The proenkephalin gene is widely expressed within the male and female reproductive systems of the rat and hamster.

The distribution of proenkephalin mRNA in reproductive tissues of the rat and hamster was examined by Northern analysis and RNA blot hybridization. In the male reproductive tract of both species, proenkephalin mRNA was detected in the testis, vas deferens, epididymis, seminal vesicles, and prostate. Except in the case of the rat testis, the size of this transcript in each organ was identical to that generally observed in tissues expressing proenkephalin (1450 nucleotides). The major proenkephalin mRNA species expressed in the rat testis migrates as a 1900-nucleotide RNA on denaturing agarose gels. In the male rat and hamster, the highest abundance of proenkephalin mRNA was found in the testis and epididymis. A 1450-nucleotide proenkephalin mRNA also was detected in each of the 3 female reproductive tissues of the rat and hamster that were examined: uterus, oviduct, and ovary. These unusual observations suggest that proenkephalin-derived peptides are synthesized at multiple sites within the male and female reproductive tracts of the rodent and may locally regulate reproductive function.