Increased sympathetic venoconstriction and reactivity to norepinephrine in mesenteric veins in anesthetized DOCA-salt hypertensive rats

Increased sympathetic nervous activity (SNA) elevates venomotor tone in deoxycorticosterone acetate (DOCA)-salt hypertension. We studied the mechanisms by which the SNA increases venomotor tone in DOCA-salt hypertension by making in situ intracellular recordings of venous smooth muscle cell (VSMC) membrane potential (E(m)) and measurement of outside diameter (OD) in mesenteric veins (MV) and mesenteric arteries (MA) of anesthetized rats. We also studied norepinephrine (NE)- and endothelin-1 (ET-1)-induced increases in MA or MV perfusion pressure (PP) in vitro. E(m) in DOCA-salt MV was depolarized compared with sham MV. Prazosin hyperpolarized VSMC E(m) in DOCA-salt but not in sham MV. NE concentration-response curves (CRCs) for OD decreases in MV from DOCA-salt rats were left-shifted with an increased maximum response (E(max)) compared with sham MV. NE CRCs for OD decreases in MA were right-shifted with reduced E(max) in DOCA-salt compared with sham rats. ET-1 CRCs were similar in DOCA-salt and sham MV but were right-shifted with reduced E(max) in DOCA-salt MA. NE CRCs for MAPP increases were left-shifted without a change in E(max) in DOCA-salt rats. NE did not change MVPP. MAPP and MVPP for ET-1 CRCs were similar in sham and DOCA-salt rats, but E(max) for MAPP was reduced in DOCA-salt rats. Hematoxylin staining revealed hypertrophy in DOCA-salt MA but not in MV. We conclude that there is increased reactivity to NE released from the sympathetic nervous system in DOCA-salt MV that causes VSMC depolarization and increased venomotor tone. In DOCA-salt rats, in vivo ET-1 reactivity is maintained in MV, but reduced in MA.     

Increased density of fluorescent adrenergic fibers around the middle cerebral arteries of stroke-prone spontaneously hypertensive rats

The distribution of fluorescent adrenergic nerve fibers in the proximal portion (horizontal segment, Hs) and the three distal portions (major branches) of the middle cerebral arteries (MCA) was examined in stroke-prone spontaneously hypertensive rats (SHRSP) aged 10, 30, 60, 90, and 180 days, by the glyoxylic acid method. The results were compared with those in agematched normotensive Wistar Kyoto (WKY) rats. While the distribution pattern of fluorescent nerve fibers in the proximal portion of WKY rats changed from a straight linear arrangement at 10 and 30 days of age to a network-like arrangement after 60 days, those from SHRSP showed a constant meshwork pattern throughout the entire examination period. In the distal portions of the MCA of both SHRSP and WKY rats at all ages examined, fluorescent nerve fibers formed a coarse network. The distribution densities of adrenergic nerve fibers in the proximal and distal portions of the MCA of SHRSP were significantly higher (P<0.01 and 0.05) than those of WKY rats at all ages examined, except in the proximal portion at 90 and 180 days of age. The difference in nerve fiber density between SHRSP and WKY rats reached a peak at 30 days of age in both proximal and distal portions, and then gradually decreased with age. The present study suggests that sympathetic hyperinnervation is an important factor in the development of hypertension, and is involved in its maintenance in SHRSP.     

