Mechanisms of enhanced basal tone of brain parenchymal arterioles during early postischemic reperfusion: role of ET-1-induced peroxynitrite generation

The contributions of vasoconstrictors (endothelin-1 (ET-1), peroxynitrite) and endothelium-dependent vasodilatory mechanisms to basal tone were investigated in parenchymal arterioles (PAs) after early postischemic reperfusion. Transient middle cerebral artery occlusion (tMCAO) was induced for 2 hours with 30 minutes reperfusion in male Wistar rats and compared with ischemia alone (permanent MCAO (pMCAO); 2.5 hours) or sham controls. Changes in lumen diameter of isolated and pressurized PAs were compared. Quantitative PCR was used to measure endothelin type B (ET_B) receptors. Constriction to intravascular pressure (‘basal tone'') was not affected by tMCAO or pMCAO. However, constriction to inhibitors of endothelial cell, small- (SK) and intermediate- (IK) conductance, Ca²⁺-sensitive K⁺ channels (apamin and TRAM-34, respectively) were significantly enhanced in PAs from tMCAO compared with pMCAO or sham. Addition of the ET_B agonist sarafotoxin caused constriction in PAs from tMCAO but not from sham animals (21±4% versus 3±3% at 1 nmol/L; P<0.01) that was inhibited by the peroxynitrite scavenger FeTMPyP (5,10,15,20-tetrakis (N-methyl-4′-pyridyl) porphinato iron (III) chloride) (100 μmol/L). Expression of ET_B receptors was not found on PA smooth muscle, suggesting that constriction to sarafotoxin after tMCAO was due to peroxynitrite and not ET_B receptor expression. The maintenance of basal tone in PAs after tMCAO may restrict flow to the ischemic region and contribute to infarct expansion.     

The pattern of coronary arteriolar bifurcations and the uniform shear hypothesis

By minimizing the cost function, which is the sum of the friction power loss and the metabolic energy proportional to blood volume, Murray derived an optimal condition for a vascular bifurcation. Murray's law states that the cube of the radius of a parent vessel equals the sum of the cubes of the radii of the daughters. We tested Murray's law against our data of pig's maximally vasodilated coronary arteriolar blood vessels at bifurcation points in control and hypertensive ventricles. Data were obtained from 7 farm pigs, 4 normal controls and 3 with right ventricular hypertrophy induced by stenosis of a pulmonary artery. Data on coronary arteriolar bifurcations were obtained from histological specimens by optical sectioning. The experimental results show excellent agreement with Murray's law in control and hypertensive hearts. Theoretically, we show that Murray's law can be derived alternatively as a consequence of the uniform vessel-wall shear strain rate hypothesis and a fluid mechanics equation based on conservation of mass and momentum. Conversely, the fluid mechanical equation, together with Murray's law, established as an empirical equation of actual measurements implies the uniformity of the shear strain rate of the blood at the vessel wall throughout the arterioles. The validity of these statements is discussed.     

Alcohol, the cerebral circulation and strokes

Inasmuch as ethanol is thought to exert its major effects on the CNS, it is important to determine whether this abused substance can exert any direct action on cerebral blood vessels. Since chronic ingestion of alcohol: (1) can produce a loss (and degeneration) of neurons and glial cells in the brain, and (2) is associated, often, with hallucinations in human subjects particularly those undergoing withdrawal, it is possible that ethanol could produce hypoxia in select regions of the brain. The available indirect evidence in man and animals, albeit equivocal, does indicate that ethanol in certain concentrations might produce deficits in cerebral blood flow in select regions of the brain. Direct in-situ observations on the rat brain, using high-resolution, quantitative TV image-intensification microscopy, indicates that administration of ethanol, irrespective of the route of administration (e.g., perivascularly, intraarterially or systemically), produces graded concentration-dependent spasms of arterioles and venules. Concentrations of ethanol approximately greater than 250 mg/dl produce intense spasms resulting in rupture of these vessels. Recent in-situ studies in conscious dogs, using radiolabelled microspheres, also indicate that ethanol can produce deficits in regional brain blood flow. Studies with isolated canine middle cerebral and basilar arteries clearly demonstrate that low concentrations of ethanol (e.g., (less than 10 mM) can produce concentration-dependent spasms by a direct vascular action. Collectively, these new findings could be used to support the concept that heavy use of alcohol or binge-drinking can produce stroke-like effects. Specific calcium antagonists prevented or reversed the alcohol-induced cerebrovasospasms in rats and may prove valuable in treating the hypertension and strokes observed in heavy users of alcohol.     

The bivalence of Juxtaglomerular cells in the maturing rat kidney

Summary A comparative immunofluorescence and light microscopical study of the three cell types of the Juxtaglomerular apparatus (pure muscle cells, pure granular cells and mixed cells) was performed on the growing and maturing kidney of the rat. Mixed cells, containing contractile protein and secretory granules, are detectable on the first postnatal day in about one third of the JGAs. From the third week, the number of bivalent cells increases, while the proportion of pure muscle or pure granular cells decreases. Morphological and functional maturation, achieved by 3 to 4 weeks, is associated with increasing numbers of bivalent cells and a shift in the main site of renin production from the inner to the outer cortical zone.The divergent internal structure of JGA cell types expresses the range of varied differentiation expressed by one cell line. Pure muscle or granular cells are at the extremes of the range and mixed cells take up an intermediate position.     

