Early regulatory changes in rat pulmonary artery of renin-dependent systemic hypertension models

Patients with systemic hypertension of various etiologies maintain their pulmonary artery pressures within normal limits. We have reported in 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, and similar results are seen in isolated small pulmonary arteries (PA) from these animals. The abdominal aorta of rats was ligated above the left and below the right renal artery (aortic coarctation, AC). The mean arterial pressure (MAP) and pulmonary artery pressure (PAP) of 24-h post-AC rats (MAP 123 +/- 7.1 mm Hg and PAP 4.2 +/- 0.9 mm Hg) showed no significant change when compared with those of sham control rats (MAP 116 +/- 7.0 mm Hg and PAP 5.0 +/- 0.04 mm Hg). Hypoxic contractions in isolated small rat PA (160 to 260 microns diameter) were significantly increased from 56.7 +/- 12.0 mg in the control group to 139 +/- 31 mg in the 24-h post-AC rats (P < 0.05). PA contractions in the presence of 100 microM nitro-L-arginine (NLA) increased from 102 +/- 34 mg among the sham control group to 261 +/- 30 mg among the 24-h post AC rats (P < 0.05). After NLA, the hypoxic contractions decreased to 15 +/- 2.9 mg in the control rats and 45 +/- 16 mg in the 24-h post-AC rats when compared with pre-NLA values (P < 0.05). Western and Northern blotting of protein and messenger ribonucleic acid (mRNA) extracted from the whole rat lung showed a significant rise in endothelial cell nitric oxide synthase (EcNOS; 207 +/- 34%) and EcNOS mRNA (2-fold) when comparing controls with 24-h post-AC rats. These data indicate that there is increased EcNOS activity and synthesis that maintain low PA tone in these rat models as early as 24 h after AC; in addition, this effect is independent of the systemic blood pressure.