Influence of temperature on basal and induced hepatic monooxygenase activity in rats of different ages.

The effect of temperature on the rates of ethylmorphine N-demethylation and ethoxycoumarin O-deethylation was studied with liver homogenates prepared from 1- to 120-day-old rats. Breaks at temperatures of 21.5-28.0 degrees C were observed in the Arrhenius plots of these reactions, differences being dependent mainly on age of the animals rather than on reaction type. No breaks could be demonstrated for ethylmorphine N-demethylation with liver homogenates of 10- and 120-day-old rats and for ethoxycoumarin O-deethylation in newborn and 120-day-old rats. In poikilothermic 3-, 10- and homothermic 30-day-old rats ethylmorphine N-demethylation rate was dependent on incubation temperature (7, 20 and 37 degrees C). The relative increase in N-demethylation rate after phenobarbital treatment was most marked in 30-day-old rats at an incubation temperature of 37 degrees C. In infantile rats the relative induction was highest at 7 degrees C.