A longitudinal assessment of hormonal and physical alterations during normal puberty in boys. II. Estrogen levels as determined by an ultrasensitive bioassay

A limited number of reports of estrogen levels in prepubertal and early pubertal boys have been published because previous estrogen assays have lacked adequate sensitivity to quantitate circulating estrogen concentrations. Development of a new ultrasensitive assay has permitted measurement of estrogen levels in 23 normally growing boys progressing through puberty. Concentrations were measured at approximately 4-month intervals over a 5- to 8-yr period. The levels increased with maturation in all and correlated directly with chronological age, bone age, weight, height, pubertal stage, and testosterone and insulin-like growth factor-I levels. Of these factors, the level of testosterone had the greatest influence on the estrogen concentration. The time from peak growth velocity also significantly correlated with estrogen level. The estrogen level correlated positively with growth velocity before the time of peak growth velocity and negatively after peak growth velocity. The estrogen levels first increased significantly an average of 3 yr after pubertal onset and reached a peak by 5 yr after pubertal onset. Peak growth velocity was attained an average of 3 yr after pubertal onset. The greatest increase in the rate of rise of the estrogen level was an 11-fold rise during the year in which puberty began. The next most significant increase was a 4.8-fold rise 3 yr after pubertal onset. With respect to pubertal stage, the greatest absolute change occurred from stage 4 to stage 5 and the greatest fold change occurred from stage 1 to stage 2. The estrogen level did not significantly correlate with the 24-h GH level. In conclusion, circulating estrogen levels are very low in all boys prepubertally and rise steadily during adolescent development. The estrogen level is closely related to testosterone concentration and to the time of peak growth velocity. These findings are consistent with the hypothesis that estrogen at low levels augments skeletal growth and maturation in boys (as well as girls). They are also consistent with the hypothesis that continued exposure to estrogen leads to epiphyseal fusion. Further studies are required to define the separate and combined roles of estrogen, GH, and testosterone, as well as other factors, on growth and sexual development at puberty.

Growth hormones and sex steroid interactions at puberty

Puberty is a period of dynamic changes mediated by GH and the gonadal steroid hormones. Although these substances exert important independent effects, their interaction is vital to normal pubertal growth and development. This is supported by observations of blunted growth and diminished levels of GH and IGF-1 during adolescence in individuals with panhypopituitarism in whom adequate replacement with both hormones had not been achieved. The independent roles of androgens and estrogens in mediating the rise in GH secretion at puberty have been studied in individuals with complete androgen insensitivity and through the administration of nonaromatizable androgens and the use of selective androgen- or estrogen-receptor blockade. The preponderance of evidence from studies of nonaromatizable (pure) androgens suggests that GH secretion is not enhanced as it is under the influence of testosterone. In addition, studies have shown increased GH secretion following androgen-receptor blockade and diminished GH release after estrogen-receptor blockade. Together these studies suggest a facilitory role of estrogen receptor-mediated processes on GH secretion and IGF-1 production. If androgens influence the GH/IGF-1 axis, it is most likely by an inhibitory mechanism. Observations of delayed skeletal maturation and deficient bone mineralization in individuals with estrogen receptor defects or mutations of the aromatase gene demonstrate the essential role of estrogen in promoting normal bone maturation, the accrual and maintenance of BMD, and control of the rate of bone turnover.

Apparent growth hormone deficiency in children with cerebral palsy

Ten children with cerebral palsy (CP) and growth failure underwent assessment of the growth hormone (GH) axis, including spontaneous GH secretion, GH secretion in response to pharmacological stimulation, and circulating levels of insulin-like growth factor-1 (IGF-1) and IGF binding protein-3 (IGFBP-3). Six of the children had subnormal GH secretion consistent with GH deficiency. Subnormal growth velocity was the best clinical predictor of GH deficiency. The large percentage of these children with apparent GH deficiency is surprising. Possible mechanisms include anatomic abnormalities of the hypothalamic-pituitary axis, psychosocial deprivation, and an interaction between suboptimal nutritional status and an abnormal central nervous system.

Mode of pulsatile follicle-stimulating hormone secretion in gonadal hormone-sufficient and -deficient women--a clinical research center study

To test the hypothesis that FSH is secreted at least in part within discrete secretory bursts in women and that the characteristics of episodic FSH secretion are altered within differing gonadal hormone environments, we measured FSH by immunoradiometric assay every 10 min for 24 h in premenopausal women during the early follicular (EF), late follicular (LF), and midluteal (ML) phases of the menstrual cycle and in postmenopausal (PM) women (n = 8 in each group). Secretory events were evaluated using multiparameter deconvolution. FSH was secreted in an episodic manner, with the number of secretory bursts (per 24 h; mean +/- SEM) detected in LF (20 +/- 0.79) and PM (20 +/- 0.90) women being greater than that in EF (16 +/- 0.88) and ML (14 +/- 0.93) women. FSH secretory burst mass (milliinternational units per mL) was significantly higher in PM (12 +/- 1.6) than in EF (1.8 +/- 0.21), LF (3.1 +/- 1.3), or ML (0.8 +/- 0.11) women and primarily reflected a relative increase in the maximal secretory rate rather than increased burst half-duration. The estimated half-life (minutes) of endogenous FSH in LF women (155 +/- 18) was shorter than those calculated in EF (251 +/- 24), ML (277 +/- 38), and PM (231 +/- 18) women. Cross-correlation analysis showed strongly positive associations between successively paired serum FSH and LH concentrations in all four groups of women. Deconvolution of simultaneously obtained LH concentration-time series revealed statistically significant concordance (13-25%) between FSH and LH secretory episodes at a lag time of 0 min in EF, LF, and PM women and when LH secretory bursts led FSH secretory bursts by 10 min in ML phase women. However, as 75-87% of FSH and LH secretory pulses were discordant, we infer the operation of distinct control mechanisms in the generation of FSH and LH release episodes. In summary, these results suggest that FSH is secreted within discrete secretory bursts in women, that the mass and frequency of FSH secretory bursts differ in women exhibiting various gonadal hormone environments, and that FSH and LH secretory bursts occur coincidentally at a higher rate than expected on the basis of chance alone, but at such a low overall rate of concordance that distinct mechanisms probably operate to direct episodic FSH and LH secretory activity.

National Cooperative Growth Study substudy. II: Do growth hormone levels from serial sampling add important diagnostic information?

The National Cooperative Growth Study includes growth data on more the 24,000 children in the United States and Canada who have been treated with growth hormone (GH). To determine whether dysregulation of GH release causes growth failure in children, we initiated the National Cooperative Growth Study substudy II to evaluate the diagnostic utility of serially sampled GH levels and to determine whether those patterns were responsible for the low growth rates in certain subsets of short children and whether children in any of the diagnostic categories would respond to GH therapy. A total of 3744 subjects whose mean height standardized for their chronological age was -2.8 SD and whose pretreatment growth rate was 4.2 cm/yr had complete 12-hour data sets-- serial samples obtained in a 12-hour overnight period. Pulsatile characteristics of GH release were assessed with the cluster algorithm. There was a virtually complete overlap of the GH pulsatile characteristics between control subjects and short children, but the insulin-like growth factor I (IGF-I) levels were markedly lower in the short children, suggesting impairment in the GH-IGF-I axis. THe growth response to administered GH showed only very weak correlations with the various cluster-derived parameters. Our results indicate that one must look beyond the release of GH to find an explanation for the short statures and low IGF-I levels in the subsets of children with idiopathic short stature.

