Flow-induced endothelium-dependent vasoreactivity in rat mesenteric arterial bed

Vimentin and laminin are altered on cheek pouch microvessels of streptozotocin-induced diabetic hamsters

OBJECTIVE

Normal endothelial cells respond to shear stress by elongating and aligning in the direction of fluid flow. Hyperglycemia impairs this response and contributes to microvascular complications, which result in deleterious effects to the endothelium. This work aimed to evaluate cheek pouch microvessel morphological characteristics, reactivity, permeability, and expression of cytoskeleton and extracellular matrix components in hamsters after the induction of diabetes with streptozotocin.

METHODS

Syrian golden hamsters (90-130 g) were injected with streptozotocin (50 mg/kg, i.p.) or vehicle either 6 (the diabetes mellitus 6 group) or 15 (the diabetes mellitus 15 group) days before the experiment. Vascular dimensions and density per area of vessels were determined by morphometric and stereological measurements. Changes in blood flow were measured in response to acetylcholine, and plasma extravasation was measured by the number of leakage sites. Actin, talin, α-smooth muscle actin, vimentin, type IV collagen, and laminin were detected by immunohistochemistry and assessed through a semiquantitative scoring system.

RESULTS

There were no major alterations in the lumen, wall diameters, or densities of the examined vessels. Likewise, vascular reactivity and permeability were not altered by diabetes. The arterioles demonstrated increased immunoreactivity to vimentin and laminin in the diabetes mellitus 6 and diabetes mellitus 15 groups.

DISCUSSION

Antibodies against laminin and vimentin inhibit branching morphogenesis in vitro. Therefore, laminin and vimentin participating in the structure of the focal adhesion may play a role in angiogenesis.

CONCLUSIONS

Our results indicated the existence of changes related to cell-matrix interactions, which may contribute to the pathological remodeling that was already underway one week after induction of experimental diabetes.

Age-associated impairment in vasorelaxation to fluid shear stress in the female vasculature is improved by TNF-α antagonism

Aging is associated with alterations in vascular homeostasis, including a reduction in flow-mediated vasodilation, which in women is related to the onset of menopause. We previously found that in female animals, aging is associated with an increase in TNF-α. Thus we investigated the role of in vivo TNF-α inhibition on vascular responses to shear stress in aging female rats. Mesenteric arteries (∼150 μm) were isolated from young (3 mo) and ovariectomized Sprague-Dawley female rats approaching reproductive senescence (12 mo) treated with either placebo or a TNF-α inhibitor (etanercept; 0.3 mg/kg) and were mounted on a pressure myograph system. Vessels were equilibrated at an intraluminal pressure of 60 mmHg and then preconstricted with phenylephrine at ∼70% of their initial diameter. Perfusate flow was increased in steps from 0 to 150 μl/min. Compared with young vessels, aged vessels have a decrease in flow-mediated dilation [maximal dilation (means ± SE): 52 ± 4 vs. 24 ± 15%; P < 0.05], which was improved by TNF-α inhibition. Moreover, in aged vessels maximal dilation to flow was achieved at higher levels of shear stress compared with young vessels. In all groups, flow-mediated dilation was abolished by either endothelial removal or nitric oxide synthase inhibition with NG-nitro-l-arginine methyl ester. However, the modulation by NG-nitro-l-arginine methyl ester was reduced in vessels from aged animals compared with young animals but was improved in the etanercept-treated aged animals. In vivo chronic TNF-α inhibition improves flow-mediated arterial dilation in resistance arteries of aged female animals.

