Tissue-Specific Stimulation of Ornithine Decarboxylase Activity by Pituitary Factors Immunologically Related to Growth Hormone11

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Abstract
Ornithine decarboxylase (L-ornithine carboxylase, EC 4.1.1.17) is an important enzyme in polyamine synthesis. Its activity is influenced by several peptide hormones, including growth hormone [GH], which may have physiological significance in various growth situations. A crude ovine pituitary GH preparation (NIH-GH-S10) was subjected to gel exclusion chromatography (Sephadex G-100) and 2 major fractions were obtained. One of these corresponded to dimeric GH. The other fraction was excluded by the gel matrix, suggesting a material of high molecular weight than GH. This was confirmed by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate [SDS]. Analysis of the 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 4 fractions, which were shown by amino acid analysis and by polyacrylamide gel electrophoresis in the presence of SDS to be distinct from GH and heterogeneous. These subfractions had different potencies for stimulating renal and hepatic ornithine decarboxylase activity. The ability of crude GH 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.

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