Apparent self-limited androgen excess in a 4 year-old male

We describe a 4 year-old male with significant virilization, but no source of endogenous or exogenous androgen excess after extensive testing. Evaluation of androgen receptor function, 5 alpha-reductase activity, steroid hormone secretion patterns, and androgen metabolite concentrations were also within the normal range. Over a 10 month period there was spontaneous resolution of the physical and behavioral signs of androgenization. We postulate a self-limited process of androgen production which may represent a yet undefined pattern of sexual precocity in males.

Sex steroids, growth hormone, insulin-like growth factor-1: neuroendocrine and metabolic regulation in puberty

The control of the onset of puberty involves the complex interaction of pituitary and gonadal hormones. At a preprogrammed time in a child's life there is an increase in the amplitude of GnRH pulses which triggers a cascade of events including increases in the amplitude of FSH and LH pulses, followed by marked increases in gonadal sex steroidal output, which in turn increases growth hormone (GH) and insulin-like growth factor-1 (IGF-1) production. Evidence suggests that there is an integral interaction between the endogenous opiate system and the hypothalamic-pituitary-gonadal axis, at least in the later stages of puberty in the male. Both androgenic and estrogenic hormones markedly increase GH production rates as measured by deconvolution models in the prepubertal human, and compelling data strongly suggest that it is indeed the estrogen which controls the feedback amplification of GH production during puberty even in the male. It appears that the prepubertal gonad is actively producing sex hormones which might be important in the control of GH production since early childhood. The translation of these neuroendocrine rhythms into distal metabolic actions is also reviewed. Utilizing isotopic tracer infusions of the essential amino acid leucine, studies clearly show a selective stimulation of whole body protein synthesis by both GH and IGF-1. GH, IGF-1 and androgenic hormones all increase in puberty, stimulating whole body protein anabolism during that period. However, we observed no protein-anabolic effect in the hypogonadal female given increasing doses of estrogen. The latter suggests that at least as it pertains to whole body protein effects, the action of androgens is probably mediated via the androgen and not the estrogen receptor, in clear distinction from the estrogen-mediated effects of androgens on the neuroendocrine axis. Calcium absorption and retention are also positively affected by the androgens as shown by significant increases in calcium absorption and retention after the administration of testosterone to the prepubertal male. This suggests an important role of sex steroidal hormones in the mineralization of the skeleton.

IN CONCLUSION

GH, IGF-1 and sex steroids all markedly increase during puberty and their actions are amplified mutually as they control growth, increase muscle mass and affect the mineralization of the skeleton. The dichotomy of androgen and estrogen effects in the male and female may regulate the differential timing of the onset of puberty and final height in the two sexes. The synergistic actions of these anabolic hormones appear to be most significant during the finite years of puberty.

Physiology of growth and development. Its relationship to performance in the young athlete

Proper grouping of children for sports is important for injury prevention and for fair competition. We have reviewed several of the classification systems presently used as well as the physiologic underpinnings of pubertal growth and development and the accrual of strength and power. It is during adolescence that the greatest physiologic differences exist mainly because of the wide variations in the timing and tempo of the pubertal growth spurt in normally growing boys and girls. Maturity-based categorization, especially in contact and collision sports, would heighten the competition and lessen rates of injury.

Absent pituitary gland in two brothers with an oral-facial-digital syndrome resembling OFDS II and VI: a new type of OFDS?

The oral-facial-digital syndromes (OFDS) comprise a group of heterogeneous genetic disorders. Considerable clinical overlap exists within the nine described types [Toriello, Clin Dysmorph 2:95-105, 1993], and with other entities such as Pallister-Hall (PH) syndrome and hydrolethalus syndrome, leading to difficulties in the classification of OFDS. We report on two brothers with findings overlapping OFDS II, VI, and Pallister-Hall syndrome who had congenital absence of the pituitary gland. This may represent a new type of OFDS or, alternatively, an example of phenotypic variability within the OFDS. It also emphasizes that agenesis of the pituitary gland can occur in a variety of syndromes with midline defects.

Dexamethasone therapy for isosexual precocious pseudopuberty caused by generalized glucocorticoid resistance

Generalized glucocorticoid resistance presents with clinical features secondary to excess production of mineralocorticoids and adrenal androgens. It is our hypothesis that these clinical and biochemical features will respond to glucocorticoid therapy. We tested this hypothesis in a boy with generalized glucocorticoid resistance and increased adrenal androgens. Dexamethasone was administered from age 7 6/12 yr until the onset of true puberty at 11 0/12 yr. Serum concentrations of cortisol and adrenal androgens decreased to the normal or near normal range. The accelerated precocity improved. Secondary sex characteristics did not progress; the difference between bone age and chronological age decreased from 3 1/2 yr to 2 yr, and the difference between height age and bone age decreased from 2 yr to 1/2 yr. We conclude that dexamethasone is effective and safe therapy for the sexual precocity of generalized glucocorticoid resistance.

Gonadal steroid hormone regulation of the somatotropic axis during puberty in humans Mechanisms of androgen and estrogen action

The adolescent growth spurt is associated with a sex steroid hormone-dependent rise in GH production; both androgens and estrogens are implicated as positive regulators of the somatotropic axis during puberty. The issue is complicated by the fact that testosterone may act both directly via the androgen receptor and indirectly, after its aromatization to 17beta-estradiol, through the estrogen receptor. Recently, a number of investigators have studied the effects of the administration of androgen and estrogen receptor antagonists, as well as nonaromatizable androgens, on GH secretion. These reports suggest that estrogen receptor-dependent processes play a facilitatory role in the pubertyassociated rise in GH secretion. If androgen receptor-mediated events are involved in the control of the somatotropic axis, their role is likely inhibitory. A hypothalamic site of action of the sex steroids is postulated.

Growth at puberty: interaction of androgens and growth hormone

Puberty is characterized by the onset and continued development of secondary sexual characteristics and an abrupt onset of linear growth. Growth in boys occurs due to the rising levels of androgens and also indirectly mediated by growth hormone (GH) and the insulin-like growth factors. Data are presented to show marked androgen-dependence of GH increases at puberty. The mode of this increase is through an augmentation in the amplitude of the pulses rather than in their frequency. Shortly after the maximal rate of growth, the pattern of GH release reverts toward that of the prepubertal child. To investigate the neuroendocrine mechanism through which androgens increase the mean circulating GH level, deconvolutional analysis has been applied. At mid-puberty the maximal rate of GH release per secretory burst and the total amount released per burst were increased. There were no significant alterations in the duration or frequency of the GH secretory burst or in the serum half-life reflecting the metabolic clearance of the hormone. Thus, the pubertal growth spurt in boys is likely subserved by the altered neurosecretory dynamics for GH. These altered hormone levels likely produce the equally profound changes in body composition, regional fat distribution, and muscular strength that occur during puberty in boys.

Relationship between age, percentage body fat, fitness, and 24-hour growth hormone release in healthy young adults: effects of gender

We investigated whether gender affects the physiological relationships between the release of GH and age, body composition, and levels of physical fitness in humans. We studied 32 eumenorrheic females (age = 31 +/- 5 yr) and 12 males (age = 27 +/- 5 yr). Significant gender differences were found for peak oxygen consumption [VO2 peak = 40.5 +/- 6.9 (females) vs. 50.1 +/- 11.6 (males) ml/kg.min-1, P < 0.05] and body composition [hydrostatic weighing, percentage body fat = 28.7 +/- 5.4 (females) vs. 18.1 +/- 9.8 (males), P < 0.05] but not for body mass index [BMI = 23.7 +/- 3.1 (females) vs. 24.0 +/- 3.3 (males)]. Blood samples were drawn every 10 min for 24 h from 0800 h to determine integrated serum GH concentration [2350 +/- 1260 (females) vs. 3110 +/- 1760 (males) microgram/L x min]; females were studied during the early follicular phase (days 4-5) of the menstrual cycle. In females, a significant relationship existed between 24-h integrated serum GH concentration and age (r = -0.35, P = 0.05) but not BMI (r = -0.19, P = 0.29); the relationship between 24-h integrated serum GH concentration and VO2 peak (r = 0.31, P = 0.08) and percentage body fat (r = 0.29, P = 0.11) approached significance. In males, significant relationships existed between 24-h integrated serum GH concentration and age (r = -0.79, P = 0.002), percentage body fat (r = -0.75, P = 0.005), and VO2 peak (r = 0.58, P = 0.05) but not between 24-h integrated serum GH concentration and BMI (r = -0.53, P = 0.08). Standardized regression coefficients revealed that for each SD change in age, BMI, percentage body fat, or VO2 peak the associated change in 24-h integrated serum GH concentration was 1.9-2.6 times greater in males than in females. We conclude that age, percentage body fat (but not BMI), and fitness are related to 24-h GH release in young adults and that these relationships are considerably stronger in males than females.

