Hormonal control of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase during development of the rat epididymis

The specific activities of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase were determined during growth of the rat epididymis. Ornithine decarboxylase activity was first detectable on day 21 and increased 10-fold in both the head and tail of epididymis prior to their rapid growth responses. Hypophysectomy reduced ornithine decarboxylase activity to undetectable levels, but enzyme activity was restored by treatment with gonadotropins or testosterone. Testosterone also induced a precocious 10-fold increase of epididymal ornithine decarboxylase in the pre-pubertal rat. In contrast, the specific activity of S-adenosyl-L-methionine decarboxylase changed little during development and merely doubled in response to hormonal treatments. The results describe a pattern of changes in these enzyme activities during hormone-dependent development of the epididymis, and suggest that ornithine decarboxylase is the rate-limiting activity in the regulation of spermidine biosynthesis by testosterone in this organ.