The contractile mechanism of beraprost sodium, a stable prostacyclin analog, in the isolated canine femoral vein.

The vascular contractile mechanism of prostacyclin (PGI2) was investigated using beraprost sodium (BPS), a stable PGI2 analog. Ring strips without endothelium isolated from canine femoral veins and arteries were used. BPS induced a dose-dependent contraction without precontraction and after precontraction with norepinephrine (NE) or 60 mM K+ in the veins. In contrast, BPS induced a dose-dependent relaxation after precontraction with U46619, a thromboxane A2 (TXA2) analog, or prostaglandin F2 alpha (PGF2 alpha) in the veins. In the arteries, BPS induced contraction at higher concentrations after precontraction with NE. However, BPS relaxed arteries dose-dependently after precontraction with PGF2 alpha. By pretreatment with 13-azaprostanoic acid (13-APA), a TXA2/endoperoxide receptor antagonist, the dose-response curve of BPS in the veins was shifted to the right. Schild plot analysis resulted in a linear regression with a slope of 0.86 +/- 0.13, which was not significantly different from unity, and the pA2 value for 13-APA against BPS was 7.10 +/- 0.06. By pretreatment with BPS, the dose-response curve of U46619 in the veins was shifted to the right. Kaumann plot analysis resulted in a linear regression with a slope of 0.89 +/- 0.09, which was not significantly different from unity, and the pA2 value for BPS against U46619 was 5.68 +/- 0.04. These findings indicate that BPS is a partial agonist for the TXA2/endoperoxide receptors.