Cerebral arterial smooth muscle contraction by thromboxane A2.

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Abstract
The contractile effects of thromboxane A2 (TxA2), a labile arachidonic acid metabolite, were studied in arterial smooth muscle strips. TxA2 was generated upon the addition of 255 nM prostaglandin cyclic endoperoxide H2 to human platelet particles in the muscle bath. Using the isometric contaction produced by 40 mM K+ in isotonic saline as the reference contraction, bovine middle cerebral artery strips contracted to 153 +/- 14% of the reference response while bovine coronary and porcine coronary, renal and common carotid strips contracted to 47 +/- 3, 26 +/- 5, 43 +/- 2 and 2 +/- 1% of reference, respectively. The cerebral artery response to the TxA2 generating system was as great as the maximum response to prostaglandin F2alpha and two times the maximum response to 5-hydroxytryptamine. Because TxA2 is formed by brain tissue and released from aggregating platelets, it may be important in the pathogenesis of spasm associated with injured brain tissue or pathologic changes leading to platelet aggregation.