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

Abstract

Two experiments were conducted to study the adrenergic regulation of thermogenesis in sheep during acute cold exposure and feeding. Propranolol, a nonselective β-blocker, metoprolol, a β1-blocker and ICI 118551, a β2-blocker, were used to investigate the β-adrenoceptor mediated whole-body and organ oxygen consumption (VO2). Whole-body oxygen consumption was measured by open circuit calorimetry. Portal-drained viscera and hindquarter oxygen consumption was the product of arterio-venous oxygen concentration difference and blood flow across the respective organs. Acute cold exposure increased (P < 0.05) whole body and hindquarters VO2 by about 60% but, not that of the portal drained viscera. Feeding induced a 41% elevation (P < 0.05) in whole body and a nonsignificant increase in the portal drained viscera VO2. The β-adrenoceptor blockers suppressed the increase in whole body VO2 associated with acute cold exposure but, only the reduction induced by the β2-adrenoceptor antagonist (ICI 118551) was significant (P = 0.02). The response to feeding was not altered by the β-blockers. This study suggests that the β-adrenoceptor system plays a role in modulating whole body but not the portal-drained viscera acute cold-induced thermogenesis, and this modulation of energy expenditure may involve a β2 receptor subtype. Key words: Calorimetry, thermogenesis, cold, feed and sheep