An unusual presentation of McCune-Albright syndrome confirmed by an activating mutation of the Gs alpha-subunit from a bone lesion

The McCune-Albright syndrome (MAS) is characterized clinically by polyostotic fibrous dysplasia, café-au-lait skin lesions, sexual precocity, and various other endocrinopathies. Recent investigations suggest an etiological role for embryonic somatic missense mutations that predict the substitution of a His or Cys for Arg at amino acid 201 of the Gs alpha-subunit (Gs alpha). Identification of these mutations in affected tissues is a sensitive assay that may help define a more complete clinical spectrum of the MAS. We investigated a woman who developed fibrous dysplasia 24 yr after premature menstruation. To determine if this was an unusual MAS variant, DNA and RNA were analyzed from affected and unaffected tissues. From samples of affected rib and normal rib DNA was extracted, amplified by polymerase chain reaction, subcloned, and sequenced. RNA was extracted from affected bone, reverse transcribed, amplified by polymerase chain reaction, subcloned, and sequenced. DNA sequence predicting a His for Arg substitution at Gs alpha amino acid 201 was found in 47% of the recombinant plasmids from DNA of affected bone and 17% of the plasmids from DNA of unaffected bone; a significant (P < 0.05) difference in frequency. The His201 substitution was found in 42% of the recombinant plasmids from RNA of affected bone. We conclude that this clinical variant is qualitatively indistinguishable from presentations of the complete MAS.

Androgen-receptor blockade enhances pulsatile luteinizing hormone production in late pubertal males: evidence for a hypothalamic site of physiologic androgen feedback action

To determine potential mechanisms by which androgens alter gonadotropin secretion and elimination in the pubertal male, we administered the potent nonsteroidal androgen receptor blocking agent, flutamide, to eight males with Tanner IV or V genital development. Venous blood samples were obtained every 10 min for 24 h and assayed for LH by a sensitive and high-precision fluorimmunoassay. Subjects were studied before and after the administration of flutamide. Deconvolution analysis was used to assess specific pulsatile LH secretory characteristics and estimate LH production and metabolic clearance rates quantitatively. After antagonism of endogenous androgen action, mean 24-h serum LH concentrations increased significantly. An increased mean 24-h LH production rate, without evident changes in serum LH half-life, accounted for the increase in average serum LH levels. The increased daily secretion rate of LH was in turn due to both an augmented mass of LH released per secretory episode and increased frequency of secretory events. There was no demonstrable change in the maximal rate of LH secretion attained within each secretory event. Serum concentrations of total testosterone, free-testosterone, and 17 beta-estradiol all increased during blockade of androgen action. Administration of the antiandrogen had no measurable effect on the pituitary response to a single maximally effective dose of exogenous gonadotropin releasing hormone (GnRH). These results indicate that, in the late pubertal male, endogenous androgen exerts negative feedback control of gonadotropin secretion primarily at a hypothalamic site reflected by regulation of the frequency of pulsatile LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered growth hormone (GH) secretion in vivo and in vitro in the diabetes-prone BB/Worcester rat

Diminished concentrations of growth hormone (GH) have been observed in the male BB/Wor rat with diabetes mellitus (DM). The precise mechanism(s) responsible for the altered GH levels is not entirely understood. We have therefore employed independent techniques to investigate potential alterations in: 1) the peripheral metabolism of the hormone; 2) GH release by somatotropes; and 3) hypothalamic regulation of GH secretion. An extra group of insulin-untreated animals was included for the studies of acute DM. The results demonstrate diminished circulating mean concentrations of GH (35 +/- 4 vs. 16 +/- 4 micrograms/l; mean +/- SEM; control vs. animal with DM; P = 0.006) due to impaired GH secretion. In particular, there was a decrease in the mass of GH secreted per burst (230 +/- 22 vs. 136 +/- 34 micrograms/l; P = 0.04) and in the GH secretory rate (24 +/- 4 vs. 9 +/- 3 micrograms/l/min; P < 0.01). No differences in the secretory burst frequency, (5.3 +/- 0.3 vs. 5.2 +/- 0.5 #/8-h; P = 0.68), secretory half-duration (10 +/- 2 vs. 17 +/- 2 min; P = 0.09), or serum GH half-life (8 +/- 1 vs. 6 +/- 1 min; P = 0.13) were observed. In vitro studies of acutely dispersed somatotropes obtained from rats with DM demonstrated increased sensitivity to GHRH (1 nM), as detected by a greater mean hemolytic plaque area following exposure to an EC50 dose of the secretagogue (14.3 +/- 3.3 vs. 17.4 +/- 3.5 microns 2 x 10(3); P = 0.049), and diminished sensitivity to SRIH (1 nM) inhibition of GH release following exposure to an EC50 dose of the secretagogue (10.0 +/- 1.2 vs. 14.9 +/- 2.3 microns2 x 10(3); P = 0.026). The number of the pituitary cells (18.0 +/- 2.8 vs. 15.3 +/- 1.0 x 10(5) cells; P = 0.38) as well as the number of somatotropes (7.3 +/- 1.4 vs. 7.6 +/- 0.9 x 10(5) cells; P = 0.87) were indistinguishable between experimental groups. Hypothalamic gene transcript levels for GH-releasing hormone (GHRH) and somatotropin release-inhibiting hormone (SRIH) were evaluated by in situ hybridization histochemistry to assess cellular synthetic activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Alterations in growth hormone secretion and clearance in adolescent boys with insulin-dependent diabetes mellitus

At puberty, elevated circulating GH concentrations are found, with a parallel increase in the levels of insulin-like growth factor-I (IGF-I). However, these hormonal changes are less well understood in children with insulin-dependent diabetes mellitus (IDDM) during the peripubertal years. Since the metabolic derangement is often associated with elevated circulating GH and diminished serum IGF-I levels, we sought to determine whether similar alterations occur in boys with IDDM. A multiple parameter deconvolution analysis was applied to serum GH concentrations measured at 20-min intervals for 24 h in 25 boys with IDDM. Subjects were divided into 3 pubertal groups, pre (n = 9), early (n = 8), and late (n = 11), according to Tanner stage. Glycosylated hemoglobin and body mass index-SD scores were indistinguishable among groups. Forty nondiabetic peripubertal boys served as controls. Similar to those in the normal boys, circulating GH concentrations and serum IGF-I levels increased during puberty in the boys with IDDM. The augmented circulating GH concentrations occur due to an increase in GH secretion, as determined by calculated daily GH production rates (760 +/- 119 vs. 1025 +/- 121 vs. 1821 +/- 266 micrograms/day, respectively for the 3 groups). IGF-I levels were decreased in prepuberty in the boys with IDDM and were overcome with increasing pubertal development (0.68 +/- 0.13 vs. 0.78 +/- 0.11 vs. 1.53 +/- 0.20 U/mL; P < 0.05). There was an increase in the maximal rate of GH secretion per burst (amplitude) during prepuberty (0.54 +/- 0.05 vs. 0.88 +/- 0.17 microgram/L.min, control vs. IDDM; P = 0.03) and early puberty (0.64 +/- 0.10 vs. 0.88 +/- 0.10 microgram/L.min; p = 0.04). The differences in amplitude between the controls and the boys with IDDM were absent once puberty was well established (1.00 +/- 0.10 vs. 1.02 +/- 0.14 microgram/L.min; P > 0.05). The metabolic clearance of GH was increased in the late pubertal boys with IDDM compared to that in their controls (GH half-life, 24.0 +/- 1.0 in control vs. 19.8 +/- 0.5 min in diabetics; P = 0.006). We conclude that comparable increments in GH secretion and serum IGF-I levels in boys with IDDM in moderate glycemic control and controls are presumably related to increased levels of testosterone in both groups. However, differences exist with respect to GH secretory burst amplitude (augmented) and serum IGF-I concentrations (decreased) before puberty is reached. These alterations disappear with the establishment of puberty.

