Steroidogenesis-stimulating activity (SSA) was examined in testicular intertubular fluid from normal, and short-term and long-term (up to 12 months) experimentally cryptorchid rats, using an in vitro Leydig cell bioassay based on testosterone production over 20 h in the presence of a maximum dose of human chorionic gonadotropin. Total fluid volume increased throughout the period of cryptorchidism, while interbular testosterone concentrations declined. SSA from cryptorchid rats was significantly greater (2- to 3-fold) than normal at all time-points; however, the major increase in activity occurred within the first 4 weeks after treatment. Similar concentrations of lipoproteins were recovered from both untreated and 4-week cryptorchid fluid by density ultracentrifugation, althoug the bioactivity of the cryptorchid testis lipoprotein fraction was 8-fold higher than the lipoprotein fraction from untreated testes. Moreover, removal of the lipoproteins led to a loss of SSA in the lipoprotein-deficient fraction of the intertubular fluid. Consequently, the in vitro bioassay conditions were modified by addition of a constant level of serum lipoproteins to all assay wells. Employing the lipoprotein-supplemented bioassay, multiple stimulatory and inhibitory activities were resolved by Sephadex G-100 gel filtration in intertubular fluid from both normal and cryptorchid testes: (i) an inhibitory activity eluting in the void volume (> 150 kDa), which decreased after cryptorchidism; (ii) a stimulatory activity (40-80 kDa), which did not appear to be affected by cryptorchidism; (iii) an inhibitory activity (20-40 kDa) which decreased after cryptochidism, and (iv) a stimulatory activity (12-20 kDa) which increased after cryptorchidism. These results indicate that the increase in testicular SSA after cryptorchidism is due to an increase in the proportion of stimulatory to inhibitory factors in intertubular fluid, and that both locally-produced and serum-derived factors are involved.
- Leydig cell