Effects of hydroxyurea and benzo(a)pyrene on DNA synthesis in the isolated perfused rat lung.

Abstract

A perfused rat lung model is described for the measurement of DNA synthesis by [3H]-thymidine incorporation in terms of its response to inhibitors of DNA synthesis and carcinogens. Hydroxyurea (5-50 mM) inhibited DNA synthesis by 95% yet did not disrupt lung energy metabolism as indicated by cytosolic NADH/NAD + measured by lactate/pyruvate ratios. Perfused lung DNA synthesis was also inhibited 60% by in vivo administration of benzo(a)pyrene (6 mg/kg, i.p.) for 3 days. The application of this system as a sensitive indicator of lung damage caused by pneumotoxic environmental compounds is discussed. A wide variety of compounds, including chemotherapeutic and other pharmacologic agents, herbicides and insecticides, industrial solvents, and various naturally occurring toxicants, produce acute pneumotoxic effects when administered to animals by oral, subcutaneous, intravenous, or intraperitoneal routes (COLLIS 1980; BOYD 1980). A potentially sensitive indicator of lung damage is alteration of lung DNA synthesis, a parameter not readily measured in intact animals. We have, therefore, investigated the feasibility of utilizing a perfused rat lung model to: (i) determine whether DNA synthesis can he measured ex vivo by [3H]-thymidine incorporation, (2) determine the response of DNA synthesis to hydroxyurea with the eventual aim of characterizing chemically-induced DNA damage by measuring unscheduled DNA synthesis, and (3) to examine the effect of in vivo pretreatment of the known pneumotoxic compound benzo(a)pyrene on DNA synthesis in the rat lung.