Phosphodiesterase isoforms in the pulmonary arterial circulation of the rat: changes in pulmonary hypertension.

Phosphodiesterase (PDE) activity was determined in pulmonary arteries removed from control and chronic hypoxia-induced pulmonary hypertensive rats. The main, first-branch, intrapulmonary and resistance pulmonary arteries were studied. We measured total cAMP PDE activity and cGMP PDE activity, as well as that of individual isoforms (PDE1-5). cAMP PDE activity in chronic hypoxic rats was increased in first-branch and intrapulmonary arteries from hypoxic rats. No changes were observed in the main or resistance pulmonary arteries. Similarly, cGMP PDE activity was increased in the main, first-branch and intra-pulmonary arteries of the hypoxic rats. No changes in cGMP PDE activity were observed in resistance arteries. There was evidence for PDE1-5 activity in all pulmonary arteries. The increased cAMP PDE activity in first-branch and intrapulmonary vessels was associated with an increase in cilostimide-inhibited PDE (PDE3) activity. Increased total cGMP PDE in main pulmonary artery was associated with increases in Ca++/calmodulin-stimulated (PDE1) activity. An increase in zaprinast-inhibited (PDE5) activity was observed in first-branch and intrapulmonary arteries. Our results suggest that decreases in intracellular cyclic nucleotide levels in pulmonary arteries from pulmonary hypertensive rats are associated with increased PDE activity. Further, these changes may reflect alterations at the level of specific types of PDE isoforms.