Cytochrome P450 (CYP) 2E1 activity is induced after 24 h of fasting bu
t no information is available for shorter fasting periods. We investig
ated the induction of CYP 2E1, 2B1/2 and 1A1 in young adult male F344
rats after 8, 16 and 24 h of fasting compared to control. Liver micros
omes were analyzed for the following enzyme activities: p-nitrophenol
hydroxylase (PNP) for CYP 2E1, pentoxyresorufin-O-dealkylase (PROD) fa
r CYP 2B1/2 and ethoxyresorufin-O-deethylase (EROD) for CYP 1A1. After
each fasting interval, the activities per mg microsomal protein for P
NP and PROD increased but the activity of EROD remained unchanged. Wes
tern blots for CYP 2E1 and CYP 2B1 showed increases comparable to the
PNP and PROD activities, respectively. On a whole organ basis, increas
es were found for PNP and PROD activities, while decreases were found
for EROD activity and total microsomal protein. The results are consis
tent with an induction of CYP 2E1 and CYP 2B1/2 activities after as li
ttle as 8 h of fasting.