The effect of mannitol following permanent coronary occlusion

Quantitative comparisons of infarcts 24 hours after ligation of the left anterior descending coronary artery (LAD) via thoracotomy were made in 13 control and 13 dogs treated with i.v. 25% mannitol, 2 ml/min for 4 hours following occlusion. Mannitol increased serum osmolarity by 44+/-4 mOsm/L (mean +/- 1 SE) with hemodynamic effects limited to a small increase in left ventricular dP/dt. Nonperfusible tissue measured by planimetry at 24 hours was similar in both groups (46+/-4% of area defined with dye injected into the distal LAD for control versus 48+/-5% for mannitol treated dogs, P = NS). Creatine phosphokinase activity in infarcted tissues was also similar in both groups. Myocardial blood flows measured with radioactive microspheres were also similar in both groups. Collateral conductance calcultaed from retrograde flow and aortic pressure increased with the 24 hour period by 146+/-23% in the control dogs; in the mannitol treated dogs, collateral increased only 38+/-14% (P less than 0.001). Thus mannitol had no effect on ultimate infarct size. Moreover, mannitol appeared to hinder the development of collateral vessels.