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Departments of Pediatrics and Neurology, Medical College of Wisconsin and Zablocki Veterans Affairs Medical Center, Milwaukee, Wisconsin 53226
We
previously found that alkalosis-induced vasodilation was mediated by
endothelium-derived nitric oxide (EDNO) in newborn piglet pulmonary
artery and vein rings precontracted with the thromboxane mimetic
U-46619. In contrast, prostacyclin or K+ channel activation
contributed to the response in other preparations. This study was
undertaken to determine whether EDNO alone also mediates
alkalosis-induced pulmonary vasodilation in piglet lungs vasoconstricted with hypoxia and, if not, to identify the mediator(s) involved. Responses to alkalosis were measured during hypoxia under
control conditions after blocking nitric oxide synthase (N
-nitro-L-arginine),
cyclooxygenase (meclofenamate), or both endothelium-derived modulators (Dual); after blocking voltage-dependent (4-aminopyridine), ATP- dependent (glibenclamide), or Ca2+-dependent
K+ (KCa; tetraethylammonium) K+
channels; and after blocking both endothelium-derived modulators and
KCa channels (Triple). Vasodilator responses measured after 20 min of alkalosis were blunted in Dual and tetraethylammonium lungs
and abolished in Triple lungs. Thus alkalosis-induced vasodilation in
hypoxic lungs appeared to be mediated by three
Ca2+-dependent modulators: EDNO, prostacyclin, and
KCa channels. In addition, a transient, unidentified
modulator contributed to the nadir of the vasodilator response measured
at 10 min of alkalosis. Future studies are needed to identify factors
that contribute to the discordance between isolated vessels and whole lungs.
isolated lungs; hypoxia; nitric oxide; prostacyclin; potassium channels
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