EFFECTS OF PHOTOISOMERS OF CYCLODIENE INSECTICIDES ON LIVER AND MICROSOMAL CYTOCHROME-P450 IN RATS

Threshold dosages of the photoisomers of cyclodiene insecticides, name ly photochlordane, photodieldrin, and photoheptachlor, for the inducti on of hepatic microsomal cytochrome P450 (P450) and liver hypertrophy in male rats were at least one-quarter of those reported for correspon ding parent cyclodienes. Maximum increase in total P450 concentration (30%) and demethylases activities (100%) was always respectively one-t hird or one-tenth of that reported for parent cyclodienes. The P450 is ozymic form induced by photoheptachlor resembled that induced by pento barbital (P4502B1) in its substrate specificity. spectral characterist ics, and electrophoretic mobility. The induction of P450 was initially followed by hepatic hypertrophy. However, higher dosages of photoisom ers caused wasting and lowered both the liver weight and the activity of aniline hydroxylase while those of mirex and endrin. which also cau sed wasting and lowered aniline hydroxylase activity, continued causin g further hepatic hypertrophy.