CARDIOVASCULAR AND METABOLIC RESPONSES TO NORADRENALINE IN MEN ACCLIMATIZED TO COLD BATHS

The purpose of this study was to see whether artificial acclimatizatio n to cold would reduce the presser response to noradrenaline (NA) as n atural acclimatization has been shown to do, and whether it would indu ce nonshivering thermogenesis. Three white men were infused with NA at four dosage levels between 0.038 and 0.300 mu g.kg(-1).min(-1) (2-23 mu g.min(-1)), before and after artificial acclimatization to cold and again 4 months later when acclimatization had decayed. Acclimatizatio n was induced by ten daily cold (15 degrees C) baths of 30-60 min foll owed by rapid rewarming in hot (38-42 degrees C) water, and was confir med by tests of the subjects' responses to whole-body cooling in air. Three control subjects also underwent the first and third tests. Accli matization substantially reduced the presser response to NA at 0.150 a nd 0.300 mu g.kg(-1).min(-1), confirming earlier findings by the same technique in naturally acclimatized men, and its decay increased this response to beyond its initial levels (P < 0.05 for both changes). Acc limatization did not change the response to NA of heart rate, subjecti ve impressions, skin temperature of finger and toe, pulmonary ventilat ion, or plasma free fatty acids and ketone bodies. At no time did NA i ncrease oxygen consumption, or increase skin temperature or heat flow over reported sites of brown fat. These findings would seem to show th at acclimatization to cold reduces sensitivity to the presser effect o f NA but does not induce nonshivering thermogenesis, and that the redu ced sensitivity is replaced by a hypersensitivity to NA when acclimati zation decays.