Vasodilatory action of inosine in the in vivo heart: a dual mechanism

Inosine--a natural modulator of contractility and myocardial blood flow in the ischemic heart?

The energetic role of inosine (INO) remains controversial. The aim of the present study was first to test whether endogenous INO consumption/production correlates with regional myocardial contractile performance and second to test whether locally increased levels of INO influence contractility and blood flow in severely ischemic myocardium. Fentanyl-anesthetized dogs with implanted sonomicrometry crystals and independently perfused left anterior descending coronary arteries were studied. Two relatively load-independent indexes of regional myocardial contractility derived from left ventricular pressure-segment length loops were used: the regional stroke work-end-diastolic segment length relationship (Wr/L(ed)) and the end-systolic pressure-segment length relationship (Plv/L(es)). Very good correlations between myocardial contractile performance (as measured by the slope of the regional Wr/L(ed) relationship) and endogenous INO consumption/production under both nonischemic and ischemic conditions were found. Ischemia severely depressed contractility, significantly shifting rightward the Wr/L(ed) and Plv/L(es) relationships. INO infused into the left anterior descending bypass, in a concentration of 600 to 800 mumol/L, partially restored contractile performance as evidenced by a significant leftward displacement of both relationships. Wr, measured at a common maximum L(ed), increased significantly by 61 +/- 5%. Border-zone collateral flow (microspheres) increased by 35 +/- 7% within the endocardial segments and by 34 +/- 9% in the epicardial segments, but no increase in flow in the ischemic region was measureable. With the current emphasis on recanalization with thrombolytic therapy and considering the apparent safety of INO, this naturally occurring nucleoside might prove to be a useful adjunctive agent in the treatment of acute myocardial ischemia.

Protective effect of inosine on adrenaline-induced myocardial necrosis

The influence of inosine (200 and 400 mg/kg i.p.) on adrenaline-induced myocardial necrosis in rats was studied. Adrenaline in a single dose (1 and 2 mg/kg s.c.) produced heart cell necrosis estimated by plasma activities of CPK-MB, CPK, blood lactates concentration and histopathological examination. In experimental groups inosine injected simultaneously and 10 minutes after adrenaline evoked significant suppression of CPK-MB and CPK enhancement measured 4 and 24 hours after adrenaline administration. The lower blood lactates concentration 4 hours after adrenaline injection was also found when preceded by inosine. Histopathological examination showed marked protection of the affected myocardium.