Hormonal responses in pubertal males to pulsatile gonadotropin releasing hormone (GnRH) administration

Twenty-two boys (9 with delayed puberty and 13 with short stature) ages 12.3 - 17.8 yr, and 10 adult males with idiopathic hypogonadotropic hypogonadism (ages 17.3 - 41.1 yr) have been studied following pulsatile, sc GnRH therapy (240 ng/kg/pulse) over 6 days. Mean pre- and post-therapy LH and FSH concentrations were estimated by 15 min blood sampling over 3-h periods immediately before and at the end of the treatment period. There were significant correlations between the mean pre- and posttreatment LH and FSH concentrations (r = 0.82, p less than 0.001 and r = 0.51, p less than 0.02, respectively) for the 2 groups of peripubertal boys when assessed together. Nine of the 10 adults with hypogonadism showed proportionately greater gonadotropin increments following pulsatile therapy when compared with the peripubertal boys. Standard bolus GnRH tests (100 micrograms iv) did not differentiate between the three groups of patients before pulsatile GnRH therapy. Bolus GnRH tests could predict the subsequent response to pulsatile therapy in the peripubertal boys only. There was no significant change in LH increments following the GnRH bolus tests in either group, after pulsatile GnRH administration (p greater than 0.1). Early response to pulsatile GnRH administration is dependent upon the maturity of the hypothalamic-pituitary-testicular axis in males with delayed puberty or short stature. Patients with hypogonadotropic hypogonadism do not show this relationship.     

Hypogonadism in congenital adrenal hypoplasia: evidence for a hypothalamic origin

Two unrelated boys with congenital adrenal hypoplasia were followed from birth for 20 yr. In spite of continuous treatment with hydrocortisone and fluorocortisone both patients had delayed growth and bone maturation since early childhood and failure of spontaneous puberty. Tests of the hypothalamic-pituitary function showed low basal plasma LH and FSH levels and blunted LH and FSH responses to standard GnRH tests and increased basal and TRH-stimulated PRL levels. Low dose pulsatile GnRH administration for 26 h, mimicking presumed physiological GnRH secretion, induced a continuing rise of plasma FSH in both patients and a slight increase of plasma LH and testosterone in one patient. These results indicate a hypothalamic origin of the gonadotropin deficiency with possible prenatal onset, since both patients had cryptorchidism during infancy. Hypogonadism in patients with adrenal hypoplasia may result from deficient steroid secretion of the hypoplastic fetal adrenals.     

Lack of gonadotropic response to pulsatile gonadotropin-releasing hormone in isolated hypogonadotropic hypogonadism associated to congenital adrenal hypoplasia

Congenital adrenal hypoplasia (AH) is a rare condition, known to be associated with isolated hypogonadotropic hypogonadism (IHH). Three studies have reported attempts to stimulate gonadotropin secretion with pulsatile gonadotropin-releasing hormone (GnRH) in a total of 4 patients presenting such a syndrome, with conflicting results. In the present study, one patient with idiopathic IHH and AH was treated with pulsatile sc GnRH--doses ranging from 2.5 to 10.0 micrograms/pulse, every 90 min--during 8 weeks in an attempt to induce puberty. The prepubertal basal plasma levels of LH, FSH and testosterone, and saliva testosterone levels remained unaltered throughout treatment, at all doses of GnRH tested. The gonadotropin response to an acute iv GnRH administration (0.1 mg) also remained at the prepubertal level after pulsatile GnRH treatment. No circulating anti-GnRH antibodies were detected. The absence of gonadotropic response to exogenous pulsatile GnRH suggests that the IHH of patients with AH is due to an abnormal pituitary function rather than to a lack of endogenous GnRH.     

Increased luteinizing hormone pulse frequency during sleep in early to midpubertal boys: effects of testosterone infusion

