Lack of a Simple Relationship Between Endogenous Growth Hormone and NSILA-s Related Peptides

Abstract

Using a liver membrane radioreceptor assay that is specific for NSILA-s and related compounds we have previously shown that plasma NSILA-s, like plasma somatomedin, is low in hypopituitary patients and rises acutely after iv hGH. In contrast to the somatomedins, however, NSILA-s, as measured in this assay, is not elevated in the sera of acromegalic patients. In an attempt to understand better the interrelationship between NSILA-s and endogenous growth hormone, a variety of physiologic and pharmacologic stimuli were studied. NSILA-s rose after oral glucose at a time when hGH levels were falling. Conversely, after iv insulin or estrogen, NSILA-s levels fell at a time when hGH levels were rising. Furthermore, oral L-Dopa and iv glucagon both produced substantial rises in plasma growth hormone without causing an acute change in NSILA-s related peptides. The most striking dissociation between endogenous hGH and NSILA-s related peptides was observed during a 48–72 h fast. In normal subjects fasting produced a rise in growth hormone and a dramatic fall in NSILA-s; whereas in obese subjects, NSILA-s rose during fasting despite no change in plasma growth hormone. Thus, within the context of these studies, there was no apparent correlation between changes in endogenous growth hormone concentration and plasma NSILA-s or NSILA-s related compounds as measured by this radioreceptor assay.