Cardiovascular actions of nitric oxide synthase inhibition in the portal hypertensive rat

1 We have investigated the actions of the nitric oxide synthase inhibitor L -NMMA in the portal hypertensive Wistar rat in vivo. Resting blood pressure in the anaesthetised portal hypertensive rat was 107.8 +/- 11.0/79.2 +/- 1 1.7 mmHg (n = 12), which was significantly lower than in sham-operated anim als (143.0 +/- 3.8/114.0 +/- 4.0 mmHg, n = 19; P < 0.01). Cardiac output wa s significantly higher in portal hypertensive (302 +/- 1.0 ml min(-1) per 1 00 g, n = 12) than sham-operated animals (23.7 +/- 2.2 ml min(-1) per 100 g , n = 13; P < 0.01). 2 Intravenous injection of L-NMMA (10 mg kg(-1)) significantly increased sy stemic blood pressure in both portal hypertensive and sham-operated animals to 123.0 +/- 15.0/93.4 +/- 14.0 mmHg and 162.1 +/- 5.7/131.6 +/- 6.0 mmHg, respectively. The magnitude of the changes were similar in both groups. Th is increase in blood pressure was accompanied by a decrease in cardiac outp ut to 88.5 +/- 2.8% and 91.5 +/- 2.4% of control in portal hypertensive and sham-operated animals, respectively (no significant difference). 3 L-NMMA (10 mg kg(-1)) had similar effects on small mesenteric arterial co nductance in both portal hypertensive and sham operated animals, reducing c onductance to 84.4 +/- 3.6% (n = 6) and 82.7 +/- 1.2% (n = 4) of control, r espectively. 4 It is concluded that L-NMMA has similar effects in vivo in portal hyperte nsive as compared with sham-operated rats. Hence, an enhancement of endothe lium-derived nitric oxide is not involved in the hyperdynamic state followi ng portal hypertension in the rat.