Diurnal rhythm of HMG CoA reductase activity in canine intestine is independent of luminal contents.

Activity of the enzyme 3-hydroxy-3-methylglutaryl coenzyme A reductase (EC 1.1.1.34) measured in isolated segments of canine intestinal mucosa showed a distinct diurnal rhythm. Total activity changed over a twofold range with a peak occurring during midday, shortly after feeding. Since the isolated segments had no contact with luminal contents, the rhythm was not directly related to food components or bile salts. Humoral or neural influences must mediate the rhythm. The diurnal rhythm persisted for at least 3-5 mo, but was lost by 10 mo following formation of the isolated segment, possibly because of mucosal involution.