Pinane thromboxane A2 analogues are non-selective prostanoid antagonists in rat and human stomach muscle

1 Pinane thromboxane A2 (PTxA2) and its epi-OH isomer were studied on rat and human stomach longitudinal muscle. 2 PTxA2 (0.5 micrograms/ml) usually caused a slight contraction of rat gastric fundus. Contractions to PGE2, PGF2 alpha, PGI2 and epoxymethano analogues of PGH2 (U-46619 and U-44069) were substantially inhibited, whereas those to PGD2 and acetylcholine were only slightly reduced. 3 In human stomach, PTxA2 0.5 micrograms/ml rarely stimulated the muscle. Contractions to PGE2, PGF2 alpha and U-46619 were antagonized, with little effect on those to acetylcholine. 4 epi-PTxA2 (0.5 micrograms/ml) did not affect rat gastric tone. It was moderately potent against PGI2 on rat gastric fundus, but was less effective than PTxA2 against U-44069.