Characterization of Immunoreactive Proopiomelanocortin-Related Peptides in Rat Testes

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Abstract
.alpha.-Endorphin, .beta.-endorphin, .gamma.-endorphin and N-terminal ACTH immunoreactivity were detectable in acid extracts of rat testes with concentrations of 0.07 .+-. 0.01, 0.18 .+-. 0.03, 0.06 .+-. 0.01, and 0.33 .+-. 0.08 (.+-. SD) pmol/g wet wt, respectively. The forms of these immunoreactive peptides were characterized by reverse phase high performance liquid chromatography. Immunoreactive .beta.-endorphin was also analyzed by gel filtration and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The major form of immunoreactive .beta.-endorphin present appears to be .beta.-endorphin-(1-31). No .alpha.-N-acetylated forms of .beta.-endorphin or .beta.-lipotropin-sized material were detected. Immunoreactive .alpha.- and .gamma.-endorphin appear to be present as .alpha.-endorphin and des-Tyr1-.gamma.-endorphin, respectively. Immunoreactive .alpha.MSH was present as its desacetylated form. No immunoreactive ACTH fractionating with ACTH-(1-39) or its glycosylated forms was detected. This peptide profile is most similar to that seen for proopiomelanocortin-derived peptides in the brain. The low concentrations of these peptides in rat testes suggest a paracrine function.