Effect of four environmental toxicants on plasma Ca and estradiol 17β and hepatic P450 in laying hens

Abstract

AbstractIn a previous study, we found that administration of phenobarbital to laying hens was associated with an increase in content of liver cytochrome P450 and a reduction in concentration of estradiol (E2) in serum Thus, we hypothesized that other xenobiotics such as environmental toxicants that affect P450 might also affect E2 in laying hens In experiment 1, we examined the effect of four environmental pollutants, three of which induce different isoenzymes of P450 and one inhibitor, on circulating E2 and related reproductive functions Aroclor 1254 (PCB), 20 mg/d, dichlorodiphenyltrichloroethane (DDT), 40 mg/d, or benzo[a]pyrene (BZ), 5 mg/d, was administered for 5 d An inhibitor, lead acetate (100 mg in glycerol/salme), was injected for 2 d Controls received corn oil or sodium acetate No significant difference was observed due to administration of lead Treatment with PCB or DDT decreased the concentration of E2 and increased P450 Only PCB significantly decreased plasma total calcium and egg lay Therefore in experiment 2, we determined the dose‐response effect of PCB The PCB was given orally at doses of 0, 5, 10, and 25 mg in corn oil for 5 d The depression of concentrations of E2 was associated with the induction of P450 in a dose dependent manner Egg production and plasma total calcium were reduced by the two highest doses, but eggshell thickness was not different from control in all regimens Plasma E2 and plasma total calcium were negatively cor related with induction of P450 BZ is not a strong inducer of P450 and had no effect on E2 or reproduction, whereas DDT and PCB had a profound effect on P450 with consequent depression of circulating E2 These data indicate that the effects of envi ronmental pollutants on reproduction in birds can be mediated through increased P450, thereby increasing the metabolism of steroid hormones and depressing concentration in circulation