Cholinergic and opioid involvement in release of growth hormone during exercise and recovery

Cholinergic and opioid pathways have been implicated as mediators of the increased growth hormone (GH) release observed during exercise. This study compared the GH responses induced by a moderate-intensity exercise bout during treatment with placebo (Plac), the opioid receptor antagonist naltrexone (Nalt), the indirect cholinergic agonist pyridostigmine (PD), or a combination of the two drugs (P + N). Ten active males served as subjects (age, 25.1 +/- 0.6 yr; wt, 79.7 +/- 2.5 kg; % body fat, 14.9 +/- 1.4; peak oxygen consumption, 46.2 +/- 2.7 ml.kg-1 x min-1). Blood samples were drawn at 5-min intervals during the 4.5-h testing period to determine the GH concentration. The testing period was divided as follows: 0600-700 h = baseline, 0700-0800 h = preexercise, 0800-0830 h = exercise, and 0830-1030 h = recovery. Drugs were administered 1 h before exercise (at 0700 h). Exercise consisted of 30 min of cycling at an individualized work load previously found to elicit a blood lactate concentration of 2.5 mM. Heart rate, oxygen consumption, blood lactate, and blood glucose were measured throughout the exercise period. Results indicated that neither the resting GH concentration nor the metabolic parameters during exercise were altered by the treatments. Peak serum GH concentration was not significantly altered by the treatments (range 7.3 +/- 2.0 to 12.6 +/- 4.4 micrograms/l).(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of pulsatile secretion and clearance of plasma cortisol in premature and term neonates using deconvolution analysis

Pulsatile secretion of cortisol (F) has not been documented in the newborn infant. Using repeated blood sampling and deconvolution analysis, we investigated F secretion and elimination dynamics in a group of five premature (gestational age, 24-34 weeks) and five term neonates. These infants had required placement of an umbilical arterial cannula for monitoring respiratory status, but were otherwise clinically stable. Blood samples were obtained at 15-min intervals for a 6-h period. All plasma F determinations were 58 nmol/L (2.1 micrograms/dL) or more, and pulsatile F secretion was observed in all infants. No significant differences were noted between the two groups with regard to 6-h mean plasma F concentration [350 +/- 129 (premature) vs. 277 +/- 54 nmol/L (term)], plasma corticosteroid-binding globulin (14 +/- 0 vs. 13 +/- 1 mg/L), F secretory burst frequency (4 +/- 0 vs. 5 +/- 1 bursts/6 h), mass of F secreted per burst [760 +/- 480 vs. 310 +/- 100 nmol/Lv [Lv, liter of F distribution volume)], F production rate (FPR; 2.7 +/- 1.4 vs. 1.1 +/- 0.2 mumol/Lv.6 h), or plasma F half-life (45 +/- 6 vs. 56 +/- 4 min). However, the premature infants had a significantly longer F secretory burst half-duration (63 +/- 18 vs. 6.7 +/- 4.0 min; P < 0.01) and a significantly lower maximal F secretory rate (9.4 +/- 3.4 vs. 100 +/- 26 nmol/Lv.min; P < 0.02) than the term infants. Body surface area and body weight were inversely correlated with F secretory burst half-duration (r = -0.74 and -0.75, respectively); both were also positively correlated with the maximal F secretory rate (r = 0.66 and 0.72). The two most premature infants had significantly greater mean plasma F and FPR than the other three premature and all of the term infants. Extrapolating to 24 h and correcting for the distribution volume of F and body surface area, we estimate FPR to be approximately 17-24 mumol/m2.24 h (6.6-8.8 mg/m2.24 h) for newborn infants of 34 weeks or more gestational age. These values are consistent with newer estimates of FPR in older children and adults determined using either deconvolution analysis or stable isotope dilution methods.

A longitudinal assessment of hormonal and physical alterations during normal puberty in boys. I. Serum growth hormone-binding protein

Previous studies have provided compelling evidence that GH secretion increases transiently during midpuberty in normally growing children. Although it is likely that the increase in GH production serves a primary role in generating the pubertal growth spurt, such a conclusion necessarily assumes that other essential "down-stream" components of the GH axis responsible for mediating the effects of GH remain unchanged. To investigate this concept, we assessed longitudinally another important component of the endogenous GH axis, the serum GH-binding protein (GHBP)/receptor system, in a cohort of 11 normal boys as they matured through normal puberty. At 4-month intervals over 4.0-5.1 yr, 24-h serum GH concentration profiles and serum GHBP activity were evaluated. Serum GHBP levels varied over a more than 12-fold range (40-504 pmol/L) among all subjects. However, the values for individual subjects consistently varied within more narrow limits. The coefficient of variation for values from all subjects was 51% compared to the mean intrasubject coefficient of variation of only 30% (P < 0.05). Although the highest GHBP level (all subjects) was 12.6-fold greater than the lowest, the mean intrasubject range was only 3.1 +/- 0.5-fold (P < 0.05). The overall mean serum GHBP level correlated directly with the overall mean body mass index (r = 0.69; P = 0.018), but correlated inversely with the mean 24-h GH concentration (r = -0.61; P < 0.05). There was no significant increase in the GHBP level during puberty. However, because mean 24-h GH concentrations did increase during midpuberty, the data suggest that an increase in the relative amounts of free vs. bound GH develops during the period of the pubertal growth spurt. These data indicate that serum GHBP levels are regulated in individual children within much more narrow limits than those present in the larger population and do not undergo the dramatic changes during puberty typical of GH secretion and linear growth velocity. As a consequence, alterations may develop in the relative amounts of free vs. bound GH present in serum during the midpubertal years compared to those present during either the prepubertal or postpubertal periods. The majority of the known age-related increase in serum GHBP levels probably occurs before the period of active pubertal development. These findings strengthen further the concept that the midpubertal changes in GH secretion serve a primary role in generating the growth spurt.(ABSTRACT TRUNCATED AT 400 WORDS)

Estimation of daily cortisol production and clearance rates in normal pubertal males by deconvolution analysis

