Proteolytic fragmentation of rat prolactin by the rat ventral prostate gland

Homogenates of rat ventral prostate diminished the immunoreactivity of rat prolactin (PRL) in a fashion dependent on time and tissue concentration, suggestive of hormone degradation. Direct evidence of PRL proteolysis was demonstrated by subjecting ventral prostate homogenates and cell fractions that were incubated with 125I-labeled rat PRL to SDS-PAGE and radioautography. Heat-labile PRL proteolysis predominated in the crude homogenate, the 3,300g pellet and the 100,000g (100 K g) supernatant of rat ventral prostate. The degradation of PRL by the 100 K g supernatant led to the formation of two stable peptide fragments weighing approximately 16,000 and 12,000 daltons. PRL proteolysis was negligible in 100 K g supernatants of the liver, salivary gland, testis, epididymis, vas deferens, seminal vesicle, and dorsolateral prostates of male rats. On the other hand, 100 K g supernatants of rat spleen, lung, and kidney did degrade rat PRL, although the patterns of peptide fragment formation differed from that of ventral prostate. Enzyme inhibitor analysis suggested that PRL degradation by the 100 K g supernatants of rat ventral prostate was due to sulfhydryl and serine proteases and not due to metalloenzyme or aspartate proteases. The functional significance of PRL fragmentation by rat ventral prostate cytosol remains to be determined.