PCB congener-specific disruption of reproductive neuroendocrine function in Atlantic croaker.

Exposure of Atlantic croaker to Aroclor 1254 has been shown to impair reproductive neuroendocrine function in this species. In addition, we have identified hypothalamic tryptophan hydroxylase (TPH), the rate-limiting enzyme in serotonin synthesis, as a target of PCB neuroendocrine toxicity. A previous study in rats has implicated di-ortho-substituted non-coplanar PCB congeners in the inhibition of a similar enzyme, tyrosine hydroxylase, which is the rate-limiting enzyme in dopamine synthesis. Therefore, the present study was designed to investigate whether di-ortho-substituted congeners (PCB 47, PCB 153) or a coplanar congener (PCB 77) present in Aroclor 1254 could be responsible for the reproductive impairment observed in croaker exposed to the PCB mixture. Fish were exposed to PCB 47 and PCB 153 in the diet (0, 0.2 and 1.0 mg/kg body weight/day) for 30 days and to PCB 77 (0.01 and 0.1 mg/kg body weight/day) for 15 days. Neither PCB 47 nor PCB 153 altered hypothalamic TPH activity or gonadal growth at doses similar to the effective doses of the Aroclor 1254 mixture. Therefore, these ortho-substituted PCB congeners known to be neurotoxic in mammalian systems are unlikely to contribute to Aroclor 1254-induced reproductive neuroendocrine disruption in croaker. In contrast, PCB 77 significantly inhibited hypothalamic TPH activity and gonadal growth at doses much lower than the effective doses of Aroclor 1254. The results provide the first evidence for PCB congener-specific disruption of reproductive neuroendocrine function in a vertebrate species.