Effect of excessive intake of ascorbic acid on hepatic and extra-hepatic phase I and phase II drug metabolism in rat.

: Guinea pig is the animal model of choice for studies on effects of ascorbic acid (AA). However, rat is one of the largely used animals for investigations related to chemical carcinogenesis. Therefore, the present study was designed to evaluate the changes induced by high intake of the vitamin in xenobiotic and carcinogen metabolizing status of the organs. Male Wistar rats, dosed daily with 50 mg AA/100 g body weight for 10 weeks, demonstrated a small non-significant increase in hepatic, pulmonary and colon cytochrome P-450 (Cyt. P-450) contents, which was accompanied with a significant increase in hepatic and pulmonary arylhydrocarbon hydroxylase (AHH) activities. Phase II enzymes of drug metabolism responded in different ways to increased intake of AA. UDP-glucuronyltransferase (UDPGT) activity was unaffected in liver and colon, but it was increased (p less than 0.005) in lung. Activities of glutathione S-transferase (GST) were decreased in the three organs. Inducibility of AHH by 3-methylcholanthrene (MCA) or phenobarbital (PB) was largely reduced due to AA feeding. Besides this, MCA and PB had differential effects on enzymatic levels in AA fed rats. When compared with our earlier observations in guinea pig, it was found that rat responded similarly to guinea pig to increased intake of AA with regard to hepatic AHH, Cyt. P-450, UDPGT and GST, pulmonary AHH, Cyt. P-450 and Cyt. b5, and all studied colon enzymes, except GST.