Increased spontaneous tone in renal arteries of spontaneously hypertensive rats

The spontaneous tone of vascular smooth muscle is augmented in hypertension. The present study examined the role of nitric oxide (NO), cyclooxygenase (COX), thromboxane A(2)/prostanoid (TP) and PGE(2)/prostanoid (EP-1) receptors, reactive oxygen species, and large-conductance Ca(2+)-activated K(+) (BK(Ca)) channels in the regulation of spontaneous tone in renal arteries of young and mature Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Rings of arteries, with and without endothelium, were suspended in a myograph for isometric force recording. Spontaneous tone (increase above initial tension) was observed only in arteries of mature SHR and was greater in arteries without endothelium. N(omega)-nitro-L-arginine methyl ester (L-NAME, an inhibitor of NO synthases) induced larger contractions in arteries of SHR than WKY. Indomethacin (a COX inhibitor), SC-19220 (an EP-1 receptor antagonist), and terutroban (a TP receptor antagonist) reduced the L-NAME-evoked contractions. Tiron (a superoxide anion scavenger), catalase (an enzyme that degrades H(2)O(2)), and deferoxamine (a hydroxyl radical scavenger) augmented the L-NAME-induced contractions in arteries of mature SHR. Charybdotoxin (a BK(Ca) channel blocker) caused contractions in arteries of mature SHR without endothelium and in arteries with endothelium incubated with L-NAME. A decreased protein level of endothelial NO synthase, an increased release of prostacyclin, and an increased expression of EP-1 receptors were observed in arteries of mature SHR. The present study suggests that spontaneous tone is precipitated by age and hypertension. The reduced production of NO, leading to decreased activation of BK(Ca) channels, may leave the actions of endogenous vasoconstrictors unopposed. COX products that activate EP-1 and TP receptors are involved in the development of spontaneous tone.     

Rod-shaped tubulated bodies in the endothelia of mesenteric arteries of hypertensive rats.

Weibel-Palade bodies were found in the endothelial cells of the mesenteric arteries of hypertensive rats. They were spherical or rod-shaped and bounded by a single membrane. They measured approximately 0.1 to 0.2 mu in diameter and up to 0.4 mu in length. The majority of them showed microtubular subunits, measuring about 200 A in width. These bodies are thought to originate from Golgi apparatus.     

Organization of cells and extracelluar matrix in mesenteric arteries of spontaneously hypertensive rats

Summary Biochemical studies have been used to assess the quantitative changes in elastin and collagen in hypertensive vs. normotensive arteries. However, the relative distribution and organization of these fibrous proteins is likely to be equal in importance to their absolute amounts. In this study we have used scanning electron microscopy in association with selective digestion techniques to assess the organization of cellular and extracellular components of the tunica media of mesenteric arteries of spontaneously hypertensive rats. Superior and small mesenteric arteries were digested with acid, alkali, or bleach to exposure cells, collagen, or collagen and elastin, respectively. We observed that hypertension does not cause a qualitative change in the 3-dimensional arrangement of cells, collagen, or elastin in spontaneously hypertensive arteries when compared to normotensive arteries. However, cells in the superior artery are significantly different in overall shape and surface features when compared to cells of small arteries. These differences in surface morphology of cells are present in hypertensive and normotensive vessels and suggest that superior and small mesenteric artery cells transmit load to the isotropic matrix in different ways. In the elasto-muscular superior artery, force is transmitted across digitations throughout the cell surface. In the muscular small artery, force is transmitted across the tapered, smooth cell surface.     

Increased density of fluorescent adrenergic fibers around the middle cerebral arteries of stroke-prone spontaneously hypertensive rats.

The distribution of fluorescent adrenergic nerve fibers in the proximal portion (horizontal segment, Hs) and the three distal portions (major branches) of the middle cerebral arteries (MCA) was examined in stroke-prone spontaneously hypertensive rats (SHRSP) aged 10, 30, 60, 90, and 180 days, by the glyoxylic acid method. The results were compared with those in age-matched normotensive Wistar Kyoto (WKY) rats. While the distribution pattern of fluorescent nerve fibers in the proximal portion of WKY rats changed from a straight linear arrangement at 10 and 30 days of age to a network-like arrangement after 60 days, those from SHRSP showed a constant meshwork pattern throughout the entire examination period. In the distal portions of the MCA of both SHRSP and WKY rats at all ages examined, fluorescent nerve fibers formed a coarse network. The distribution densities of adrenergic nerve fibers in the proximal and distal portions of the MCA of SHRSP were significantly higher (P less than 0.01 and 0.05) than those of WKY rats at all ages examined, except in the proximal portion at 90 and 180 days of age. The difference in nerve fiber density between SHRSP and WKY rats reached a peak at 30 days of age in both proximal and distal portions, and then gradually decreased with age. The present study suggests that sympathetic hyperinnervation is an important factor in the development of hypertension, and is involved in its maintenance in SHRSP.     

