Experimental hypertension studies are few in the hooded (Aguti) rat. The present study was designed to investigate the possibility that salt-induced hypertension and/or hypertension due to nitric oxide synthase (NOS) inhibition may be associated with attenuation of relaxation to certain vasodilator agonists. Hypertension was induced in hooded rats (n=8 each) by administering 8% salt in the diet (Sofola et al. 2003) and /or 100 mg/kg/day N^ω-nitro-L-arginine-methyl-ester (L-NAME) in the drinking water (Pollock et al. 1993). Aortic rings from the rats were obtained under anaesthesia using a 25% urethane and 1% chloralose mixture given intraperitoneally at a dose of 5mg/kg. They were mounted in a tissue bath containing a physiological salt solution (composition in mM: NaCl, 119; KCl, 4.7; KH₂PO₄, 1.2; MgSO₄, 1.2; NaHCO₃, 15.0; CaCl₂, 1.6; glucose, 11.5; pH: 7.4) gassed with a 95% O₂-5% CO₂ gas mixture and maintained at 37°C. Relaxation responses to acetylcholine, histamine and sodium nitroprusside (SNP) were obtained following precontraction with 10^-7M noradrenaline. Relaxation response to SNP was obtained in endothelium-denuded rings. Results are presented as mean ± S.E.M. Statistical analysis was done using one way ANOVA and a post hoc Student-Newman-Keuls test. P< 0.05 was taken as statistically significant. The IC₅₀ of acetylcholine in aortic rings from L-NAME rats (7.9 x 10^-1 ± 6.0 x 10^-3) was significantly higher than the IC₅₀ in rings from control (9.4 x 10^-8 ± 2.8 x 10^-8), salt (7.8 x 10^-7 ± 4.7 x 10^-7) and salt + L-NAME (3.3 x 10^-7 ± 2.1 x 10^-7) rats (P<0.05). The IC₅₀ of histamine and SNP in the rings from the test groups of rats showed no significant difference from control. These results suggest that in the hooded (Aguti) rat, endothelium dependent and independent relaxations are preserved in the various forms of hypertension studied except in chronic NOS inhibition where only endothelium dependent relaxation to acetylcholine was attenuated.