Twenty-kilodalton human growth hormone (20K hGH) secretion from growth hormone-secreting pituitary adenoma cells in vitro

Circulating human growth hormone (GH) consists of several molecular isoforms. Increased proportion of circulating non-22K hGH and 20K hGH was reported in active acromegaly. In this study, we studied the release of 20K and 22K hGH from cultured GH-producing human pituitary adenoma cells in vitro. Pituitary adenoma cells obtained from 6 acromegalic patients were cultured and submitted to perifusion experiments. Concentrations of 20K and 22K hGH in the serum and the perifusion effluent were determined by specific enzyme-linked immunosorbent assays recently developed. The %20K value varied in a wide range from 3.58 to 8.72% in vitro and was lower than in the serum (mean+/-SD: 6.57+/-1.88% vs 9.08+/-2.12%, P<0.05). There was no correlation between the %20K values in vitro and in vivo (r=0.31, P>0.05). The in vitro secretions of 20K and 22K hGH were in parallel and strongly correlated (r=0.953, P<0.001). These findings suggest that different GH-producing pituitary adenoma cells secrete 20K hGH in variable amounts and that the proportion of 20K hGH in the serum might be affected by metabolic clearance of hGH isoforms. It was also suggested that 20K and 22K hGH might be secreted in toto from GH-producing human pituitary adenoma cells.