Abstract
The relevance of immune‐endocrine interactions to the regulation of testicular steroidogenesis in teleosts is virtually unexplored. The objectives of the present study were: 1) to investigate the effects of murine cytokines, tumor necrosis factor‐α (TNFα) and interleukin‐1β (IL‐1β), and trout (Oncorhynchus mykiss) macrophage conditioned media (MCM) on testosterone (T) production by goldfish (Carassius auratus) testis pieces in vitro; and 2) to identify the site(s) of the inhibitory action of TNFα on hCG‐stimulated T formation. TNFα (0–100 ng/ml) affected basal T production differentially depending on the gonadosomatic index (GSI) value of the fish. TNFα stimulated basal T of fish with a relatively low GSI (average 1.99), but inhibited T production by testis of fish with a higher GSI (average 5.14). The remaining studies used fish with only high GSI values. IL‐1β (0–10 ng/ml) inhibited basal T production, while MCM (0–25% v/v) had no effect. The cytokines significantly inhibited hCG‐stimulated T production at all doses tested, whereas MCM was inhibitory only at the lower doses of 2.5–5% v/v. TNFα did not affect basal or hCG‐stimulated cAMP levels, but did inhibit forskolin (0.5 μM; adenylate cyclase activator) and 8‐bromo‐cAMP (0.15 mM; cAMP analog) stimulated T levels. The inhibitory actions of TNFα on T production were greatly reduced by treatment of testis with 25‐hydroxycholesterol (1 and 10 μg/ml), pregnenolone (50 and 100 ng/ml), and 17α‐hydroxypregesterone (50 ng/ml). TNFα caused a moderate decrease in pregnenolone (100 ng/ml)‐stimulated T production. Together, these data demonstrate that regulatory actions of TNFα may occur at multiple sites within the steroid biosynthetic pathway, but the major effect appears to be related to cholesterol availability in the mitochondria. In conclusion, the results of this study implicate macrophage‐derived factors in the regulation of teleost testicular androgen biosynthesis. J. Exp. Zool. 292:477–486, 2002. © 2002 Wiley‐Liss, Inc.