Tissue-specific stimulation of ornithine decarboxylase activity by pituitary factors immunologically related to growth hormone.

Abstract

Ornithine decarboxylase (L-ornithine carboxylase, EC 4.1.1.17) is an important enzyme in polyamine synthesis. Its activity is influenced by several peptides hormones, including growth hormones, which have physiological significance in various growth situations. A crude ovine pituitary growth hormone preparation (NIH-GH-S10) was subjected to gel exclusion chromatography (Sephadex G-100) and two major fractions were obtained. One of these corresponded to dimeric growth hormone (GH). The other fraction was excluded by the gel matrix, suggesting a material of higher molecular weight than GH. This was confirmed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. Analysis of a high molecular weight fraction by radioimmunoassay (antisera prepared against GH) and by bioassay (weight gain in hypophysectomized rats) gave apparent GH contents of 19% and 6%, respectively. On a weight basis, the high molecular weight fraction was more effective than GH in stimulating the activity of hepatic and adrenal ornithine decarboxylase, but GH was more effective in stimulating renal ornithine decarboxylase activity. Subfractionation of the high molecular weight fraction using a high porosity gel (Sephadex G-200) gave four fractions, which were shown by amino acid analysis and by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate to be distinct from GH and heterogenous. These subfractions had different potencies for stimulating renal and hepatic ornithine decarboxylase activity. The ability of crude growth hormone preparations to stimulate ornithine decarboxylase activity in some tissues may be a function of pituitary factors, in addition to GH, which have minimal growth promoting activity.