Effect of chronic exposure to cold on some responses to catecholamines

An objective of these studies was to test the responsiveness of cold-adapted (8 wk, 5 degrees C) rats to a specific beta-adrenergic agonist. Twenty-four hours after removal from cold, increases in tail skin temperature (Tsk) and colonic temperature (Tco) were measured for 2 h in air at 25 degrees C following subcutaneous (sc) administration of 28, 70 or 136 mug d,l-isoproterenol sulfate dihydrate/kg body wt to restrained male rats. Cold-adapted rats responded to each dose of isoproterenol with greater increases in Tsk than controls. Tco of both groups increased at the two highest doses, but cold-adapted rats showed a greater rise. Thus, cold-adapted rats showed greater metabolic (Tco) and vascular (Tsk) responsiveness to the beta-adrenergic agonist, isoproterenol, than nonadapted controls. No effect of the alpha-adrenergic agonist, phenylephrine (50 or 100 mug/kg body weight, sc), was observed on Tco or Tsk. A second objective was to study the tension developed by aortic smooth muscle rings of cold-adapted and control rats both during stimulation of alpha-adrenergic receptors by norepinephrine and membrane depolarization by KCl. Adaptation to cold air appeared to suppress alpha-adrenergic responsiveness in aortic segments but did not alter responsiveness to KCl. This suggests an unchanged contractile mechanism in aortic rings of cold-adapted rats and a reduced responsiveness either at the level of the alpha-receptor or at a site immediately beyond.