The effects of nitroglycerin on exercise-induced regional myocardial contractile dysfunction are not diminished by pretreatment with dihydroergotamine.

Abstract

1 Because controversy exists regarding the effects of dihydroergotamine (DHE) on the performance of underperfused myocardium, the effects of DHE were investigated in a model of exercise-induced regional myocardial dysfunction in conscious dogs. 2 We also investigated a possible functional antagonism between DHE and nitroglycerin that might reduce the latter drug's antianginal efficacy. 3 Investigations were carried out in conscious dogs. After stenosis of the circumflex branch of the left coronary artery that minimally affected resting myocardial function, treadmill exercise induced transient regional contractile dysfunction. Heart rate, arterial blood pressure, left ventricular dp/dtmax and left ventricular end-diastolic pressure were registered. Regional contractile performance was assessed by ultrasonic distance measurement in the underperfused and in a normally perfused area. 4 DHE (5 micrograms kg-1, i.v.) induced a decrease in left ventricular dp/dtmax at rest and during exercise. DHE did not cause a deterioration in contractile function in the ischaemic myocardium, but led to a slight although not significant improvement in regional myocardial function. 5 After pretreatment with DHE, infusion of nitroglycerin (15 micrograms kg-1, i.v.) induced an improvement in the underperfused myocardial area during treadmill exercise, accompanied by a decrease in diastolic arterial pressure and left ventricular end-diastolic pressure and an increase in left ventricular dp/dtmax. 6 These results suggest that DHE will not worsen exercise-induced angina pectoris, and that the antianginal efficacy of nitroglycerin will not be neutralized by pretreatment with DHE.