Increased reactivity in the mesenteric artery of spontaneously hypertensive rats to phorbol ester

The contraction responses of mesenteric artery from 10 week old spontaneously hypertensive rats (SHRs) and normotensive Wistar Kyoto controls (WKYs) to phorbol 12, 13 - dibutyrate (PDBu) and agents acting on the potential-operated calcium channels were compared. The vessels from the SHR were significantly more sensitive to PDBu than those from the WKY. The PDBu-induced contractions were inhibited by nifedipine. The vessels from the SHR were also more sensitive to Bay K 8644 and KCl than the WKY. Low concentrations of PDBu (1 nM) potentiated the KCl contraction significantly more in the SHR than the WKY. It is suggested that the increased reactivity to PDBu in the SHR may in part be related to changes in the activity of the potential-operated calcium channels.     

Aldosterone increases RAMP1 expression in mesenteric arteries from spontaneously hypertensive rats

OBJECTIVE: We analysed the effect of aldosterone on calcitonin gene-related peptide (CGRP) mediated vasodilation in noradrenaline precontracted endothelium denuded mesenteric arteries segments from Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) and the effect of aldosterone on calcitonin receptor-like receptor (CL receptor) and receptor activity modifying protein 1 (RAMP1) expression in endothelium-denuded mesenteric arteries from SHR rats. RESULTS: CGRP 0.1 nM-0.1 microM induced a concentration-dependent relaxation that was enhanced by aldosterone 1 microM in SHR only. Incubation with RU 486 10 microM significantly reduced the enhancement of CGRP-relaxation produced by aldosterone in SHR. CL receptor expression was not modified in either strain, while RAMP1 expression was enhanced in SHR by aldosterone 1 microM 120 min and 0.1 microM 120 min. This up-regulation of RAMP1 was prevented by RU 486 10 microM. CONCLUSIONS: Aldosterone, through glucocorticoid receptor activation, increases the vasodilatory effect of CGRP in SHR mesenteric arteries, which seems to be mediated by increased RAMP1 expression.     

Tension-velocity relationships in hypertensive mesenteric resistance arteries

Increased total peripheral resistance is the cardinal haemodynamic disorder in essential hypertension. This could be secondary to alterations in the mechanical properties of vascular smooth muscle. Adequate study has not been made of the tension-velocity (T-V) relationship in hypertensive resistance arterial smooth muscle. Increased narrowing in such arteries would result in increased resistance. The objectives of this investigation were to determine whether there is (i) increased narrowing capacity (-delta C/C omicron, where C stands for arterial internal circumference and C omicron is the optimal arterial internal circumference for maximum tension development); (ii) an increased maximum velocity of isobaric narrowing (Vmax) measured in C omicron per second; (iii) an increased wall thickness (h); and (iv) an increased active stress development (Tmax) in the spontaneously hypertensive rat (SHR; n = 5) compared with the normotensive Wistar Kyoto (WKY; n = 5) and MK-421 (an angiotensin I converting enzyme inhibitor) treated spontaneously hypertensive rat (MK-421 trt. SHR; n = 5) mesenteric resistance (diameter, less than 300 micron) arteries. Analysis of the data for arteries constricting isobarically against a range of pressures revealed that (a) the SHR -deltaC/C omicron values at pressures ranging from 20 to 120 mmHg (1 mmHg = 133.322 Pa) showed significantly increased narrowing compared with the MK-421 trt. SHR and WKY -deltaC/C omicron values in this same pressure range (p less than 0.01), and (b) the SHR derived Vmax of 0.83 +/- 0.08 C omicron/s was significantly faster than either the MK-421 trt.(ABSTRACT TRUNCATED AT 250 WORDS)     

