Effects of the thromboxane‐receptor antagonist L‐636,499 on feline cerebral arteries

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Abstract
The effects of the thromboxane‐receptor antagonist L‐636,499 on contractions induced by U46619 and prostaglandin (PG)F2αwere studied in the isolated feline basilar artery (BA). L‐636,499 (10‐6‐3 times 10‐5mol l‐1) shifted concentration‐response curves induced by U46619 to the right in a parallel manner. By contrast, concentration‐response curves induced by PGF2αwere displaced only when L‐636,499 concentrations of 10‐53 times 10‐5mol l‐1were used. The Schild plot using U46619 as the agonist revealed a slope index (0.69) which was significantly less than unity.PA2‐values calculated according to the method of van Rossum differed significantly between different concentration intervals of L‐636,499. At 10‐6to 3 times 10‐6mol l‐1thePA2value was 5.99, whereas at 10‐5to 3 times 10‐5mol 1‐Iit was 5.59. Using PGF2αas the agonist thePA2‐value at the L‐636,499 concentration interval 10‐5to 3 times 10‐5mol 1‐Iwas 5.69. It may be concluded that the feline BA contains two receptor sites mediating prostanoid‐induced contraction, one of which may be characterized as a thromboxane‐sensitive (TP) receptor. L‐636,499 can interact with both receptor sites with highest affinity for the TP receptor site.