To investigate daily cortisol production and clearance rates in a group (n = 18) of normal unstressed pubertal males, we applied deconvolution analysis to serum cortisol concentrations obtained every 20 min for 24 h. Subject-specific characterization of adrenocortical secretory episodes, cortisol production rate, and serum hormone half-life for nine early pubertal (Tanner I or II; early) and nine late pubertal (Tanner IV or V; late) subjects was undertaken to assess potential roles of sexual maturation and changing gonadal steroid hormone concentrations on glucocorticoid physiology. The estimated cortisol production rate for the early group [16.8 +/- 1.3 mumol/m2 x day (6.1 +/- 0.4 mg/m2 x day)] was indistinguishable from that of the late subjects [14.8 +/- 1.4 mumol/m2 x day (5.3 +/- 0.5 mg/m2 x day)]. No differences were observed between the two pubertal groups in the secretory burst frequency and half-duration, mass of cortisol released per secretory episode, average maximal rate of hormone secretion, and serum cortisol half-life. A significant diurnal pattern of cortisol secretion was observed for all subjects manifest by nyctohemeral variations in the frequency of adrenocortical secretory bursts, the amplitude (maximal rate of cortisol secretion) and the mass of cortisol released per secretory episode. Maximum serum hormone concentrations occurred between 0706 and 1114 h. We conclude that in normal pubertal males: 1) cortisol production rates as estimated by deconvolution analysis are in agreement with other recent independent isotopic estimates, but are lower than many previous estimates; 2) the rise in serum gonadal steroid hormone levels is unassociated with alterations in the production rate or metabolic clearance of cortisol; and 3) increased secretory burst frequency, increased amplitude (maximal rate of cortisol secretion attained within each secretory event), and increased mass of cortisol released per adrenocortical secretory episode give rise to the normal diurnal rhythm of circulating cortisol.

Alterations in the neuroendocrine control of growth hormone secretion in the uremic rat

Chronic renal insufficiency (CRI) is associated with growth failure in children and laboratory rats and is considered to be due, in part, to co-existent malnutrition. Alterations in hypothalamic control of growth hormone (GH) secretion have been suggested in uremic patients. We sought to determine whether factors unique to CRI play a role in this disturbance of GH regulation. Using in situ hybridization histochemistry, we compared messenger RNA (mRNA) levels for the hypothalamic neurohormones GH-releasing hormone (GHRH) and somatostatin (SRIH) in three groups: rats with CRI induced by 5/6 nephrectomy (NPX, N = 4); sham-operated, ad libitum fed rats (SAL, N = 5); and sham-operated, pair-fed rats (SPF, N = 5). We also measured plasma GH at 10 minute intervals for a six hour period via intra-atrial cannulae. The NPX group had significantly lower hypothalamic GHRH mRNA concentrations than both other groups; in addition, these levels were significantly lower in the SPF than in the SAL group. Concentrations of hypothalamic SRIH mRNA did not differ significantly among the three experimental groups. Six-hour mean plasma GH concentrations were significantly lower in the SPF (18.3 +/- 1.8 micrograms/liter) than in either the SAL (27.0 +/- 3.3 micrograms/liter) or the NPX groups (36.8 +/- 7.2 micrograms/liter); the difference in the mean plasma GH levels in the NPX vs. the SAL group did not attain statistical significance. This study provides evidence for an effect of CRI on the neuroendocrine control of GH secretion not related to caloric intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Altered growth hormone secretory dynamics in prepubertal males with constitutional delay of growth

We have used the technique of deconvolution analysis to determine if abnormalities in growth hormone (GH) secretion or metabolic clearance underlie the observed alterations in circulating hormone concentrations in a group of seven prepubertal males with constitutional delay of growth (SHORT-DBA). The results were compared with data obtained from 13 healthy, short prepubertal males (SHORT) and 11 healthy prepubertal male subjects of normal stature (NORMAL). Although the mean 12-h overnight GH production rates were invariant among the groups (8.0 +/- 1.0 versus 7.3 +/- 0.7 versus 6.7 +/- 1.2 micrograms/L, NORMAL versus SHORT versus SHORT-DBA for all comparisons), different secretory mechanisms were operative. The secretory burst half-duration (time interval of the secretory event at half-maximal amplitude) of the SHORT-DBA subjects (26 +/- 1 min) was greater (p = 0.02) than that of the SHORT group (20 +/- 1 min); values for both the SHORT and SHORT-DBA subjects were indistinguishable from that of NORMAL controls (22 +/- 2). Both the mass of GH released per secretory episode and the maximal rate of hormone secretion were less (p < or = 0.02 and the p < 0.01, respectively) for the SHORT-DBA subjects [16 +/- 2 micrograms/unit of body distribution volume (Lv) and 0.6 +/- 0.1 microgram/Lv/min, respectively] compared with those of the NORMAL (26 +/- 2 micrograms/L, and 1.1 +/- 0.1 micrograms/Lv/min, respectively) and SHORT (28 +/- 4 micrograms/Lv and 1.3 +/- 0.2 micrograms/Lv/min, respectively) groups; values for the latter two groups were indistinguishable.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term endurance training alters the hypothalamic-pituitary axes for gonadotropins and growth hormone

In a prospective fashion we have studied the impact of chronic exercise of two intensities on the hypothalamic-pituitary-end organ axes for gonadotropins and GH in gynecologically mature, previously sedentary women. Physiologic alterations are evident in both axes with a doubling of 24-hour mean serum GH concentrations at 1 year and smaller, transient changes in pulsatile LH release during the first four menstrual cycles. The latter period of physiologic adaptation should be studied more intensively with more frequent exercise evaluation. Perhaps more significant "adaptation to stress" would be quantitated. We also emphasize that gynecologically less mature women were not studied and only the early follicular phase was evaluated. Adaptive changes of greater magnitude (including amenorrhea) might have been produced if a different group of women, a markedly different training regimen, or a different phase of the menstrual cycle were studied. Finally, whether or not they participate in physical training, younger amenorrheic women are at increased risk for diminished lumbar spine bone mineral content and skeletal fractures.

Dietary patterns, eating behaviors, and bone mineral density in women runners

Although reduced gonadal steroid hormone concentrations appear to play a major role in lower trabecular bone mineral density (BMD) in women with athletic amenorrhea, dietary deficiencies and eating behaviors may also affect BMD in women runners. To investigate this possibility, dietary patterns (7-d records), eating-disorders inventory (EDI), and BMD were examined in nine nonrunning eumenorrheic control (Contl) and 32 women runners classified as eumenorrheic (n = 19, Eumen) and oligo/amenorrheic (a group in which some were oligomenorrheic and some were amenorrheic; Ol/Am, n = 13). Runner groups had similar cardiorespiratory fitness, body composition, and training characteristics. Lumbar spine BMD was lower in the Ol/Am runners (-12%, P less than 0.05) but proximal femur BMD did not differ. Dietary intake and EDI subscale scores were similar among the groups. However, there was an inverse trend between EDI subscale scores for bulimia and ineffectiveness and femoral BMD in the Ol/Am runners (r = -0.62 to -0.71, P less than 0.05). These results suggest that self-reported dietary intake and/or eating behaviors do not predict reproductive-function alterations in women runners, but eating behaviors may be associated with lower BMD in Ol/Am runners.