Gonadotropin secretion is pulsatile in prepubertal and early pubertal boys, and the onset of puberty is characterized by a sleep-associated rise in LH pulse amplitude. To determine whether an augmentation in LH pulse frequency as well as amplitude occurs at the onset of puberty, we studied gonadotropin secretion in 21 early to midpubertal boys. Blood samples were taken every 20 min (every 15 min in 4 boys) for LH determinations. A 2-fold increase in LH pulse frequency occurred during the nighttime sampling period (2200-0400 h) compared to that in the hours when the boys were awake (1000-2200 h). The maximum frequency (0.7 pulses/h) occurred between 2400 and 0200 h. The mean plasma LH concentration increased during the night from 2.3 +/- 0.2 (+/- SE) mIU/mL (2.3 +/- 0.2 IU/L) between 2000-2200 h to a maximum of 6.2 +/- 0.4 (6.2 +/- 0.4 IU/L) between 0200-0400 h. The mean plasma LH decreased to 5.5 +/- 0.4 mIU/mL (5.5 +/- 0.4 IU/L) between 0400-0600 h and to 4.2 +/- 0.5 (4.2 +/- 0.5 IU/L) between 0600-0800 h. Plasma testosterone rose during the night to a mean maximum value of 2.4 +/- 0.5 (+/- SE) ng/mL (8.3 +/- 1.7 nmol/L). This finding suggested that the rise in testosterone might play a role in decreasing LH secretion during the later hours of sleep (after 0400 h). To address this question and to study further the effects of testosterone in early puberty, we measured plasma LH concentrations every 10 min from 2000-0800 h in 8 early to mid-pubertal boys before and during short term testosterone administration. Saline or testosterone at a concentration of 9.33 micrograms/mL (32 mumol/L) was infused at a rate of 10 mL/h from 2100-1200 h to shift the nighttime testosterone rise 3 h earlier than would occur spontaneously. Blood samples were obtained every 10 min for LH and every 30 min for testosterone determinations from 2000-0800 h. Pituitary responsiveness was assessed by administering sequential doses of synthetic GnRH (25 and 250 ng/kg) at 1000 and 1200 h, respectively. The nighttime increase in LH pulse frequency and mean plasma LH concentration occurred between 2300 and 0200 h despite testosterone infusion. However, testosterone infusion was associated with significantly lower mean plasma LH concentrations from 0200-0800 h compared to those on the night of the saline infusion. Pituitary responsiveness to synthetic GnRH was unaltered by testosterone administration.(ABSTRACT TRUNCATED AT 400 WORDS)     

LUTEINIZING HORMONE AND FOLLICLE STIMULATING HORMONE SECRETION PATTERNS IN GIRLS THROUGHOUT PUBERTY MEASURED USING HIGHLY SENSITIVE IMMUNORADIOMETRIC ASSAYS

Pulsatile gonadotrophin secretion patterns were studied in 36 healthy girls by measuring every 10 min and applying immunoradiometric assays (IRMA). Different stages of puberty were associated with significant changes in the plasma LH and FSH levels, pulse numbers (Pno) and pulse amplitudes (pA). Plasma LH was not detectable by day or night in young prepubertal girls (B1), neither was plasma oestradiol (E2); however, plasma FSH was detectable in a pulsatile pattern. In the older prepubertal girls (B1-onset) a discrete pulsatile LH pattern became detectable only during the night; plasma FSH tended to rise, while E2 became just detectable. In the early pubertal girls (B2) most daytime LH values were above the detection limit, in some with low-amplitude pulses. At night, pulses with a wide range of pulse amplitudes were detected. Plasma FSH increased further, plasma E2 only slightly. With the progression of puberty the plasma LH and FSH levels, Pno and pA increased significantly from stage B2 to B3 during the day (P less than or equal to 0.05) and close to significance during the night (0.05 less than or equal to P less than or equal to 0.1). However, in stage B4 the secretory characteristics tended to decline, while from stage B3 onwards plasma E2 started to rise rapidly (P less than or equal to 0.05, during the night from stage B2 to B3, during the day from B3 to B4m-). Simultaneous LH and FSH pulses were observed throughout puberty, usually during the night. Using these IRMA methods nocturnal LH in older prepubertal girls and both diurnal and nocturnal FSH pulsatility could be demonstrated in young prepubertal girls. From this study we conclude that (1) puberty in girls, as in boys, may be brought about by an increasing GnRH secretion both in frequency and amplitude, first appearing during the night. This increased GnRH stimulation results in LH secretion only during the night; (2) a cyclical pulsatile LH pattern including an LH surge can be established before the menarche; the capacity for positive feedback activity is not the final maturation characteristic to achieve an ovulatory menstrual cycle.     

Diagnostic value of fluorometric assays in the evaluation of precocious puberty.

