Paracrine regulation of Leydig cells by the seminiferous tubules.

Testes of adult control and unilateral cryptorchid rats were fixed by vascular perfusion. The cell profile area of peritubular Leydig cells surrounding tubules in different stages of spermatogenesis, and the cell profile area of perivascular Leydig cells were determined. The size of peritubular Leydig cells was dependent on which type of tubulus the cells were surrounding. Some peritubular Leydig cells, especially those surrounding stages VII-VIII (88.1 +/- 7.1 micrometers2, mean +/- SD, n = 6 rats), were larger than perivascular Leydig cells (69.3 +/- 5.9 micrometers2). The size of Leydig cells surrounding stages IX-XIV was similar to that of perivascular cells. In the abdominal testes no spermatogenic cycle was present and the sizes of peritubular and perivascular Leydig cells were equal (63.0 +/- 5.1, vs 66.7 +/- 7.3 micrometers2, mean +/- SD, n = 5 rats). It is suggested that the tubules and the spermatogenic cycle locally modulate Leydig cell activity and that Leydig cell malfunction in abdominal testes may be due to a decreased stimulatory influence from the damaged tubules.