烫伤大鼠脑底动脉壁内含内皮素-1能神经纤维的形态学变化

目的探讨烫(烧)伤损伤时大鼠脑血管内皮素-1能神经纤维分布与脑血管神经源性调节的关系,以及烫(烧)伤对脑血管损伤的影响。方法应用免疫组织化学技术观察烫(烧)伤大鼠脑底动脉(包括大脑前动脉、大脑中动脉、大脑后动脉和基底动脉)内皮素-1能神经纤维的分布。结果烫(烧)伤大鼠和正常大鼠脑底动脉均可见棕褐色的内皮素-1能免疫反应阳性神经纤维,似细线状,攀附于血管壁上,烫(烧)伤大鼠脑底动脉各主要分支内皮素-1能免疫反应阳性纤维密度较正常大鼠明显增加,纤维走行大多呈网状。结论烫(烧)伤可引起大鼠脑底动脉内皮素-1能免疫反应阳性神经纤维增加,增加的内皮素-1能神经纤维可能诱发脑血管痉挛和脑血液循环紊乱。提示内皮素-1能神经纤维在烫(烧)伤后在脑血管的神经源性调节中可能起重要的作用。     

Angiotensin II increases neurogenic nitric oxide metabolism in mesenteric arteries from hypertensive rats

We investigated, in mesenteric arteries from hypertensive rats (SHR), the possible changes in neurogenic nitric oxide (NO) release produced by angiotensin II (AII), and the possible mechanisms involved in this process. In deendothelialized segments the NO synthase inhibitor N(G)-nitro-L-arginine (L-NAME, 10 microM) increased the contractions caused by electrical field stimulation (EFS, 200 mA, 0.3 ms, 1-16 Hz, for 30 s). AII (0.1 nM) enhanced the response to EFS, which was unmodified by the subsequent addition of L-NAME. The AII antagonist receptor saralasine (0.1 microM) prevented the effect of AII, and the subsequent addition of L-NAME restored the contractile response. SOD (25 u/ml) decreased the reponse to EFS and the subsequent addition of L-NAME increased this response. AII did not modify the decrease in EFS response induced by SOD, and the addition of L-NAME increased the response. None of these drugs altered the response to exogenous noradrenaline (NA) or basal tone except SOD, which increased the basal tone, an effect blocked by phentolamine (1 microM). In arteries pre-incubated with [3H]-NA, AII did not modify the tritium efflux evoked by EFS, which was diminished by SOD. AII did not alter basal tritium efflux while SOD significantly increased it. These results suggest that EFS of SHR mesenteric arteries releases neurogenic NO, the metabolism of which is increased in the presence of AII by the generation of superoxide anions.     

Day-night variation in the in vitro contractility of aorta and mesenteric and renal arteries in transgenic hypertensive rats

TGR(mREN2)27 (TGR) rats develop severe hypertension and an inverted circadian blood pressure profile with peak blood pressure in the daytime rest phase. The present study investigated the in vitro responsiveness of different arteries of TGR rats during day and night. Twelve-week-old TGR rats and normotensive Sprague-Dawley (SPRD) controls, synchronized to 12h light, 12h dark (LD 12:12) (light 07:00 19:00), were killed at 09:00 (during rest) and 21:00 (during activity), and endothelium-dependent relaxation by acetylcholine and vascular contraction by angiotensin II were studied by measuring isometric force in ring segments of abdominal aorta and mesenteric and renal arteries. In SPRD rats, consistent day-night variation was found, with greater responses to angiotensin II during the daytime rest span. In TGR rats, biological time-dependent differences were found in the renal vasculature, but not in the aorta and mesenteric artery. Relaxation of SPRD rat aorta and mesenteric artery by acetylcholine was greater at 09:00, whereas in TGR rats, day-night variation was absent (mesenteric artery) or inverted (aorta). In conclusion, based on the study of two time points, daynight variation in vascular contractility of aorta and mesenteric artery is blunted in TGR rats, whereas renal artery segments showed an unchanged daynight pattern compared to SPRD controls. (Chronobiology International, 18(4), 665 681, 2001)     

