Mismatch between patterns of circulating and testicular androgens in African catfish, Clarias gariepinus

11-Ketotestosterone (11-KT) is an important plasma androgen in male African catfish. The quantitatively predominating androgen produced by the testis, however, is 11 beta-hydroxyandrostenedione (OHA). Our working hypothesis to explain this mismatch assumed that OHA is converted to 11-KT at extratesticular sites. First, we examined the in vivo metabolism of [H-3]-OHA in mature males after sham-operation or removal of either the testes (TC), the seminal vesicles (SVC), or both (TSVC) by analysing the pattern of circulating [H-3]-androgens two hours after intravenous injection of [H-3]-OHA. [H-3]-OHA was converted to [H-3]-11-KT to the same extent in all groups, indicating that neither ablation of testes nor of seminal vesicles, or both attenuates this conversion. We then examined the in vitro metabolism of [H-3]-OHA by several types of tissues. Liver and seminal vesicle tissue were found to produce significant amounts of [H-3]-11-KT. The conversion capacity in vivo was assessed by injecting TSVC-castrated males with increasing doses of radioinert OHA, followed by the quantification of OHA and 11-KT plasma levels. Saturation of the conversion capacity was not reached but the 11-KT production capacity is at least 80 ng per ml of plasma per hour. Moreover, liver fragments were tested for their OHA to 11-KT conversion capacity in vitro using increasing concentrations of radioinert OHA. The 11-KT producing increased with time and OHA concentration. The production rate was 90 pg 11-KT mg(-1) liver h(-1). Considering the results of the surgical experiments and the fact that the total hepatic mass by far exceeds that of the seminal vesicles, we conclude that the hepatic conversion is of primary relevance in vivo.