We previously found equally increased expression of L-arginine metabolising enzymes in both kidneys of rats with induced renal hypertension implied a direct role of Angiotensin II (AngII) in their regulation. The aim of the present study was to investigate the expression of these genes in AngII infused rats. 40 male wistar rats were implanted with Alzet micropumps and infused with either 80 ng/min AngII (n=20) or saline (n=20) for 14 days. Ten animals from each group received the AngII AT1 receptor blocker Losartan (60 mg/kg/day) in the drinking water. Blood pressure was monitored using the tail cuff method. After 14 days the rats were sacrificed and preglomerular vessels were isolated. mRNA expression was investigated using RTPCR with 18S RNA as internal control. Mean arterial pressure (MAP) was increased by AngII infusion from 1026 mmHg to 1479 mmHg (P<0.05). Losartan decreased MAP in Ang II treated rats (946 mmHg, P<0.05) but had no effect in controls (1014 mmHg). The expressions of eNOS (0.880.26 vs. 1.10.34), DDAH-1 (1.470.41 vs. 1.580.45) and Arginase-2 (1.460.62 vs. 1.80.78) were not changed by AngII infusion and were not affected by Losartan treatment. The expression of CAT-1 (0.380.07 to 0.730.12, P<0.05), CAT-2 (1.140.29 to 2.740.48, P<0.05), DDAH-2 (1.090.27 to 2.30.46, P<0.05) and Arginase-1 (1.080.17 to 1.820.22, P<0.05) were significantly increased in AngII infused rats and the increase was abolished by Losartan treatment. In conclusion, the mRNA expressions of CAT-1, CAT-2, DDAH-2 and Arginase-1 in renal resistance vessels are regulated by AngII stimulation of the AT1 receptor. This may be important for nitric oxide synthesis and the regulation of renal blood flow.