Elevated growth hormone secretory rate in premature infants: deconvolution analysis of pulsatile growth hormone secretion in the neonate

Premature infants have higher circulating concentrations of growth hormone (GH) than term infants. Previous investigations of these differences have used sampling frequencies of every 30 min with subsequent application of pulse detection algorithms, such as the CLUSTER program, to assess serum GH pulse parameters. To determine differences in GH secretory rates or GH t1/2 values between premature and term infants, we have sampled 11 neonates at 15-min intervals. We performed deconvolution analysis of the resultant plasma GH values to estimate GH secretory and clearance parameters. Five premature infants (gestational age range 24-34 wk) and six term infants (gestational age range 38-42 wk) were sampled every 15 min for 6 h. All subjects had indwelling arterial catheters. GH was measured (in duplicate) by RIA using 10 microL of plasma. Premature infants had higher secretory burst amplitudes (2.2 +/- 0.13 micrograms/L/min versus 1.4 +/- 0.27 micrograms/L/min, p = 0.02), higher production rates (product of the total number of bursts and the mean mass of GH secreted per burst, 811 +/- 173 micrograms/L/6 h versus 283 +/- 77 micrograms/L/6 h, p = 0.03), and a higher mass of GH per secretory burst (106 +/- 25 micrograms/L versus 38 +/- 11 micrograms/L, p = 0.049) than term infants. The integrated plasma GH concentration exhibited a strong trend toward a higher value in the premature infants (18,100 +/- 800 micrograms/L versus 10,200 +/- 2,700 micrograms/L, p = 0.067).(ABSTRACT TRUNCATED AT 250 WORDS)

Exogenous androgen does not alter hypothalamic proopiomelanocortin gene transcript levels in the sexually immature male rat

To investigate possible mechanisms whereby the augmentation of hypothalamic proopiomelanocortin (POMC) messenger ribonucleic acid (mRNA) levels occurs with pubertal development, we employed the techniques of testosterone administration and in situ hybridization histochemistry in sexually immature male rats. Six animals from each of the following groups were studied: (1) untreated controls (CTRL); (2) empty capsule (SHAM); (3) testosterone capsule (TEST), and (4) untreated adults (ADLT). Capsules were implanted at 21 days of age. Groups 1-3 were sacrificed at 35 days of life; group 4 at 55 days. Ventral prostate and seminal vesicle weights were obtained to assess the biologic effect of testosterone. Hybridizations were performed on coronal brain slices through the region of the arcuate nucleus using a 35S-labeled oligonucleotide probe complementary to a 30-base sequence within POMC mRNA. Anatomically matched tissue sections (11 per animal, from the retrochiasmatic region rostrally to the premammillary nucleus caudally) were exposed to x-ray film, followed by densitometric analysis. The mean serum testosterone concentration of the TEST group was significantly greater than that of the ADLT animals; values for the CTRL and SHAM rats were undetectable. The accessory sex organ weights of the ADLT animals were greater than those of the TEST rats; both values were greater than those of the CTRL and SHAM groups which were indistinguishable. Increased levels of hypothalamic POMC mRNA were observed in the male rat after pubertal development.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of opioid receptor blockade on luteinizing hormone (LH) pulses and interpulse LH concentrations in normal women during the early phase of the menstrual cycle

To determine the role of endogenous opioid peptides in regulating pulsatile luteinizing hormone (LH) release in the early follicular phase of the menstrual cycle of eumenorrheic women, we evaluated serum LH concentrations in blood collected every 10 min for 12 h in 27 women each studied during two menstrual cycles: (1) without pretreatment and (2) following oral administration of naltrexone, a mu opiate receptor blocking agent, at a dose of 1.0 mg/kg. Pulsatile LH release was assessed by the CLUSTER algorithm. The mean (+/- SE) integrated serum LH concentration (IU/L/min) increased following the administration of naltrexone (4715 +/- 298) in comparison to the control day (3997 +/- 381; p = 0.0008). The mean number of LH pulses (/12 h) detected on the naltrexone day (10.3 +/- 0.3) was higher than on the control day (8.9 +/- 0.4; p = 0.0068). Mean maximal LH peak height (IU/L) was greater on the naltrexone (7.8 +/- 0.5) vs control (6.7 +/- 0.5) days (p = 0.0064) as was the interpulse valley mean serum LH concentration (IU/L; 6.3 +/- 0.4 vs 5.0 +/- 0.4; p = 0.0013). No difference was noted in the mean incremental LH pulse amplitude (IU/L; 1.9 +/- 0.1 vs 2.1 +/- 0.1; p = 0.13), or peak duration (min; 40 +/- 1.8 vs 45.0 +/- 2.4; p = 0.06). Mean LH peak area (IU/L/min) was greater on the control (45.0 +/- 2.4) vs naltrexone (40 +/- 1.8) days (p = 0.0475).(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of training intensity on ratings of perceived exertion

We examined the effects of intensity of training on ratings of perceived exertion (RPE) at the lactate threshold (LT), fixed blood lactate concentrations (FBLC) of 2.0, 2.5 and 4.0 mM and peak in 25 untrained eumenorrheic women (mean +/- SD: age = 30.9 +/- 4.1 yrs; height = 165.7 +/- 5.9 cm; weight = 65.5 +/- 7.6 kg) who completed one year of run training. Subjects were recruited as sedentary controls or were randomly assigned to one of two training groups: 1) at the lactate threshold (at LT) or 2) above the lactate threshold (greater than LT). The at LT group trained at velocity LT and the greater than LT group trained at the velocity midway between velocity LT and peak velocity. Training subjects were reevaluated every fourth menstrual cycle and training intensity was adjusted. The control group was reassessed at menstrual cycle 12. Before training no among group differences were observed for VO2 or velocity at LT, FBLC and peak. Both training groups increased VO2 at LT, FBLC and peak as a result of training (p less than 0.05), with the greater than LT group exhibiting greater improvement than the at LT group (VO2 at LT, FBLC of 2.0, 2.5 and 4.0 mM and peak increased by 6.4, 5.3, 5.1, 4.0 and 4.7 ml/kg.min-1 for at LT and by 10.4, 9.2, 8.6, 5.1 and 5.9 ml/kg.min-1 for greater than LT; p less than 0.05). Similar findings were observed for the velocity associated with these lactate concentrations. No pre/post differences were observed in VO2 or velocity for the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Endurance training amplifies the pulsatile release of growth hormone: effects of training intensity

The effects of intensity of run training on the pulsatile release of growth hormone (GH) were investigated in 21 eumenorrheic untrained women. The O2 consumption (VO2) at the lactate threshold (LT); fixed blood lactate concentrations (FBLC) of 2.0, 2.5, and 4.0 mM; peak VO2; maximal VO2; body composition; and pulsatile release of GH were measured. Subjects in both the at-lactate threshold (/LT, n = 9) and above-lactate threshold (greater than LT, n = 7) training groups increased VO2 at LT and FBLC of 2.0, 2.5, and 4.0 mM and VO2max after 1 yr of run training. However, the increase observed in the greater than LT group was greater than that in the /LT group (P less than 0.05). No change was observed for the control group (n = 5). No among- or within-group differences were observed for body weight, although trends for reductions in percent body fat (P less than 0.06) and fat weight (P less than 0.15) were observed in the greater than LT group, and both training groups significantly increased fat-free weight (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive hormones and bone mineral density in women runners

We examined the relationships among reproductive hormone concentrations and bone mineral density (BMD) in 43 women runners classified as eumenorrheic (n = 24), oligomenorrheic (n = 8), or amenorrheic (n = 11). Results were compared with a eumenorrheic nonrunner control group (n = 11). Serum 17 beta-estradiol, progesterone, and dehydroepiandrosterone sulfate concentrations were determined in daily blood samples for 21 days, and integrated concentrations (areas under the curve) were calculated. BMD was assessed at the lumbar spine and proximal femur by dual-photon absorptiometry. As expected, 17 beta-estradiol, progesterone, and lumbar spine BMD were higher in the control and eumenorrheic runner groups than in the oligomenorrheic and amenorrheic runner groups (P less than 0.05). Progesterone concentration was significantly correlated with lumbar spine BMD in the eumenorrheic runners (r = 0.61). None of the steroid hormones was significantly related to BMD in the oligomenorrheic/amenorrheic group. The present data suggest that circulating levels of gonadal steroid hormones affect axial BMD in eumenorrheic runners.

