Changes in the Metabolism of the Shivering Hind Leg of the Young Ox During Several Days of Continuous Cold Exposure

Abstract

The effect of 4 days of continuous exposure to a cold environment on blood flow in, and oxygen and energy substrate uptake by the shivering hind leg has been studied in young steers. The animals shivered throughout the period of cold exposure and total oxygen consumption (total V0o) remained 40-50% greater than Vo, during thermoneutrality. Leg blood flow (leg 0) and oxygen uptake (leg Vo,) increased two-and four-fold respectively on the first day of cold. Both had declined significantly by the final day, leg Q to a level 37% greater than, and leg Vo, to about double, pre-cold levels. The change in the relationships of leg 0 and leg Vo2 to total V0r was examined by linear regression analysis, which suggested that the changing contribution of leg V01 to total Vo2 was entirely due to changes in leg Q, rather than in the arteriovenous difference in blood oxyhaemoglobin saturation across the leg. The net uptakes by the leg of free fatty acids (FFA), acetate, glucose and lactate all increased on the first day of cold. Both glucose and acetate uptakes were greater on day 4 than on day 1 in the cold, in spite of the lower leg Vo , but net uptakes of FFA and lactate were considerably lower. The decrease in net uptake of FFA is attributed mainly to an increase in the rate of lipolysis and release of FFA from fat depots in the leg, because of the associated progressive increase in the release of glycerol and oleic acid from the leg. The molar ratios of net carbohydrate substrate, acetate and FFA uptakes to leg Vo, are compared.The results suggest that tissues other than the leg muscles become increasingly important as sites of heat production, and that there are changes in the utilization of glucose, acetate and FFA by shivering muscle, during prolonged cold exposure.When the young steer is exposed to cold for several hours, vigorous shivering in the muscles of the hind legs is associated with substantial increases in leg blood flow (leg 0) and oxygen uptake (leg Vo,) [Bell, Thompson and Findlay, 1974]. This increase in leg metabolism is supported by increases in the net leg uptake of plasma volatile fatty acids (VFA) [Bell, Gardner and Thompson, 1974] and free fatty acids (FFA) and blood glucose and lactate [Bell, Gardner, Manson and Thompson, 1975], the relative importance of these substrates depending on time after feeding. However, under natural conditions, cattle can be subjected to cold for periods much longer than several hours. It has been reported that ex'posure of mature non-lactating, non-pregnant cows to sub-zero temperatures for 3 days results in continuous shivering, which is most vigorous after 1 day in the cold, and in elevated peripheral plasma FFA and glucose levels on all 3 days [Olsen and Trenkle, 1973]. However, little is known about the metabolism of shivering muscle during other than acute cold exposure in cattle or any other species.The present experiments were therefore done to measure any changes which might occur in oxygen uptake and the pattern of energy substrate utilization by the leg during ...

The distribution of blood flow between individual muscles and non‐muscular tissues in the hind limb of the young ox (Bos taurus): values at thermoneurality and during exposuer to cold.

“…The detection of an increased blood flow during cold exposure is therefore all the more notable and it seems likely that an even greater response would have been obtained if only the subcutaneous and intermuscular depots had been considered. This increase is consistent with the apparent increase in the rate of lipolysis in bovine leg adipose tissue during cold exposure (Bell et al 1975), although during noradrenaline infusion, at least, lipolysis and vasodilatation in adipose tissue are not necessarily directly related (Mjos & Akre, 1971).…”

“…For this reason, and because of its surgical accessibility, the hind limb has been extensively used in this laboratory as a means of studying the metabolism of shivering muscle in vivo in the conscious ox (e.g. Bell et al 1975). However, dissection of hind limbs from the young steers used in these experiments showed that almost 40 % of the limb consists of the non-muscular tissues bone, skin, connective tissue and fat.…”

Acute Cold Exposure and the Metabolism of Glucose and Some of Its Precursors in the Liver of the Fed and Fasted Sheep

“…However, liver glycogen reserves could not support the observed rate of glucose release for more than several hours. The sustained elevation in glucose production and utilization during more prolonged cold exposure of sheep [McKay et al, 1974] and young cattle [Bell, Clarke and Thompson, 1975] must therefore be associated with a substantially increased rate of gluconeogenesis, because little glucose is of directly dietary origin in the normally-fed ruminant [Leng, 1970]. The present results and those of Thompson et al [1975] for hepatic uptake of non-hexose glucose precursors, in sheep exposed to cold for several hours, support this contention.…”