8例高血压急症相关性肾损害的临床病理分析

目的探讨高血压急症相关肾损害的临床、病理特点和预后。方法回顾性分析2003年1月至2014年1月我院明确诊断的8例高血压急症相关性肾损害患者,所有患者均行肾活检病理检查,及相关实验室及影像学检查。结果患者初始平均收缩压/舒张压（232±30/140±13）mm Hg,平均血肌酐值（452±172）μmol/L（190-922）μmol/L。光镜检查显示：所有的肾活检标本均有小动脉洋葱皮样增厚,及肾小球毛细血管袢缺血皱缩,然而未见到小动脉纤维素样坏死。降血压治疗对所有患者有效,并明显改善患者肾功能。结论高血压急症相关肾损害最常见的病理表现是小动脉洋葱皮样增厚和肾小球毛细血管袢缺血性皱缩;严格控制血压可显著改善高血压急症相关肾损害的预后。     

食管壁微动脉及毛细血管的观测

目的;观察食管壁内动脉血供及微血管构筑的基础性研究资料。方法：随机选取新鲜胎尸25具,墨汁灌注,组织切片;家兔5只,钙钴法碱性磷酸酶染色。光学显微镜下观测。结果;食管壁内各层均存在动脉网,粘膜下层动脉网丰富,分深浅两层;各层毛细血管特点各异,外膜层稀,肌层有肌束间血管网,粘膜下层呈丛状,粘膜层最丰富;食管各段毛细血管密度差异不大,但颈段前壁纵形肌、胸上段后壁粘膜层有相对毛细血管贫乏区。结论：食管的各段各层均存在动脉网,毛细血管密度差异不大,能有限代偿食管壁外供血动脉的阻断。     

Openers of small conductance calcium-activated potassium channels selectively enhance NO-mediated bradykinin vasodilatation in porcine retinal arterioles

Background and purpose:

Small (SK_Ca or K_Ca2) and intermediate (IK_Ca or K_Ca3.1) conductance calcium-activated potassium channels are involved in regulation of vascular tone and blood pressure. The present study investigated whether NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) and CyPPA (cyclohexyl-[2-(3,5-dimethyl-pyrazol-1-yl)-6-methyl-pyrimidin-4-yl]-amine), which are selective openers of SK_Ca and IK_Ca channels and of SK_Ca2 and SK_Ca3 channels, respectively, enhance endothelium-dependent vasodilatation in porcine retinal arterioles.

Experimental approach:

In porcine retinal arterioles, SK_Ca3 and IK_Ca protein localization was examined by immunolabelling. Endothelial cell calcium was measured by fluorescence imaging. For functional studies, arterioles with internal diameters of 116 ± 2 µm (n = 276) were mounted in microvascular myographs for isometric tension recordings.

Key results:

SK_Ca3 and IK_Ca protein was localized in the endothelium. Bradykinin, but not NS309 or CyPPA increased endothelial cell calcium. Pre-incubation with NS309 or CyPPA enhanced bradykinin relaxation without changing endothelial cell calcium. This enhanced relaxation was abolished by blocking SK_Ca channels with apamin. In the presence of NS309 or CyPPA, mainly inhibition of NO synthase with asymmetric dimethylarginine, but also inhibition of cyclooxygenase with indomethacin, reduced bradykinin relaxation. Bradykinin relaxation was completely abolished by NO synthase and cyclooxygenase inhibition together with a NO scavenger, oxyhaemoglobin.

Conclusions and implications:

In porcine retinal arterioles, bradykinin increases endothelial cell calcium leading to activation of SK_Ca and IK_Ca channels. Without altering endothelial cell calcium, NS309 and CyPPA open SK_Ca channels that enhance NO-mediated bradykinin relaxations. These results imply that opening SK_Ca channels improves endothelium-dependent relaxation and makes this channel a potential target for treatments aimed at restoring retinal blood flow.     

Theophylline dilates rat diaphragm arterioles via the prostaglandins pathway

1. We investigated by intravital microscopy in rats, the in vivo direct effects of theophylline on the diameters of second and third order diaphragm arterioles.
2. Theophylline (1–100 μM) dilated second and third order diaphragm arterioles significantly, and with an amplitude which was not statistically different from the one obtained with adenosine (1–100 μM). Enprofylline (1–100 μM), a theophylline analogue with poor adenosine-receptor antagonism but with similar or higher phosphodiesterases inhibition properties than theophylline, also dilated diaphragm arterioles, causing however, a significantly smaller dilatation than theophylline.
3. Neither the A1 adenosine receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (CPX, 50 nM), nor the A₂ adenosine receptor antagonist 3,7-dimethyl-1-proparglyxanthine (DMPX, 10 μM) reduced significantly theophylline-induced arteriolar dilatation.
4. Theophylline (100 nM) abolished adenosine-induced arteriolar dilatation.
5. The dilatation induced by theophylline was unchanged by the nitric oxide (NO) synthase inhibitor Nω-nitro-L-arginine (NNA, 300 μM).
6. Theophylline-induced arteriolar dilatation was abolished by the prostaglandin synthesis inhibitors mefenamic acid or indomethacin (20 μM).
7. These findings show that theophylline induced a significant dilatation of diaphragm arterioles via the release of prostaglandins.