Evidence for “Big” and “Little” Components of Human Plasma and Pituitary Growth Hormone

Abstract

Plasma growth hormone as well as immunochemical grade pituitary growth hormone is comprised of at least two discrete immunoreactive components. “Little” growth hormone elutes from columns of Sephadex G-100 (superfine) co-incident with the major component of pituitary growth hormone. “Big” growth hormone is less retarded on the gel and approximately twice the molecular weight of “little” growth hormone. In many plasma samples, a small and broader peak of immunoreactive growth hormone is eluted between “big” growth hormone and the void marker. When freed from plasma, “little” growth hormone maintains its characteristic gel nitration migration whereas from 8 to 33% of “big” growth hormone is converted to “little” growth hormone with prolonged storage. Lyophilization results in the preferential loss of “little” growth hormone. In non-lyophilized samples “big” growth hormone constitutes from 6–14% of the total immunoreactive growth hormone in acromegalics studied in the basal state and 24–37% in normal subjects following insulin hypoglycemia.The chemical nature and physiologic significance of “big” growth hormone are unclear; the heterogeneity of endogenous plasma and pituitary growth hormone must be taken into account, however, in a host of physiologic and pathologic conditions where the immunoreactive growth hormone concentration does not correlate with the expected biologic response.