Abstract

The positive inotropic responses to catecholamines are potentiated by cooling, whereas the positive chronotropic responses are inhibited. The possible site of this temperature-dependence was examined by determining the cAMP production in paced left and spontaneous right guinea-pig atria during orciprenaline-induced tension and rate responses. The time course of cAMP production preceded that of the respective responses at both 38 and 25°C. cAMP production in the left and right atria 15 seconds after addition of a concentration of orciprenaline (1.4 x 10^-4 M) above that needed for maximum mechanical responses was determined at different temperatures in the presence of theophylline (10^-3 M). These changes were compared with the effects of temperature upon complete tension and rate responses to a submaximal concentration of orciprenaline (9.5 x 10^-8). The increases in cAMP levels in the left and right atria and their respective mechanical responses were affected in parallel by temperature. The optimum temperatures for left (30°C) and right (38°C) atria were the same for cAMP and mechanical response. This close association is further evidence that cAMP plays an important role in these β-adrenoceptor mediated responses. Furthermore, the hypothermia-induced supersensitivity of the positive inotropic responses appears to be related to cAMP production.