Diurnal variation in the elimination rate of human growth hormone (GH): the half-life of serum GH is prolonged in the evening, and affected by the source of the hormone, as well as by body size and serum estradiol.

Abstract

The half-lives of endogenous and exogenous (biosynthetic monomeric) GH were compared in the morning and evening in healthy young men (n = 10). In group A, a bolus of GHRH was injected either at 0800 or at 2000 h, whereas in group B hGH was injected iv after suppression of endogenous GH by somatostatin. GH was sampled every 10 min and the t1/2 for GH was determined by deconvolution analysis (two compartments). The GH elimination half-life was shorter in the morning: for endogenous GH, t1/2 was 23 +/- 1.1 min (mean +/- SE) in the morning compared to 26 +/- 1.7 min in the evening (P < 0.02). T1/2 correlated negatively with estradiol (r = -0.78; P < 0.01) and positively with sex hormone-binding globulin (r = 0.71; P < 0.03). The half-life of exogenous 22-kilodalton GH was shorter compared to endogenous GH (P < 0.002), and diurnal variation was even more pronounced: t1/2 was 14 +/- 1.0 min in the morning and 19 +/- 1.0 min in the evening (P < 0.01). These effects were not due to differences in GH distribution volumes. The half-life of exogenous GH was significantly affected by weight (r = -0.8; P < 0.01) and height (r = 0.67; P < 0.05). We conclude that in young males, the rate of GH disappearance from the circulation depends on both diurnal mechanisms as well as the source or structural composition of the hormone. Body size and sex steroids contribute to the variability of GH clearance in healthy man.

Age-Dependent Suppression of Nocturnal Growth Hormone Levels during Sleep Deprivation

“…It is known that both half-life and pulse frequency of GH decrease with age in healthy males between 21 and 71 years [26], but this negative correlation with half-life was not found for nocturnal GH within the relatively narrow range of ages we present here [31], We are not in a posi tion to discuss secretion and depiction rates in plasma due to our sampling interval. Nevertheless, it is reasonable to expect a longer half-life to result in a relatively higher noc turnal peak level.…”

Circulating non-22 kDa growth hormone isoforms in healthy children of normal stature: relation to height, body mass and pubertal development

“…However, it is not known if modifications in the pattern of secretion of GH are associated with changes in the nature of GH secreted by the pituitary gland. Another possibility is that the elimination rate of individual GH isoforms from the circulation changes according to body size, as demonstrated by Holl et al (39) in healthy young males.…”

“…For example, the elimination rate of 20 kDa GH (37) and oligomeric isoforms (38) is reduced in comparison with 22 kDa GH. The serum levels of estradiol have been shown to correlate inversely with the half-life of endogenous GH in the circulation (39), and this may be one explanation for possible sex-related differences in the molecular nature of circulating GH isoforms. The proportion of non-22 kDa GH isoforms plotted against height S.D.…”

Receiver-Operated Characteristic Curve Analysis of Two Algorithms Assessing Human Growth Hormone Pulsatile Secretion (PULSAR, CLUSTER): Comparison of Peak Detection Efficacy

“…Another assumption is that the disappearance rate constant, the distribution volumes, and the standard de viations of the secretory impulses are uniform over obser vation time [26]. There is evidence, however, that the elimination rate of hGH shows diurnal variation, sup posedly influenced by fluctuations in estradiol, and varies according to the source of hGH [27], The need to add new parameters and interactions to the model, e.g. the effect of hGH binding proteins [28], sex steroids, time of day, source of hGH and body composition, also adds mathe matical complexity [27], requiring complex computation.…”