Sympathectomy causes aggravated lesions and dedifferentiation in large rabbit atherosclerotic arteries without involving nitric oxide.

Previously [Histochem J 1997;29:279-286], we found that sympathectomy induced neointima formation in ear but not cerebral arteries of genetically hyperlipidemic rabbits. To clarify the influence of sympathetic nerves in atherosclerosis, and whether their influence involves vascular NO activity, we studied groups of normocholesterolemic intact (NI) and sympathectomized (NS), and hypercholesterolemic intact (HI) and sympathectomized (HS) rabbits (diet/6-hydroxydopamine for 79 days). Segments of basilar (BA) and femoral (FA) arteries were studied histochemically, to evaluate differentiation (anti-desmin, anti-vimentin, anti-h-caldesmon, and nuclear dye), by confocal microscopy, and by in vitro myography. In BAs, staining of NI and NS groups was similar. In hypercholesterolemic groups, a small neointima developed, more frequently in HS segments where smooth muscle cells (SMCs) positive for all antibodies appeared to be migrating into the neointima. In FAs, SMCs stained for the three antibodies in the NI group, but we observed desmin- and h-caldesmon-negative, vimentin-positive cells in some external medial layers of the NS, HI and HS groups, identical to adventitial fibroblasts. Large neointimas of the HS group contained vimentin-positive and largely desmin- and h-caldesmon-negative cells. Relaxation of BA or FA segments to acetylcholine was not decreased by sympathectomy. Sympathectomy increased the contraction of resting FAs to nitro-L-arginine (p = 0.0379). Thus, sympathectomy aggravates the tendency for FA SMCs to migrate and dedifferentiate, increasing atherosclerotic lesions, without decreasing NO activity, but has only minor effects on BAs.

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.

Acetylcholine-induced relaxation of rabbit basilar artery in vitro is rapidly reduced by reactive oxygen species in acute hyperglycemia: role of NADPH oxidase.

We examined the effects of acute hyperglycemia on the function of rabbit cerebral arteries in vitro. It was hypothesized that increased formation of reactive oxygen species (ROS) could occur, which could explain how hyperglycemia aggravates certain pathologic situations such as cerebral ischemia. Three-millimeter basilar artery segments were incubated in either normoglycemic (NG, 5.5 mM D-glucose) or hyperglycemic (HG, 25 mM D-glucose) solution containing 3.10(-6) M indomethacin. After 90 minutes equilibration, a test (=T1) of relaxation to acetylcholine (Ach) at three concentrations was performed on histamine-precontracted segments. Three further identical tests were performed (T2-T4), after 30-minute rest periods. Ach responses in NG solution were stable, whereas those in HG solution, although greater at T1, fell progressively from one test to the next (P < 0.0001 versus NG), whereas nitroprusside responses did not change. In separate experiments, this time-dependent fall in Ach responses was significantly prevented by superoxide dismutase (SOD) plus catalase (P = 0.0003), but not by SOD alone. It was also significantly prevented by the NAD(P)H oxidase inhibitors diphenyleneiodonium (P = 0.020) and apocynin (P = 0.0179), but not by allopurinol (xanthine oxidase inhibitor). Control experiments with l-glucose ruled out a hyperosmotic or non-specific glucose effect. We conclude that, in HG solution in vitro, rapidly increasing ROS production largely derived from NAD(P)H oxidase reduced relaxation to acetylcholine. The rapidity of this effect suggests that the function of these arteries may be affected during brief periods of hyperglycemia in vivo.

Critical role of endothelial nitric oxide synthase and cyclooxygenase in response of rabbit basilar artery to serotonin.

The modes of action of serotonin (5-HT) on the tone of the rabbit basilar artery were investigated in vitro with the aim of determining the exact role of the endothelium. After sacrificing the animal under pentobarbital anesthesia, 3-mm segments of the artery were removed and mounted in a 5-ml myograph for isometric tension recording. Vessels precontracted by histamine were relaxed by acetylcholine. Mean maximum relaxation at 10(-4) M was reduced from 79% to 22% (P < 0.001) by 10(-5) M N-nitro-L-arginine (L-NA), and from 73% to 63% (NS) by 3.12(-6) M indomethacin. Intact non-precontracted vessels were contracted by 5-HT (10(-9) M to 10(-5) M): 10(-5) M L-NA significantly increased the contractile force (approximately twofold), whereas 3.10(-6) M indomethacin significantly decreased it (to approximately 35%). In histamine-precontracted vessels, 5-HT induced at low concentrations (3.10(-9) M to 3.10(-8) M) a reduction in tone and induced an increase in tone at higher concentrations. At 10(-5) M, L-NA abolished the relaxant phase of the response, whereas 3.10(-6) M indomethacin potentiated it. In uridine triphosphate-precontracted segments, there was not a net reduction in tone under 5-HT at 3.10(-9) to 3.10(-8) M, but further contraction appeared at higher concentrations. The presence of 10(-5) M L-NA significantly increased the contraction to 5-HT, but 3.10(-6) M indomethacin did not significantly reduce it. Endothelial lesion reduced by about 50% the contractile response of L-NA-treated arteries to 5-HT; and conversely, endothelial lesion increased approximately twofold the contraction of indomethacin-treated arteries to 5-HT. We conclude that 5-HT causes the release from the endothelium of two vasoactive factors, one of which is probably the vasodilator nitric oxide, but the size of the relaxation may depend on the prevailing level of nitric oxide synthase activation. The second factor is a cyclooxygenase-dependent contractile agent. However, the contraction to 5-HT was not modified by the presence of the thromboxane synthase inhibitor CGS 13080 (10(-4) M), suggesting that thromboxane A2 is not the main contractile agent released.