Precursors and inhibitors of hydrogen sulfide synthesis affect acute hypoxic pulmonary vasoconstriction in the intact lung

Abstract

The effects of hydrogen sulfide (H(2)S) and acute hypoxia are similar in isolated pulmonary arteries from various species. However, the involvement of H(2)S in hypoxic pulmonary vasoconstriction (HPV) has not been studied in the intact lung. The present study used an intact, isolated, perfused rat lung preparation to examine whether adding compounds essential to H(2)S synthesis or to its inhibition would result in a corresponding increase or decrease in the magnitude of HPV. Western blots performed in lung tissue identified the presence of the H(2)S-synthesizing enzymes, cystathionine γ-lyase (CSE) and 3-mercaptopyruvate sulfur transferase (3-MST), but not cystathionine β-synthase (CBS). Adding three H(2)S synthesis precursors, cysteine and oxidized or reduced glutathione, to the perfusate significantly increased peak arterial pressure during hypoxia compared with control (P < 0.05). Adding α-ketoglutarate to enhance the 3-MST enzyme pathway also resulted in an increase (P < 0.05). Both aspartate, which inhibits the 3-MST synthesis pathway, and propargylglycine (PPG), which inhibits the CSE pathway, significantly reduced the increases in arterial pressure during hypoxia. Diethylmaleate (DEM), which conjugates sulfhydryls, also reduced the peak hypoxic arterial pressure at concentrations >2 mM. Finally, H(2)S concentrations as measured with a specially designed polarographic electrode decreased markedly in lung tissue homogenate and in small pulmonary arteries when air was added to the hypoxic environment of the measurement chamber. The results of this study provide evidence that the rate of H(2)S synthesis plays a role in the magnitude of acute HPV in the isolated perfused rat lung.