To establish normative data and determine the value of fluorometric AutoDELFIA assays (Wallac Oy) in the investigation of precocious puberty, we determined serum levels of LH, FSH, testosterone, and estradiol under basal and GnRH-stimulated conditions in 277 normal subjects at various pubertal stages and in 77 patients with precocious puberty. A substantial overlap was observed in basal and GnRH-stimulated gonadotropin levels in normal individuals of both sexes with pubertal Tanner stages 1 and 2. The 95th percentile of the normal prepubertal population was the cut-off limit between prepubertal and pubertal levels. These limits were 0.6 IU/L in both sexes for basal LH, 9.6 IU/L in boys and 6.9 IU/L in girls for peak LH after GnRH stimulation, 19 ng/dL in boys for basal testosterone, and 13.6 pg/mL in girls for basal estradiol. Basal and peak LH exceeding these limits were considered positive tests for the diagnosis of gonadotropin-dependent precocious puberty. According to these criteria, the sensitivities of basal and peak LH for the latter diagnosis were 71.4% and 100% in boys, and 62.7% and 92.2% in girls. The specificity and positive predicted value were 100% in both sexes for basal and peak LH levels. The negative predicted values for basal and peak LH were 62.5% and 100% in boys, and 40.6% and 76.5% in girls. Basal and GnRH-stimulated FSH levels overlapped among the various pubertal stages in normal subjects and were, in general, not helpful in the differential diagnosis of precocious puberty. In conclusion, basal LH levels were sufficient to establish the diagnosis of gonadotropin-dependent precocious puberty in 71.4% of boys and 62.7% of girls. In the remaining patients, a GnRH stimulation test was still necessary to confirm this diagnosis. Finally, suppressed LH and FSH levels after GnRH stimulation indicate gonadotropin-independent sexual steroid production.     

Hypogonadotropic hypogonadism: hormonal responses to low dose pulsatile administration of gonadotropin-releasing hormone

Patients with isolated gonadotropin deficiency were studied to determine whether pulsatile low dose gonadotropin-releasing hormone (GnRH) could induce the hormonal changes seen during normal puberty. Four male and two female patients with immature responses to a standard GnRH test (2.5 micrograms/kg) were given GnRH (0.025 micrograms/kg) iv every 2 h for 5 days. FSH responses varied between the sexes, and FSH concentrations in males rose continuously to 17.2 +/- 4.7 mIU/ml on day 5. In the females, FSH peaked at 13.8 and 15.8 mIU/ml on days 3-4 and then declined. The males showed increasing and the females decreasing incremental FSH responses to GnRH. LH concentrations and incremental responses to GnRH rose throughout the study in both sexes. Plasma testosterone rose slightly in the males to 0.7 +/- 0.2 ng/ml (P < 0.05), but in females estradiol increased to follicular range concentrations of 128 and 102 pg/ml. Standard GnRh tests on day 6 revealed maturation of gonadotropin responses in all patients. After termination of pulsatile GnRH, four patients were given single low dose GnRH injections on two to seven occasions over a period of 2-32 days. Initial LH responses were 2- to 14-fold greater than those seen on day 5 of pulsatile GnRH, and decreased over the next 3 weeks. FSH responses showed less initial augmentation and declined more slowly. Low dose pulsatile administration of GnRH to patients with isolated gonadotropin deficiency results in changing patterns of hormone secretion similar to those seen during puberty. Exaggerated pituitary sensitivity to GnRH may be present long after a brief period of GnRH stimulation, and may indicate previous rather than current secretion of GnRH.     

Serum leptin levels in males with delayed puberty during short-term pulsatile GnRH administration

