty.     

Developmental correlation between hypothalamic somatostatin and hypophysial growth hormone

Summary The objective of the present study was to determine, by means of immunocytochemistry, the age in fetal development at which GH is first detectable in the pituitary gland and somatostatin in the median eminence, and to correlate temporally the development of these two hormones throughout the remainder of pregnancy. Mice were studied at 15–19 days of gestation with the peroxidase-antiperoxidase (PAP) technique of Sternberger. Somatotropes in the pars distalis were initially detected at 16 days of gestation and by 17 days they were a prominent component of the parenchymal cell population of the hypophysis. These cells were ovoid and distributed uniformly throughout the pars distalis; many were located adjacent to sinusoidal capillaries. Their number and staining intensity increased by 19 days. Somatostatin was not consistently observed in the median eminence until 19 days of gestation. Reaction product indicative of the presence of somatostatin in presumptive nerve endings was located on the ventral surface of the median eminence and in the external lamina of the infundibulum in proximity to the superficial portal capillaries. Results of the present investigation support the concept that the potential for neuroendocrine control of GH secretion exists in the mouse by the end of fetal development. Several hypotheses concerning the temporal relationship between the appearance of somatostatin in the hypothalamus and of GH in the anterior pituitary gland are discussed.Supported by a Biomedical Research Support Grant (NIH RR 5417). Appreciation is extended to the National Pituitary Agency, NIAMDD for the following radioiodination-grade hormones: hGH, rPRL, rTSH, rFSH and hCG     

Plasma LH,FSH, testosterone,and age at puberty in ram lambs actively immunized against an inhibin alpha-subunit peptide

Active immunization against inhibin has been shown to advance puberty and increase ovulation rate in ewe lambs; but in ram lambs, effects on puberty and sperm production are equivocal. The objective of the present study was to determine whether active immunization against an inhibin alpha-subunit peptide advances the onset of puberty in ram lambs. St. Croix hair sheep ram lambs were assigned to inhibin-immunized (n = 7) and control (n = 8) treatment groups. Lambs in the inhibin-immunized group were immunized against a synthetic peptide-carrier protein conjugate, alpha-(1-25)-human alpha-globulin (halpha-G), and control lambs were immunized against halpha-G. Lambs were immunized at 3, 7, 13, 19, 25, 31, and 37 weeks of age. On the day of immunization a blood sample was collected and lambs were weighed. Another blood sample was collected 1 week following each immunization. At 20 weeks of age additional blood samples were collected at 20 min intervals for 8h. Beginning at 20 weeks of age and at weekly intervals thereafter, scrotal circumference (SC) was measured and semen was collected using electroejaculation. A subsequent ejaculate was collected 1 week following onset of puberty, which was defined as the week of age when an ejaculate first contained > or =50 x 10(6) sperm cells. In control lambs, plasma alpha-(1-25)-antibody (Ab) was nondetectable. In inhibin-immunized lambs, alpha-(1-25)-Ab titer increased from 7 to 25 weeks of age and then plateaued at a level that varied (P<0.001) among animals. Body weight and SC of control and inhibin-immunized lambs were similar at the onset of puberty. At pubertal onset inhibin-immunized lambs were older than control lambs (31.9+/-0.5 vs. 29.5+/-0.7 weeks of age, P<0.05). Plasma FSH concentrations were similar in control and inhibin-immunized lambs from 3 to 38 weeks of age. Plasma LH levels were lower (P<0.01) in inhibin-immunized than control lambs. During the 8-h blood sampling period at 20 weeks of age, LH and testosterone concentrations were lower (P<0.05) in inhibin-immunized than control ram lambs, and the LH pulse frequency was similar in the two groups of animals. The decreased LH secretion is consistent with the immunoneutralization of a putative inhibin alpha-subunit-related peptide that stimulates LH secretion in ram lambs. Present findings show that active immunization against an inhibin alpha-peptide delays rather than advances puberty in ram lambs.     

Growth hormone secretion during sleep. I. Comparison with GH responses to conventional pharmacologic stimuli in pubertal and early pubertal short subjects. Effects of treatment with human GH in patients with discrepant measurements of GH secretion

Growth hormone (GH) was measured in 215 short children (147 males and 68 females, 123 prepubertal, 92 at early pubertal stages), comparing GH responses to classical pharmacologic stimulation tests and spontaneous GH secretion during sleep. GH secretion during sleep, but not GH responses to stimuli, was higher in early pubertal than in prepubertal subjects. The patients were classified into five groups, according to the agreement between GH responses to stimuli and GH secretion during sleep: group I, normal GH-secreting children; group II, completely GH-deficient; group III, partially GH-deficient; group IV, with normal secretion during sleep and low responses to stimuli; group V, with the reverse situation. 30% of the patients were in groups IV and V, both at prepubertal and early pubertal stages. 46 patients of groups II-V were treated with extracted human GH(hGH). The growth rate was enhanced in groups IV and V, to the same extent as in groups II and III. Four points can be concluded: (1) the rise of GH secretion during sleep is an early event at the onset of puberty; (2) the discrepancy between the GH responses to classical stimuli and GH secretion during sleep are of pathological significance; (3) disturbances of GH secretion might be diagnosed by measuring GH secretion during sleep rather than by using conventional stimulation tests; (4) a trial course of hGH treatment could be proposed in patients with both kinds of discrepancies between GH responses to stimuli and GH secretion during sleep.     

