Immunohistochemical localization of two angiotensin I-converting isoenzymes in the reproductive tract of the male rabbit.

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Abstract
The male reproductive tract contains two different isoenzymes of angiotensin I-converting enzyme (ACE), i.e., pulmonary and testicular ACE. The present study shows selectively the cellular distribution of the ACE isoenzymes in the reproductive tract of male rabbit, using indirect immunofluorescence or immunoperoxidase methods. Testicular ACE was found in the seminiferous tubules of the testes in spermatocytes containing mature spermatids, and in spermatids within the epididymal tubular lumen in sexually mature, but not in immature, rabbits. Epididymal tubular cells contained pulmonary ACE. In the young rabbit, epididymal tissue contained more ACE than that in adult rabbit, since ACE was observed in principal cells in addition to basal cells. In mature rabbit, ACE was observed in basal cells only. Strong staining for pulmonary ACE was observed in cells of the vas deferens in both young and adult rabbit. Therefore, synthesis of epididymal ACE, unlike the testicular isoenzyme, was not stimulated by sexual maturation. Enzymatically active ACE in seminal fluid corresponds to the pulmonary isoenzyme. The present study indicates that this seminal fluid ACE may originate from cells of the epididymal tubules, particularly those of the vas deferens. Endothelial cells of blood vessels lying in the interstitium of both testicular and epididymal tissue contained the pulmonary isoenzyme.