Release of the 22,000- and the 20,000-Dalton Variants of Growth Hormone in Vivo and in Vitro by Human Anterior Pituitary Cells*

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Abstract
Using a combination of polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate and immunoblotting with antihuman GH (anti-hGH) serum, we quantitatively and independently measured the major 22,000-dalton form of hGH (hGH22K) and the 20,000-dalton form (hGH20K). This technique was equally effective in assaying cell culture media or human sera. We studied isolated human pituitary cell cultures during a 16-day incubation period with and without stimulation by GHreleasing hormone (GHRH). Under basal conditions, the cells released 2.83 ± 0.24 (±SEM) μg hGH22K/ml· day. and 0.67 0.17 µg hGH20Kml·day. GHRH (10−8 M) treatment resulted in stimulation of both hGH22K and hGH20K by 24 h. We also measured both hGH22K and hGH20K in the sera of normal subjects before and after an iv bolus injection of 100 μg GHRH. hGH20K increased as did hGH22K. Peak concentrations of both variants occurred 45 min after GHRH administration. The results of this study indicate, that the combination of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and immunoblotting is an accurate and effective means of separately assaying hGH22K and hGH20k We also demonstrated that primary monolayer cultures of human pituitary cells are an excellent model system for study of the secretion of these two hGH variants.

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