On the late antiischaemic action of the stable PgI2 analogue: 7-oxo-PgI2-Na and its possible mode of action.

Earlier we have shown in the dog model mimicking angina on effort a delayed antiischaemic effect of PgI2 and its stable analogue 7-oxo-PgI2-Na, appearing only when the drug induced marked vasodilatation was over [1]. In the present experiments we could show that the protective effect appears at a time when the blood pressure returned to normal and in addition the marked platelet aggregation inhibitory effect has also faded away. In the rat 7-oxo-PgI2 could substantially diminish vasopressine induced T-wave elevation in the ECG if given 2 hours before administration of vasopressin. In addition it could moderate the vasopressin induced metabolic changes appearing as diminution of the myocardial CP and ATP-level and increase of the myocardial lactate content. A similar metabolic protection was found in the heart of rats pretreated with 7-oxo-PgI2 2 hours before taking myocardial samples and exposing them for 1 minute to ischaemia by incubation in Ringer solution. It is concluded that a direct metabolic and hemodynamic effect could be at least partly responsible for the late antiischaemic effect of 7-oxo-PgI2. This effect was also present in the early phase of experimental myocardial infarction in conscious rats if animals were pretreated with 7-oxo-PgI2 2 hours before occlusion. However treatment did not increase survival rate and failed to reduce the incidence and severity of arrhythmias.