Secretion of multiple forms of human luteinizing hormone by cultured fetal human pituitary cells

Previous studies of the heterogeneity of human LH have employed LH stored within the pituitary gland. In this study we characterized LH secreted by dispersed fetal human pituitary cells. Chromatofocusing across a pH 9-6 gradient of the medium in which fetal pituitary cells had been grown yielded at least eight distinct peaks of LH immunoreactivity. The more basic LH peaks bound more strongly to Concanavalin-A-Sepharose than did the more acidic ones, suggesting that the more basic LH molecules contain more hybrid oligosaccharides, in which one antenna terminates in a mannose, and that the more acidic human LH molecules contain more complex oligosaccharides, in which both antennae terminate in negatively charged groups, sialic acid and/or N-acetylgalactosamine-sulfate. The biological/immunological activity (B/I) ratios of the secreted LH varied directly and dramatically with the pI, from 8.1 at pI 8.4 to 1.1 at pI 6.3. Secreted LH, therefore, exhibits similar heterogeneity of glycosylated forms as does stored LH, raising the possibility that the hormones that control overall LH secretion could affect the secretion of some isohormones more than others and thereby influence LH biological activity to a degree not predicted by measuring total LH immunoreactivity.