Inotropic effect of histamine on papillary muscle of guinea pig with right ventricular hypertrophy

The effects of histamine and its antagonists on guinea pig right ventricular papillary muscle rendered hypertrophy by chronic pulmonary artery constriction were observed. In the HT-I group (hypertrophy 10-15 d), the dose-response (D-R) curves of PT, +dT/dtmax of histamine, compared with CTL-I (age-matched sham-opcrated group), shifted leftward and upward. In the HT-II group (hypertrophy 30-35 d), while the histamine dosages ranged 0.1-1 vmol/L the D-R curves only slightly changed from CTL-II, but remarkably shifted rightward and downward in high concentrations (3-30 vmol/L), showing an augrnentation of response in the early stage and an attcnuation of response in the late stage. The pattern of D-R curves of epinephrine was virtually similar to those of histamine. In the presence of cimetidine, these curves all parallelly shifted to the right; and the biphasic inotropism were still clearly shown.