The role of prostacyclin in the hypercapnic and hypoxic cerebrovascular dilations.

The cerebral blood flow (CBF H/A) and the production of a stable prostacyclin metabolite, 6-Keto PGF 1 alpha ( 6KPGF ) was studied in 5 baboons in control, hypercapnic and hypoxic conditions. In steady-state conditions CBF H/A was measured by the clearance of an intra-arterial bolus injection of 133xenon and arterial and cerebral venous blood was sampled for assay of 6KPGF by radioimmunoassay. Both hypercapnia and hypoxia significantly increased CBF H/A and both increments were abolished by indomethacin. However, only hypoxia showed an increased 6KPGF production. Thus, hypoxia, but not hypercapnia, appears to produce cerebral vasodilation by increasing prostacyclin production.