Leptin may be a possible trigger for puberty. In normal males, it has been shown that leptin increases from the pre-pubertal to the early pubertal stage, and then declines in the late pubertal stage. We examined leptin levels in six male adolescents (mean age 16.3+/-0.6 yr; range 14.2-17.6 yr) with delayed puberty (constitutional delay of puberty no.=2; idiopathic hypogonadotropic hypogonadism no.=4) during 120 days of subcutaneous pulsatile GnRH administration. A group of subjects in pre-puberty (no.=11), early-puberty (n=10) and mid-puberty (no.=7) were evaluated as controls. Morning blood samples were taken for determination of leptin, testosterone, LH and FSH levels. In delayed puberty subjects blood samples were taken every 30 days after the start of GnRH administration. At each examination BMI and testicular volume were evaluated. A follow-up examination was performed in the 6 patients 1.3-7.5 yr after the end of the 120 days of GnRH therapy. At baseline evaluation in delayed puberty mean leptin levels were 11.3+/-2.0 microg/l (median 11.3 microg/l; range 4.7-17.3 microg/l) and were higher than those found in pre-puberty (p=0.04) and mid-puberty (p=0.001). During GnRH administration there was no change in BMI and leptin levels but there was an increase in gonadotrophin levels, testosterone and testicular volume. One hundred and twenty days after, mean serum leptin were 10.1+/-2.1 microg/l (median 9.1 microg/l; range 3.4-16.8 microg/l). At the end of the study, leptin levels were higher in delayed puberty than in mid-puberty (p=0.002). At the follow-up examination leptin levels were 4.3+/-1.3 microg/l (median 3.4 microg/l; range 1.4-9.1 microg/l) (p=0.03 vs end of 120 days GnRH therapy) while testosterone and BMI were not changed. In conclusion 120-day pulsatile GnRH administration induced in males with delayed puberty physiological-like pubertal changes but not the decline in leptin levels reported during the progression of puberty. Therefore, in males with delayed puberty an impairment in the phenomenon of leptin decline associated with progression of puberty could be suggested. However after retrospective diagnosis of pubertal delay and long-term therapy in subjects with idiopathic hypogonadotropic hypogonadism leptin levels declined. These data seem to indicate that time more than increase in testosterone levels and testicular volume is the determinant of leptin decline at puberty.     

X-linked adrenal hypoplasia congenita: a mutation in DAX1 expands the phenotypic spectrum in males and females

X-linked adrenal hypoplasia congenita (AHC) is a disorder associated with primary adrenal insufficiency and hypogonadotropic hypogonadism (HH). The gene responsible for X-linked AHC, DAX1, encodes a member of the nuclear hormone receptor superfamily. We studied an extended kindred with AHC and HH in which two males (the proband and his nephew) were affected with a nucleotide deletion (501delA). The proband's mother, sister, and niece were heterozygous for this frameshift mutation. At age 27 yr, after 7 yr of low dose hCG therapy, the proband underwent a testicular biopsy revealing rare spermatogonia and Leydig cell hyperplasia. Despite steadily progressive doses of hCG and Pergonal administered over a 3-yr period, the proband remained azoospermic. The proband's mother, sister (obligate carrier), and niece all had a history of delayed puberty, with menarche occurring at ages 17-18 yr. Baseline patterns of pulsatile gonadotropin secretion and gonadotropin responsiveness to exogenous pulsatile GnRH were examined in the affected males. LH, FSH, and free alpha-subunit were determined during 12.5-24 h of frequent blood sampling (every 10 min). Both patients then received pulsatile GnRH (25 ng/kg) sc every 2 h for 6-7 days. Gonadotropin responses to a single GnRH pulse iv were monitored daily to assess the pituitary responsiveness to exogenous GnRH. In the proband, FSH and LH levels demonstrated a subtle, but significant, response to GnRH over the week of pulsatile GnRH therapy. Free alpha-subunit levels demonstrated an erratic pattern of secretion at baseline and no significant response to pulsatile GnRH. We conclude that 1) affected males with AHC/HH may have an intrinsic defect in spermatogenesis that is not responsive to gonadotropin therapy; 2) female carriers of DAX1 mutations may express the phenotype of delayed puberty; and 3) although affected individuals display minimal responses to pulsatile GnRH, as observed in other AHC kindreds, subtle differences in gonadotropin patterns may nevertheless exist between affected individuals within a kindred.     

Influence of blindness on plasma luteinizing hormone, follicle-stimulating hormone, prolactin, and testosterone levels in prepubertal boys

The aim of this study was to determine if changes in LH, FSH, PRL, and testosterone (T) secretion occur in blind prepubertal boys. Eight blind and six normal boys, aged 7-10 yr, living at an institute for blind subjects in Naples, Italy, were studied. Each had a combined GnRH (100 micrograms) and TRH (200 micrograms) test at 0800 h after nocturnal rest. Plasma LH, FSH, PRL, and T levels were measured by RIA. The blind boys had basal plasma LH, FSH, and T levels significantly lower than those in the normal boys (P less than 0.01 for all three); plasma PRL basal levels were similar to those in the normal boys. The blind boys, moreover, had lower peak LH, FSH, and PRL (P less than 0.01 for all three peaks) levels in response to GnRH-TRH. Our results, similar to those found by others in patients with delayed puberty or with hypogonadotropic hypogonadism, suggest that light stimuli influence neuroendocrine-gonadal activity in humans, as in other mammals; and in blind prepubertal boys, impaired hormone secretion could cause a delay of pubertal development or more severe hypogonadism.     

