Rate-limiting, diurnal activity of hepatic microsomal cholesterol-7 alpha-hydroxylase in pigeons with high serum cholesterol.
Efficiency of regulating serum cholesterol by cholesterol-7 alpha-hydroxylase was studied in pigeon strains hypo-(SR-39) and hypercholesterolemic (SR-37) with respect to dietary cholesterol. Diurnal hydroxylase activity in SR-37 was 10% of that in strain SR-39 adapted to a light-dark cycle and fed a non-cholesterol diet. Acrophase (6 p.m.) activity was 54-fold greater in SR-39 than in SR-37 pigeons. Dietary cholesterol elevated enzyme activity 2.8-fold in SR-37 pigeons. Dietary cholestyramine plus cholesterol increased hydroxylase activity 21-fold in SR-37 and 3-fold in SR-39 strain; yet, activity remained greater in SR-39. Cholestyramine feeding prevented elevated cholesterol levels in both groups. The circadian rhythms of hydroxylase and serum corticosterone were determined. The diurnal activity in SR-37 was 10% of that in SR-39 and acrophase activity was 34-fold greater in SR-39. Hormone levels were comparable. Programmed acrophase was asynchronous between strains. Hydroxylase activity was positively correlated with corticosterone levels and inversely correlated with serum cholesterol. A defect in the up-regulation of cholesterol-7 alpha-hydroxylase is proposed which limits the catabolism of cholesterol in strain SR-37.
D000818:Animals; D002784:Cholesterol / Q000097:blood*; D002790:Cholesterol 7-alpha-Hydroxylase / Q000378:metabolism*; D002791:Cholesterol, Dietary / Q000494:pharmacology; D002792:Cholestyramine Resin / Q000494:pharmacology; D002940:Circadian Rhythm; D010856:Columbidae / Q000378:metabolism*; D003345:Corticosterone / Q000097:blood; D003600:Cytosol / Q000201:enzymology; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D013250:Steroid Hydroxylases / Q000378:metabolism*
D002791:Cholesterol, Dietary; D002792:Cholestyramine Resin; D002784:Cholesterol; D013250:Steroid Hydroxylases; D002790:Cholesterol 7-alpha-Hydroxylase; D003345:Corticosterone