Recent studies have indicated that sphingosine 1-phosphate (Sph-1-P) is released into the blood flow from activated platelets upon stimulation to exhibit a wide spectrum of biological functions. The purpose of the present study was to assess the acute cardiovascular effects of circulating Sph-1-P in the in vivo rat model. Intravenous administration of Sph-1-P decreased the heart rate, ventricular contraction and blood pressure, while it hardly affected the atrioventricular and intraventricular conduction. Sph-1-P did not affect the adenylate cyclase activities of the membrane preparations made from the right atrium and left ventricle. These results suggest that functional receptors like lysophospholipid receptor Edg-1, which can inhibit adenylate cyclase via Gi protein, are lacking in the rat heart. Moreover, these observations will provide a clue to better understand the various types of Sph-1-P-related pathophysiological processes.