Oxygen-induced vasodilation in pulmonary arterioles from fetal rats

Hypoxic Pulmonary Vasoconstriction

It has been known for more than 60 years, and suspected for over 100, that alveolar hypoxia causes pulmonary vasoconstriction by means of mechanisms local to the lung. For the last 20 years, it has been clear that the essential sensor, transduction, and effector mechanisms responsible for hypoxic pulmonary vasoconstriction (HPV) reside in the pulmonary arterial smooth muscle cell. The main focus of this review is the cellular and molecular work performed to clarify these intrinsic mechanisms and to determine how they are facilitated and inhibited by the extrinsic influences of other cells. Because the interaction of intrinsic and extrinsic mechanisms is likely to shape expression of HPV in vivo, we relate results obtained in cells to HPV in more intact preparations, such as intact and isolated lungs and isolated pulmonary vessels. Finally, we evaluate evidence regarding the contribution of HPV to the physiological and pathophysiological processes involved in the transition from fetal to neonatal life, pulmonary gas exchange, high-altitude pulmonary edema, and pulmonary hypertension. Although understanding of HPV has advanced significantly, major areas of ignorance and uncertainty await resolution.

Oxygen dilation in fetal pulmonary arterioles: role of K(+) channels

BACKGROUND

Oxygen is a potent stimulus for pulmonary vasodilation. Potassium channels have been implicated as both sensors and effectors for oxygen-induced changes in pulmonary vascular tone. We have examined the effect of potassium channel blockers on oxygen-induced vasodilation in isolated pulmonary arterioles from fetal rats at term.

MATERIALS AND METHODS

Third generation pulmonary arterioles were isolated from fetal rats on Day 22 of gestation, cannulated, pressurized at constant distending pressures, and preconstricted by suffusion with a salt solution bubbled with a "hypoxic gas" mixture (pO(2) <or=50 mm Hg). Oxygen-induced vasodilation was measured as percentage reversal of the "hypoxic" vasoconstriction after 30 min of suffusion with "normoxic" solution (pO(2) 90-145 mm Hg). Responses were recorded in the absence of blockers (controls) or in the presence of a voltage-gated K(+) channel (K(v)) blocker, 4-aminopyridine; an ATP-sensitive K(+) channel (K(ATP)) blocker, glibenclamide; a Ca(2+)-activated K(+) channel (K(Ca)) blocker, charybdotoxin; or a nonspecific K(+) channel blocker, tetraethylammonium.

RESULTS

In control arterioles, normoxic suffusion for 30 min reversed hypoxic preconstriction by 83 +/- 19%. 4-aminopyridine significantly attenuated (44 +/- 9%), and glibenclamide and charybdotoxin had no effect (80 +/- 16 and 79 +/- 20%) on the magnitude of normoxic vasodilation.

CONCLUSIONS

Our results are consistent with a contribution of K(v) channels, but not K(ATP) or K(Ca) channels, to oxygen-induced vasodilation in third generation pulmonary arterioles from term fetal rats.