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PCB congener-specific disruption of reproductive neuroendocrine function in Atlantic croaker
1The University of Texas at Austin, Marine Science Institute, Port Aransas, TX 78373, USA. ikhan@utmsi.utexas.edu
Abstract:
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.
Insights
Polychlorinated biphenyls (PCBs) disrupt fish reproduction. Coplanar PCB 77, but not ortho-substituted congeners, significantly inhibited reproductive neuroendocrine function in Atlantic croaker by reducing tryptophan hydroxylase activity.
Area of Science:
- Environmental Toxicology
- Endocrinology
- Neuroscience
Background:
- Aroclor 1254 exposure impairs Atlantic croaker reproductive neuroendocrine function.
- Hypothalamic tryptophan hydroxylase (TPH), key for serotonin synthesis, is a target of PCB neuroendocrine toxicity.
- Di-ortho-substituted PCBs may inhibit enzymes like tyrosine hydroxylase in mammals.
Purpose of the Study:
- Investigate if specific PCB congeners (PCB 47, 153, 77) in Aroclor 1254 cause reproductive impairment in Atlantic croaker.
- Determine if di-ortho-substituted or coplanar PCBs are responsible for observed neuroendocrine disruption.
Main Methods:
- Atlantic croaker were fed diets containing PCB 47 and PCB 153 (0.2, 1.0 mg/kg/day) for 30 days.
- Fish were exposed to PCB 77 (0.01, 0.1 mg/kg/day) for 15 days.
- Hypothalamic TPH activity and gonadal growth were measured.
Main Results:
- PCB 47 and PCB 153 did not alter TPH activity or gonadal growth at relevant doses.
- Coplanar PCB 77 significantly inhibited hypothalamic TPH activity and gonadal growth at lower doses than Aroclor 1254.
- Ortho-substituted PCBs are unlikely contributors to Aroclor 1254-induced reproductive neuroendocrine disruption.
Conclusions:
- PCB congener-specific effects on reproductive neuroendocrine function were demonstrated in Atlantic croaker.
- Coplanar PCB 77 is a likely causative agent for Aroclor 1254-induced reproductive neuroendocrine disruption in this species.
- This study provides the first evidence of PCB congener-specific disruption in a vertebrate.
