Impaired growth hormone secretion in the adult population: relation to age and adiposity.

Abstract

A B S T R A C T Growth hormone (GH) release was studied in adults of normal stature, ages 21-86 yr. The subjects were 85-115% of ideal body weight, between the 5th and 95th percentiles in height, and free ofactive or progressive disease. 9 to 12 individuals in each decade from third to ninth were evaluated. The following criteria of GH status were measured: serum GH concentration, analyzed by radioimmunoassay at halfhour intervals for 4 h after onset of sleep, and at 1-h intervals from 8 a.m. to 4 p.m. in 52 subjects; daily retention of N, P, and K in response to 0.168 U human (h)GH/kg body wt314/day in 18 subjects; and plasma somatomedin C (SmC) level before and during exogenous hGH treatment in 18 subjects.All 10 individuals, 20-29 yr old, released substantial amounts of endogenous GH during both day and night (average peak serum GH obtained during day and night was 7.3 and 20.3 ng/ml, respectively); average plasma SmC was 1.43 U/ml (95% tolerance limits, 0.64-2.22 U/ ml). There was no significant effect of exogenous hGH on elemental balances or on plasma SmC. In contrast, 6 of 12 individuals 60-79 yr old showed the following evidences of impaired GH release: peak waking and sleeping seruim GH < 4 nglml; plasma SmC < 0.38 U/ ml; a significant retention in N, P, and K; and a significant rise in plasma SmC, in response to exogenous hGH.Plasma SmC, serum GH during sleep, serum GH during the day, retentions of N, P, and K in response to exogenous hGH, and rise in plasma SmC in response to hGH were all intercorrelated (P < 0.05). Plasma SmC < 0.38 U/ml corresponded to peak nocturnal serum GH < 4 ng/ml. The prevalence of plasma SmC < 0.38 U/ml

Relationship of chronic endurance exercise to the somatotropic and sex hormone status of older men

“…First, consistent with our previous study of resistance-trained older people, it appears that habitual endurance exercise does not ameliorate the age-related decline in circulating IGF-I or its most abundant binding protein, in one estimate of IGF-I bioavailability, the calculated ratio of IGF to IGFBP-3, or, by inference, the decline in GH secretion. With regard to the latter inference, although we did not measure GH in this study, previous work from our laboratory and from others clearly shows that healthy older men uniformly show decreased GH secretory capacity, either spontaneously or in response to provocative stimuli such as exercise (1)(2)(3)(4), and that even an intense and sustained program of exercise training did not restore these deficits (11). The second major finding of this study was that our group of very active older men showed striking increases in circulating SHBG, sufficient to misrepresent calculated estimates of bioavailable testosterone.…”

“…In contrast, in a study of young adults, Weltman et al (32) demonstrated an inverse relationship between fat mass and IGF-I concentration. Others that examined the same parameters in young and older men did not report subgroup analyses in the same age range as our participants (1,33). The absence of a correlation between IGF-I and percent body fat in older men that we have demonstrated is consistent with the age-related, exerciseindependent suppression of GH/IGF-I that we observed: that is, age per se appears to exert a more potent effect on GH/IGF-I secretion than does adiposity.…”

“…From about the fourth decade, human aging is associated with a decline in secretion of growth hormone (GH) (1) and insulin-like growth factor (IGF)-I (2), a process that has been termed the 'somatopause'. Although mechanisms responsible for this phenomenon are incompletely understood, impaired GH release in response to a variety of physiologic and pharmacologic stimuli has been repeatedly documented (3,4).…”

Changes in muscle mass and phenotype and the expression of autocrine and systemic growth factors by muscle in response to stretch and overload

“…In recent work in which we have used RNase protection to distinguish and quantify the expression of different muscle IGF-1 isoforms we have found that both the autocrine (MGF) and the systemic type (muscle L.IGF-1) that is also produced by the muscle are both markedly upregulated by stretch and stretch combined with stimulation (McKoy et al 1999). During ageing, however, the circulating growth hormone and IGF-1 are known to decrease markedly particularly after the initial growth spurt (Rudman et al 1981). Although IGF-1s produced via growth hormone stimulation are important during early postnatal muscle development, it appears that IGF-1 produced by muscle during exercise becomes more important for the maintenance of muscle mass.…”

Serum Insulin-Like Growth Factor-I (IGF-I) in Normal Japanese Adults.

“…The concentration of IGF-I had been known to be influenced by age [1][2][3][4][5][6]. However, there was no reference value for serum IGF-I in adults based on the extraction method, except in a recent Swedish report [7].…”