Enzyme inducing effect of muscular exertion in the rat.

The activity of hexobarbital oxidase in vivo was found to be higher in rats forced to swim regularly (sleeping time studies). The enzyme inducing effect of spironolactone and norandrostenolone was reduced in trianed animals. Inactivation of the inducing agents is suggested to be faster in animals trained by swimming. The difference observed between test and control sleeping times was ascribed to an increased capacity of the liver to inactivate hexobarbital, while an alteration of central nervous responsiveness could be excluded since the difference in serum hexobarbital concentratios was negligible when the animals awoke. Elimination of canrenone (dethioacetylated spironolactone) was faster in trained rats. Immediately after the swimming exercise hexobarbital elimination was slower in both the trained and the control groups. Accelerated elimination, a characteristic of physical fitness, could be observed to return 5 hours after terminating the exercise.