Control of hepatic triacylglycerol synthesis. Diurnal variations in hepatic phosphatidate phosphohydrolase activity and in the concentrations of circulating insulin and corticosterone in rats

Abstract

Male rats were kept for 14 days with alternating 12h periods of light and darkness. The hepatic activity of soluble phosphatidate phosphohydrolase and the concentration of serum insulin were maximum at about 2h after dark. The peak concentration of serum corticosterone occurred 2h before the dark period. It is proposed that corticosterone is partly responsible for the increased phosphohydrolase activity, and that this enables the liver to increase its capacity to synthesize triacylglycerols during the period of maximum feeding.

Effects of starvation, corticotropin injection and ethanol feeding on the activity and amount of phosphatidate phosphohydrolase in rat liver

“…Special care was taken to avoid undue stress when the rats were killed, and this may explain why our results show a decrease in phosphohydrolase activity, whereas previous work showed increases [I 8,191. We also killed all rats at the same time of day since there is a diurnal variation in phosphohydrolase activity [20]. The present results are compatible with the observation that fatty acids are preferentially oxidized in the liver in starvation, but the capacity for triacylglycerol synthesis is retained [21,22].…”

Regulation of lipin-1 gene expression by glucocorticoids during adipogenesis*

“…In addition, lipin-1 exhibits a circadian pattern of expression in liver and adipose tissue of mice, and the rhythmicity of lipin-1 mRNA expression is lost in adrenalectomized mice, suggesting control by glucocorticoids (36). Also, in rats, the maximum PAP1 activity in the liver occurs about 4 h after the diurnal peak in corticosterone concentrations (37). The ethanol-induced increase in PAP1 in the livers of rats is also strongly attenuated by adrenal- Fig.…”

Acute effects of starvation and treatment of rats with anti-insulin serum, glucagon and catecholamines on the state of phosphorylation of hepatic 3-hydroxy-3-methylglutaryl-CoA reductase in vivo

“…Although we have previously demonstrated that insulin reversed the effects of experimentally induced diabetes (Easom & Zammit, 1985), the doses of insulin used, as well as the state of the animals, in those experiments were non-physiological. In the present experiments we have induced relatively mild alterations of circulating insulin concentrations at times of the day that are characterized by low and high insulin concentrations [4 h into the light period (L4) and 4 h into the dark period (D-4) respectively (see Knox et al, 1977)]. Acute elevation of plasma insulin concentration in animals at L4 was achieved by intraperitoneal injection of glucose (200 mg;Stansbie et al, 1976).…”

“…These results suggested that the major determining signal for the high value of the E/T activity ratio at D-4 in normal animals occurred between the L/D (light/dark transition) and D-4 time points. This is a period of most active feeding and is associated with peak circulating insulin concentrations (Knox et al, 1977). By contrast, the liver appeared to be committed to the attainment of the high total activity of the enzyme interval in 4 h-starved rats.…”

“…By contrast, the liver appeared to be committed to the attainment of the high total activity of the enzyme interval in 4 h-starved rats. It is possible that the signal for the induction of synthesis of reductase mRNA is represented by the surge in corticosterone secretion that occurs at around L-10 ( Knox et al, 1977) in anticipation of active feeding in normal animals.…”