Receptors In Mesenteric Arteries Research Articles

Ameliorative effect and mechanism of Si-Ni-San on chronic stress-induced diarrhea-irritable bowel syndrome in rats.

Background: Chronic stress-induced diarrhea is a common clinical condition, characterized by an abnormal bowel movement and loose stools, which lacks effective treatment in the clinic. Si-Ni-San (SNS) is a compound traditional Chinese medicine extensively used in China for stress-related diarrhea. However, the mechanism is unclear. Methods: Male Wistar rats (200 ± 20 g) were placed in a restraint cylinder and fixed horizontally for 3 h once daily for 21 consecutive days to establish a chronic restraint stress (CRS) rat model. SNS (0.6944 g/kg or 1.3888 g/kg) was given by gavage 1 h before the restraint once daily for 21 consecutive days. We examined the fecal score, dopamine β hydroxylase (DβH), and c-fos expression in locus coeruleus, norepinephrine (NE) content in ileum and plasma, expression of α1 adrenergic receptors, MLCK, MLC, and p-MLC in the colon and mesenteric arteries, contraction of isolated mesenteric arteries, The expression of subunit δ of ATP synthase (ATP5D) in intestinal tissues, ATP, ADP, and AMP content in the ileum and colon, occludin expression between ileum epithelial cells, the number of enterochromaffin cells (ECs) and mast cells (MCs) in the ileum, and 5-hydroxytryptamine (5-HT) content in the ileum and plasma. Results: After SNS treatment, the fecal score was improved. The increased expression of DβH and c-fos in locus coeruleus was inhibited. SNS suppressed the increased NE content in the ileum and plasma, down-regulated α1 adrenergic receptors in mesenteric arteries and MLCK, MLC, p-MLC in the colon and mesenteric arteries, and inhibited the contraction of mesenteric arteries. SNS also increased the ATP content in the ileum and colon, inhibited low expression of ATP5D in intestinal tissues, inhibited the decrease of ATP/ADP in the ileum and ATP/AMP in the colon, and up-regulated the occludin expression between ileum epithelial cells. In addition, SNS inhibited the increase of ECs and MCs in the ileum and the increase of 5-HT content in the ileum and plasma. Conclusion: This study demonstrated that SNS could improve CRS-induced abnormal feces in rats. This effect was related to the inhibition of CRS-induced increased expression of DβH and c-fos in the locus coeruleus, NE content in the ileum and plasma, and the contraction of isolated mesenteric arteries; inhibition of energy metabolism abnormality and decreased occludin expression; inhibition of increased ECs and MCs in the ileum, and 5-HT content in the ileum and plasma.

Differential targeting and signalling of voltage-gated T-type Cav 3.2 and L-type Cav 1.2 channels to ryanodine receptors in mesenteric arteries.