Isolated deficiency of immunocytochemically detected somatostatin in Snell dwarf, but not in “little,” mice

Immunocytochemical staining of the neuropeptide somatostatin was evaluated in the brains of two growth hormone-deficient mouse mutants, Snell dwarf (dw/dw), and “little” (lit/lit). In Snell dwarf mice, in which GH is undetectable, an isolated somatostatin deficiency was observed in hypothalamic median eminence and in anterior periventricular hypothalamic neurons which are afferent to median eminence, compared to somatostatin staining in normal mice of the same strain (DW/?). Somatostatin staining in all other CNS areas in dwarfs was identical to that in normal mice. In contrast, in little mice, which exhibit 5–10% of normal GH levels, somatostatin expression was comparable between mutants and normal mice (LIT/?) in all CNS areas, including median eminence-afferent neurons in anterior periventricular hypothalamus. The results suggest that expression of somatostatin in hypophysiotropic CNS is dependent upon minimal pituitary GH secretion.     

Blunted pubertal growth after leukemia: a new pattern of growth hormone insufficiency

Growth, age at menarche and spontaneous GH secretion were studied in girls after treatment for acute lymphoblastic leukemia (ALL). These girls had normal prepubertal growth but subnormal pubertal growth. Mean final height was 1 SD less than expected before puberty. The average age at menarche was significantly lower than the normal mean for Swedish girls. The mean 24-hour GH secretion was severely blunted and there was no increase during puberty. We suggest that girls treated for ALL, including CNS irradiation, have a relative GH insufficiency which becomes clinically obvious only when the girls cannot respond to the increased demands for GH in puberty.     

Prenatal androgen exposure and growth and secretion of growth hormone and prolactin in ewes postweaning

Growth and secretion of growth hormone (GH) and prolactin (PRL) in ewe lambs exposed to androgen during fetal development were investigated. Testosterone cypionate was administered to the pregnant dams from approximately Days 28 to 84 of gestation. Ewe lambs from dams that received androgen exhibited masculinized external genitalia and some masculine behavioral characteristics. Intact androgenized ewe lambs grew faster (P less than 0.05) and were more efficient in conversion of food to body gain (P less than 0.05) than ewe lambs born to untreated dams over the period from 70 to 224 days of age. One-half of the ewe lambs in each group was ovariectomized at 58 days of age. Ovariectomy had no effect on subsequent growth or efficiency of growth in the control ewe lambs. However, ovariectomy of androgenized ewe lambs abolished the observed stimulated rate of growth and decreased the improvement in efficiency of food conversion. Blood samples were collected from the lambs at 85 and 136 days of age at 15-min intervals for 8 hr to determine parameters of GH and PRL secretion. Prenatal androgen exposure had no effect on any parameter of GH or PRL secretion. These data indicate that prenatal androgen exposure altered differentiation of growth potential in ewe lambs, but the growth response was not mediated through dramatic changes in secretion of adenohypophysial somatotropic hormones, GH and PRL.     

Effect of arginine on the GHRH-stimulated GH secretion in patients with hyperthyroidism.

Patients with hyperthyroidism have reduced GH responses to pharmacological stimuli and reduced spontaneous nocturnal GH secretion. The stimulatory effect of arginine on GH secretion has been suggested to depend on a decrease in hypothalamic somatostatin tone. The aim of our study was to evaluate the effects of arginine on the GH-releasing hormone (GHRH)-stimulated GH secretion in patients with hyperthyroidism. Six hyperthyroid patients with recent diagnosis of Graves' disease [mean age +/- SEM, 39.2 +/- 1.4 years; body mass index (BMI) 22 +/- 0.4 kg/m2] and 6 healthy nonobese volunteers (4 males, 2 females; mean age +/- SEM, 35 +/- 3.5 years) underwent two experimental trials at no less than 7-day intervals: GHRH (100 micrograms, i.v.)-induced GH secretion was evaluated after 30 min i.v. infusion of saline (100 ml) or arginine (30 g) in 100 ml of saline. Hyperthyroid patients showed blunted GH peaks after GHRH (13.2 +/- 2.9 micrograms/l) as compared with normal subjects (23.8 +/- 3.9 micrograms/l, p < 0.05). GH peaks after GHRH were only slightly enhanced by arginine in hyperthyroid subjects (17.6 +/- 2.9 micrograms/l), whereas, in normal subjects, the enhancement was clear cut (36.6 +/- 4.4 micrograms/l; p < 0.05). GH values after arginine + GHRH were still lower in hyperthyroid patients with respect to normal subjects. Our data demonstrate that arginine enhances but does not normalize the GH response to GHRH in patients with hyperthyroidism when compared with normal subjects. We hypothesize that hyperthyroxinemia may decrease GH secretion, both increasing somatostatin tone and acting directly at the pituitary level.     

