Hormonal Regulation of Spermidine Formation during Spermatogenesis in the Rat*

The activities of ornithine decarboxylase and S-adenosyl-L-methionine decarboxylase have been correlated with spermidine content and morphological criteria of cell differentiation during hormone-dependent spermatogenesis in the rat. The specific activity of ornithine decarboxylase was maximal at 3 days of age at a time when only Sertoli cells were present in the seminiferous tubules, but the specific activity was markedly reduced with the formation of additional cell types. The specific activity of S-adenosyl-L-methionine decarboxylase increased steadily during spermatogenesis, reaching a plateau with spermatozoan maturation. Spermidine concentration generally paralleled the specific activity of ornithine decarboxylase, and evidenced an increase during spermatid maturation. Hypophysectomy prevented these characteristic developmental enzyme changes and reduced testis spermidine content. Stimulation with daily injections of FSH and LH or of testosterone maintained the normal developmental pattern and the specific activity of S-adenosyl-Lmethionine decarboxylase, but the specific activity of ornithine decarboxylase and spermidine concentration were not returned to normal by these hormonal treatments. However, ornithine decarboxylase was rapidly induced after each injection of gonadotropins, reaching maximal values after 6 hr, and then rapidly declining. Albumin density gradient separation of cell types indicated that spermatids and several other cell types have no detectable ornithine decarboxylase activity and that this enzyme is associated almost entirely with rapidly sedimenting cell types, particularly Sertoli cells. These studies demonstrate a characteristic pattern of hormone-dependent changes in enzymes utilized for spermidine synthesis during spermatogenesis in the rat. They suggest that biochemical cooperativity exists between cells for the accumulation of spermidine: the Sertoli "nurse" cells alone synthesize putrescine which may be utilized subsequently as a substrate in them or in other cells to form the spermidine found in spermatids and spermatozoa. (Endocrinology92: 595, 1973)