In arterial smooth muscle, Ca2+ sparks are elementary Ca2+ -release events generated by ryanodine receptors (RyRs) to cause vasodilatation by opening maxi Ca2+ -sensitive K+ (BKCa ) channels. This study elucidated the contribution of T-type Cav 3.2 channels in caveolae and their functional interaction with L-type Cav 1.2 channels to trigger Ca2+ sparks in vascular smooth muscle cells (VSMCs). Our data demonstrate that L-type Cav 1.2 channels provide the predominant Ca2+ pathway for the generation of Ca2+ sparks in murine arterial VSMCs. T-type Cav 3.2 channels represent an additional source for generation of VSMC Ca2+ sparks. They are located in pit structures of caveolae to provide locally restricted, tight coupling between T-type Cav 3.2 channels and RyRs to ignite Ca2+ sparks. Recent data suggest that T-type Cav 3.2 channels in arterial vascular smooth muscle cells (VSMCs) and pits structure of caveolae could contribute to elementary Ca2+ signalling (Ca2+ sparks) via ryanodine receptors (RyRs) to cause vasodilatation. While plausible, their precise involvement in igniting Ca2+ sparks remains largely unexplored. The goal of this study was to elucidate the contribution of caveolar Cav 3.2 channels and their functional interaction with Cav 1.2 channels to trigger Ca2+ sparks in VSMCs from mesenteric, tibial and cerebral arteries. We used tamoxifen-inducible smooth muscle-specific Cav 1.2-/- (SMAKO) mice and laser scanning confocal microscopy to assess Ca2+ spark generation in VSMCs. Ni2+ , Cd2+ and methyl-β-cyclodextrin were used to inhibit Cav 3.2 channels, Cav 1.2 channels and caveolae, respectively. Ni2+ (50μmolL-1 ) and methyl-β-cyclodextrin (10mmolL-1 ) decreased Ca2+ spark frequency by ∼20-30% in mesenteric VSMCs in a non-additive manner, but failed to inhibit Ca2+ sparks in tibial and cerebral artery VSMCs. Cd2+ (200μmolL-1 ) suppressed Ca2+ sparks in mesenteric arteries by ∼70-80%. A similar suppression of Ca2+ sparks was seen in mesenteric artery VSMCs of SMAKO mice. The remaining Ca2+ sparks were fully abolished by Ni2+ or methyl-β-cyclodextrin. Our data demonstrate that Ca2+ influx through CaV 1.2 channels is the primary means of triggering Ca2+ sparks in murine arterial VSMCs. CaV 3.2 channels, localized to caveolae and tightly coupled to RyR, provide an additional Ca2+ source for Ca2+ spark generation in mesenteric, but not tibial and cerebral, arteries.

Histamine-dependent prolongation by aldosterone of vasoconstriction in isolated small mesenteric arteries of the mouse

In arterioles, aldosterone counteracts the rapid dilatation (recovery) following depolarization-induced contraction. The hypothesis was tested that this effect of aldosterone depends on cyclooxygenase (COX)-derived products and/or nitric oxide (NO) synthase (NOS) inhibition. Recovery of the response to high K(+) was observed in mesenteric arteries of wild-type and COX-2(-/-) mice but it was significantly diminished in preparations from endothelial NOS (eNOS)(-/-) mice. Aldosterone pretreatment inhibited recovery from wild-type and COX-2(-/-) mice. The NO donor sodium nitroprusside (SNP) restored recovery in arteries from eNOS(-/-) mice, and this was inhibited by aldosterone. Actinomycin-D abolished the effect of aldosterone, indicating a genomic effect. The effect was blocked by indomethacin and by the COX-1 inhibitor valeryl salicylate but not by NS-398 (10(-6) mol/l) or the TP-receptor antagonist S18886 (10(-7) mol/l). The effect of aldosterone on recovery in arteries from wild-type mice and the SNP-mediated dilatation in arteries from eNOS(-/-) mice was inhibited by the histamine H2 receptor antagonist cimetidine. RT-PCR showed expression of mast cell markers in mouse mesenteric arteries. The adventitia displayed granular cells positive for toluidine blue vital stain. Confocal microscopy of live mast cells showed loss of quinacrine fluorescence and swelling after aldosterone treatment, indicating degranulation. RT-PCR showed expression of mineralocorticoid receptors in mesenteric arteries and in isolated mast cells. These findings suggest that aldosterone inhibits recovery by stimulation of histamine release from mast cells along mesenteric arteries. The resulting activation of H2 receptors decreases the sensitivity to NO of vascular smooth muscle cells. Aldosterone may chronically affect vascular function through paracrine release of histamine.

