Thapsigargin stimulates increased NO activity in hypoxic hypertensive rat lungs and pulmonary arteries.
This study addressed the controversy of whether endothelium-derived nitric oxide (NO) activity is increased or decreased in the hypertensive pulmonary vasculature of chronically hypoxic rats. Thapsigargin, a receptor-independent Ca2+ agonist and stimulator of endothelial NO production, was used to compare NO-mediated vasodilation in perfused lungs and conduit pulmonary artery rings isolated from adult male rats either kept at Denver's altitude of 5,280 ft (control pulmonary normotensive rats) or exposed for 4-5 wk to the simulated altitude of 17,000 ft (chronically hypoxic pulmonary hypertensive rats). Under baseline conditions, thapsigargin (10(-9)-10(-7) M) caused vasodilation in hypertensive lungs and vasoconstriction in normotensive lungs. Whereas the sustained vasodilation in hypertensive lungs was reversed to vasoconstriction by the inhibitor of NO synthase N(omega)-nitro-L-arginine (L-NNA; 10(-4) M), a transient vasodilation to thapsigargin in acutely vasoconstricted normotensive lungs was potentiated. As measured by a chemiluminescence assay, the recirculated perfusate of hypertensive lungs accumulated considerably higher levels of NO-containing compounds that did normotensive lungs, and thapsigargin-induced stimulation of NO-containing compounds accumulation was greater in hypertensive than in normotensive lungs. Similarly, low concentrations of thapsigargin (10(-10)-10(-9) M) caused greater endothelium-dependent L-NNA-reversible relaxation of hypertensive than of normotensive pulmonary artery rings. The increased sensitivity of hypertensive arteries to thapsigargin-induced relaxation was eliminated in nominally Ca(2+)-free medium and was not mimicked by ryanodine, a releaser of intracellular Ca2+. These results with thapsigargin, which acts on endothelial cells to stimulate Ca2+ influx and a sustained rise in intracellular Ca2+ concentration, support the idea that pulmonary vascular endothelium-derived NO activity is increased rather than decreased in chronic hypoxia-induced pulmonary hypertension in rats.
Muramatsu
M
M
Department of Medicine, University of Colorado Health Sciences Center, Denver 80262 USA.
Tyler
R C
RC
Rodman
D M
DM
McMurtry
I F
IF
D000818:Animals; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D006973:Hypertension / Q000503:physiopathology*; D000860:Hypoxia / Q000503:physiopathology*; D008297:Male; D009569:Nitric Oxide / Q000378:metabolism*; D011651:Pulmonary Artery / Q000187:drug effects*; D051381:Rats; D017207:Rats, Sprague-Dawley; D019284:Thapsigargin / Q000494:pharmacology*; D013997:Time Factors
D004791:Enzyme Inhibitors; D009569:Nitric Oxide; D019284:Thapsigargin