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 BETA-ADRENOCEPTOR BLOCKADE

Two experiments were conducted to study the adrenergic regulation of t hermogenesis in sheep during acute cold exposure and feeding. Proprano lol, a nonselective beta-blocker, metoprolol, a beta(1)-blocker and IC I 118551, a beta(2)-blocker, were used to investigate the beta-adrenoc eptor mediated whole-body and organ oxygen consumption (VO2). Whole-bo dy 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 dra ined viscera. Feeding induced a 41% elevation (P < 0.05) in whole body and a nonsignificant increase in the portal drained viscera VO2. The beta-adrenoceptor blockers suppressed the increase in whole body VO2 a ssociated with acute cold exposure but, only the reduction induced by the beta(2)-adrenoceptor antagonist (ICI 118551) was significant (P = 0.02). The response to feeding was not altered by the beta-blockers. T his study suggests that the beta-adrenoceptor system plays a role in m odulating whole body but not the portal-drained viscera acute cold-ind uced thermogenesis, and this modulation of energy expenditure may invo lve a beta(2) receptor subtype.