Intake of high sucrose during pregnancy altered large-conductance Ca2+-activated K+ channels and vessel tone in offspring’s mesenteric arteries

Antenatal malnutrition could be linked to hypertension and vascular diseases in fetal origins. This study determined the influence of maternal intake of high sucrose (HS) during pregnancy on vessel tone, intracellular Ca(2+) ([Ca(2+)](i)), K(+) channels, especially large-conductance Ca(2+)-activated K(+) channels (BK), in mesenteric arteries in the offspring rats exposed to prenatal HS. Vessel tension and [Ca(2+)](i) induced by angiotensin II were higher in the small mesenteric arteries of the HS offspring. In the vascular smooth muscle cells (VSMCs) from the HS offspring, electrophysiological studies showed depressed BK current density and depolarized membrane. Western blot showed altered expressions of BK α-subunits, AT1 and AT2 receptors in mesenteric arteries. The results suggest that decreased BK channel activity and depolarized membrane potential in the VSMCs partly contributed to the increased vessel tone and [Ca(2+)](i) in the HS offspring, adding new information for understanding mechanisms in vascular malfunctions in fetal origins, and novel insights for early prevention and treatments against such vascular diseases.

Impaired function of prejunctional adenosine A1 receptors in sympathetic nerves supplying mesenteric arteries in deoxycorticosterone acetate (DOCA)‐salt hypertensive rats

Increased sympathetic nervous system activity contributes to DOCA‐salt hypertension in rats. ATP and norepinephrine (NE) are released from sympathetic nerves. NE acts at prejunctional α2 adrenoceptors to inhibit NE release and prejunctional α2 adrenoceptor function is impaired in DOCA‐salt rats. Adenosine is a product of ATP hydrolysis and adenosine acts at prejunctional A1 adenosine receptors to inhibit NE release. We tested the hypothesis that prejunctional A1 receptor function is impaired in sympathetic nerves associated with mesenteric arteries (MA) and veins (MV) of DOCA‐salt rats. Electrically‐evoked NE release and constrictions of MA and MV were measured in vitro using amperometry and video microscopy, respectively. Adenosine and N6‐cyclopentyl‐adenosine (CPA, A1 receptor agonist) constricted MV but not MA. Adenosine and CPA caused concentration‐dependent (0.001‐10 μM) inhibition of MA constrictions. Adenosine and CPA concentration responses curves (CRCs) in DOCA‐salt MA were right shifted (P<0.05) compared to control MA. CPA inhibited NE release in MA and MV. The CPA CRC in DOCA‐salt MA, but not MV, was right shifted compared to control MA. These data indicate that there are prejunctional A1 receptors in MA and pre and postjunctional A1 receptors in MV. Prejunctional A1 receptor function is impaired in MA, but not MV, from DOCA‐salt rats. These data indicate that prejunctional α2 adrenoceptors are not selectively affected in DOCA‐salt hypertension. There is a more general disruption of prejunctional mechanisms controlling sympathetic neurotransmitter release.

Female sex steroid hormones and pregnancy regulate receptors for calcitonin gene-related peptide in rat mesenteric arteries, but not in aorta.

Calcitonin gene-related peptide (CGRP) is a potent vasodilator neuropeptide known to be involved in the regulation of vascular tone. Results of previous studies from our laboratory and others suggest that vascular sensitivity to CGRP is enhanced during pregnancy and that the female sex steroid hormones estradiol-17beta (E2) and progesterone (P4) may be involved in this process. We hypothesized that CGRP receptors in the mesenteric artery are increased during pregnancy and with sex steroid hormone treatments. In the present study, we investigated whether pregnancy and female sex steroid hormones modulate the CGRP-receptors CGRP-A and CGRP-B in the mesenteric artery in the rat. The CGRP-A receptor consists of calcitonin receptor-like receptor (CRLR) and receptor activity-modifying protein 1 (RAMP1); however, the CGRP-B receptor needs to be further characterized. Messenger RNA levels for CRLR and RAMP1 were assessed by reverse transcription-polymerase chain reaction, and CGRP-B receptor proteins levels were determined by Western blot analysis. In addition, [125I]CGRP binding was measured by Scatchard analysis. Both mRNA for CGRP-A (CRLR and RAMP1) and the protein for CGRP-B receptors in mesenteric arteries were increased with pregnancy compared to nonpregnant, diestrous animals. A P4 antagonist, RU-486, downregulated and P4 upregulated these receptors in mesenteric arteries (P < 0.05) in pregnant rats. In adult ovariectomized rats, P4 upregulated CRLR and RAMP1 mRNA levels as well as [125I]CGRP-binding sites. The CGRP-B-receptor protein levels were significantly (P < 0.05) elevated by P4 and by combined E2 and P4 treatment. Together with earlier findings, these data suggest that increases in the expression of CGRP-A (CRLR and RAMP1) and CGRP-B receptors in mesenteric arteries may be important in reducing vascular resistance and in vascular adaptations that occur during pregnancy; in addition, P4 may be involved in this process.

