Effects of Methylene Blue on Hypoxic Cerebral Vasodilatation in

The present studies were conducted to examine the role of cerebrovascular guanylate cyclase in hypoxic cerebral vasodila-tation. In arteries mounted in vitro for measurements of isometric tension, 20 mm of hypoxia (bath oxygen partial pressure, 1 5 Torr) significantly increased cyclic GMP levels from 1 6 to 32, from 1 5 to 25 and from 20 to 38 pmol/g in rabbit common carotid, internal carotid and basilar arteries. These increases were blocked either by pretreatment with 3 M methylene blue, or by removal of the vascular endothelium. Methylene blue also significantly delayed hypoxic relaxation in the basilar and internal carotid arteries, and blocked transient hypoxic vasoconstnction in the common carotid. Together, these in vitro results demon-strate that vascular cytosolic guanylate cyclase participates in an endothelium-dependent manner in the direct effects of hy