Selective action of hypoxia on rat lung cyclic AMP.

The effect of three different levels of 24-h hypobaric hypoxia (630 mm Hg, 520 mm Hg, and 340 mm Hg) on rat lung cAMP and cGMP was studied. Liver was also examined to evaluate comparatively with lung. Lung cAMP concentration averaged 33.6 +/- 2.2 (SE) pmol/mg protein, and cGMP averaged 2.4 +/- 0.21 (SE) pmol/mg protein. Twenty-four-hour hypoxia resulted in a significant 40% decrease in lung cAMP at 520 and 340 mm Hg. The magnitude of change was the same for both hypoxic levels suggesting threshold dependency. In contrast, liver cAMP was not affected by the hypoxic exposure. Lung and liver cGMP were also relatively refractory to hypoxia. The decreased cAMP concentration seen in the hypoxic lung returned to normal level within 24 hours. These data show that acute hypoxia has a selective action on lung cAMP.