We investigated the vasorelaxation in renal arteries isolated from spontaneously hypertensive rats (SHRs) fed a basal, a high-salt, or a high-cholesterol diet for 8 weeks. In renal arterial rings from the control group, acetylcholine (ACh)-induced endothelium-dependent relaxations were markedly increased by indomethacin (IND) and ONO-3708, a prostaglandin H2/thromboxane A2-receptor antagonist, but not affected by OKY-046, a thromboxane A2 synthetase inhibitor. These increased relaxations were partially inhibited by either NG-nitro-L-arginine methyl ester (L-NAME) or charybdotoxin (CTX), and almost completely abolished by the combination of L-NAME plus CTX. The ACh-induced endothelium-dependent relaxations in the absence of IND were significantly attenuated by the high-salt intake but not affected by the high-cholesterol intake. The degrees of relaxations in the presence of IND were approximately equal among the three diet groups. On the other hand, the relaxations in the presence of IND plus L-NAME were significantly augmented by a high-cholesterol intake and abolished by a high-salt intake, and the relaxations in the presence of IND plus CTX were slightly reduced by a high-cholesterol intake and significantly augmented by a high-salt intake. The production of cyclic guanosine monophosphate (cGMP) in response to ACh was significantly decreased by a high-cholesterol intake and tended to be increased by a high-salt intake. These findings indicate that in the renal artery of SHRs, ACh causes production of a sufficient amount of nitric oxide (NO), together with a relaxing factor resembling endothelium-derived hyperpolarizing factors (EDHFs) and also endothelium-derived contracting factors (EDCFs), probably prostaglandin H2. Our results also suggest that excessive salt intake increases the release of EDCF and NO and decreases that of an EDHF-like factor, whereas excessive cholesterol intake increases release of an EDHF-like factor and decreases that of NO.