EFFECT OF 4 ENVIRONMENTAL TOXICANTS ON PLASMA CA AND ESTRADIOL-17-BETA AND HEPATIC P450 IN LAYING HENS

In a previous study, we found that administration of phenobarbital to laying hens was associated with an increase in content of liver cytoch rome P450 and a reduction in concentration of estradiol (E2) in serum. Thus, we hypothesized that other xenobiotics such as environmental to xicants that affect P450 might also affect E2 in laying hens. In exper iment 1, we examined the effect of four environmental pollutants, thre e of which induce different isoenzymes of P450 and one inhibitor, on c irculating E2 and related reproductive functions. Aroclor 1254 (PCB), 20 mg/d; dichlorodiphenyltrichloroethane (DDT), 40 mg/d; or benzo[a]py rene (BZ), 5 mg/d, was administered for 5 d. An inhibitor, lead acetat e (100 mg in glycerol/saline), was injected for 2 d. Controls received corn oil or sodium acetate. No significant difference was observed du e to administration of lead. Treatment with PCB or DDT decreased the c oncentration of E2 and increased P450. Only PCB significantly decrease d plasma total calcium and egg lay. Therefore in experiment 2, we dete rmined the dose-response effect of PCB. The PCB was given orally at do ses of 0, 5, 10, and 25 mg in corn oil for 5 d. The depression of conc entrations of E2 was associated with the induction of P450 in a dose-d ependent manner. Egg production and plasma total calcium were reduced by the two highest doses, but eggshell thickness was not different fro m control in all regimens. Plasma E2 and plasma total calcium were neg atively correlated with induction of P450. BZ is not a strong inducer of P450 and had no effect on E2 or reproduction, whereas DDT and PCB h ad a profound effect on P450 with consequent depression of circulating E2. These data indicate that the effects of environmental pollutants on reproduction in birds can be mediated through increased P450, there by increasing the metabolism of steroid hormones and depressing concen tration in circulation.