LUTEINIZING HORMONE AND FOLLICLE STIMULATING HORMONE SECRETION PATTERNS IN BOYS THROUGHOUT PUBERTY MEASURED USING HIGHLY SENSITIVE IMMUNORADIOMETRIC ASSAYS

Pulsatile gonadotrophin secretion patterns were studied in 32 normal boys (chronological age, CA 7.2-14.6 years) at different stages of pubertal development (5 in stage G1, 11 in G2, 5 in G3, 4 in G4, 7 in G5). Plasma LH and FSH concentrations were measured at 10 min intervals from 1200 to 1800 h and from 2400 to 0600 h using an immunoradiometric assay with a lower limit of detection of 0.15 IU/l for both LH and FSH. Plasma testosterone (T) was measured hourly. In the young prepubertal boys plasma LH was not detectable during day or night. In contrast, plasma FSH ranged from 0.7 to 1.4 IU/l. Plasma T was not detectable either (less than 0.25 nmol/l). In the older prepubertal boys a discrete pulsatile LH pattern (2 per 6 h) became discernible only during the night (range 0.1-0.4 IU/l). Plasma FSH also revealed a pulsatile pattern only during the night (2 per 6 h), while plasma T still remained undetectable. In the early pubertal boys (G2) a median daytime LH value of 0.37 IU/l was determined with 1 pulse per 6 h and at night definite LH pulses (4 per 6 h) were found in all boys (range 0.4-4.7 IU/l). Plasma FSH increased considerably to a median level of 2.50 IU/l during the day; most boys had a pulsatile FSH pattern (one per 6 h). Plasma T became detectable during the day (median 0.54 nmol/l) and night (median 1.16 nmol/l). With the progression of puberty the mean plasma level of LH and FSH, the LH/FSH pulse number and the LH/FSH pulse amplitude increased; plasma T rose as well, more obviously during the night. In G5, however, the LH pulse number decreased, while the LH level and pulse amplitude still increased, presumably as a result of the increased negative feedback action of sex steroids. Simultaneous LH/FSH pulses developed during the night at onset of puberty but during the day only towards the end of pubertal development. The use of these novel highly sensitive IRMA methods demonstrated nocturnal LH and both diurnal and nocturnal FSH pulsatility to be present in older prepubertal boys. The early detectable FSH level plus the existence of solitary FSH pulses throughout puberty as well as in adult men support the hypothesis of the existence of a GnRH-independent FSH secretion in men. Our results are in accordance with the following hypotheses: (1) puberty is brought about by GnRH secretion increasing with time, both in frequency and amplitude, and first appearing during the night.(ABSTRACT TRUNCATED AT 250 WORDS)     

The effect of distinct activating mutations of the luteinizing hormone receptor gene on the pituitary-gonadal axis in both sexes

OBJECTIVE: Familial or sporadic male-limited precocious puberty is a distinct and unusual gonadotrophin-independent form of sexual precocity caused by constitutively activating mutations of the luteinizing hormone receptor (LHR). In the present study, we evaluated the effect of known activating mutations at different sites of the LHR gene on the pituitary-gonadal axis in both sexes. PATIENTS: Four unrelated Brazilian boys (I-IV) with gonadotrophin-independent precocious puberty and two asymptomatic females (V-VI), a sister and mother of two of the affected boys, were studied. Patients I, II and V carried the Ala568Val mutation located at the third intracellular loop of the LHR. Patient III carried the Leu457Arg mutation at the third transmembrane helix, and patients IV and VI carried the Thr577Ile mutation at the sixth transmembrane helix of the LHR. MEASUREMENTS: Serum levels of LH, FSH, testosterone, and oestradiol under basal and GnRH-stimulated conditions were determined in all patients. Testosterone levels were also measured after a hCG stimulation test in patient III. RESULTS: Basal LH and FSH levels were prepubertal in all boys studied. The GnRH-stimulated serum LH and FSH levels were prepubertal in three boys (I, II and IV), whereas patient III showed totally suppressed LH and FSH levels at ages 2 and 7 years (bone ages 6 and 14 years, respectively). Serum testosterone levels ranged from 3.8 to 69.5 nmol/l in the four boys. Patient III had the highest testosterone levels that did not respond to hCG stimulation. The 4 year-old girl (patient V) was phenotypically normal and the acute response to GnRH was indicative of prepubertal status. Patient VI had normal menstrual cycles and fertility. CONCLUSIONS: These findings indicate variable effects of LHR activating mutations on the pituitary-gonadal axis in boys that can result in lack of normal LH and FSH release. In contrast, prepubertal and adult females were asymptomatic and had normal basal and GnRH-stimulated LH and FSH levels.     

