The responses of intact rats to cold-exposure (4°C) include vasoconstriction, piloerection, shivering, adrenocorticotrophin (ACTH) hypersecretion and increased mobilization of free fatty acids and glucose. Adrenal demedullation prevents the increased mobilization of glucose and decreases survival time. Chemical sympathectomy blocks all of the responses except ACTH hypersecretion. Such animals lose body heat rapidly and die in a few hours. Total adrenalectomy has a similar effect. The damaging actions of chemical sympathectomy are reversed by administration of catecholamines while those of total adrenalectomy are reversed by cortisone. Thus, the sympathetic nervous system appears to be essential for existence at low environmental temperature.
http://jpet.aspetjournals.org/cgi/content/abstract/157/1/103