Up-regulation of calcitonin gene-related peptide receptors underlying elevation of skin temperature in ovariectomized rats.

We investigated the mechanism for the augmentation of the calcitonin gene-related peptide (CGRP)-induced elevation of skin temperature in ovariectomized (OVX) rats. I.v. injection of alphaCGRP (10 micro g/kg) elevated skin temperature of the hind paws. The elevation was significantly greater in OVX rats than in sham-operated rats and was inhibited by pretreatment with human CGRP(8-37) (100-1000 micro g/kg i.v.), a CGRP receptor antagonist, in a dose-dependent manner. In addition, ovariectomy not only potentiated vasorelaxation due to alphaCGRP but increased the number of CGRP receptors in mesenteric arteries. Further, the plasma concentration of endogenous CGRP was significantly lower in OVX rats. These results suggest that the low concentration of plasma CGRP due to ovarian hormone deficiency may induce the increase in the number of CGRP receptors due to up-regulation. Therefore, the increased number of CGRP receptors may be responsible for potentiation of exogenous alphaCGRP-induced elevation of skin temperature in OVX rats. The mechanism underlying the hot flashes observed in menopausal women may also involve, in part, the up-regulation of CGRP receptors following ovarian hormone deficiency.

In vivo measurement of 1,4-dihydropyridine receptors in mesenteric arteries of spontaneously hypertensive rats and effect of nifedipine and cilnidipine.

The present study was undertaken to measure 1,4-dihydropyridine (DHP) receptor binding sites in vivo in the mesenteric artery and other tissues of spontaneously hypertensive rats (SHR) and to examine the effect of nifedipine and cilnidipine. Specific in vivo binding of (+)-[3H]PN 200-110 in the SHR mesenteric artery was dose dependently reduced by oral administration of nifedipine at relatively low doses. Oral administration of cilnidipine (6.09 micromol/kg) significantly reduced the specific in vivo binding of (+)-[3H]PN 200-110 in the mesenteric artery, aorta, and myocardium. A significant reduction in (+)-[3H]PN 200-110 binding was seen at 1-12 h in the mesenteric artery and at 1-7 h in the aorta and myocardium. In contrast, oral administration of nifedipine (28.9 micromol/kg) markedly reduced in vivo (+)-[3H]PN 200-110 binding in all tissues of SHR at 1-6 h, and the degree and time course of the reduction did not differ much among the tissues. The area under the curve (AUC) for receptor occupancy vs. time was calculated from the reduction rate (%) of specific in vivo (+)-[3H]PN 200-110 binding. The ratio (1.4 or 1.7) of the AUC(mesenteric artery) to AUCaorta or AUCmyocardium after oral administration of cilnidipine was greater than the corresponding value (1.1) for nifedipine. In conclusion, the present study demonstrates that cilnidipine, but not nifedipine, may occupy 1,4-DHP receptors in the small artery in a more selective and sustained manner than in other tissues of SHR, and thus such receptor binding specificity may be responsible for the long-lasting hypotensive effect of this drug.

Vascular expression of angiotensin type 2 receptor in the adult rat: influence of angiotensin II infusion.