Adrenergic and cholinergic innervation of rat cerebral arteries

Summary A consecutive demonstration of both aminergic and cholinergic nerves of rat cerebral arteries was carried out on whole mount preparations. For demonstration of aminergic nerves the glyoxylic acid method was used, while for cholinergic nerves Karnovsky's technique was utilized consecutively. This procedure provided a highly sensitive and reproducible demonstration of the two systems on the same specimen. The results obtained were as follows: 1) Aminergic and cholinergic nerves were distributed densely in the proximal portions of the major cerebral arteries examined. They were dense in the arteries of the anterior circulation and sparse in the posterior circulation. Each nerve had two different patterns, i.e. circular and longitudinal. Both circular and longitudinal patterns were observed in the proximal portions of the arteries, while in the distal portions, longitudinal fibres were predominantly present. 2) Superior cervical ganglionectomy produced no change in cholinergic nerve distribution, while it caused decreased density of aminergic nerves on the ipsilateral side on the arteries of the anterior circulation. The contralateral anterior cerebral arteries were partially affected. Bilateral sympathectomies abolished aminergic nerves in all arteries except the vertebral artery.     

Oxidative stress attenuates NO-induced modulation of sympathetic neurotransmission in the mesenteric arterial bed of spontaneously hypertensive rats

Current evidence suggests that hyperactivity of the sympathetic nervous system and endothelial dysfunction are important factors in the development and maintenance of hypertension. Under normal conditions the endothelial mediator nitric oxide (NO) negatively modulates the activity of the norepinephrine portion of sympathetic neurotransmission, thereby placing a "brake" on the vasoconstrictor ability of this transmitter. This property of NO is diminished in the isolated, perfused mesenteric arterial bed taken from the spontaneously hypertensive rat (SHR), resulting in greater nerve-stimulated norepinephrine and lower neuropeptide Y (NPY) overflow from this mesenteric preparation compared with that of the normotensive Wistar-Kyoto rat (WKY). We hypothesized that increased oxidative stress in the SHR contributes to the dysfunction in the NO modulation of sympathetic neurotransmission. Here we demonstrate that the antioxidant N-acetylcysteine reduced nerve-stimulated norepinephrine and increased NPY overflow in the mesenteric arterial bed taken from the SHR. Furthermore, this property of N-acetylcysteine was prevented by inhibiting nitric oxide synthase with N(omega)-nitro-l-arginine methyl ester, demonstrating that the effect of N-acetylcysteine was due to the preservation of NO from oxidation. Despite a reduction in norepinephrine overflow, the nerve-stimulated perfusion pressure response in the SHR mesenteric bed was not altered by the inclusion of N-acetylcysteine. Studies including the Y(1) antagonist BIBO 3304 with N-acetylcysteine demonstrated that this preservation of the perfusion pressure response was due to elevated NPY overflow. These results demonstrate that the reduction in the bioavailability of NO as a result of elevated oxidative stress contributes to the increase in norepinephrine overflow from the SHR mesenteric sympathetic neuroeffector junction.     

Effect of captopril on neurally induced contraction and relaxation of mesenteric arteries of renal hypertensive rats

The effect of captopril treatment on neurally induced vasoconstrictor and vasodilator responses was examined in the isolated mesenteric arterial bed from normotensive and one-kidney, one clip hypertensive (1K1C) rats. In isolated mesenteric beds, electrical field stimulation (EFS) of perivascular nerves at basal tone induced a frequency-dependent increase in perfusion pressure that was greater in preparations from hypertensive rats compared with those from normotensive rats. Captopril treatment was associated with a decrease in vasoconstrictor responses in the hypertensive group compared with its non-treated control. Responses to norepinephrine (320 ng) were greater in hypertensive than normotensive groups; captopril reduced this response only in the hypertensive group. In preconstricted mesenteric arteries perfused with solutions containing guanethidine (5 microM) and atropine (1 microM), EFS elicited a frequency-dependent decrease in perfusion pressure that was abolished by tetrodotoxin (1 microM). Vasodilator responses to EFS were not affected by captopril treatment, although they were smaller in the hypertensive group. Acetylcholine (10 ng) induced similar decreases in perfusion pressure of normotensive and 1K1C groups; captopril did not influence these responses. These results indicate that captopril treatment does not affect the reduced neurogenic vasodilation but normalizes the augmented sympathetic-mediated vasoconstrictor responses of mesenteric resistance vessels of chronic 1K1C hypertensive rats.     

