Differential impact of age, sex steroid hormones, and obesity on basal versus pulsatile growth hormone secretion in men as assessed in an ultrasensitive chemiluminescence assay.

Abstract

A chemiluminescence-based GH assay with 30- to 100-fold increased sensitivity recently disclosed combined basal and pulsatile GH secretion in men. However, how age, sex steroid hormones, and obesity singly and jointly influence the basal vs. pulsatile modes of GH release is not known. We used the foregoing assay (detection threshold, 0.002-0.005 microgram/L) and high sensitivity and specificity (> or = 90% each) deconvolution analysis to quantitate basal and pulsatile GH secretion from 24-h serum GH concentration profiles in 26 healthy lean and obese men, whose ages spanned 18-63 yr and whose percentage body fat ranged from 12-47%. Concentrations of serum insulin-like growth factor I (IGF-I), IGF-I-binding protein-1 (IGFBP-1), and IGFBP-3 were related to specific measures of basal or pulsatile GH release. We observed that mean (24-h) serum GH concentrations embraced a 140-fold range from 0.013-1.8 micrograms/L and were related negatively to age (r = -0.50; P < 0.01), percentage body fat (r = -0.620; P < 0.01), and their interaction (r = -0.610; P < 0.01). In contrast, testosterone was a robustly positive statistical determinant of mean serum GH values (r = 0.628; P = 0.0006). Stepwise multivariate regression analysis disclosed that percentage body fat alone and jointly with the serum testosterone concentration controlled, respectively, 38% and 50% of the total variability in GH levels (P = 0.0013 and P = 0.0008). As assessed by deconvolution analysis, GH secretory burst mass was negatively related to percentage body fat (r = -0.621; P < 0.01) and positively to serum testosterone (r = 0.529; P = 0.0054). The calculated half-life of GH correlated positively with serum estradiol (r = 0.447; P = 0.032), and negatively with percentage body fat (r = -0.437; P = 0.048). Basal GH secretion rates were negatively related to serum estradiol (r = -0.485; P = 0.016). In contrast, GH secretory burst frequency and duration were unrelated to age, percentage body fat, or sex steroids. The fraction of total GH secreted in bursts was negatively correlated with the body mass index (r = -0.540; P < 0.01). Serum IGF-I concentrations were positively related to total pulsatile GH secretion (r = 0.690; P = 0.0011) and negatively to age (r = -0.597; P = 0.007) and percentage body fat (r = -0.611; P = 0.009).(ABSTRACT TRUNCATED AT 400 WORDS)

Gender governs the relationship between exercise intensity and growth hormone release in young adults

“…Akin to previous reports (10,26,30), there was no gender difference in mean GH interpulse interval or GH half-life. There was also no significant interaction between gender and mean mass of GH secreted per burst, although there was a trend for a main effect of gender (P Ͻ 0.10).…”

“…However, recent data from our laboratory indicate that, in young men, the magnitude of GH release rises with increasing exercise intensity in a linear doseresponse relationship (as opposed to a threshold relationship) (20). Whether females have similar GH responses to varying exercise intensities is not known.GH release at rest is greater in young women than in comparably aged men (7,26,30,34). This gender difference is accounted for by a twofold greater mass of GH secreted per burst in young women (26,30).…”

“…GH release at rest is greater in young women than in comparably aged men (7,26,30,34). This gender difference is accounted for by a twofold greater mass of GH secreted per burst in young women (26,30).…”

“…This gender difference is accounted for by a twofold greater mass of GH secreted per burst in young women (26,30). Wideman et al (34) reported that women have higher serum GH concentrations at rest and during a single exercise intensity and attain their peak GH concentration sooner than men.…”

Testosterone monitoring for men with advanced prostate cancer: Review of current practices and a survey of Canadian physicians

“…[3][4][5] The limits of measurement imposed by these assays led to the target testosterone suppression definition of less than 1.7 nmol/L; 4,6 however, more recent studies measuring serum testosterone levels after surgical castration with the use of more modern techniques, using improved radioimmunoassay (RIA) and chemiluminescent immunoassay (CLIA) and mass spectrometry (MS) methods, have reported mean testosterone levels as low as 0.003 nmol/L. 4,[7][8][9][10][11] Several studies since the early 1990s have therefore challenged the outdated benchmark of 1.7 nmol/L and recommended revisiting the definition, with many suggesting a new benchmark of 0.7 nmol/L. 4,[12][13][14] In light of conflicting opinion on the ideal goal for suppression of serum testosterone in men with advanced cancer, we conducted a survey of Canadian urologists, uro-oncologists, and radiation oncologists to gain a better understanding of their testosterone monitoring practices when managing men with hormone-sensitive prostate cancer.…”