The heterogeneity of bovine growth hormone. Extraction from the pituitary of components with different biological and immunological properties

Bovine growth hormone (somatotropin) was extracted from anterior pituitaries and fractionated into four protein peaks (A-D) by chromatography on DEAE-Sephacel. Analysis by high-pressure liquid chromatography and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis indicated that the homogeneity of the material increased from fraction A through to D. The properties of the fractions were examined in the following manner: immunological activity (radioimmunoassays for ruminant growth hormone and prolactin); growth-promoting activity (rat tibia test); lipolytic activity (release of glycerol from rat epididymal fat in the presence of dexamethasone); diabetogenic activity (rate of glucose transport in epididymal fat of hypophysectomized rats and intravenous insulin-tolerance tests in goats). None of the fractions contained immunoreactive prolactin and all were equally lipolytic. Although fraction A contained a small quantity of immunoreactive growth hormone it had no growth-promoting or diabetogenic activities. Both fractions B and C were diabetogenic and contained high concentrations of immunoreactive growth hormone, consistent with their growth-promoting activity. Although the growth-promoting activity of fraction D was higher than that of the other three fractions, it was not diabetogenic and was only weakly immunoreactive. These results for bovine growth hormone support the contention that growth hormone, as commonly extracted, is a mixture of different molecular forms and that these different metabolic properties of the hormone might be explained in terms of this heterogeneity.