Effects of Glucagon and Isoproterenol on Severity of Acute Myocardial Ischemic Injury

Abstract

Comparison was made between the effects of isoproterenol and glucagon on myocardial ischemic injury following acute coronary artery occlusion in 8 dogs. Maximal rate of left ventricular pressure rise (dP/dt) was similarly increased by isoproterenol (63 ± 6 %) (mean ± S.E.M.) and glucagon (65 ± 5 %) infusions. Ischemic injury was measured as the sum of S-T segment elevations in epicardial ECG recordings from 8–10 sites (σST). σST during coronary artery occlusion alone averaged 22 ± 1 mV. Reocclusion of the artery performed during isoproterenol infusion increased σST to 70 ± 7 mV, while during glucagon σST rose to only 51 ± 7 mV. The difference in σST obtained with isoproterenol and glucagon was statistically significant (P < 0.001). Arterial concentrations of free fatty acids (FFA_a) were raised from 225 ± 26 to 1213 ± 166 μEq/l by isoproterenol (P < 0.001), whereas glucagon had no significant effect upon FFA_a. The experiments were repeated after inhibition of catecholamine-induced lipolysis with β-pyridyl carbinol (Ronicol® ‘Roche’) reducing FFA_a to 136 ± 25 μEq/l. In this condition reocclusions of the coronary artery during isoproterenol and glucagon infusions gave similar increments in σST, averaging 40 ± 3 mV. The present measurements indicate that the severity of acute myocardial ischemic injury following coronary artery occlusion might be influenced by changes in the delivery of FFA to the heart, as well as by changes in cardiac mechanical activity.

Key Words:

• β-pyridyl carbinol
• coronary insufficiency
• epicardial ECG
• glucagon
• isoproterenol
• lipolysis
• myocardial FFA uptake
• myocardial infarction
• myocardial ischemia
• S-T segment elevation