A marked molecular heterogeneity of growth hormone (GH) detected in the plasma but not pituitary of a patient with acromegaly: comparison with other acromegalics and an implication for discrepant plasma levels of GH and insulin-like growth factor

Abstract

We experienced a 41-year-old acromegalic male (Case 1) in whom the basal plasma GH was extremely high (320-450 ng/mL) but plasma IGF-I was only slightly elevated (2.0-2.8 U/mL). His nutritional condition and associated diabetes mellitus did not appear to be responsible for the relatively low IGF-I level, and a GH-autoantibody in the plasma was absent. We thus performed gel filtration analyses of his plasma and somatotroph adenoma to determine elution patterns of immunoreactive (IR) and receptor active (RA) GH. For comparison, the same studies were carried out on plasmas and somatotroph adenomas obtained from three other acromegalics (Cases 2-4) whose basal plasma GH and IGF-I levels were 22-45 ng/mL and 3.5-6.0 U/mL, respectively. IR GH in Case 1's plasma distributed over an extremely wide range keeping similar titers rather than showing three discernible components (big-big, big, and little GH) as did plasmas and adenomas from Cases 2-4. And, most of the IR GH in Case 1's plasma was eluted in such fractions that contained low levels of RA GH, indicating a minor proportion of biologically active GH. However, interestingly, the chromatographic profile and total GH content of Case 1's adenoma were similar to those of Cases 2-4's adenomas. These results may, at least in part, explain the discrepancy between the plasma GH and IGF-I levels of Case 1. The unexpectedly different GH elution patterns between the plasma and adenoma from this patient, may suggest a contribution of certain plasma factor(s) to the unusual chromatographic profile of plasma GH.