Circadian rhythms of sterol 12 alpha-hydroxylase, cholesterol 7 alpha-hydroxylase and DBP involved in rat cholesterol catabolism

Circadian rhythms of important enzymes involved in the conversion of choles terol to bile acids [sterol 12 alpha -hydroxylase (12 alpha -hydroxylase) a nd cholesterol 7 alpha -hydroxylase (7 alpha -hydroxylase)] and an albumin site D-binding protein (DBP) were examined in rats. When the animals were f ed freely, they usually ate in the dark and the circadian rhythms of activi ties of 12 alpha -hydroxylase and 7 alpha -hydroxylase showed the same peak s (at 10 p.m,) and lows (at 2 p.m.), Their mRNA levels were determined at f our timepoints: 3 a.m., 10 a.m., 3 p.m, and 10 p.m, A maximum of the rhythm of 12 alpha -hydroxylase was observed at 3 p.m. and the minimum at 3 a.m. These results are distinct from those of 7 alpha -hydroxylase, whose maximu m point was at 10 p.m. and minimum at 3 p.m. When the rats were fed only in the daytime (from 9 a.m. to 5 p.m.), a marked shift of the activity and mR NA rhythms was observed with both enzymes. The circadian rhythms of the act ivities of both enzymes showed the same peaks (at 3 p.m.), but the mRNA lev els of 12 alpha -hydroxylase were distinct from those of 7 alpha -hydroxyla se, whose maximum point was at 3 a.m. and minimum at 10 p.m. Differences be tween the maximum and the minimum points of each enzyme mRNA level were sta tistically significant (P < 0.01 for 12<alpha>-hydroxylase and 0.05 for 7 a lpha -hydroxylase). Moreover, circadian rhythms of DBP were also markedly s hifted with the change of feeding period. The maximum mRNA level was observ ed at 10 p.m. instead of 10 a.m. and the minimum was at 10 a.m, instead of 10 p.m.