Plasma Biological and Immunore active Human Growth Hormone-like Activity¹

Abstract

Plasma samples from normal and acromegalic and patients were fractionated by gel filtration and then concentrated by ultrafiltration. The amounts of protein, immunoreactive HGH (IR-HGH), and the in vitro sulfation factor (SF) activity of the fractions were determined and expressed per 0.1 distribution coefficient (Kd) intervals. More than 50% of the total IRHGH in all plasmas was eluted in a molecular size range greater than extracted pituitary HGH (ep-HGH), indicating plasma IR-HGH activity in a molecular size larger than ep-HGH or in association with other plasma proteins. Significant IR-HGH activity was found in the Kd areas corresponding to a molecular size smaller than ep-HGH. Acromegalic patient plasma showed a relatively greater amount of IR-HGH in the ep-HGH molecular size area compared to normal plasma. The maximal total SF activity occurred in a molecular size range greater than ep-HGH but the maximum SF potency of the eluted proteins, prior to Kd 0.65, occurred in the ep-HGH molecular size area. Acromegalic plasma contained a greater amount of more potent SF activity-stimulating substance (s). In vitro SF activity is not stimulated by ep-HGH in physiologic amounts; however, plasma SF activity is dependent on pituitary HGH. The general parallelism between SF and IR-HGH activity in the plasma fractions suggests that the SF is similar in size to ep-HGH; however, they cannot be identical. It is possible that ep-HGH is different from plasma HGH and from endogenous pituitary HGH. Native pituitary HGH may be modified before or after secretion into plasma so that it has one or more biologic activities perhaps associated with different portions of the HGH molecule or it may induce the synthesis of an in vitro biologically active substance (s) in other tissue with subsequent secretion into the circulation. Characterization of the in vitro biologically active substances in plasma which are pituitary HGH dependent would be of value in directing attempts at synthesis as well as explaining certain clinical discrepancies. (Endocrinology87: 506, 1970)