Effect of prostacyclin on the severity of ischaemic injury in rabbit hearts subjected to coronary ligation.

The hypothesis that prostacyclin (PGI2) might have a direct cytoprotective action in ischaemic cardiac tissue was investigated. Myocardial ischaemia was induced in perfused rabbit hearts by ligating the left main coronary artery. Coronary flow, oxygen uptake, and turnover of lactate and purines were measured before and up to 120 min after coronary occlusion. After this, ischaemic tissue was separated from perfused myocardium, and levels of lactate, adenine nucleotides and creatine phosphate were determined in specimens from non ischaemic, ischaemic and border zones. PGI2 (final conc. 10(-7) M) was infused before or 30 min after ligation and the results were compared to those in control hearts. Coronary ligation reduced coronary flow and oxygen consumption by about 50%. The fractional extraction of lactate decreased from 20% to close to zero and purine release increased 5-fold. In the non-ischaemic area the tissue levels of ATP and creatine phosphate were high, with a low content of lactate, but in the ischaemic area the levels of ATP and creatine phosphate were considerably reduced and the content of lactate was high. Although coronary flow and oxygen uptake were elevated after treatment with PGI2, no change in lactate or purine turnover was observed. Neither the weight of the non-perfused myocardium nor the tissue levels of the adenine nucleotides, creatine phosphate and lactate were affected by PGI2 treatment. The data indicate that in this model, in which effects on cardiac work, collateral flow and platelets are eliminated, PGI2 does not limit ischaemic myocardial injury. Hence, the hypothesis of a direct cytoprotective action of PGI2 in ischaemic myocardial tissue was not supported.