Effect of chronic exposure to cold on some responses to catecholamines

Abstract

An objective of these studies was to test the responsiveness of cold-adapted (8 wk, 5.degree. 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.degree. C following s.c. administration of 28, 70 or 136 .mu.g 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 2 highest doses, but cold-adapted rats showed a greater rise. 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 .mu.g/kg body wt, s.c.), was observed on Tco or Tsk. A 2nd 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 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.