Antagonism of PGD2 vasodepressor responses in the rat in vivo by the novel, selective antagonist, BW A868C.

1. Bolus intravenous injection of prostaglandin D2 (PGD2, 1-160 micrograms kg-1), the hydantoin prostanoid BW245C (0.25-160 micrograms kg-1) or prostacyclin (PGI2, 0.05-0.5 microgram kg-1) caused a dose-dependent fall in systemic arterial blood pressure (BP) in the anaesthetized rat, lasting 2-4 min. 2. Intravenous infusion of the novel 3-benzyl substituted hydantoin, BW A868C (1-10 micrograms kg-1 min-1), in doses that had no direct effect on BP, dose-dependently reduced the vasodepressor action of PGD2. 3. Bolus injection of BW A868C (30 and 100 micrograms kg-1, i.v.) likewise dose-dependently antagonized the vasodepressor responses to PGD2, causing a 3.4 and 13.2 fold rightward shift of the dose-response curve. 4. The thromboxane-receptor antagonist, BM 13.177 (2.5 mg kg-1 i.v.) had little effect on the PGD2 vasodepressor responses, suggesting minimal contribution of a PGD2 interaction at thromboxane receptor-sites in the systemic vasculature of this species. 5. BW A868C (10 micrograms kg-1 min-1 i.v.) caused a rightward shift (59 fold) of the dose-response relationship for BW245C, the putative PGD2-receptor agonist. This antagonism lasted for at least 1h after termination of the BW A868C infusion. Higher doses of BW A868C (20-100 micrograms kg-1 min-1) caused no further antagonism of the vasodepressor responses to BW245C, suggesting that this prostanoid also acts at vascular receptors other than of the DP-type. 6. BW A868C (10 micrograms kg-1 min-1, i.v.) failed to alter the vasodepressor actions of prostacyclin. 7. These findings in the rat in vivo support the characterization of BW A868C as a potent and selective antagonist of the cardiovascular actions of PGD2 at the DP-receptor.