In vitro hepatic drug and anesthetic metabolism of rats with dietary-induced obesity.

The mechanism for enhanced metabolism of inhaled anesthetics in obese rats and humans is unknown. In this study, hepatic microsomes from normal-weight chow-fed rats and rats fed a high fat diet for approximately 54 weeks to induce obesity were examined for their ability to metabolize fluorinated inhalation anesthetics. Body composition of rats on diet for 54 weeks revealed a significantly elevated lipid content of both the whole body and liver in obese compared to normal-weight rats. Protein per g liver was not significantly different. The hepatic microsomal content of cytochromes b5 and P-450 per mg protein was not different between obese and normal-weight rats. Hepatic microsomal defluorination rates of the anesthetics, methoxyflurane, enflurane and isoflurane, were not altered by high fat diets of 54 weeks duration. The activity rate of aminopyrine N-demethylase was not changed by the diet; however, p-nitroanisole O-demethylase activity was significantly increased in microsomes from obese rats to approximately 150% of control activity. Thus the enhanced in vivo anesthetic metabolism of obese Fischer 344 rats does not appear to be the result of an increase in the specific activity of anesthetic metabolizing enzymes.