Properties of spontaneous growth hormone secretory bursts and half-life of endogenous growth hormone in boys with idiopathic short stature. Genentech Collaborative Group

We analyzed endogenous GH secretory dynamics and MCRs by a novel quantitative deconvolution technique in 20 boys with idiopathic short stature (ISS) and 35 boys of normal stature in Tanner stage I of puberty. We tested the null hypotheses that 1) ISS is not associated with any alterations in the frequency, mass, amplitude, or duration of spontaneous GH secretory bursts and/or the 24-h GH production rate; and 2) the half-life of endogenous GH is not altered in ISS. The boys with ISS had a mean (+/- SEM) bone age of 8.0 +/- 0.42 yr and a chronological age of 10 +/- 0.50 yr. The latter was similar to the chronological (and bone) age of the normal boys of 9.8 +/- 0.23 (and 9.3 +/- 0.34) yr. Mean height SD scores were significantly lower in ISS boys, viz. -2.7 +/- 0.15 in ISS vs. +0.34 +/- 0.13 in normal boys (P less than 0.001). Plasma insulin-like growth factor-I concentrations were similar in the two groups, as were (24-h) mean serum GH concentrations, viz. 3.5 +/- 0.29 micrograms/L in ISS and 4.1 +/- 0.49 micrograms/L in normal boys (P = NS). Deconvolution analysis revealed that the mean number of GH secretory events per 24 h was similar in normal and ISS boys, viz. 9.6 +/- 0.76 (normal) vs. 8.4 +/- 0.55 (ISS), and that there was no significant difference in mean GH interburst intervals. The amplitude, mass, and duration of computer-resolved GH secretory bursts also did not differ in normal and ISS boys. The half-lives of endogenous GH were estimated to be 16 +/- 0.77 min in the ISS and 18 +/- 0.93 min in the control boys (P = NS). The calculated daily GH secretion rate per unit distribution volume was not significantly reduced in ISS, i.e. 194 +/- 19 micrograms/L.day in ISS vs. 177 +/- 19 micrograms/L.day in control boys. Moreover, daily GH secretion rates corrected for body mass index (weight/height2) in the twp groups were not significantly different. In summary, the present cohort of boys with ISS manifested no significant alterations in GH secretory burst frequency, duration, mass, or amplitude or in the half-life of endogenous GH compared to normal boys in Tanner stage I of pubertal development. Indeed, whether daily GH secretion rates are expressed per unit distribution volume or per unit body mass index, groups of boys with ISS and normal height controls secrete similar total amounts of GH. We conclude that the overall dynamics of GH secretion and clearance in boys with ISS considered as a whole cannot be distinguished readily from physiological patterns observed in prepubertal boys of normal height.

Exercise training at and above the lactate threshold in previously untrained women

We examined the effects of training at and above the lactate threshold in previously untrained women. Twenty-four untrained eumenorrheic women (age = 31.3 +/- 4.0 yrs, wt = 66.2 +/- 7.6 kg, ht = 166.4 +/- 5.8 cm) were assessed at baseline [during days 1-3 of the menstrual cycle (MC)] and every 4 MC after that (for 1 year) for VO2 and velocity (V) at LT, fixed blood lactate concentrations (FBLC) of 2.0, 2.5, and 4.0 mM, and Max. Subjects were assigned to control (C, n = 7), at LT/LT, trained 6 days/week at the velocity associated with LT, (n = 9) or above LT (greater than LT, trained 3 days/week at the velocity midway between V LT and V Max and 3 days/week at V LT, n = 8) groups. Exercise prescriptions were adjusted after each assessment and each group progressed similarly in weekly mileage. No between group differences were observed before training. After training the greater than LT group had significantly higher values than the C and /LT groups for LT (p less than 0.05). For FBLC of 2.0, 2.5, and 4.0 mM and Max, the greater than LT group values were greater than the C group (p less than 0.05). No differences were observed after training between the /LT and C groups. Although the greater than LT group had higher VO2 and V Max values than the /LT group after training, these differences were not statistically significant.(ABSTRACT TRUNCATED AT 250 WORDS)

Durability of the reproductive axis in eumenorrheic women during 1 yr of endurance training

Menstrual cycle (MC) alterations occur in some endurance-training women. We hypothesized that a prospective running program would evoke alterations in MC phase lengths and in the physiological frequency of pulses of luteinizing hormone (LH) and/or diminish 24-h integrated serum LH concentrations in some women. In addition, we postulated that women who train more intensively (above the lactate threshold) would show alterations in gonadotropin release earlier in the training program or to a greater degree. To test these hypotheses, we examined the effects of different exercise intensities on physiological and endocrine responses. Twenty-three healthy eumenorrheic gynecologically mature (postmenarchal age 17.8 +/- 0.9 yr) untrained women undertook a 1-yr training program at one of two exercise intensities, one at a velocity corresponding to the lactate threshold (LT) and the other halfway between that of LT and peak running velocity, or served as controls. Training distance was the same in each exercise group. Physiological measurements were repeated every four MC to track changes in fitness and readjust training velocities. The lengths of the MC and the follicular and luteal phases were determined from hormonal concentrations. Body composition, nutritional intake, and pulsatile release of LH were determined. The women ran approximately 790 miles. Each group improved physiologically, with the greater than LT group improving to a greater degree. A less than 2-day decrease in the luteal phase length was observed only in the greater than LT group. No significant changes for any parameter of pulsatile LH release were noted between exercise groups. No significant changes in nutritional intake and only small changes in body composition were noted in either exercise group despite the added energy expenditure of exercise. We conclude that a progressive exercise program of moderate distance and intensity does not adversely affect the robust reproductive system of gynecologically mature eumenorrheic women.

Anabolic-androgenic steroids and the adolescent

This article has reviewed some of the hormonal and behavioral maturation that occurs during adolescence, which are characterized by remarkable physical changes and behavioral vulnerability. Risk taking of many varieties is common and drugs (including anabolic-androgenic steroids) form a part of the prevailing culture in many places. These steroids probably are not severe health hazards when taken intermittently and in low to moderate doses. The 17-alkylated derivatives are clearly the more likely to cause hepatotoxicity. Thus, the scare tactics formerly used (severe constitutional side effects) are doomed to failure. The tenuous link between these drugs and objective behavioral and addictive effects must be strengthened before health strategies based on this issue can be validated. Clearly, the lack of scientific information has impeded, if not precluded, the formulation of an effective health education strategy. The most potent deterrent to the use of steroid drugs by athletes must be the moral issue of fair play and maintaining a "level playing field." We strongly support directed research in these areas and hope that the credibility of the scientific community can be regained after its faulted "stop steroid use" campaigns based on the lack of steroid efficacy in bringing about desired results or on their dire consequences have been replaced with credible evidence to refute their use on these and other grounds.