Effects of anthocyanidin derivative (HK-008) on relaxation in rat perfused mesenterial bed

Anthocyanins, which are responsible for a variety of bright colors (including red, blue, and purple) in fruits, vegetables, and flowers, are consumed as dietary polyphenols. Anthocyanin-containing fruits are thought to decrease coronary heart disease and are used in anti-diabetic preparations. Diabetes is associated with a variety of cardiovascular complications that may be mediated by endothelial dysfunction, and so this study was designed mainly to characterize the influence of a synthesized anthocyanidin derivative (HK-008) over acetylcholine (ACh)-induced relaxation in mesenteric arterial beds isolated from rats. In a glucose-tolerance test in intact rats, HK-008 (30 mg/kg) reduced the glucose level as effectively as the same dose of glibenclamide. The aortic relaxation induced by pinacidil (an ATP-sensitive potassium channel opener) was greatly inhibited by glibenclamide (10 microM), and also significantly inhibited by HK-008 (10 microM). Interestingly, the ACh-induced relaxation in the perfused, preconstricted mesenteric arterial bed was significantly enhanced by HK-008 (10 microM), and this enhancement was significantly attenuated by indomethacin (10 microM). The ACh-induced mesenteric relaxation was impaired by an increase in oxidative stress, viz. superoxide-generating treatment [xanthine oxidase (XO; 0.1 U/ml) plus hypoxanthine (HX; 10 microM)]. However, this impairment was strongly suppressed by HK-008 (10 microM). These results suggest that HK-008 increases endothelium-induced relaxation by suppressing oxidative stress or modulating prostanoids signaling. This compound may therefore be useful against certain cardiovascular disorders.

Acetylcholine-induced vasodilation in the perfused kidney of the streptozotocin-induced diabetic rat: role of prostacyclin

Using the perfused kidneys of age-matched controls and streptozotocin (STZ)-induced diabetic rats, we previously demonstrated that endothelial dysfunction is present in STZ-induced diabetic rats and that acetylcholine (ACh) increases the level of 6-keto-prostaglandin F(1 alpha) (a metabolite of prostacyclin) in the effluent from such perfused kidneys. Here, we investigated whether the ACh-induced relaxation in the perfused kidney is modulated by prostacyclin and/or thromboxane A(2) (TXA(2)) in the STZ-induced diabetic state. ACh-induced renal vasodilatation was significantly weaker in STZ-induced diabetic rats than in age-matched controls, and it was not affected by treatment with 10 microM furegrelate (TXA(2) -synthase inhibitor) or 1 microM SQ29548 (TXA(2) -receptor antagonist) in either group. However, it was attenuated by 10 microM tranylcypromine (prostacyclin-synthesis inhibitor), but only in the diabetic group. These results suggest that the endothelium-dependent relaxation induced by ACh in the renal vascular bed of STZ-induced diabetic rats is regulated by prostacyclin, not by TXA(2). Increased prostacyclin-signaling may occur to help compensate for the impaired endothelial function seen in the kidney in long-term diabetic states.

Effects of dual-action genistein derivatives on relaxation in rat aorta

Protein tyrosine kinases and nitric oxide (NO) play important roles in several cardiovascular diseases. In this study, we examined the actions of two compounds, each has structure of genistein (a tyrosine kinase inhibitor) and an NO donor, on endothelium-independent relaxation responses in the isolated rat aorta. By rational drug design, genistein was modified to acquire an NO donor, and we synthesized two such compounds (G-II, G-VI). These compounds and genistein induced dose-dependent relaxation responses in endothelium-denuded aortic strips, the rank order of potencies being G-VI > G-II > genistein. Incubation of endothelium-denuded strips with 1H-[1,2,4] oxadiazolo[4,3-a]-quinoxalin-1-one (ODQ, 10 microM), a guanylyl cyclase inhibitor, inhibited both the G-II- and G-VI-induced relaxations, but not the genistein-induced relaxation. The residual relaxations induced by these two compounds were similar to the genistein-induced relaxation. Incubation of endothelium-denuded strips with lysophosphatidylcholine (LPC, 20 microM)-which is a major atherogenic lysophospholipid component of oxidized low-density lipoprotein and is known to activate tyrosine kinase-caused a significant rightward shift in the dose-response curve for genistein. LPC also shifted the G-II- and G-VI-induced relaxation curves to the right; however, these relaxations in the presence of LPC were greater than that induced by genistein. The sodium nitroprusside-induced relaxation in endothelium-denuded strips was similar between in the absence and presence of LPC. These results suggest that each of our newly developed G-II and G-VI compounds has a dual action, as an NO donor and a tyrosine kinase inhibitor. These compounds may be useful against certain cardiovascular diseases.