Desensitization of rat cardiomyocyte adenylyl cyclase stimulation by plasma of noradrenaline-treated patients with septic shock.

The purpose of this study was to test the possibility that the mechanisms of catecholamine-induced desensitization of cardiac beta-adrenoceptor stimulation are modified in septic shock. Exposure of neonatal rat cardiomyocytes for 48 hr to plasma of noradrenaline-treated patients with septic shock led to a down-regulation of beta-adrenoceptors by 35%, an increase in the level of inhibitory G protein alpha-subunits by 60%, and a decrease in isoproterenol-stimulated adenylyl cyclase activity by 50% in membranes prepared from the rat cardiomyocytes. Similar alterations were observed following pretreatment of the cells with plasma of adrenaline-treated patients with cardiogenic shock. In contrast, exposure of the cardiomyocytes to plasma of intensive care patients without shock, and to plasma of dopamine-treated patients with septic shock did not induce alterations of the cardiomyocyte adenylyl cyclase system. The dosage of the catecholamines had to be increased within the first two days of treatment in the noradrenaline-treated patients, but not in the dopamine-treated patients with septic shock. Thus, this observed tolerance to noradrenaline in the treatment of septic shock may, in part, be due to a desensitization of cardiac beta-adrenoceptor stimulation induced by the beta-adrenoceptor stimulatory effect of noradrenaline.