In vivo receptor binding of benidipine and amlodipine in mesenteric arteries and other tissues of spontaneously hypertensive rats

The present study was undertaken to characterize the in vivo 1,4-dihydropyridine (DHP) receptor binding of long-acting 1,4-DHP calcium channel antagonists in the mesenteric artery and other tissues of SHR. In vivo specific binding of (+)-[3H]PN 200-110 in the SHR mesenteric artery was significantly (36.6-49.7 %) reduced 1-8 h after oral administration of benidipine (1.84 micromol/kg). A greater reduction in (+)-[3H]PN 200-110 binding in the mesenteric artery was observed at a higher dose (5.53 micromol/kg) of this drug. This dose of benidipine also reduced significantly the in vivo specific (+)-[3H]PN 200-110 binding in the aorta but not in the myocardium and cerebral cortex. Following oral administration of amlodipine (17.6 micromol/kg), a significant (51.7-94.2 %) reduction in (+)-[3H]PN 200-110 binding was seen at 1-18 h in the mesenteric artery and at 1-12 h in the aorta. Only a slight reduction in myocardial and cerebral cortical (+)-[3H]PN 200-110 binding was seen following amlodipine administration. In contrast, oral administration of nifedipine (28.9 micromol/kg) reduced markedly in vivo (+)-[3H]PN 200-110 binding in all the tissues of SHR at 1-6 h, and the degree and time-course of the reduction did not differ significantly among the tissues. The area under the curve (AUC) for the receptor occupancy vs time was calculated from the reduction rate (%) of in vivo specific (+)-[3H]PN 200-110 binding. The ratios of the AUCmesenteric artery to AUCaorta or AUCmesenteric artery to AUCmyocardium after oral administration of benidipine and amlodipine were greater than the corresponding value for nifedipine. The degree and time-course of arterial receptor occupancy by benidipine and amlodipine agreed well with those of their hypotensive effects in the conscious SHR. In conclusion, the present study demonstrates that benidipine and amlodipine may occupy, in a more selective and sustained manner, 1,4-DHP receptors in arterial tissues than in other tissues of SHR, and thus, such receptor binding specificity may be responsible for the long-lasting hypotensive effects of these drugs.     

Structure and sympathetic innervation of the intracranial arteries in the giraffe (Giraffa camelopardalis)

Fluorescence histochemistry discloses that the carotid rete mirabile in the giraffe has a poor sympathetic innervation. In contrast, the efferent artery of the rete (internal carotid artery) and the cerebral arteries show moderate sympathetic innervation. A certain degree of regional variability was noted in which the rostral arteries (anterior and middle cerebral) receive more sympathetic nerves than the caudal (posterior communicating and basilar) arteries. The sympathetic nerves on the giraffe cerebral vessels may constitute part of a host of mechanisms by which regional blood flow to the brain is regulated. Conversely, the paucity of sympathetic innervation of the carotid rete mirabile may indicate that this structure does not play an active role in vasoconstrictor responses during postural changes of the head.     

Effect of nifedipine on calcium-induced contractions to potassium in the aorta and mesenteric arteries of spontaneously hypertensive and normotensive rats

Graded contractions to cumulative additions of calcium in the presence of KCl were obtained in strips of aorta and mesenteric arteries of normotensive (WKY) and spontaneously hypertensive (SHR) rats. In calcium-free medium, a maximally effective concentration of KCl produced a response that was larger in the mesenteric arteries (43-51% of control) than in the aorta (12-14% of control). The calcium channel blocker nifedipine (NFD, up to 10(-7) M) did not significantly alter these calcium-insensitive responses. The Ca2+-induced responses were inhibited by NFD, in a concentration-dependent fashion, in both vessel types of WKY and SHR rats. The aortic responses were more sensitive to inhibition by NFD than the responses of mesenteric arteries. Moreover, the aortic responses of WKY were inhibited to a greater extent than those of the SHR. The results suggest: (a) a differential calcium dependence of contractions to KCl in the vessels studied; (b) that aortic responses are dependent on NFD-sensitive voltage-sensitive Ca2+ channels to a greater extent than the responses of mesenteric arteries; and (c) that hypertension results in a decreased sensitivity of the aorta Ca2+ channels to NFD.