Effect of hypophysectomy on pituitary adenylate cyclase-activating polypeptide gene expression in the rat testis

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a member of the secretin/glucagon/vasoactive intestinal peptide (VIP) family. Our immunohistochemical and in situ hybridization histochemical studies indicated that PACAP-like immunoreactivity (PACAP-LI) and its mRNA were present in the germ cells in the rat testis. Because the testicular function is regulated by the pituitary gonadotropins, effect of hypophysectomy on the PACAP gene expression was investigated in the rat testis as an attempt to reveal the regulation of the testicular PACAP by the pituitary. The levels of testicular PACAP mRNA, which were determined by RNase protection assay, increased 2 weeks after hypophysectomy. In contrast, the levels of radioimmunoassayable PACAP decreased 2 weeks after the surgery. Immunohistochemistry showed that hypophysectomy did not change the distribution of PACAP-LI, although the number of immunopositive cells was markedly reduced after hypophysectomy. The replacement treatments of hypophysectomized animals with FSH or LH+FSH restored testicular PACAP mRNA to the levels in the control animals. On the other hand, all of these treatments (testosterone, LH, FSH, or LH+FSH) significantly increased radioimmunoassayable PACAP in the hypophysectomized rat testis. The results suggest that both testicular PACAP and its mRNA expression are regulated by the hypothalamic-pituitary-gonadal activity, and that FSH may play a major role in this regulation.