Development of the diurnal rhythm of chick 3‐hydroxy‐3‐methylglutaryl‐CoA reductase

Abstract

Chick liver and intestine 3-hydroxy-3-methylglutaryl-CoA reductase did not show diurnal rhythm at hatching. Differences in activity between light and dark periods appeared during the first week and remained more or less constant between 10-14 days after hatching. Hepatic and intestinal reductase activities were maximal during the light period and minimal during the dark period. Amplitude of the rhythm was practically similar in both tissues (about 3-fold) although specific activities and differences between peak and nadir values were always higher in liver. Chick brain reductase did not show significant diurnal variations in the age range assayed.

Regulation of Cholesterol Biosynthesis

“…A diurnal cycle in hepatic cholesterol synthesis has been demonstrated in rodents (38,93,135,136), swine (122), and chickens (117). Similar fl uctua tions in cholesterol synthesis have also been demonstrated in small intestine (135) and transplantable hepatomes (59) .…”

Research Communications

“…41 A similar inhibition of reductase activity by cholesterol feeding also was observed in chick intestine 40 and in isolated enterocytes from chick duodenum, jejunum, and ileum, 42 although in this tissue differences between peak and nadir values were always smaller than those observed in liver. 43 The hypercholesterolemic effect of cholesterol was generally accompanied by the accumulation of cholesterol in liver, thus interfering with the hepatic cholesterogenesis. In fact, dietary cholesterol supplementation to the newborn chick after 10 to 15 days produced a near 10-fold increase in the hepatic esterified cholesterol, whereas no significant variations were found in free cholesterol.…”

Cyclic fluctuations of 3‐hydroxy‐3‐methylglutaryl‐CoA reductase in aortic smooth muscle cell cultures

“…In this animal, both reductase activities were maximal dur-ing the light period, in agreement with chick feeding habits. However, chick liver and intestine reductase do not show diurnal rhythm at hatching (5) or during the first week of life, when the chick is still reabsorbing the yolk (12) and thereby developing a transient hypercholesterolemia, which becomes almost three times higher in cholesterol-fed chicks (13). Indeed, the rise in reductase activity is depressed in hypercholesterolemic chicks (13) and following cholesterol or mevalonate feeding in cell cultures (14).…”

“…The rate of cholesterol biosynthesis from different tissues was shown to have a diurnal rhythm many years ago (2)(3)(4). These rhythmic changes are associated with changes in HMG-CoA reductase activity (1,2,5,6). In rodent liver, diurnal variation of hepatic cholesterol synthesis is driven primarily by varying the steady-state mRNA levels for HMG-CoA reductase (6)(7)(8)(9)(10)(11).…”

“…Although it has been well established that the diurnal rhythm of hepatic HMG-CoA reductase is associated with variations in food consumption over a 24-h cycle in the whole animal (5,6,8,27,28), the marked change that the reductase activity shows in cell cultures is not so well established and cannot be explained by the contribution of nutrients. This fluctuation of reductase in cell cultures has been associated with feeding the cells or with the cell cycle and DNA replication.…”