Endothelium-dependent responses in carotid and renal arteries of normotensive and hypertensive rats.

Endothelium-dependent relaxations are impaired in the aorta of various models of hypertension, but no data are available regarding the cerebral or renal circulation. Endothelium-dependent relaxations were studied in the carotid and renal artery of Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Rings with and without endothelium were suspended in organ chambers for isometric tension recording. Acetylcholine and adenosine 5'-diphosphate (ADP) caused endothelium-dependent relaxations in both arteries that were impaired in the carotid, but not in the renal artery, of the SHR, similar to those to the endothelium-independent vasodilator sodium nitroprusside. Indomethacin did not affect relaxations to acetylcholine in the carotid artery, but it significantly augmented them in the renal artery. This finding suggests that an impaired vascular responsiveness to endothelium-derived relaxing factor is responsible for the decreased relaxations in the carotid artery of the SHR. In the renal artery, acetylcholine appears to release both endothelium-derived relaxing factor and a vasoconstrictor prostanoid. Carotid arteries of SHR were more sensitive to the constrictor effects of serotonin than were those of WKY. Endothelium removal caused a twofold to eightfold increase in sensitivity to serotonin in both strains. Thus, endothelium-dependent relaxations to acetylcholine and ADP are reduced and constrictions to serotonin are enhanced in the carotid, but not in the renal, artery of the SHR.