The Oxygen Consumption, Fatty Acid and Glycerol Uptake of the Liver in Fed and Fasted Sheep During Cold Exposure

Abstract

The effect of a short period (3-4 hr) of exposure to cold on the liver's circulation and metabolism has been studied in sheep fed 6 hr or 21 hr before experiment.In the cold the animals had a significantly increased heart rate, cardiac output, hepatic portal blood flow, mean arterial blood pressure and pulse pressure. Total peripheral resistance fell in the fasted animals when they were exposed to cold, but not the more recently fed animals. Exposure to cold significantly increased the total body oxygen consumption and oxygen consumption of the liver, but not that of the portal-drained viscera (gut, spleen, pancreas, omental adipose tissue). Recent feeding significantly increased the net rate of release of volatile fatty acids from the portal-drained viscera, and significantly increased their net rate of uptake by the liver. In the recently fed animals, exposure to cold further increased the visceral release, portal plasma concentration, and hepatic uptake of volatile fatty acids. Exposure to cold, and fasting, both significantly increased the circulating (arterial) plasma level of free fatty acids and glycerol, and increased their net rate of uptake by the liver, significantly in cold exposure but not in fasting.The results show that the liver makes a small contribution to the total increase in oxygen consumption in the cold. The liver also has an increased uptake of fatty acids and glycerol during cold exposure.Mammals increase their total body oxygen consumption (V02), and therefore heat production, when they are exposed to cold. It is not known precisely which tissues are responsible for this increase. In particular it is not known to what extent the liver is one of the organs in the body that has an increased heat production during cold exposure. Functional evisceration of anaesthetized cold-acclimated rats, which includes ligation of the portal vein, does not prevent them from increasing their total body VO2 in the cold, by the same amount as control animals. However, this technique does not eliminate the possibility that other tissues may compensate for any loss of liver heat production [Depocas, 1958]. Measurements of the temperature difference between the hepatic vein and the hepatic portal vein in unanaesthetized dogs show an increase in the temperature difference when ice is applied to the skin of the animal [Fedorov and Shur, 1942] suggesting an increase in liver heat production in response to a cold stimulus. Similar measurements of liver temperature, corrected for liver blood flow (Q), show a fall in liver heat production when unanaesthetized rats, acclimated to 20°C, are put into a warmer environment [Stoner, 1973].The present experiments were designed to measure the V02 of the liver and relate this to total body V02 during acute cold exposure of unanaesthetized sheep. In view of the reported changes in lipid oxidation in sheep during cold exposure [Graham, Wainman, Blaxter and Armstrong, 1959] and the increase in circulating free fatty acids (FFA) [Bost and Dorleac, 1965] and glycerol 107

Metabolic responses of the whole body, portal-drained viscera and hind quarter to acute cold exposure and feeding in sheep: Effects of nonselective and selective β-adrenoceptor blockade

“…The significant increase in whole-body oxygen consumption in response to cold is consistent with previous observations reported in the literature (Thompson et al 1975;Webster et al 1969). These authors showed that cold exposure caused at least a two-fold increase in metabolic activity, a change comparable with the response observed in the present study.…”

“…The increase in whole body oxygen consumption in response to feeding is in agreement with published results (Webster and Hays 1968;Thompson et al 1975;Christopherson and Brockman 1989). The lack of response to the β-blockers only partially agrees with the data of Christopherson and Brockman (1989) For personal use only.…”

“…These data also confirm previous conclusion by other workers that cold exposure had little or no effect on the oxygen consumption of the portal-drained viscera of the sheep (Thompson et al 1975). Evidently, the endogenous release of adrenaline, unlike the exogenous adrenaline (Miaron and Christopherson 1997) was not sufficient to induce an increase in portal-drained viscera metabolism in sheep during an acute cold exposure.…”

“…The portal-drained-viscera oxygen consumption was slightly, but not significantly, increased by the acute cold exposure confirming the data reported by Thompson et al (1975) in which the liver but not the portal-drained viscera was found to be involved in cold-induced thermogenesis. The nonselective and selective β-blockers had no apparent effects on portal-drained viscera oxygen consumption.…”

“…The nonselective and selective β-blockers had no apparent effects on portal-drained viscera oxygen consumption. Our data differ somewhat from those of Thompson et al (1975) in that we observed no increase in portal vein blood flow in response to cold exposure. However, our data are consistent with those of their later study (Thompson et al 1978) in which a small nonsignificant increase in the portal blood flow in response to an acute cold exposure was observed.…”