Adverse Effects of Cadmium on Brook Trout Testis and on in Vitro Testicular Androgen Synthesis

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Abstract
Testes of mature brook trout exposed to 25 ppb Cd for 24 h in soft freshwater (8°–12°C) showed marked discolorations. Histological examination revealed extensive hemorrhagic necrosis and disintegration of lobule-boundary cells. The nuclei of the lobule boundary cells were pyknotic. There was no detectable damage to the primordial germ cells, which in fish are the initial sites of spermatogenesis. In another experiment in which 16 male fish were continuously exposed to 10 ppb Cd, 7 out of 8 fish examined immediately postmortem showed similar injury but the damage was not as extensive. There was no testicular damage observed in the corresponding 20 male controls. A very weak sudanophilic staining reaction was observed in the lobule boundary cells of the damaged testes when compared with control testes. This result indicated reduction of lipid content and suggested some disturbance of steroid production in the Cd-damaged testes. When equal amounts of tissue from the midtestes of the fish exposed to 25 ppb Cd and that of the control were each incubated with [4-14C]pregnenolone in vitro, 14C-labeled 11-ketotestosterone was detectable in the control but not in the Cd-damaged tissue incubation mixture. The yields of 11β-hydroxytestosterone and testosterone were significantly higher in the control than in the Cd-damaged tissue incubation. The effects of varying concentrations of Cd (0, 10, 100, and 1000 µg Cd/1 g tissue) on normal mature brook trout testis incubated with [4-14C]pregnenolone in vitro gave the following significant results: (1) Cd inhibited the biosynthesis of 11-ketotestosterone from the radioactive precursor and the conversion of exogenous pregnenolone to “free” steroid metabolites; (2) Cd also altered the biosynthesis of unknown radioactive metabolites, not included in our analyses, as shown by x-ray autoradiography of the initial thin-layer chromatogram of the dichloromethane extracts of the control and Cd-treated tissue incubation mixtures. Synthesized steroids were identified by repeated chromatography and crystallization with authentic radioinert steroids. Our experimental results give conclusive evidence that Cd directly affects testicular steroidogenesis in the brook trout in vitro.

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