Different sensitivity of basilar and saphenous arteries to thromboxane A2-induced contractions. Effect of imidazole 2-hydroxybenzoate (ITF 182).

Superfused rings of rabbit basilar arteries are more sensitive than those of saphenous arteries to the contractions induced by a prostaglandin endoperoxide analogue (U-46 619) and by a thromboxane A2 (TXA2) generating system. 5-Hydroxytryptamine aggravates the latter. Prostaglandin I2 (PGI2) on the other hand, relaxes only the basilar rings without affecting the saphenous. Imidazole 2-hydroxybenzoate (ITF 182), at doses that do not interfere with platelet cyclooxygenase, reduces the contractions induced by the TXA2 generating system on both arteries because it reduces the platelet TXA2 synthetase enzyme. TXA2 is involved in the aetiology of strokes and cerebral vasospasms while PGI2 plays a physiological role in the maintenance of cerebral arterial tone. The high sensitivity of cerebral arteries to contractures caused by TXA2 together with the ability of ITF 182 to reduce them by inhibiting TXA2 production and to spare physiological PG production suggest a beneficial effect of the drug in cerebral vasospasms.