Epithio-11, 12-methano-thromboxane A
2 (STA
2), a stable analog of thromboxane A
2 (TXA
2), stimulated inositol phosphates (IPs) accumulation in canine mesenteric artery strips, but not in cerebral (basilar) artery strips. When canine mesenteric artery strips were incubated with 0.1 μM [
3H]
myo-inositol for 15 min and then stimulated with 10 μM STA
2 for 30 min, there was a significant increase in
3H-IPs accumulation as measured by anion exchange chromatography (2, 028 ± 204 and 3, 526 ± 210
* dpm/mg protein for basal and stimulated accumulations, respectively; means ± S.E.M., n = 3,
*P < 0.01, significantly different from the basal value). This effect of STA
2 was dose-dependent with an EC
50 value of 1.6 ± 0.2 μM. The presence of equimolar concentrations of TXA
2 receptor antagonists, either ONO-3708 (9, 11-dimethylmethano-11, 12-methano-13, 14-dihydro-13-aza-14-oxo-15-cyclopental-16, 17, 18, 19, 20-pentanor-15-epi-thromboxane A
2) or S-1452 (5Z-7-(3-
endo-phenylsulfonylamino (2.2.1.)-bicyclohept-2-
exo-yl)heptenoic acid), completely blocked the effect of STA
2. These results suggest the presence of TXA
2 receptors coupled with IPs accumulation in canine mesenteric artery strips. The exact location of the TXA
2 receptor-IPs system, however, remains unknown.
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