The phagocytic function of Sertoli cells: a morphological, biochemical, and endocrinological study of lysosomes and acid phosphatase localization in the rat testis.

The lysosomal population of the seminiferous tubules of the rat was studied by conventional electron microscopy and electron microscopic histochemistry. Biochemical determinations of acid phosphatase were carried out in whole cell suspensions of seminiferous tubular cells or in different cell populations purified by sedimentation in albumin gradients. Lysosomes were rarely found in spermatogonia and primary spermatocytes. Young spermatids showed up to six lysosomes per section, and this number increased as spermatid maturation proceeded. Residual bodies had a very heterogeneous lysosomal content. Sertoli cells showed cyclical variations in their lysosomes. These were present in small numbers from stages I-IV of the cycle of the seminiferous epithelium and progressively increased to be numerous in Sertoli cells at stages VI-VIII. After spermiation, their rapidly decreased. Acid phosphatase contents were (nanomoles of nitrophenol formed per mg protein/min): whole cell suspension, 67.5 +/- 7.8; pachytene spermatocytes (72% purity), 76.5 +/- 10.6; round spermatids (73% purity), 95.0 +/- 2.8; residual bodies (88% purity), 96.0 +/- 14.2; and Sertoli cell-enriched fraction, 278.5 +/- 75.7. In a group of rats, endogenous LH and testosterone were lowered by administration of anti-LH antibodies. There was an intense degeneration of meiotic spermatocytes, which were phagocytized and digested by these immature testosterone-depleted Sertoli cells. It is concluded that lysosomes of the seminiferous epithelium show cyclical variations, with an increase toward the time of spermiation and a decrease after the residual bodies have been digested; the acid phosphatase and lysosomal contents of Sertoli cells are higher than those of germ cells, residual body disposal is probably initiated by autophagy and completed by Sertoli cell phagocytosis; and the phagocytic function of Sertoli cells is not hormone (testosterone) dependent.