Augmentation of the effects of vasoactive intestinal peptide aerosol on pulmonary hypertension via coapplication of a neutral endopeptidase 24.11 inhibitor.

A deficiency of the pulmonary vasodilative vasoactive intestinal peptide (VIP) has been suggested to be involved in the pathophysiology of pulmonary hypertension (PH). Supplementation of VIP as an aerosol is hampered by the fact that it is rapidly inactivated by neutral endopeptidases (NEP) located on the lung surface. Coapplication of thiorphan, an NEP 24.11 inhibitor, could augment the biological effects of inhaled VIP alone. A stable pulmonary vasoconstriction with a threefold increase of pulmonary artery pressure was established by application the thromboxane mimetic U46619 in the isolated rabbit lung model. VIP and thiorphan were either applied intravascularly or as an aerosol. VIP caused a significant pulmonary vasodilation either during intravascular application or inhalation. These effects were of short duration. Thiorphan application had no effects on pulmonary vasoconstriction per se but significantly augmented the effects of VIP aerosol. Thiorphan, not only augmented the maximum hemodynamic effects of VIP aerosol, but also led to a significant prolongation of these effects. VIP causes pulmonary vasodilation in a model of acute experimental PH. The hemodynamic effects of VIP aerosol can be significantly augmented via coapplication of an NEP inhibitor.

Preserved pulmonary vasodilative properties of aerosolized brain natriuretic peptide.

INTRODUCTION: Inhalation of vasoactive substances is an effective treatment of pulmonary hypertension. The B-type natriuretic peptide (BNP) leads to relaxation of smooth muscle cells, caused by an increased formation of cyclic guanosine monophosphate (cGMP). The biologic activity of BNP using an inhalative approach has not been addressed. METHODS: In order to assess the vasorelaxing capacity of exogenous BNP in the isolated ventilated and buffer perfused rabbit lung model, a stable pulmonary vasoconstriction was established by either the application of endothelin-1 or the thromboxane A(2) mimetic U46619. This was followed by an intravascular or aerosol application of BNP. CGMP was measured in the recirculating buffer fluid using a radioimmunoassay technique. RESULTS: During a stable plateau of U46619 induced pulmonary vasoconstriction (mean pulmonary artery pressure, PAP 25.5+/-0.23 mmHg), the intravascular administration of BNP induced a rapid vasodilation (mean PAP 18.13+/-0.95 mmHg, p<0.001). This vasodilation was dose dependent and was paralleled by a 6-fold increase of cGMP. When BNP was aerosolized, pulmonary vasoconstriction was also significantly alleviated in the U46619 model (mean PAP 22+/-2.1 mmHg) and during endothelin-1 induced vasoconstriction (mean PAP 17.1+/-2.47 mmHg). Correspondingly, inhalation caused a significant augmentation of cGMP levels was. CONCLUSION: The vasodilative capability of BNP as an indicator of the biologic activity of this peptide is preserved during its aerosolization. Presumably these vascular actions are caused at least in part by an increased availability of cGMP.