The administration of mesenchymal stem cells (MSCs) has been proposed for the treatment of pulmonary hypertension. However, the effect of intratracheally administered MSCs on the pulmonary vascular bed in monocrotaline-treated rats has not been determined. In the present study, the effect of intratracheal administration of rat MSCs (rMSCs) on monocrotaline-induced pulmonary hypertension and impaired endothelium-dependent responses were investigated in the rat. Intravenous injection of monocrotaline increased pulmonary arterial pressure and vascular resistance and decreased pulmonary vascular responses to acetylcholine without altering responses to sodium nitroprusside and without altering systemic responses to the vasodilator agents when responses were evaluated at 5 wk. The intratracheal injection of 3 x 10(6) rMSCs 2 wk after administration of monocrotaline attenuated the rise in pulmonary arterial pressure and pulmonary vascular resistance and restored pulmonary responses to acetylcholine toward values measured in control rats. Treatment with rMSCs decreased the right ventricular hypertrophy induced by monocrotaline. Immunohistochemical studies showed widespread distribution of lacZ-labeled rMSCs in lung parenchyma surrounding airways in monocrotaline-treated rats. Immunofluorescence studies revealed that transplanted rMSCs retained expression of von Willebrand factor and smooth muscle actin markers specific for endothelial and smooth muscle phenotypes. However, immunolabeled cells were not detected in the wall of pulmonary vessels. These data suggest that the decrease in pulmonary vascular resistance and improvement in response to acetylcholine an endothelium-dependent vasodilator in monocrotaline-treated rats may result from a paracrine effect of the transplanted rMSCs in lung parenchyma, which improves vascular endothelial function in the monocrotaline-injured lung.

Nitric oxide (NO), a mediator involved in penile erection, is synthesized by the nitric oxide synthase (NOS) family of enzymes. It has been shown that NOS activity decreases with age. To determine whether adenoviralmediated overexpression of endothelial NOS (eNOS) could enhance erectile responses, we administered a recombinant adenovirus containing the eNOS gene (AdCMVeNOS) into the corpora cavernosum of the aged rat. Adenoviral expression of the ␤-galactosidase reporter gene was observed in cavernosal tissue 1 day after intracavernosal administration of AdCMV␤gal; 1 day after administration of AdCMVeNOS, transgene expression was confirmed by immunoblot staining of eNOS protein, and cGMP levels were increased. The increase in cavernosal pressure in response to cavernosal nerve stimulation was enhanced in animals transfected with eNOS, and erectile responses to acetylcholine and zaprinast were enhanced at a time when the erectile response to the NO donor sodium 1-(N,N-diethylamino)diazen-1-ium-1,2-diolate was not altered. These results suggest that in vivo gene transfer of eNOS, alone or in combination with a type V phosphodiesterase inhibitor, may constitute a new therapeutic intervention for the treatment of erectile dysfunction.

Abstract-The effects of transfer of the endothelial nitric oxide synthase (eNOS) gene to the lung were studied in mice.After intratracheal administration of AdCMV␤gal, expression of the ␤-galactosidase reporter gene was detected in pulmonary airway cells, in alveolar cells, and in small pulmonary arteries. Gene expression with AdCMV␤gal peaked 1 day after administration and decayed over a 7-to 14-day period, whereas gene expression after AdRSV␤gal transfection peaked on day 5 and was sustained over a 21-to 28-day period. One day after administration of AdCMVeNOS, eNOS protein levels were increased, and there was a small reduction in mean pulmonary arterial pressure and pulmonary vascular resistance. The pressure-flow relationship in the pulmonary vascular bed was shifted to the right in animals transfected with eNOS, and pulmonary vasodepressor responses to bradykinin and the type V cGMP-selective phosphodiesterase inhibitor zaprinast were enhanced, whereas systemic responses were not altered. Pulmonary vasopressor responses to endothelin-1 (ET-1), angiotensin II, and ventilatory hypoxia were reduced significantly in animals transfected with the eNOS gene, whereas pressor responses to norepinephrine and U46619 were not changed. Systemic pressor responses to ET-1 and angiotensin II were similar in eNOS-transfected mice and in control mice. Intratracheal administration of AdRSVeNOS attenuated the increase in pulmonary arterial pressure in mice exposed to the fibrogenic anticancer agent bleomycin. These data suggest that transfer of the eNOS gene in vivo can selectively reduce pulmonary vascular resistance and pulmonary pressor responses to ET-1, angiotensin II, and hypoxia; enhance pulmonary depressor responses; and attenuate pulmonary hypertension induced by bleomycin. Moreover, these data suggest that in vivo gene transfer may be a useful therapeutic intervention for the treatment of pulmonary hypertensive disorders. (Circ Res. 1999;84:1422-1432.)Key Words: gene transfer Ⅲ in vivo Ⅲ pulmonary vascular bed Ⅲ mouse Ⅲ nitric oxide L ow-baseline vascular resistance in the lung is maintained by endothelium-dependent and -independent mechanisms. 1-3 Nitric oxide (NO) is released locally and plays an important role in maintaining pulmonary vascular resistance (PVR) at low levels. 1-3 NO is formed from the enzymatic conversion of L-arginine by NO synthase (NOS), which exists in 3 isoforms, endothelial (eNOS; constitutive or NOS III), neural (NOS I), and inducible (iNOS, NOS II). 4 -6 The constitutive forms of the enzyme, eNOS and neural NOS, are regulated by calcium and calmodulin. 4 -6 Although iNOS has been shown to be constitutively expressed and present in cells exposed to cytokines, expression is upregulated in pathophysiological conditions. 4 -6 NO binds to the ferrous heme moiety of soluble guanylate cyclase in vascular smooth muscle and platelets to increase intracellular cGMP levels, inhibit platelet aggregation, and relax vascular smooth muscle. [1][2][3][4][5][6][7] NO is believed to play an important role ...