Low vasa vasorum densities correlate with inflammation and subintimal thickening: potential role in location--determination of atherogenesis.

OBJECTIVES: To assess the role of coronary vasa vasorum (VV) spatial distribution in determining the location of early atherosclerotic lesion development. METHODS AND RESULTS: Six, 3-month-old, female, crossbred swine were fed 2% high-cholesterol (HC) diet for 3 months prior to euthanasia. Six other pigs were fed normal diet (N) for the entire 6 months. Right coronary arteries were harvested and scanned intact with micro-CT (20mum cubic-voxel-size). After scanning, randomly selected cross-sectional histological sections were stained for nuclear-factor kappaB (NF-kappaB), hypoxia-inducible factor-1alpha (HIF-1alpha), macrophages, von-Willebrand-factor, dihydroethidium (DHE), tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6). The number of positive stained cells, as well as intima-to-media ratio, were compared with VV density (#/mm(2)) obtained from micro-CT images (which closely matched the location of the histological sections) in each of four equal quadrants of the coronary vessel wall. In normal, as well as HC pigs, the number of NF-kappaB (r=0.73 and 0.70), HIF-1alpha (r=0.74 and 0.77), TNF-alpha (r=0.58 and 0.72) and IL-6 (r=0.70 and 0.72) positive cells as well as the expression of DHE (Kendall tau coefficient -0.64 and -0.63) inversely correlated with VV density. In HC the VV density also inversely correlated with intima/media ratios (r=0.65). CONCLUSIONS: Our data suggest that low VV density territories within the coronary vessel wall are susceptible to hypoxia, oxidative stress and microinflammation and may therefore be starting points of early atherogenesis.

Impact of coronary vasa vasorum functional structure on coronary vessel wall perfusion distribution.

Noncoronary vasa vasorum have been described as networks of microvessels in the wall of arteries and veins. However, we have shown, using microcomputerized tomography (micro-CT) imaging methods, that porcine coronary vasa vasorum have a tree-like branching structure similar to the vasculature in general. In this study, we elucidate functional aspects of coronary vasa vasorum perfusion territories. Three pig hearts were injected with radiopaque Microfil via the coronary sinus to fill the left anterior descending coronary arteries (LADs) retrogradely at atmospheric pressure. In three other hearts, LADs were injected antegradely at 100-mmHg pressure via the left main carotid artery. Additionally, six LADs were injected in vivo with a suspension of 100- or 300-microm-diameter microspheres before harvesting of the hearts and injection of the LADs with Microfil. All harvested LADs were scanned intact with micro-CT (20 microm cubic voxels). The spatial density of vasa vasorum (no. of vasa/mm2) was measured in 20-microm-thick cross sections (at 0.4-mm intervals). Retrogradely injected LADs showed high and uniformly distributed vasa vasorum densities in the adventitia (means +/- SE; 5.38 +/- 0.09 vs. 3.58 +/- 0.1 vasa/mm2 in antegradely prepared LADs; P < 0.001). Antegradely prepared LADs showed patchy distributed, low-vasa-vasorum-density territories especially on the myocardial side of the coronary artery wall (epicardial density: 4.29 +/- 0.13 vasa/mm2 vs. myocardial density: 2.80 +/- 0.1 vasa/mm2, P < 0.001). Microembolization reduced vasa vasorum densities significantly (100-mum-diameter microspheres: 3.26 +/- 0.07 vasa/mm2, P < 0.05; 300-microm-diameter microspheres: 2.66 +/- 0.07 vasa/mm2, P < 0.001 vs. antegrade controls) and increased the size of low-vasa-vasorum-density territories. We conclude that coronary vasa vasorum are functional endarteries not connected via a plexus. This characteristic may have a significant impact on the spatial distribution of perfusion and drainage of the coronary vessel wall.

The nitric oxide synthase inhibitor L-NMMA potentiates noradrenaline-induced vasoconstriction: effects of the alpha2-receptor antagonist yohimbine.

OBJECTIVE: Alpha2-adrenoceptors can be found both on vascular smooth muscle cells and on the endothelium, where they exert opposing effects on vascular tone. In vitro, the stimulation of alpha2-adrenoceptors on endothelial cells leads to the release of vasodilating substances like nitric oxide (NO) and prostanoids. Little is known of this mechanism in vivo. DESIGN AND METHODS: We investigated the effects of the NO-synthase inhibitor L-NMMA (10(-6) mol) and the alpha2-adrenoceptor antagonist yohimbine (YO, 10(-10)-10(-6) mol) on noradrenaline (NA, 10(-12)-10(-8) mol)-induced vasoconstriction in the forearm skin microcirculation of 16 healthy volunteers using double injection technique and laser Doppler flowmetry. Results are expressed in perfusion units (PU) as differences from baseline and control in mean +/- SEM; the area under the time-response-curve was calculated (AUC). RESULTS: NA (10(-8)- 10(-12) mol) caused a marked, dose-dependent reduction in blood flow (mean effect -745 +/- 84 AUC PU; P< 0.001 versus saline). NA-induced vasoconstriction was enhanced by L-NMMA (mean effect -916 +/- 72 AUC PU; P< 0.001 versus NA). YO (10(-6)-10(-10) mol) induced a significant, dose-dependent vasodilation (mean effect +/- 446 +/- 110 AUC PU; P < 0.05 versus control); high doses of YO (10(-6) mol) inhibited NA constriction (P < 0.001 versus NA), whereas lower doses of YO (10(-8)/10(-10) mol) had no effect or even increased NA-induced constriction. In the presence of L-NMMA, YO (10(-8) and 10(-10) mol) further potentiated NA-induced vasoconstriction (mean effect -1165 +/- 108 AUC PU; NS versus NA). CONCLUSION: These data demonstrate, that in humans in vivo, endogenous NO attenuates noradrenergic constriction. The effects of YO suggest that endothelial alpha2-adrenoceptors are involved in the release of NO and other vasodilating substances. Furthermore, there is an additive NO-independent vasodilation, which can be unmasked by L-NMMA.