Idiopathic hypogonadotropic hypogonadism in men: dependence of the hormone responses to gonadotropin-releasing hormone (GnRH) on the magnitude of the endogenous GnRH secretory defect

Idiopathic isolated gonadotropin deficiency (IGD) is associated with a spectrum of clinical findings as well as variable gonadotropin responses to GnRH. In this study we investigated whether patterns of gonadotropin and testosterone responses to pulsatile GnRH therapy (25 ng/kg, iv, every 2 h for 4 days) were related to the magnitude of the GnRH secretory defect in patients with IGD. Eight men with IGD were studied. Patients with partial IGD (p-IGD) and those who had no evidence of GnRH secretion (n-IGD) were differentiated by the presence or absence of spontaneous LH secretory pulses during 24 h of every 20-min blood sampling. In response to the first GnRH injection, no LH rise occurred in the n-IGD patients, while LH increases in the p-IGD patients were similar to those in normal men. Continuation of GnRH therapy in patients with n-IGD resulted in predominant FSH secretion and absent or minimal augmentation of LH and T secretion. In contrast, predominant LH secretion occurred in the p-IGD patients and resulted in a significant increase in serum testosterone. A bolus dose of GnRH 2 days after the termination of GnRH therapy caused significant augmentation of gonadotropin responses in the n-IGD, while in the p-IGD group, both LH and FSH responses were unchanged compared to those after the first GnRH pulse. These results indicate that IGD is characterized by variable degrees of endogenous GnRH deficiency. Moreover, the hormone responses to GnRH in IGD patients depend on the magnitude of the underlying GnRH secretory defect.     

Resistance of hypogonadic patients with mutated GnRH receptor genes to pulsatile GnRH administration

We have studied a kindred with three siblings with isolated hypogonadotropic hypogonadism caused by compound heterozygote mutations in the GnRH receptor gene. The disorder was transmitted as an autosomal recessive trait. The R262Q mutation in intracellular loop 3 of the receptor was associated with a mutation in the third transmembrane domain of the receptor, A129D, that has never been described before. This A129D mutation results in a complete loss of function, indicated by the lack of inositol triphosphate (TP3) 3 production by transfected Chinese hamster ovary (CHO) cells after GnRH stimulation. The two brothers had microphallus and bilateral cryptorchidism and were referred for lack of puberty, whereas their sister had primary amenorrhea and a complete lack of puberty. Their basal gonadotropin concentrations were below the reference range, and their endogenous LH secretory patterns were abnormal, with a low-normal frequency of small pulses or no apparent LH pulse. Pulsatile GnRH administration (10 microg/pulse every 90 min for 40 h) resulted in increased mean LH without any significant changes in testosterone levels in the two brothers, whereas the LH secretory profile of their sister remained apulsatile. Larger pulses of exogenous GnRH (20 microg every 90 min for 24 h) caused the sister to produce recognizable low amplitude LH pulses. The concentrations of free alpha-subunit significantly increased in all patients during the pulsatile GnRH administration. Thus, these hypogonadal patients are partially resistant to pulsatile GnRH administration, suggesting that they should be treated with gonadotropins to induce spermatogenesis or ovulation rather than with pulsatile GnRH.     

The ontogeny of pulsatile growth hormone secretion and its temporal relationship to the onset of puberty in the agonadal male rhesus monkey (Macaca mulatta)

The pubertal amplification of GH secretion in primates has been thought to reflect an increase in gonadal steroid hormones due to gonadotropin stimulation induced by hypothalamic GnRH release. Previous studies in agonadal, peripubertal, male rhesus monkeys have estimated the age of GnRH activation (defined as d 0) using analyses of nocturnal, pulsatile LH patterns derived from sequential blood samples. Using samples from these earlier studies, secretory patterns of GH were analyzed using Cluster at approximately 30-d intervals in the youngest prepubertal ages and at approximately 10- to 20-d intervals in the period immediately preceding and following the onset of puberty. Pulse frequency, amplitude, and mean GH increased significantly between early prepubertal ages (up to 30 d before d 0) and the late prepubertal period (between -20 d and d 0). Pulsatile GH activity increased earlier than pulsatile LH secretion in four of five animals. These findings support the conclusion that pulsatile GH secretion increases developmentally in the absence of gonadal steroids. Furthermore, the present observation that the developmental increase in GH secretion occurs earlier than previously reported is consistent with the possibility that GH itself either directly or indirectly participates in the pubertal reinitiation of GnRH pulse generator activity.     

