Lung cyclic nucleotides in exercise-trained rats attenuate hypoxic pulmonary vasoconstriction.

We examined the effects of exercise training on pulmonary arterial blood pressure (Ppa) and on adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (GMP) concentrations in lung tissue at rest and during exercise under hypoxic conditions in catheter-implanted rats. Male Wistar rats were divided into an exercise-trained group (ET, n = 32) and nonexercised control group (control, n = 32). ET rats exercised 40 min/day 6 days/week for 6 weeks, at an altitude of 610 m on a treadmill. The mean Ppa levels of the ET were significantly lower than those of controls at rest and during exercise at 610- and 2500-m altitudes. The exercise-induced mean Ppa increase in the ET was less than that in controls at both 610- and 2500-m altitudes. Resting lung cAMP increased more in the ET than in controls at both 610- and 2500-m altitudes. In ET, cGMP was significantly greater at the 2500-m altitude than at the 610-m altitude at rest and just after exercise. Hypoxic exercise in ET was accompanied by a preferential increase in cGMP but not in cAMP. These results suggest that the intracellular augmentation of cAMP and cGMP in ET plays an important role in attenuating hypoxic pulmonary vasoconstriction (HPV) and exercise-induced increases in Ppa.