INCREASE BY N-G-NITRO-L-ARGININE METHYL-ESTER (L-NAME) OF RESISTANCE TO VENOUS RETURN IN RATS

1 The effects of the nitric oxide (NO) synthase inhibitor, N-G-nitro-L -arginine methyl ester (L-NAME), on mean circulatory filling pressure (MCFP), total peripheral resistance (TPR), cardiac output (CO) and res istance to venous return (R(v)) were studied in rats. 2 In conscious, unrestrained rats, L-NAME (0.5-16 mg kg(-1)) dose-dependently increase d mean arterial pressure (MAP) but not MCFP, an inverse index of venou s compliance, either in the absence of presence of the ganglionic bloc ker mecamylamine (10 mg kg(-1)). 3 In pentobarbitone-anaesthetized rat s, L-NAME (2, 4, 8 mg kg(-1)) increased MAP and reduced CO in a dose-r elated manner but did not change MCFP. TPR (+84, +140 and +192%) as we ll as R(v) (+62, +72, +110%) were dose-dependently increased by L-NAME . 4 Our results show that L-NAME reduces CO by increasing arterial as well as venous resistances. L-NAME does not affect MCFP.