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Regulation of N-Nitrosodimethylamine Demethylase in Rat Liver and Kidney¹

Department of Biochemistry, UMDNJ-New Jersey Medical School, Newark, New Jersey 07103-2757

In previous work, the low K_m form of N-nitrosodimethylamine (NDMA) demethylase has been demonstrated to be due to a specific form of cytochrome P-450 (designated as P-450ac) and to be the enzyme required for the metabolic activation of NDMA. The present work deals with the regulation of P-450ac in rat liver during development as well as the mechanism of induction of P-450ac in rat liver and kidney by inducers. NDMA demethylase activity was almost undetectable in the liver of newborn rats, increased after day 4, and remained elevated throughout the first 17 days of the neonatal period. The enhancement of NDMA demethylase activity during development was accompanied by corresponding increases of P-450ac content and P-450ac mRNA levels as determined by Western and slot blot analyses, respectively. No sex differences with respect to this enzyme were observed in the developing rats. Acetone treatment on late-term pregnant rats for 2 days resulted in transplacental inductions of P-450ac and P-450ac mRNA in the newborn rats. Pretreatment of young male rats and adult female rats with acetone or isopropyl alcohol caused increases of NDMA demethylase activity and P-450ac content in the liver but no significant change in the P-450ac mRNA level. These facts suggest the possible existence of a posttranscription regulatory mechanism under these induction conditions. The presence of P-450ac in rat kidney was demonstrated by Western and Northern blot analyses. The renal form of P-450ac seemed to be regulated in a fashion similar to the hepatic P-450ac regarding its response to inducing factors such as fasting and acetone treatment.

¹ This work was supported by Grants ES-03938 and CA-37037 from the NIH.

² To whom requests for reprints should be addressed.

Received 4/29/87. Revised 8/20/87. Accepted 8/24/87.

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