Altered profiles of biological activity of growth hormone fragments on adipocyte metabolism.

A highly purified preparation of human GH (hGH) and two large fragment complexes (Da1 and Dc2) isolated from plasmin digests of reduced and S-carbamidomethylated hGH were tested for their ability to produce five different biological responses in segments of epididymal fat obtained from hypophysectomized rats. Judging by the minimal concentration of hormone needed to produce a statistically significant response, hGH was 3-10 times as potent as Da1 and Dc2 in increasing the oxidation of [U-14C]glucose to 14CO2, hGH and Da1 were equipotent in stimulating the oxidation of L-[1-14C]leucine to 14CO2, antagonizing the lipolytic effect of epinephrine, and inducing refractoriness to the insulin-like action of hGH. At least 3 times as much Dc2 was required to produce significant responses. Da1 was 10 times more active than hGH in producing delayed lipolysis in the presence of theophylline and 30 times as effective as Dc2. These findings suggest that the various responses to GH that can be measured in adipose tissue may result from more than one kind of interaction between GH and adipocytes. (Endocrinology 108: 553, 1981)