The influence of temperature upon reserpine-induced supersensitivity of guinea-pig isolated atria to isoprenaline and salbutamol.

1. The aim of this investigation was to determine whether supersensitivity of isolated atria to sympathomimetic amines following pretreatment with reserpine was evident at low temperatures, which alone induced supersensitivity. 2. Cumulative dose-response curves for the positive inotropic and chronotropic responses of isolated guinea-pig atria to isoprenaline and the partial agonist salbutamol were plotted as a percentage of the maximum response to isoprenaline. 3. In atria from reserpine-pretreated guinea-pigs set up at 38 degrees C, supersensitivity of both rate and tension responses was observed as a shift of the curves to the left and an increase of the maximum responses to salbutamol. Tension responses were potentiated more than rate responses. At 30 degrees C the supersensitivity became less apparent and at 25 degrees C was virtually absent. 4. The dose-response curves in untreated atria at low temperatures revealed that hypothermia itself produced supersensitivity of rate and tension responses. The dose-response curves were displaced to the left and the salbutamol maxima were raised so that at 25 degrees C it became almost a full agonist. The hypothermia-induced supersensitivity was therefore sufficient to mask any supersensitivity resulting from pretreatment with reserpine. 5. The hypothermia-induced supersensitivity of the rate response was dependent upon the method of plotting. When plotted in absolute units of beats per min no supersensitivity of the rate response was evident. Supersensitivity of the tension response at the lower temperatures and of both rate and tension responses following pretreatment with reserpine were independent of the plotting method.