Effect of protein deficiency on some hypothalamic and pituitary hormones in growing male lambs. An immunohistochemical study

Growing male lambs were fed with diets containing 14.0, 10.8 and 7.6% protein for 3 months to determine their effects on the content of hypothalamic LHRH and SRIH and pituitary LH and GH, using immunohistochemical methods. Lowering the concentration of dietary proteins caused marked changes in the immunoreactivity of these hormones. The immunoreactive (IR) content of LHRH stored in the median eminence was enhanced, and the proportion of LH cells and their IR content increased. Opposite effects were observed in the SRIH/GH system; IR SRIH content stored in the median eminence markedly diminished, and, although hyperplasia of GH cells was observed, their IR content was diminished. This study indicates that prolonged restrictions of protein in the diet of growing male sheep affects the immunoreactive content of the investigated hormones. It seems that they suppress LHRH/LH release and augment GH release, possibly via suppression of hypothalamic somatostatin.     

Pinealectomy delays puberty in ewe lambs

Fifteen pinealectomized and 15 unoperated ewes were exposed to constant light for 3 weeks before and 10 weeks after lambing. Fourteen pinealectomized and 15 unoperated ewes were allowed to lamb outdoors. Five ewe lambs born in constant light to the 2 groups of dams were pinealectomized at 10 weeks of age. Ewes and lambs were then returned to the field. Puberty (determined by weekly progesterone analysis) was significantly delayed (P less than 0.05) in the pinealectomized ewe lambs. Median pubertal age in pineal-intact ewe lambs was 37 weeks compared to 49 weeks in pinealectomized lambs. Constant light during the first 10 weeks of life had no effect upon puberty onset nor did the pineal status of the dam. Control lambs entered seasonal anoestrus at the time pinealectomized ewe lambs were entering puberty. Pinealectomized lambs entered anoestrus at the same time as control lambs were beginning their second breeding season. These results confirm a key role of pineal-mediated hormonal signals in the control of puberty in the sheep.     

Selection for superior growth advances the onset of puberty and increases reproductive performance in ewe lambs

The reproductive efficiency of the entire sheep flock could be improved if ewe lambs go through puberty early and produce their first lamb at 1 year of age. The onset of puberty is linked to the attainment of critical body mass, and therefore we tested whether it would be influenced by genetic selection for growth rate or for rate of accumulation of muscle or fat. We studied 136 Merino ewe lambs with phenotypic values for depth of eye muscle (EMD) and fat (FAT) and Australian Sheep Breeding Values at post-weaning age (200 days) for live weight (PWT), eye muscle depth (PEMD) and fat depth (PFAT). First oestrus was detected with testosterone-treated wethers and then entire rams as the ewes progressed from 6 to 10 months of age. Blood concentrations of leptin and IGF-I were measured to test whether they were related to production traits and reproductive performance (puberty, fertility and reproductive rate). In total, 97% of the lambs reached first oestrus at average weight 39.4 ± 0.4 kg (mean ± s.e.m.) and age 219 days (range 163 to 301). Age at first oestrus decreased with increases in values for PWT (P < 0.001), and concentrations of IGF-I (P < 0.05) and leptin (P < 0.01). The proportion of ewe lambs that achieved puberty was positively related with increases in values for EMD (P < 0.01), FAT (P < 0.05) or PWT (P < 0.01), and 75% of the ewe lambs were pregnant at average weight 44.7 ± 0.5 kg and age 263 days (range 219 to 307). Ewe lambs that were heavier at the start of mating were more fertile (P < 0.001) and had a higher reproductive rate (P < 0.001). Fertility and reproductive rate were positively correlated with increases in values for EMD (P < 0.01), FAT (P < 0.05), PWT (P < 0.01) and leptin concentration (P < 0.01). Fertility, but not reproductive rate, increased as values for PFAT increased (P < 0.05). Leptin concentration increased with increases in values for EMD (P < 0.001), FAT (P < 0.001), PWT (P < 0.001), PEMD (P < 0.05) and PFAT (P < 0.05). Many of these relationships became non-significant when PWT or live weight was added to the statistical model. We conclude that selection for genetic potential for growth can accelerate the onset of puberty and increase fertility and reproductive rate of Merino ewe lambs. The metabolic hormones, IGF-I and leptin, might act as a physiological link between the growing tissues and the reproductive axis.