METABOLISM OF THE RAT LUNG AND ESOPHAGEAL CARCINOGEN N-NITROSOHEPTAMETHYLENEIMINE BY RAT LUNG FRACTIONS IN VITRO

Abstract

This thesis represents the first attempt to study the metabolism of the rat lung and esophageal carcinogen, nitrosoheptamethyleneimine (NO-HEP), by rat lung fractions in vitro.[¹⁴C]-labeled NO-HEP (labeled at the a-position) which is totally extractable from aqueous solution with methylene chloride, is maximally converted to radioactive nonmethylene chloride-extractable products by a combination of microsomes plus supernatant. This reaction does not result in the evolution of ¹⁴CO₂ The conversion of NO-HEP to aqueous-extractable products occurs optimally at pH 8.0, is inhibited by ions (Ca²⁺, Co²⁺, Fe²⁺, Fe³⁺, KC⁺, Mg²⁺, and Mn²⁺ ), and requires NADPH plus an NADPH generating system for optimal activity. The initial rate of conversion of NO-HEP to aqueous-extractable products is nearly linear for 1 hr and has an apparent Kₘ of 2.4 x 10⁻⁴M NO-HEP. Chromatographic procedures were developed for the identification and isolation of NO-HEP metabolites using Sephadex G-10, Sephadex LH-20, and the Waters high pressure liquid chromatography (HPLC) μBondapak C₁₈ columns. Although none of the metabolites was isolated in sufficient quantity for identification, there appeared to be at least six aqueous-extractable products as determined by HPLC.