Biological activity of bacterial derived human growth hormone in adipose tissue of hypophysectomized rats.

Abstract

Segments of epididymal fat from hypophysectomized rats were incubated in Krebs-Ringer bicarbonate buffer for 1-4 h. Responses to three bacterially synthesized human GH (hGH) preparations were compared with responses to two highly purified pituitary hGH preparations. Hormones of both bacterial and pituitary origin increased the rate of oxidation of [U14C] glucose to 14CO2 and antagonized epinephrine-stimulated lipolysis. These insulin-like effects were produced over a range of 30-300 ng/ml hGH, and their concentration dependence was quite similar regardless of the source of hormone. Exposure of tissues to GH in the first hour of incubation makes them refractory to the insulin-like actions of a test dose of GH added in the fourth hour of incubation. hGH of either pituitary or bacterial origin also appeared to be equipotent in producing such refractoriness. The minimal effective concentration for this response fell between 10 and 30 ng/ml. Hormones from both sources were also capable of displacing 125I-labeled hGH from specific binding sites on isolated adipocytes, and the displacement curves were superimposable. Fifty percent displacement was seen at concentrations in the range of 10-20 ng/ml. Cell preparations produced a delayed increase in lipolysis which was evident in the presence of 0.3 mg/ml of theophylline in the fourth hour of incubation. In this regard, two of the bacterial hGH preparations were more potent than pituitary hGH and produced statistically significant increases in lipolysis at concentrations 10-30 times lower than pituitary hGH studied simultaneously in tissues of the same rats. Despite the presence of less than 1% contamination with bacterial protein, the greater potency of the bacterial hGH may be due to material of bacterial origin, since one bacterial hGH preparation, which was further purified to remove 99% of the remaining bacterial contamination was equipotent with pituitary hGH. These data indicate that a protein hormone synthesized in bacteria, and therefore likely to be free of peptides which might contaminate hGH purified from pituitary extracts, has all of the diverse physiological effects in adipose tissue that have been observed with preparations of GH derived from pituitary glands. These findings lend strong support to the conclusion that both insulin-like and lipolytic actions of GH are intrinsic properties of the molecule and cannot be attributed to contaminants present in the pituitary extract.