Effect of substrate on hypoxic response of pulmonary artery.

Main pulmonary arteries (MPA) were isolated from young guinea pigs and incubated in a modified Krebs-Henseleit solution containing either glucose and sucrose, or sucrose alone. Experimental hypoxia (PO2=30 mmHg) was induced by aerating the muscle chamber with a gas mixture of 95% nitrogen and 5% carbon dioxide. In must experiments the MPA was electrically stimulated, whereas in some no electrical stimulation was used. The isometric tension of electrically stimulated MPA was analyzed by means of resting tension (RT), active tension (ATmax), and maximum rate of tension development (dT/dt). It was demonstrated that when MPA was exposed to acute hypoxia in a glucose-free medium a significant increase in resting tension was observed in both electrically stimulated and nonstimulated preparations. However, the significantly hypoxic response was inhibited by the presence of glucose in the experimental medium. This tonic response of MPA is suggestive of the in vivo hypoxic pressor response of pulmonary circulation. A lower oxygen tension (PO2=95 mmHg) exposure prior to hypoxia significantly potentiated this hypoxic response of the MPA. In a separate series of experiments, isolated aortas demonstrated a similar response when exposed to acute hypoxia in vitro. Similarly, as in experiments with MPA, the presence of glucose inhibited the hypoxic tonic response of isolated aorta.