Expression of the Prodynorphin Gene in Male and Female Mammalian Reproductive Tissues

Recent studies suggest that opioid peptides may be involved in modulating the hypothalamus-pituitary-gonadal axis at a variety of levels in both males and females. We report here the presence of mRNA coding for the opioid peptide precursor prodynorphin in rat ovary, uterus, and testis. Expression of this opioid peptide precursor gene is compared to expression of two other opioid peptide precursor genes, proenkephalin and proopiomelanocortin, in mammalian reproductive tissues. Immunohistochemical analysis reveals that in the rat testis, prodynorphin-derived peptides are present in Leydig cells. The distribution of dynorphin immunoreactivity in various reproductive tissues was determined. Male reproductive tissues of the rat, rabbit, and guinea pig as well as rat ovary and uterus all contain detectable levels of dynorphin immunoreactivity. These observations suggest that prodynorphin-derived peptides may exert paracrine and/or autocrine effects in mammalian reproductive tissues.