The immunohistochemical localization of alpha 2-macroglobulin in rat testes is consistent with its role in germ cell movement and spermiation.

alpha 2-Macroglobulin (alpha 2-MG) is a nonspecific protease inhibitor and binding protein for peptide hormones that was recently isolated from Sertoli cell-enriched culture medium and shown to be the same protein as alpha 2-MG in serum. The present study was conducted to determine the localization of alpha 2-MG in the seminiferous epithelium in order to gain insight into its possible site(s) of action. Immunostainable alpha 2-MG was present in the lumen of the tubules consistent with its proposed role as a protease inhibitor needed to inactivate the protease released from defective spermatozoa in the male reproductive tract. Immunoreactive alpha 2-MG was also localized adjacent to the heads of elongated spermatids, the most mobile cells in the seminiferous epithelium; immunostainable alpha 2-MG was not observed adjacent to round spermatids and spermatocytes, which are relatively less mobile. The intensity of the staining around the elongated spermatids was dependent on the stage of the spermatogenic cycle. Stainable alpha 2-MG was present adjacent to the spermatids in stage XI soon after the elongation process began. Immunoreactive product was in stages XI-XIV but only faintly visible. The most intense staining reaction for alpha 2-MG was in stages I-VI; it was reduced in stage VII; and virtually no alpha 2-MG was detectable in stages VIII-X at and just after spermiation. The postnatal changes of alpha 2-MG in the testis was also examined. During the first 2 weeks after birth, alpha 2-MG was not detected in the seminiferous epithelium.(ABSTRACT TRUNCATED AT 250 WORDS)