Noradrenaline-induced secretions of pancreatic hormones in cold- and heat-acclimated rats.

Effects of noradrenaline on the portal and aortic plasma pancreatic hormone concentrations were studied in the cold- and heat-acclimated rats in order to know possible roles of these hormones in temperature acclimation. Noradrenaline (NA) infusion (2 micrograms/min, i.v., 30 min) effected greater elevation of colonic temperature (Tc) in the cold-acclimated rats (CA) than in the warm controls (WC), and did not influence Tc in the heat-acclimated rats (HA) under hexobarbital anesthesia. Portal and aortic glucagon levels increased in the NA-infused CA and HA, but no changes were observed in the NA-infused WC. NA-infusion did not affect the portal and aortic insulin levels in WC and CA, but increased aortic insulin level in HA. Aortic glycerol and free fatty acid (FFA) levels increased in all NA-infused groups. Portal and jugular vein FFA levels increased in NA-infused WC, but did not in NA-infused CA and HA. Neither NA infusion, nor glucagon was related to the elevation of Tc in HA. These results suggest that temperature acclimation modifies a glucagon-releasing action of NA and the NA-released glucagon could cooperate with NA to enhance nonshivering thermogenesis in the cold.