Regulation of stages VI and VIII of the rat seminiferous epithelial cycle in vitro

Abstract

Plasminogen activator (PA) is secreted cyclically (in stages VII and VIII) by rat seminiferous tubules. To investigate whether this can be maintained and influenced in vitro, tubule segments from stages VI and VIII of the epithelial cycle were cultured for 3 days in chemically defined medium supplemented with testosterone, FSH, or a combination of testosterone, FSH, insulin and retinoic acid (4F). Morphological and flow cytometric analyses of stage VI tubules suggested a roughly normal differentiation to stage VIII. They developed an increased PA secretion on day 3 of culture. Stage VIII tubules, however, did not develop all the characteristics of stage XII. Step 8 spermatids did not elongate and step 19 spermatids failed to develop into spermatozoa. Secretion of PA on day 3 was not significantly different to that on day 1. The 4F combination very significantly stimulated PA secretion in both stages, but FSH alone was effective only in stage VIII. Most of the secreted PA had a molecular weight of 43,000 in both stages, suggesting that it is of urokinase type. The results suggest that stage VI is more able to differentiate in vitro for 3 days than stage VIII; the cyclic secretion pattern of PA was partially maintained in tubule segments from stage VI. Follicle-stimulating hormone had an effect on PA secretion only in stage VIII, whereas the 4F combination was stimulatory in both stages. The retinoic acid in this combination may be of importance in the regulation of PA secretion by seminiferous tubules.