Basic and clinical reevaluation of tyramine and histamine tests for the investigation of adrenomedullary sympathetic functions.

In vitro and in vivo studies using histamine and tyramine tests were carried out to investigate adrenomedullary sympathetic functions. Administration of 10(-3) M tyramine enhanced catecholamine release from both the perifused swine adrenal medulla and human pheochromocytoma tissue, whereas histamine did not show this effect. Tyramine also induced release of catecholamine from the isolated catecholamine granules in vitro, but histamine did not. The tyramine or histamine test was performed in vivo on groups of 16 subjects, respectively, consisting of healthy adults and hypertensive patients. In all cases, a rise in blood pressure was observed after loading with either tyramine or histamine. On the other hand, when urinary catecholamine output was examined during the first 2 h after loading, a significant increase was not observed in 4/16 after tyramine administration, and in 6/16 after histamine loading. Thus, using an in vitro system, we showed a difference between tyramine and histamine in the mode of direct action on adrenal medulla. We also conclude that urinary catecholamine output is of less significance than the blood pressure response as an index of tyramine or histamine test.