The aim of this study was to investigate the relative role of the angiotensin type 1 (AT1) and type 2 (AT2) receptors in mediating angiotensin II-induced regulation of AT2 receptor in mesenteric artery. Sprague-Dawley rats were infused with either angiotensin II or vehicle for 14 days at a dose of 58.3 ng/min. Ang II-infused rats were allocated to receive either an AT1 antagonist, valsartan at a dose of 30 mg/kg per day or the AT2 receptor antagonist PD123319 at a dose of 830 ng/min. Gene and protein expression of the AT2 receptor in the mesenteric vasculature was assessed by quantitative reverse transcriptase polymerase chain reaction, immunohistochemistry and by in vitro autoradiography with a specific radioligand, 1251-CGP 42112B. The AT2 receptor mRNA and protein were detected in the mesenteric artery from adult rats. Both nuclear emulsion and immunohistochemical staining showed expression of the AT2 receptor in the adventitial and medial layers. Compared to control rats, angiotensin II infusion was associated with a significant increase in the AT2 receptor expression. Valsartan treatment significantly reduced AT2 receptor gene expression, with no significant effect of PD123319 on this parameter. This study confirms that the presence of the AT2 receptor in mesenteric arteries in adult rats, shows an up-regulation of the AT2 receptor following angiotensin II infusion and suggests a role for the AT1 receptor in this regulation. In view of the recently demonstrated effects of the AT2 receptor, these findings may be relevant to the role of the AT2 receptor in the pathophysiology of vascular remodeling.

Loss of acetylcholine-induced relaxation by M3-receptor activation in mesenteric arteries of spontaneously hypertensive rats.

This study investigated which subtype of muscarinic receptor in mesenteric arteries from SHRs mediates the loss of the release of nitric oxide (NO) or endothelium-derived hyperpolarizing factor (EDHF) in spontaneously hypertensive rats (SHRs) and Wistar-Kyoto (WKY) rats. After SHRs and WKY rats were killed, their superior mesenteric arteries were isolated to perform the vascular relaxation study. Acetylcholine (ACh, 1 nM-1 microM)-induced relaxation was in a concentration-dependent manner and was impaired in mesenteric arterial rings obtained from the SHR group, whereas nitroglycerin (10 nM-1 microM)-induced relaxation was not affected in endothelium-denuded rings obtained from the hypertensive rat. In the presence of N(omega)-nitro-L-arginine (L-NNA; 0.1 mM) or methylene blue (10 microM), the ACh-induced relaxation was partially attenuated in both SHRs and WKY rats. The relaxation of ACh was partially inhibited by 4-aminopyridine (4-AP; 1 mM), apamin (APM; 1 microM), or charybdotoxin (CTX; 0.1 microM) in WKY rats, whereas that relaxation was not affected by 4-AP, APM, or CTX in SHRs. However, the L-NNA-resistant relaxation of ACh was further inhibited by APM or CTX in WKY rats but not in SHRs. When arterial rings were precontracted by 60 mM K+, the ACh-induced relaxation was not significantly different in SHRs and WKY rats. However, this relaxation was abolished by L-NNA (0.1 mM) in both strains. In addition, the M3 muscarinic antagonist, 4-diphenylacetoxy-N-methylpiperidine was the most potent in inhibiting the relaxation of ACh, being more potent than pirenzepine and methoctramine, which preferentially block M1 and M2 receptors in the mesenteric artery of WKY rats, respectively. 2-Nitro-4-carboxyphenyl-N,N-diphenylcarbamate (1 microM) almost abolished the relaxation of ACh, but not of A23187, in SHRs and WKY rats. These results suggest that NO and EDHF are released from the endothelium of rat mesenteric artery on the activation of muscarinic M3-receptor by ACh, and the loss of ACh-induced relaxation in small arteries of SHRs is mainly through reducing the release or activity or both of EDHF.

