Expression of preproenkephalin-like mRNA and its peptide products in mammalian testis and ovary.

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Abstract
The distributions of preproenkephalin mRNA and proenkephalin-derived peptides have been examined in gonadal tissues from rats, hamsters, and cattle. A preproenkephalin mRNA band was detected in the ovaries of all three species and in hamster testis that is identical in size to the 1450-nucleotide mRNA typically found in tissues that express proenkephalin. Rat testis, on the other hand, expresses at least one preproenkephalin-like mRNA that is substantially greater in size (1900 nucleotides). [Met]enkephalin-containing peptides were also detected in each of the gonadal tissues examined. Although the abundance of preproenkephalin-like mRNA in rat testis was comparable to that in rat brain, the testicular content of proenkephalin-derived [Met]enkephalin sequences was < 4% of the rat brain content. Together these data suggest that (i) proproenkephalin-like mRNA in rat testis is not efficiently translated, (ii) proenkephalin-derived peptides undergo rapid turnover in this tissue, or (iii) the mRNA in rat testis has a frameshift resulting in an altered coding sequence.