It has previously been established that a single systemic administration of retroviral vector containing angiotensin II type I receptor antisense (AT1R-AS) in the neonatal spontaneously hypertensive rat (SHR) prevents development of hypertension, and in addition cardiac hypertrophy and endothelial dysfunction. However, these studies could not determine whether the effects of AT1R-AS on high blood pressure (BP) and endothelial function were independent. Angiotensin receptor blockers have been shown to reduce BP in the L-NAME (N ω-nitro-L-arginine methyl ester hydrochloride)-induced rat model of hypertension. Our objective in the present study was to use the L-NAME model of hypertension to determine whether AT1R-AS treatment would lower high BP and attenuate cardiac hypertrophy under conditions of permanent endothelial damage. A single bolus of LNSV-AT1R-AS viral particles in neonatal Wistar-Kyoto (WKY) rats was without affect on basal BP. Efficacy of the transgene incorporation was assessed by observing a significant reduction in angiotensin-induced dipsogenic response in the AT1R-AS-treated animals. Introduction of L-NAME in the drinking water for 10 weeks resulted in the establishment of hypertension only in the WKY rats treated with vector alone. These hypertensive (BP, 179 ± 4 mmHg) animals showed a 17 % increase in heart weight/body weight ratio and a 60 % reduction in ACh-induced vasorelaxation in phenylephrine-preconstricted arteries. The L-NAME-induced high BP and cardiac hypertrophy were attenuated in rats expressing AT1R-AS. However, endothelial dysfunction could not be prevented with the antisense therapy. These observations demonstrate that attenuation of endothelial dysfunction is not a prerequisite for the antihypertensive effects of AT1R-AS treatment. Experimental Physiology (2003) 88.4, 467-473.