Comparison of the effects of dihydroergotamine and ergonovine on functional changes caused by beta-adrenergic stimulation in normally and underperfused canine myocardium.

We studied the effects of dihydroergotamine (DHE) and ergonovine on myocardial function in normally perfused myocardial areas and in myocardial areas with restricted coronary flow. Regional function at rest and during isoproterenol (ISO)-induced cardiac stimulation was assessed by two pairs of piezoelectric transducers. Constriction of the circumflex branch with a decrease in coronary blood flow from 24.9 +/- 2.6 to 18.1 +/- 2.2 ml/min had little effect on resting regional function. Intravenous bolus injection of ISO (0.5 microgram/kg) prior to constriction induced a marked decrease in end-diastolic segment length and an increase in percentage shortening. Intravenous bolus injection of ISO (0.5 microgram/kg) after constriction of the circumflex branch induced transient regional dysfunction, as shown by a maximum decrease of percentage shortening by 54.4% in the underperfused area. Intravenous infusion of DHE (2 micrograms/kg; 5 min) did not significantly affect resting function and effectively inhibited ISO-induced regional dysfunction. This improvement in regional function during ISO-induced cardiac stimulation can be attributed to the fact that DHE decreased heart rate and left ventricular power, thus reducing myocardial oxygen demand and improving the energetic situation in the underperfused myocardium. In contrast, ergonovine (5 micrograms/kg; 5 min) induced an impairment in regional function in both segments at rest and further aggravated ISO-induced transient dysfunction. The present study confirms the adverse effect of ergonovine on blood flow and regional function in underperfused myocardial areas and demonstrates a beneficial effect of DHE on regional function in underperfused myocardial areas during ISO-induced cardiac stimulation.