The Induction of Cytochrome P-450 by Hypoxia

Abstract

A number of apparently unrelated observations have led us to look for daily fluctuations in the level of liver cytochrome P-450. We have observed that there seems to be a rather wide variation in P-450 concentrations in different animals of the same sex, age, and species. In addition the Chouteau phenomenon is pronounced in men after midnight, whereas the same stress has no effect in the afternoon. The third observation is that the response to certain drugs is greater in man after midnight than during the day, whereas in nocturnal species the same phenomenon is seen twelve hours out of phase. Since cytochrome P-450 appears to play an important role in both tissue oxygen transport and drug inactivation, these latter effects could be associated with a diurnal variation in the concentration of this pigment.