The metabolic effects in man of bovine growth hormone digested with trypsin

Abstract

Purified bovine growth hormone was subjected to controlled tryptic proteolysis, the reaction being terminated with soybean trypsin inhibitor. The extent of hydrolysis, as determined by alkali uptake on a pH-stat and change in zone electrophoretic pattern, has been correlated with growth-promoting activity in the rat. Nearly complete disappearance of the electrophoretic components present in untreated bovine growth hormone occurred after 10 min. of tryptic digestion, accompanied by an alkali uptake of 5 to 6 moles/mole of protein. The 10 min. digests, although containing a series of intermediate, faster migrating components, retained growth promoting activities in the rat as high as 1 USP unit/mg. or more. Digestion for 60 minutes increased the alkali uptake to over 13 moles/mole of protein and produced a mixture of yet faster moving components containing activity of only 0.1 unit/mg. Under conditions of complete metabolic balance, 19 studies were performed in 10 hypophysectomized and one hypopituitary patient injected with tryptic digests of bovine growth hormone, undigested bovine growth hormone or human growth hormone. In studies employing tryptic digests of bovine growth hormone, responses were noted among diabetic patients of aggravated hyperglycemia and glycosuria, decreased carbohydrate tolerance, and production of ketonuria. Such digests also produced increased insulin resistance. In other studies, the digests promoted retention of nitrogen, phosphorus, sodium and potassium, increased urinary calcium, and caused depression of blood urea nitrogen and elevation of serum inorganic phosphorus. Instances were also noted of increased urinary hydroxyproline and decreased urinary creatine. In 3 of 4 studies, typical metabolic responses to human growth hormone occurred but not to undigested bovine growth hormone administered to one patient. No correlation was readily apparent between the electrophoretic components present in the digests and the metabolic responses resulting from their administration.