NITRIC-OXIDE SYNTHASE AND GUANYLATE-CYCLASE LEVELS IN CANINE BASILAR ARTERY AFTER SUBARACHNOID HEMORRHAGE

Endothelium-dependent vasodilation may be impaired during cerebral vas ospasm following subarachnoid hemorrhage. Under normal circumstances n itric oxide (NO) released by endothelial cells induces relaxation of s mooth muscle by activating the soluble form of guanylate cyclase withi n muscle cells. In this study the levels of both endothelial NO syntha se, the enzyme that produces NO, and soluble guanylate cyclase were de termined in canine basilar arteries in a double-hemorrhage model using Western blot immunoassays. Thirty dogs were assigned to three groups: Group DO, control; Group D2, dogs sacrificed 2 days after cisternal i njection of blood; and Group D7, dogs given double cisternal injection s of blood and sacrificed 7 days after the first injection. Constricti on of the basilar artery was confirmed by arterial angiography. Portio ns of the affected arteries or the corresponding region in control ani mals were solubilized for sodium dodecylsulfate-polyacrylamide gel ele ctrophoresis and Western blotting. A specific monoclonal antibody agai nst endothelial NO synthase was used. The extract from basilar arterie s showed two bands on the blots: 135 kD, characteristic of endothelial NO synthase, and 120 kD, which may be a degradation product of the en zyme. The densitometer values of the bands were presented as percentag es of DO control values. Although the total signal in the D7 group was less than that of the DO control group (D2, 97% +/- 22%; D7, 78% +/- 40%), it was not statistically significant. The proportion of the 135- kD form decreased between Groups DO and D7, but the difference was not significant. A single major band corresponding to the alpha-subunit o f soluble guanylate cyclase was seen at 70 kD in the basilar artery ex tracts. The signals of D2 and D7 samples were 69% +/- 40% and 25% +/- 18%, respectively. There was a significant difference between D7 and D O (p < 0.001). The reduced expression of soluble guanylate cyclase may be related to the impairment of endothelium-dependent vasodilation in vasospasm.