Endogenous growth hormone secretion and clearance rates in normal boys, as determined by deconvolution analysis: relationship to age, pubertal status, and body mass

Mean plasma GH concentrations increase in normal boys during mid- to late-puberty. To investigate the nature of the pituitary secretory events and/or altered metabolic clearance responsible for these serum GH concentration changes, we performed multiple-parameter deconvolution analysis of 46 24-h serum GH concentration-time series obtained from normal boys at various stages of puberty and young adulthood. The subjects ranged in chronological age from 7-27 yr. The height and weight of each subject were between the 5th and 95th percentile for age. The calculated daily mass of GH secreted was greatest (P less than 0.001) in late pubertal boys (mean +/- SE, 1810 +/- 250 micrograms/24 h) and was triple the value in prepubertal boys (610 +/- 65 micrograms/24 h). When the values were normalized and expressed as mass of GH secreted per unit (m2) body surface area or per L distribution volume, GH secretion in late pubertal boys was still significantly greater than that in any other group (P less than 0.05). These values for late pubertal boys were nearly double the corresponding values for prepubertal boys (1160 +/- 160 vs. 600 +/- 58 micrograms GH/m2.24 h and 440 +/- 63 vs. 270 +/- 25 micrograms GH/L vol.24 h, respectively). When the effect of clearance mechanics on serum GH concentrations was removed mathematically, the primary change in predicted GH secretory burst parameters during pubertal development was an increase in GH mass released per burst resulting from an increase in the maximal rate of GH secretion attained within the bursts. These changes in the amplitude of GH release events were specific, in that they were largely independent of any accompanying alterations in duration or frequency of the GH secretory bursts or in serum GH half-life. Correlation analysis revealed that the 24-h GH secretion rate varied inversely with the subjects' body mass index SD score (r = -0.65; P less than 0.01), suggesting that differences in body mass, even within the normal range, contribute to the wide variability in daily GH secretion rates among normally growing children. The plasma insulin-like growth factor-I concentrations of all subjects correlated positively with the calculated 24-h GH secretion rate (r = 0.51; P less than 0.001). In summary, the primary neuroendocrine alteration responsible for the augmented serum GH concentrations characterizing mid- to late-puberty in boys is an increased mass of GH released per pituitary secretory episode resulting from an increased maximal rate of GH secretion within each burst.(ABSTRACT TRUNCATED AT 400 WORDS)

Estrogenic modulation of the gonadotropin-releasing hormone-stimulated secretory activity of the gonadotrope and lactotrope in prepubertal females with Turner's syndrome

The nature of estrogen's modulation of GnRH-stimulated secretion of the female prepubertal gonadotrope and lactotrope was studied in nine girls with primary gonadal failure (Turner's syndrome; mean age, 10.0 +/- 0.25 yr). LH, FSH, and PRL release was evaluated by sampling blood every 20 min from 2000-0800 h. Hormone secretion was stimulated by one of two randomized doses of GnRH (50 or 750 ng/kg) delivered at fixed intervals of every 90 min in an attempt to replace the function of the endogenous GnRH pulse generator with an exogenous GnRH clamp. To evaluate the time dependency of estrogen action, studies were conducted at baseline and after 1 and 5 weeks of oral administration of ethinyl estradiol (EE; 100 ng/kg.day). In vivo gonadotropin secretory dynamics were quantitated by deconvolution mathematical modeling. We found a suppression of total LH secretion in response to repeated fixed doses of GnRH after 1 and 5 weeks of EE exposure, viz. a 10% (1 week) and 60% (5 weeks) reduction in the total mass of LH released after six consecutive GnRH pulses. Before estrogen exposure, patients manifested a decreasing mass of LH secreted per burst (slope of mass/burst vs. GnRH injection number was -3.3 +/- 1.44), suggesting down-regulation of the LH secretory response. However, after 5 weeks of EE treatment, the same series of GnRH doses elicited a progressive increase in the mass of LH secreted per burst (slope, 1.06 +/- 0.036; P = 0.041). Such serial amplification of LH secretory responses (despite overall suppression of the mean serum LH concentrations by EE) is consistent with the emergence of priming of GnRH actions. This phenomenon was specific, since the half-life of LH and the LH secretory burst duration were not altered. FSH responses to GnRH were significantly suppressed after 5 weeks of EE exposure (mean serum FSH concentrations, 61.9 +/- 11.4 IU/L at baseline vs. 14.4 +/- 6.9 at week 5; P = 0.003). However, in contrast to the LH responses on a given study day, there was increased FSH responsivity to successive doses of GnRH, suggesting a priming effect of serial GnRH exposure on GnRH-stimulated FSH secretion regardless of the estrogen milieu. PRL secretion was stimulated by GnRH at baseline (16.8 +/- 0.88 micrograms/L), but release was reduced at week 5 on estrogen (11.6 +/- 0.4 micrograms/L). This may represent withdrawal of the paracrine effects of endogenous GnRH and/or increased dopaminergic tone induced by estrogen.(ABSTRACT TRUNCATED AT 400 WORDS)

Function of the growth hormone-insulin-like growth factor I axis in the profoundly growth-retarded diabetic child: evidence for defective target organ responsiveness in the Mauriac syndrome

Mauriac syndrome (MS) consists of a triad of poorly controlled diabetes, profound growth retardation, and hepatomegaly. The mechanisms involved in the growth retardation of those patients are not well understood. In an attempt to determine whether the growth retardation was secondary to somatroph secretory failure, abnormal pulsatile secretion, deletion of the growth hormone (GH) receptor, inadequate insulin-like growth factor I (IGF-I) generation, or abnormal IGF-I binding proteins (IGFBPs) two patients with MS were studied and their results compared with those of age-matched diabetic boys of similar glycemic control who were growing well. Overnight GH profiles in the MS and normally growing diabetics were analyzed by the CLUSTER program. The mean 12-hour GH concentrations, pulse amplitude, and pulse frequency were not different in either group of patients and did not change during acute normalization of the serum glucose overnight in the MS patients. The GH-binding proteins (GHBPs) relative binding were found to be the same in both groups of patients and did not differ from normal nondiabetic sera (62% +/- 8.0% relative specific binding in MS patients, v 53% +/- 4.3% in diabetic controls). The IGF-I concentrations were normal and comparable in both groups of patients (1.1 +/- 0.1 U/mL MS, v 1.1 +/- 0.3 diabetic controls). The IGFBPs were comparable in both groups of patients as well. One of the patients with MS had no meaningful increase in his growth velocity after 1 year on GH therapy despite good compliance. In conclusion, our data show normal hypothalamic-pituitary function, normal GHBP, IGF-I generation, and IGFBPs in two patients with MS when compared with normally growing diabetic children. These data, and the lack of linear growth in response to exogenous GH therapy in one patient, suggest a GH-resistant state, either secondary to impaired bioactivity of IGF-I, or a defect at or distal to the IGF-I receptor.

Growth hormone-binding protein activity is inversely related to 24-hour growth hormone release in normal boys

To investigate the physiological relationship between serum GH-binding proteins and 24-h GH release, we compared the 24-h GH pulse attributes in serum samples obtained at 20-min intervals to the serum GH-binding protein activity (GH-BP) from 38 normal boys between 7 5/12 and 18 4/12 yr of age. GH-BP was determined in a serum sample from each study (containing less than 1.0 micrograms/L GH) using a standardized GH-BP assay. GH-BP results are expressed as the percentage of [125I]human GH bound to the high affinity GH-BP complex (peak II) per 160 microL serum. There were significant inverse relationships between the high affinity (receptor-related) GH-BP and several characteristics of 24-h GH release. Specifically, GH-BP was significantly (P less than 0.005 for all), but negatively, correlated with mean 24-h GH concentration (r = -0.62), sum of the GH pulse amplitudes (r = -0.57), sum of the GH pulse areas (r = -0.55), interpulse mean GH concentration (r = -0.53), and number of GH pulses per 24 h (r = -0.53). In addition, GH-BP correlated positively with the mean time interval between pulses (r = 0.59). There was also a significant positive correlation (r = 0.75; P less than 0.001) between GH-BP and the subject's age-adjusted body mass index SD score (BMI-SDS). Each characteristic of 24-h GH release correlating inversely with GH-BP also correlated inversely with BMI-SDS (P less than 0.01 for all comparisons). GH-BP did not, however, correlate with plasma insulin-like growth factor-I levels, serum testosterone concentrations, or height SDS. Binding to the low affinity GH-BP (peak I) did not correlate significantly with any of the examined GH pulse attributes, BMI-SDS, or the degree of binding to the high affinity GH-BP (peak II). We conclude that an inverse relationship exists between the high affinity serum GH-BP and 24-h GH release in boys under normal physiological conditions. We speculate that abnormalities in this relationship probably also exist and may underlie some disorders of growth.