Pathogenesis of Arterial Lesions Induced by Dopaminergic Compounds in the Rat

Fenoldopam mesylate (FM), a selective post-junctional dopaminergic (DA1) vasodilator, causes lesions of large caliber splanchnic arteries (100-800 microns) in the rat characterized by necrosis of medial smooth muscle cells and hemorrhage. FM does not induce lesions in other vascular beds of the rat, or in dogs or monkeys. Dopamine, like FM, causes hemorrhagic lesions of large caliber splanchnic arteries in the rat, as well as fibrinoid necrosis of small caliber arteries (less than 100 microns) of the splanchnic, cerebral, coronary and renal vascular beds. Dopamine is an alpha- and beta-adrenoceptor and a dopaminergic receptor agonist. Because these arterial lesions are thought to result from the pharmacologic activity of these 2 compounds, we sought to ascertain the presence of DA1 receptors in mesenteric arteries of the rat and to determine the role of these or other vascular receptor subtypes in lesion induction. We also studied the process of repair after arterial injury caused by FM or dopamine. The presence of DA1 receptors was confirmed in isolated perfused mesenteric arteries by standard pharmacologic techniques; stimulation by FM resulted in vasodilation which was inhibited by the DA1 receptor antagonist SK&F 83566-C. Likewise, SK&F 83566-C prevented the induction of hemorrhagic lesions of large caliber arteries in rats upon infusion of FM or dopamine. In rats co-exposed to the alpha-adrenoreceptor antagonist phenoxybenzamine (PBZ) and either FM or dopamine, the incidence and severity of hemorrhagic lesions of large caliber arteries were increased, but PBZ prevented the formation of dopamine-induced fibrinoid lesions in arteries of small caliber. Rats exposed concurrently to dopamine, phenoxybenzamine, and SK&F 83566-C were free of all arterial lesions. Thus, the induction of splanchnic arterial lesions in the rat by dopamine and FM is caused by stimulation of, and interaction between, alpha-adrenoceptors and dopaminergic DA1 receptors. Fibrinoid lesions of small arteries (alpha-adrenoceptor-mediated) were repaired, as observed morphologically by 14 d after exposure to dopamine. Hemorrhagic lesions of large caliber arteries (DA1 receptor-mediated) had undergone significant repair by 28 d after exposure to FM but these arteries possessed a thicker media surrounded by adventitial fibrosis. Thus, morphologically distinct receptor-mediated splanchnic arterial lesions induced by dopaminergic and alpha-adrenoceptor agonists follow a markedly different course of repair. Arterial lesions induced by FM or dopamine by activation of post-junctional dopaminergic DA1 receptors may represent a model of polyarteritis nodosa.

Alpha1 adrenergic receptors in mesenteric arteries of rats with chronic renal failure

In previous studies we have shown that patients or rats with chronic renal failure display reduced blood pressure response to norepinephrine (NE). This abnormality is related to the high levels of parathyroid hormone (PTH) which stimulates vasodilator prostaglandin production. To determine whether chronic renal failure (CRF) also affects pressor response to NE through changes in the properties of alpha 1 adrenoceptors, we have measured plasma NE and the number of binding sited (Bmax) and the KD of these receptors in isolated mesenteric arteries of normal CRF rats and of CRF rats previously parathyroidectomized (PTX). Plasma NE was greater (P less than 0.01) in CRF than in control (67 +/- 14 vs. 32 +/- 3.1 ng/dl), but it was not different from CRF-PTX rats. The Bmax of alpha 1 adrenoceptors was lower (P less than 0.05) in CRF than control (80 +/- 10 vs. 173 +/- 29 fmol/mg protein), but it was similar in CRF and CRF-PTX rats. The KD was not significantly different among the three groups of rats studied. The data show that the number of alpha 1 adrenoceptors is reduced in CRF and this is not related to excess PTH. This abnormality may contribute to the reduced pressor response to NE in CRF. The effect of PTH, on the vascular response to NE is not related to changes in plasma levels of NE or in binding sites for NE.