EFFECTS OF TCDD ON VITAMIN-A STATUS AND LIVER MICROSOMAL-ENZYME ACTIVITIES IN A TCDD-SUSCEPTIBLE AND A TCDD-RESISTANT RAT STRAIN

To investigate the relationship between vitamin A status and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) lethality, the influence of TCDD on tissue and serum vitamin A levels was determined in the most TCDD-susceptible (Long-Evans) and the most TCDD-resistant (Han/Wistar) rat strains. The TCDD LD50 values of these two strains differ by a factor of more than 300. Groups of three rats per strain were used in a dose-response study (given single ip doses of 0, 4, 40, 400, 800 or 1600 μg TCDD/kg body weight and killed on day 11) and in a time-course experiment (given single ip doses of 0, 4 and, in the case of Han/Wistar rats only, 1600 μg TCDD/kg body weight, and killed on days 4, 11, 23, 50 and 76). The strains showed similar responses over the 76-day study with respect to vitamin A levels in the liver, kidneys, testicles and serum after exposure to a sublethal dose of TCDD (4 μg/kg body weight). In contrast, TCDD doses lethal to the Long-Evans strain only (40-1600 μg/kg, day 11) markedly increased kidney and serum vitamin A levels in Han/Wistar rats, while they were practically without effect in Long-Evans rats. Hepatic cytochrome P-450 concentration, and the activities of 7-ethoxyresorufin O-deethylase, ethylmorphine N-demethylase, and uridine diphosphate glucuronosyltransferase (towards p-nitrophenol) were affected by the TCDD doses in much the same manner in both strains. These findings show that the correlations between TCDD lethality and changes in vitamin A status found among species of laboratory animals do not hold for Long-Evans and Han/Wistar strains of rat. © 1990.