the causative agent in variant angina myocardial infarction sudden cardiac death and stroke thromb haemostasis 1977 38 132 studies in rabbits have shown that ecg changes typical of these conditions were produced when freshly prepared thromboxane a 2 was injected directly into the animal 39 s heart biochem aspects of prostaglandins and thromboxanes editors n kharasch and j fried academic press 1977 page 189 this technique is considered to represent a unique animal model of the heart attacks of coronary patients and has been used to show that administration of a compound believed to antagonise the effects of thromboxane a 2 protects the rabbits from the adverse consequences of thromboxane a 2 injection another area where a pgi 2 txa 2 imbalance is considered to be a contributory factor is that of migraine the migraine headache is associated with changes in intra and extra cerebral blood flow in particular a pre headache reduction of cerebral blood flow followed by dilatation in both vascular areas during the headache phase prior to the development of the headache blood levels of 5 hydroxytryptamine are elevated and this suggests the occurrence of in vivo aggregation and release of the amine from the platelet stores it is known that the blood platelets of migraine patients are more prone to aggregate than are those or normal individuals j clin pathol 1971 24 250 j headache 1977 17 101 furthermore it has now been postulated that not only is an abnormality of platelet.