Abstract:Two genetically distinct substrains of the Wistar rat (RR and rr) were used to study the tissue distribution of the inducibility of aldehyde dehydrogenase (ALDH). The RR substrain is responsive to phenobarbital (PB), as far as the induction of the hepatic ALDH activity is concerned, whereas the rr substrain is deprived of this biochemical property. Both substrains, however, respond to treatment with methylcholanthrene (MC), exhibiting a uniform increase of the ALDH activity in the liver. It is known that PB and MC induce two different isozymes of the hepatic cytosol. The effect of PB (1 g/l in drinking water, for 12 days) on the inducibility of ALDH in extrahepatic tissues was examined in the RR substrain. On the contrary, MC was given (50 mg/kg x 4, intraperitoneally) to rr animals. The activity of ALDH was found to be induced by PB in the liver and the intestinal mucosa, when measured with NAD and propionaldehyde (P/NAD) or phenylacetaldehyde (Ph/NAD). An increase of the activity was also noticed when ALDH was measured with NADP and benzaldehyde (B/NADP). In rr animals, MC induced the B/NADP activity in the liver, the intestinal mucosa, the kidneys, the lungs, the spleen, the brain, the urinary bladder and the heart. The effect of MC on various tissues was less distinct, when ALDH was measured as P/NAD or Ph/NAD activity. It is concluded, that PB and MC not only induce different types of ALDH activity, but they also reveal differences in the tissue distribution of the inducibility of ALDH.