Naloxone-induced luteinizing hormone secretion in normal, precocious, and delayed puberty

The aim of the present study was to evaluate the activity of opiate receptors involved in the control of LH secretion during pubertal development, as determined by the LH response to naloxone. Normal children (n = 28) of both sexes, subdivided according to breast (girls) or testicular (boys) development, and patients with idiopathic precocious puberty (n = 7), delayed puberty (n = 8), or hypergonadotropic hypogonadism (n = 4) were studied. Plasma LH levels were measured after the administration of naloxone (NLX; 0.08 mg/kg BW, iv), GnRH (50 micrograms, iv) or placebo. In healthy subjects, NLX significantly increased plasma LH levels only in girls and boys at the most advanced stage of gonadal maturation. NLX was ineffective in prepubertal and early pubertal children, and it did not significantly alter LH levels in children with delayed puberty or hypogonadism or in most of the children with precocious puberty. GnRH injection consistently increased plasma LH levels in healthy subjects as well as in the children with pubertal disturbances. These results indicate that the LH response to NLX occurs only at the most advanced stages of pubertal maturation when normal or precocious and is absent in early puberty or in children with pubertal disturbances. Furthermore, the results suggest that opioid regulation of LH secretion in humans changes during puberty, reaching an adult-like functional state with maturation of the hypothalamus-pituitary-gonadal axis.     

STEROIDOGENIC RESPONSE TO A SINGLE INJECTION OF hCG IN PRE- AND EARLY PUBERTAL CRYPTORCHID BOYS

The temporal response patterns of the concentrations of serum testosterone, oestradiol, 17-hydroxyprogesterone, pregnenolone, progesterone, androstenedione and 5 alpha-dihydrotestosterone to a single i.m. dose of hCG (5000 IU/1.7 m2) were investigated in prepubertal and early pubertal cryptorchid boys, and compared with the response patterns obtained earlier in adult men. The rapid response (at approximately 2-4 h) of serum testosterone was lacking in all boys, whereas the slow response at 2-5 days was constant. The relative response (the maximum stimulated concentration vs. the basal level) of serum testosterone was 70-fold in prepubertal boys and 6-fold at early puberty, compared with 2.4-fold in adult men. Serum oestradiol and 17-hydroxyprogesterone concentrations did not increase in the prepubertal boys, but did increase at early puberty, revealing a pattern similar to that observed in adult men. Hence, the prepubertal endocrine testis appears to be very responsive to hCG stimulation, and this responsiveness is rapidly lost with advancing puberty. The absolute increases, however, were smallest in prepubertal boys, perhaps reflecting the small potential Leydig cell mass. The responses of serum oestradiol and 17-hydroxyprogesterone to hCG appeared later during the boys' development than the response of serum testosterone. The relative testosterone response was maximal in the absence of an oestradiol response. It is suggested that testicular oestradiol production in response to LH/hCG appears in the course of puberty and results in intratesticular short-loop feed-back inhibition of androgen production. This is reflected by the appearance of a 17-hydroxyprogesterone response and by a decrease in relative testosterone response.     

Increase of serum leptin after short-term pulsatile GnRH administration in children with delayed puberty

OBJECTIVE: Leptin is known to play an important role in pubertal development in humans, probably acting as one permissive factor for the onset of puberty. Leptin serum concentrations change during pubertal development and an initial increase before the onset of puberty has been reported. The underlying mechanism for this increase in leptin levels is unknown. We hypothesized that the pulsatile release of GnRH stimulates leptin metabolism. In this study, the effect of short-term pulsatile GnRH administration on leptin levels in children with delayed onset of puberty was investigated. METHODS: Nineteen children (15 males and four females, mean age 15.5 years, range 13.1-20.5 years), who underwent evaluation for delayed sexual maturation, were included in the study. Sixteen subjects received 36 h of pulsatile intravenous GnRH, using an infusion pump that released 5 microg GnRH every 90 min. Serum concentrations of LH, FSH, testosterone, estradiol and leptin were analysed before and up to 36 h after GnRH administration. Eight patients received a single dose GnRH-agonist stimulation test (buserelin acetate test, 10 microg/kg body weight) with a 24-h follow-up (five patients underwent both tests). RESULTS: Mean (+/-s.e.m.) serum leptin increased significantly (P<0.01) after 36 h of pulsatile GnRH administration (7.26+/-1.35 vs 9.75+/-1.76 ng/ml). In contrast, no increase in leptin concentrations was observed after administration of a single dose of buserelin. CONCLUSIONS: These findings suggested that the increase in serum leptin at the onset of puberty is triggered by the pulsatile release of GnRH.     

