Sphingolipids such as sphingosine-1-phosphate (SPP) and sphingosylphosphorylcholine (SPPC) can act both intracellularly and at G-protein-coupled receptors, some of which were cloned and designated as Edg-receptors. Sphingolipid-induced vascular effects were determined in isolated rat mesenteric and intrarenal microvessels. Additionally, sphingolipid-induced elevations in intracellular Ca(2+) concentration were measured in cultured rat aortic smooth muscle cells. SPPC and SPP (0.1-100 micromol l(-1)) caused concentration-dependent contraction of mesenteric and intrarenal microvessels (e.g. SPPC in mesenteric microvessels pEC(50) 5.63+/-0.17 and E(max) 49+/-3% of noradrenaline), with other sphingolipids being less active. The vasoconstrictor effect of SPPC in mesenteric microvessels was stereospecific (pEC(50) D-erythro-SPPC 5.69+/-0.08, L-threo-SPPC 5.31+/-0.06) and inhibited by pretreatment with pertussis toxin (E(max) from 44+/-5 to 19+/-4%), by chelation of extracellular Ca(2+) with EGTA and by nitrendipine (E(max) from 40+/-6 to 6+/-1 and 29+/-6%, respectively). Mechanical endothelial denudation or NO synthase inhibition did not alter the SPPC effects, while indomethacin reduced them (E(max) from 87+/-3 to 70+/-4%). SPP and SPPC caused transient increases in intracellular Ca(2+) concentrations in rat aortic smooth muscle cells in a pertussis toxin-sensitive manner. Our data demonstrate that SPP and SPPC cause vasoconstriction of isolated rat microvessels and increase intracellular Ca(2+) concentrations in cultured rat aortic smooth muscle cells. These effects appear to occur via receptors coupled to pertussis toxin-sensitive G-proteins. This is the first demonstration of effects of SPP and SPPC on vascular tone and suggests that sphingolipids may be an hitherto unrecognized class of endogenous regulators of vascular tone.