Participation of Skeletal Muscle and Kidney During Nonshivering Thermogenesis in Cold-Acclimated Rats

Abstract

The oxygen consumption of the partly isolated leg muscles and of the kidney was measured in situ in cold-acclimated rats before and during exposure to cold or during noradrenaline infusion. All rats had been anesthetized with sodium barbital and those exposed to cold had been fully curarized to prevent muscle activity. During cold exposure and noradrenaline infusion oxygen consumption of the rats was approximately doubled, and the oxygen consumption of leg muscles was approximately doubled without increase in blood flow. No increase in oxygen consumption was observed in the kidney during exposure to cold or noradrenaline infusion in spite of an increase of 75% in the oxygen consumption of the whole animal. Direct evidence for significant participation of striated muscles in non-shivering thermogenesis has thus been obtained. However, it appears unlikely that the maximal potential increase in oxygen consumption of cold-acclimated rats at very low temperatures could be attributed solely to the metabolic activity of skeletal muscles.

Seasonal Changes in Body Mass, Composition, and Organs of Northern Red-Backed Voles in Interior Alaska

“…Acclimatization to winter conditions is associated with declines in the size of muscle tissue (red and white muscle fibers) in small rodents (Wiclder, 1981). This is important because muscle tissue is the site of shivering thennogenesis and a contributor to non-shivering thermogenesis (Jansky and Hart, 1963), Results of regressions of log muscle mass of the hind quarter versus log body mass indicated that changes in muscle had a proportionally greater effect on the overall changes in body mass for males compared with females.…”

Multiple actions of β-adrenergic agonists on skeletal muscle and adipose tissue

“…Skeletal muscle, due to its bulk, may be an important site of adrenergicinduced thermogenesis in human as well as in other animals. Adrenergic agonists have been demonstrated to increase oxygen consumption in skeletal muscle [110][111][112][113]. Although f-receptors in skeletal muscle are shown to be predominantly f2 [22][23][24][25], Challiss et al [1 14] recently compared the activity of various f-agonists and antagonists on the glycogen synthesis and lactate production in incubated muscle, and concluded that the 'A2' receptor in skeletal muscle is different from the classical fl2 receptor in smooth muscle.…”

Na+channel and Na+-K+ATPase involvement in norepinephrine- and veratridine-stimulated metabolism in perfused rat hind limb

“…This may provide a mechanism for the facultative thermogenesis seen in resting skeletal muscle in response to NE demonstrated by us Clark et al 1995) and others (Jansky and Hart 1963;Grubb and Folk 1977;Richter et al 1982;Côté et al 1985;Shiota and Masumi 1988) in the constant flow perfused muscle preparation. However, there still remains uncertainty as to the identity of the tetrodotoxininsensitive sodium channel that NE, angiotensin II, and related vasoconstrictors indirectly activate and the mechanism(s) by which this activation occurs.…”

“…However, the exact function of UCP-3 is unknown, even though the involvement of this protein in skeletal muscle thermogenesis has been implied (Gong et al 1997;Larkin et al 1997). A third candidate mechanism for resting muscle thermogenesis relates to the observed stimulatory effects of adrenergic vasoconstrictors, particularly in perfused muscle preparations (Jansky and Hart 1963;Grubb and Folk 1977;Richter et al 1982;Côté et al 1985), where apart from an accompanying increase in perfusion pressure, little is known about the underlying mechanism. Studies from this laboratory have extended those original findings by showing, in the perfused rat hind limb preparation, that thermogenesis is stimulated by other vasoconstrictors including angiotensin II (AII) and vasopressin (Colquhoun et al 1988;Ye et al 1990).…”