EFFECTS OF CALCIUM-CHANNEL ANTAGONISTS AND PERTUSSIS TOXIN ON NORADRENALINE-INDUCED CONTRACTIONS IN PULMONARY-ARTERY FROM PULMONARY HYPERTENSIVE RATS

The influence of calcium channel antagonists, felodipine and cadmium, as well as pertussis toxin on noradrenaline-induced contractions in pu lmonary artery rings from rats with pulmonary hypertension induced by monocrotaline (MCT) were examined. MCT-treated rats had pulmonary hype rtension, right ventricular hypertrophy and lung oedema, as compared t o corresponding vehicle-treated rats. The MCT-treated animals did not have polycythemia as compared to vehicle-treated rats. Pre-treatment o f pulmonary artery rings from MCT-treated rats with felodipine and cad mium significantly reduced the maximum response without altering the E C(50) or the Hill coefficient of concentration-response curve to norad renaline. In pulmonary artery rings from vehicle-treated rats, felodip ine significantly increased the EC(50) and reduced the maximum respons e and the Hill coefficient of the concentration-response curve to nora drenaline. In contrast, cadmium did not alter these parameters in pulm onary artery rings from vehicle-treated rats. Pertussis toxin did not affect noradrenaline-induced contractions in pulmonary artery rings fr om vehicle- or MCT-treated rats. Felodipine, cadmium and pertussis tox in were ineffective in inhibiting noradrenaline-induced contractions i n aortic rings from either vehicle- or MCT-treated rats. Our results c an be interpreted to indicate that alteration to voltage operated, fel odipine-sensitive, calcium channels as well as, cadmium-sensitive site s contribute to the changes observed in the functional behavior of pul monary blood vessels from pulmonary hypertensive rats.