Cyclic ADP-Ribose Is the Primary Trigger for Hypoxic Pulmonary Vasoconstriction in the Rat Lung In Situ

Hypoxic pulmonary vasoconstriction (HPV) is unique to pulmonary arteries, and it aids ventilation/perfusion matching. However, in diseases such as emphysema, HPV can promote hypoxic pulmonary hypertension. We recently showed that hypoxia constricts pulmonary arteries in part by increasing cyclic ADP-ribose (cADPR) accumulation in the smooth muscle and, thereby, Ca(2+) release by ryanodine receptors. We now report on the role of cADPR in HPV in isolated rat pulmonary arteries and in the rat lung in situ. In isolated pulmonary arteries, the membrane-permeant cADPR antagonist, 8-bromo-cADPR, blocked sustained HPV by blocking Ca(2+) release from smooth muscle ryanodine-sensitive stores in the sarcoplasmic reticulum. Most importantly, we showed that 8-bromo-cADPR blocks HPV induced by alveolar hypoxia in the ventilated rat lung in situ. Inhibition of HPV was achieved without affecting (1) constriction by membrane depolarization and voltage-gated Ca(2+) influx, (2) the release (by hypoxia) of an endothelium-derived vasoconstrictor, or (3) endothelium-dependent vasoconstriction. Our findings suggest that HPV is both triggered and maintained by cADPR in the rat lung in situ.