A new test of combined pituitary-testicular function using the gonadotropin-releasing hormone agonist nafarelin in the differentiation of gonadotropin deficiency from delayed puberty: pilot studies

There is evidence that the capacity to synthesize gonadotropins is less in teenage boys with gonadotropin deficiency (GD) than in those with constitutional delay of puberty (DP). We hypothesized that this might predispose the latter group to have a greater pituitary-testicular response to the potent long-acting GnRH agonist nafarelin. We evaluated GD patients 14.3-24.0 yr of age (n = 8) and prepubertal DP boys 14.8-17.6 yr of age (n = 3). In most subjects the response to nafarelin was compared to that of frequent nocturnal blood sampling for LH and testosterone levels. All subjects received a single dose of nafarelin (1.0 micrograms/kg, sc), and blood was then sampled at 0.5- to 4.0-h intervals for 24 h. Patients with GD could not be distinguished from those with DP by pubertal staging criteria or by baseline values of LH, FSH, or testosterone. Patients with GD exhibited no rise in plasma LH levels during sleep, in contrast to those with DP. All GD patients had LH and FSH responses distinctly less than those of the DP group between 3-24 h postnafarelin. The peak incremental responses of GD and DP to nafarelin were, respectively: LH, 5.5 +/- 2 3 (+/- SEM and 77.2 +/- 8.6 IU/L (P less than 0.02); FSH, 2.7 +/- 1.2 and 9.4 +/- 0.8 IU/L (P less than 0.005). Testosterone peak responses were lower as well (0.26 +/- 0.2 vs 1.6 +/- 0.5 nmol/L, P = 0.05). This pilot study suggests that the response to a single test dose of nafarelin distinguishes GD from DP in the teenage years as well as does measurement of nocturnal LH levels. The testosterone response to the GnRH agonist adds a new dimension to GnRH testing. Nafarelin also allows assessment of the bioactivity of endogenous gonadotropin, is a more potent stimulus of pituitary-testicular function than endogenous GnRH secretion, and is more cost-effective than nocturnal sampling.     

Bioactive follicle-stimulating hormone responses to intravenous gonadotropin-releasing hormone in boys with idiopathic hypogonadotropic hypogonadism

To test the hypothesis that exogenous pulsatile administration of GnRH will increase serum bioactive FSH (bFSH) levels, we studied four boys with suspected idiopathic hypogonadotropic hypogonadism (IHH). These boys presumably secreted relatively little GnRH. By virtue of their low baseline serum gonadotropin levels yet responsive pituitary gonadotrophs, these boys with IHH proved to be an excellent clinical model to test this hypothesis. Administration of GnRH (0.025 microgram/kg.dose) iv at 1- or 2-h intervals for 3-5 days resulted in an increase in serum bFSH after 91% of the GnRH doses. Serum immunoreactive FSH (iFSH) and LH (iLH) levels increased after 42% and 64% of the GnRH doses, respectively. Ninety percent of the iLH responses were concordant with bFSH responses, but only 33% of the iLH responses were concordant with iFSH responses. The serum bFSH responses occurred consistently within 20 min after GnRH administration and resulted in an increased serum bioactive to immunoreactive FSH ratio. By 60 min, serum bFSH levels had returned to preinjection levels. Serum testosterone and estradiol levels did not change during the period of GnRH administration in three of the four boys. We conclude that pulsatile, low dose iv GnRH administration in boys with IHH elicits significant serum bFSH increases by 20 min; the newly secreted FSH is preferentially enriched with increased in vitro FSH bioactivity, and it is rapidly cleared from serum (60 min). Therefore, serum bFSH measurements may provide a sensitive index of GnRH effects on the gonadotrophs.