Local differences in Leydig cell morphology in the adult rat testis: evidence for a local control of Leydig cells by adjacent seminiferous tubules

In order to test the hypothesis that Leydig cell function in the adult rat testis is influenced by the surrounding tubules, Leydig cell morphology was compared in different types of interstitial areas. Triangular interstitial areas surrounded by 3 cross-sectioned tubules in nearly the same stage of spermatogenesis were chosen for quantitative light microscopy. It was found that the volume density of Leydig cells in such areas was about 30%, except when the surrounding tubules were in stages IX-X or XI-XII, when it was only about 20%. This variation in total Leydig cell mass seemed to be due to a variation in Leydig cell size and not in Leydig cell number. The largest Leydig cell profile area, 118 +/- 6 micrometers 2 (mean +/- SE n = 6 rats), was observed when the surrounding tubules were in stages VII-VIII, i.e. just prior to sperm release. The smallest Leydig cells were seen when the surrounding tubules were in stages IX-X and XI-XII (68 +/- 3 and 66 +/- 4 micrometers 2). The present results indicate that there may be a Leydig cell cycle in the adult rat testis, which is regulated by the adjacent tubules.