Unusual heterogeneity of circulating prolactin in an acromegalic

Plasma from a 69-year-old acromegalic woman with hyperprolactinemia (350-570 ng/ml) was chromatographed on dextran gel. Three components of immunoactive prolactin were observed. Component I eluted with an apparent molecular weight (MWapp) of greater than 100,000, Component II with MWapp of 45,000 and Component III with MWapp of 21,500 daltons (indistinguishable from monomeric pituitary prolactin). Components I and II comprised more than 70% of the total circulating prolactin. All components had similar activities in immunoassays and in receptor assays. Components II and III maintained their elution positions on re-chromatography. Component I whether frozen or stored at 4 C eluted in the position of Component II on rechromatography, suggesting that Component I is a loosely-bound oligomer of Components II or III, or Component III loosely-bound to another constituent of plasma. The gel chromatography pattern for immunoactive growth hormone was indistinguishable from that of other acromegalic patients.