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

The Lutcher Brown Department of Biochemistry The Whittier Institute for Diabetes and Endocrinology La Jolla, California 92037
The Department of Pediatrics, University of California, San Diego La Jolla, California 92093

Address all correspondence and requests for reprints to: Edith Markoff, Ph.D., The Whittier Institute, 9894 Genesee Avenue, La Jolla, California 92037.

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 (hGH_22K) and the 20,000-dalton form (hGH_20K). 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 hGH_22K/ml· day. and 0.67 0.17 µg hGH_20Kml·day. GHRH (10^–8 M) treatment resulted in stimulation of both hGH_22K and hGH_20K by 24 h. We also measured both hGH_22K and hGH_20K in the sera of normal subjects before and after an iv bolus injection of 100 µg GHRH. hGH_20K increased as did hGH_22K. 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 hGH_22K and hGH_20k 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.

^* This work was supported by Grants HD-06153 and BRSG-S07 RR-05876 from the NIH. A portion of this work was conducted through the Clinical Research Center of the University of California, San Diego Medical Center, supported by NIH Grant RR-00827.

Received June 19, 1985.