Immunoblotting of contractile and cytoskeletal proteins of canine basilar artery in vasospasm

Dexamethasone preventing contractile and cytoskeletal protein changes in the rabbit basilar artery after subarachnoid hemorrhage

OBJECT

The aim of this project was to study the perturbations of four smooth-muscle proteins and an extracellular protein, type I collagen, after subarachnoid hemorrhage (SAH) and to examine the possible preventive effects of dexamethasone.

METHODS

Using a one-hemorrhage rabbit model, the authors first examined the effects of SAH on the expression of alpha-actin, h-caldesmon, vimentin, smoothelin-B, and type I collagen; second, they studied whether post-SAH systemic administration of dexamethasone (three daily injections) corrected the induced alterations. Measurements were obtained at Day 7 post-SAH. The proteins were studied by performing immunohistochemical staining and using a laser-scanning confocal microscope. Compared with control (sham-injured) arteries, the density of the media of arteries subjected to SAH was reduced for alpha-actin (-11%, p = 0.01) and h-caldesmon (-15%, p = 0.06) but increased for vimentin (+15%, p = 0.04) and smoothelin-B (+53%, p = 0.04). Among animals in which SAH was induced, arteries in those treated with dexamethasone demonstrated higher values of density for alpha-actin (+13%, p = 0.05) and h-caldesmon (+20%, p = 0.01), lower values for vimentin (-55%, p = 0.05), and nonsignificantly different values for smoothelin-B. The density of type I collagen in the adventitia decreased significantly after SAH (-45%, p = 0.01), but dexamethasone treatment had no effect on this decrease.

CONCLUSIONS

The SAH-induced alterations in the density of three of four smooth-muscle proteins were prevented by dexamethasone treatment; two of these proteins--alpha-actin and h-caldesmon--are directly related to contraction. This drug may potentially be useful to prevent certain morphological and functional changes in cerebral arteries after SAH.

Changes of beta-actin mRNA expression in canine vasospastic basilar artery after experimental subarachnoid hemorrhage

The aim of this study was to investigate whether vascular remodeling occurs during cerebral vasospasm after subarachnoid hemorrhage (SAH). Beta-actin mRNA expression and structural change of its 3' untranslated region (UTR) which are considered a non-specific marker for vascular remodeling, were examined by Northern analysis and polymerase chain reaction analysis in a canine basilar artery after experimental SAH. The changes in the area of tunica media in the basilar artery were also examined histopathologically. Increased beta-actin mRNA expression and its structural changes of 3' UTR in the vasospastic basilar artery were markedly seen 7 and 14 days after SAH accompanied by increased area of tunica media in the basilar artery. The results suggest that vascular remodeling occurs and takes part in the luminal narrowing during cerebral vasospasm.

Confocal microscopic evidence of decreased alpha-actin expression within rabbit cerebral artery smooth muscle cells after subarachnoid haemorrhage

Our objective was to determine whether subarachnoid haemorrhage modifies cerebral artery smooth muscle cell phenotype and the contractile protein alpha-actin measured 7 days after haemorrhage. We used a rabbit subarachnoid haemorrhage model and immunofluorescence labelling of alpha-smooth muscle actin, vimentin and desmin. The paired comparison between the haemorrhage and sham rabbits was performed using confocal laser-scanning microscopy. We found in the haemorrhage group significantly less intense alpha-actin immunostaining (p = 0.036) and more intense vimentin immunostaining (p = 0.043) but no significant change in the intensity of desmin staining. Our results indicate an absolute decrease after subarachnoid haemorrhage in the amount of functional alpha-actin and in the light of the literature may suggest a certain degree of dedifferentiation of smooth muscle cells in the cerebral artery wall.

Impaired calcium regulation of smooth muscle during chronic vasospasm following subarachnoid hemorrhage

The intracellular calcium level was determined in the canine basilar artery to investigate whether Ca2+ regulation of its smooth muscle is altered during chronic vasospasm following subarachnoid hemorrhage. A double-hemorrhage model was used. The occurrence of vasospasm was confirmed angiographically 7 days after initial hemorrhage. The intracellular calcium concentration ([Ca2+]i) of smooth muscle was measured using Fura-2. Fluorescence to excitation at 340 and 356 nm was monitored and the ration R340/356 was used as the indicator of [Ca2+]i. When the extracellular calcium concentration ([Ca2+]e) was increased from pCa 8 to 2, [Ca2+]i also increased. In the spastic arteries, the [Ca2+]e - [Ca2+]i curve was elevated as compared with the normal arteries. Treatment with ionomycin elevated the curve in the normal group, but it had little effect in the spastic arteries. Values of [Ca2+]i, calculated in multiples of Kd, were greater in the spastic arteries. Diltiazem (10(-5) mol/L) partially suppressed the augmented [Ca2+]i signal in the spastic arteries, whereas it did not affect the curve in the control group. These results indicate that the calcium regulation of smooth muscle is impaired after subarachnoid hemorrhage, which may contribute to the pathogenesis of chronic vasospasm.

Nitric oxide synthase and guanylate cyclase levels in canine basilar artery after subarachnoid hemorrhage

Endothelium-dependent vasodilation may be impaired during cerebral vasospasm following subarachnoid hemorrhage. Under normal circumstances nitric oxide (NO) released by endothelial cells induces relaxation of smooth muscle by activating the soluble form of guanylate cyclase within muscle cells. In this study the levels of both endothelial NO synthase, the enzyme that produces NO, and soluble guanylate cyclase were determined in canine basilar arteries in a double-hemorrhage model using Western blot immunoassays. Thirty dogs were assigned to three groups: Group D0, control; Group D2, dogs sacrificed 2 days after cisternal injection of blood; and Group D7, dogs given double cisternal injections of blood and sacrificed 7 days after the first injection. Constriction of the basilar artery was confirmed by arterial angiography. Portions of the affected arteries or the corresponding region in control animals were solubilized for sodium dodecylsulfate-polyacrylamide gel electrophoresis and Western blotting. A specific monoclonal antibody against endothelial NO synthase was used. The extract from basilar arteries showed two bands on the blots: 135 kD, characteristic of endothelial NO synthase, and 120 kD, which may be a degradation product of the enzyme. The densitometer values of the bands were presented as percentages of D0 control values. Although the total signal in the D7 group was less than that of the D0 control group (D2, 97% +/- 22%; D7, 78% +/- 40%), it was not statistically significant. The proportion of the 135-kD form decreased between Groups D0 and D7, but the difference was not significant. A single major band corresponding to the alpha-subunit of soluble guanylate cyclase was seen at 70 kD in the basilar artery extracts. The signals of D2 and D7 samples were 69% +/- 40% and 25% +/- 18%, respectively. There was a significant difference between D7 and D0 (p < 0.001). The reduced expression of soluble guanylate cyclase may be related to the impairment of endothelium-dependent vasodilation in vasospasm.