Peripheral hypertension and alterations in pulmonary vascular regulation

We have recently reported in normal isolated-perfused rat lungs that low basal tone appears to be regulated by nitric oxide (NO)-dependent and -independent mechanisms of soluble guanylate cyclase activation. In this study, we examnined the role of NO in the regulation of pulmonary artery (PA) tone from rats with renin-dependent hypertension. Rats were made hypertensive by ligating the abdominal aorta above the left and below the right renal artery (aortic coarctation, AC). Mean arterial pressure significantly increased from 119 +/- 8.4 mmHg in control animals to 156 +/- 15 mmHg 7-14 days after AC surgery. PA pressures, however, remained unchanged (8.5 +/- 3.4 mmHg in control animals vs. 11 +/- 3.3 mmHg in AC animals). Hypoxic contractions in U-46619 precontracted isolated small PA (160-260 mu m diameter) were significantly increased from 51 +/- 13 mg in the control group to 142 +/- 38 mg (P less than or equal to 0.05) in AC animals. Nitro-L-arginine (NLA; 100 mu M) contractions were also enhanced in the AC animal. The enhanced NLA response may correlate with an increase in endothelial cell NO synthase (NOS) as detected by Western blotting (132 +/- 28% of control; P < 0.05). These data suggest that, in this renin-dependent model of systemic hypertension, there is increased endothelial cell NOS activity that maintains low PA tone, preventing the lung from developing increased pressures.