RESUMO
BACKGROUND AND PURPOSE: Damage to the insula results in cardiovascular complications. In rats, activation of N-methyl-d-aspartate receptors (NMDARs) in the intermediate region of the posterior insular cortex (iIC) results in sympathoexcitation, tachycardia and arterial pressure increases. Similarly, focal experimental hemorrhage at the iIC results in a marked sympathetic-mediated increase in baseline heart rate. The dorsomedial hypothalamic region (DMH) is critical for the integration of sympathetic-mediated tachycardic responses. Here, whether responses evoked from the iIC are dependent on a synaptic relay in the DMH was evaluated. METHODS: Wistar rats were prepared for injections into the iIC and DMH. Anatomical (tracing combined with immunofluorescence) and functional experiments (cardiovascular and sympathetic recordings) were performed. RESULTS: The iIC sends dense projections to the DMH. Approximately 50% of iIC neurons projecting to the DMH express NMDARs, NR1 subunit. Blockade of glutamatergic receptors in the DMH abolishes the cardiovascular and autonomic responses evoked by the activation of NMDARs in the iIC (change in mean arterial pressure 7 ± 1 vs. 1 ± 1 mmHg after DMH blockade; change in heart rate 28 ± 3 vs. 0 ± 3 bpm after DMH blockade; change in renal sympathetic nerve activity 23% ± 1% vs. -1% ± 4% after DMH blockade). Experimental hemorrhage at the iIC resulted in a marked tachycardia (change 89 ± 14 bpm) that was attenuated by 65% ± 5% (p = 0.0009) after glutamatergic blockade at the DMH. CONCLUSIONS: The iIC-induced tachycardia is largely dependent upon a glutamatergic relay in the DMH. Our study reveals the presence of an excitatory glutamatergic pathway from the iIC to the DMH that may be involved in the cardiovascular alterations observed after insular stroke.
Assuntos
Núcleo Hipotalâmico Dorsomedial , Acidente Vascular Cerebral , Animais , Pressão Sanguínea , Frequência Cardíaca , Humanos , Hipotálamo , Ratos , Ratos Wistar , Transmissão Sináptica , Taquicardia/etiologiaRESUMO
We have shown that angiotensin II (Ang II) does not diffuse across the vessel wall, remaining intravascularly confined and acting solely on the coronary endothelial luminal membrane (CELM) receptors. A sustained intracoronary infusion of Ang II causes transient coronary vasoconstriction (desensitization) due to membrane internalization of CELM Ang II type 1 receptors (CELM-AT1R). In contrast, sustained intracoronary infusion of a non-diffusible polymer of Ang II (Ang II-Pol, 15,000 kDa) causes a sustained vasoconstriction by preventing CELM-AT1R internalization. In addition, a sustained intracoronary infusion of Ang II leads to a depressed response following a secondary Ang II administration (tachyphylaxis) that is reversed by Ang II-Pol. These findings led us to hypothesize that the rate of desensitization, tachyphylaxis, and AT1R internalization were dependent on Ang II-Pol molecular weight. To test this hypothesis, we synthesized Ang II-Pols of the following molecular weights (in kDa): 1.3, 2.7, 11, 47, 527, 3270 and 15,000. Vasoconstriction was measured following intracoronary infusion of Ang II-Pols in Langendorff-perfused guinea pig hearts at constant flow. The CELM protein fraction was extracted using the silica pellicle technique at different time points in order to determine the rate of AT1R internalization following each Ang II-Pol infusion. CELM-AT1R density was quantified by Western blot. We found that the rate of desensitization and the tachyphylaxis effect varied inversely with the molecular weight of the Ang II-Pols. Inversely proportional to the molecular weight of Ang II-Pol the CELM-AT1R density decreases over time. These results indicate that the mechanism responsible for the decreased rate of desensitization and tachyphylaxis by higher molecular weight Ang II polymers is due to reduction in the rate of CELM-AT1R internalization. These Ang II polymers would be valuable tools for studying the relationship between AT1R internalization and physiological effects.
Assuntos
Angiotensina II/metabolismo , Endotélio Vascular/metabolismo , Polímeros/química , Receptor Tipo 1 de Angiotensina/metabolismo , Vasoconstrição/efeitos dos fármacos , Angiotensina II/administração & dosagem , Angiotensina II/química , Animais , Western Blotting , Vasos Coronários/efeitos dos fármacos , Vasos Coronários/metabolismo , Endotélio Vascular/efeitos dos fármacos , Cobaias , Peso Molecular , Fatores de TempoRESUMO
Diverse intracoronary hormones cause their cardiac effects solely via activation of their coronary endothelial luminal membrane (CELM) receptors. To test this hypothesis for Ang II, we synthesized: a) two large polymers of Ang II (Ang II-POL) and Losartan (Los-POL) which act only in the CELM's AT1R because they cannot cross the endothelial barrier and b) biotin-labeled Ang II (Ang II-Biotin) and Ang II-POL-Biotin to be identified by microscopy in tissues. Sustained coronary perfusion of Ang II (potentially diffusible) or Ang II-POL caused a positive inotropic effect (PIE) and an increase in coronary perfusion pressure (CPP) of equal magnitude that were blocked by Losartan and Los-POL. However, Ang II effects, in contrast to Ang II-POL effects, were transient due to desensitization and resulted in tachyphylaxis to a second administration of Ang II or Ang II-POL. Furthermore, if Ang II and Ang II-POL acted differently on the same receptor; a competition of effects would be expected. This was demonstrated by infusing simultaneously a molar ratio of Ang II:Ang II-POL. As this molar ratio decreased, Ang II-induced desensitization and tachyphylaxis decreased. Intravascularly-administered Ang II-Biotin and Ang II-POL-Biotin remained bound and confined to the endothelium. Our results support the hypothesis and indicate intravascular Ang II, not by mass exchange with the interstitium, but by an action restricted to the CELM's AT1R, causes release of endothelial chemical messengers that exert physiological effects and modulate the effects and metabolism of paracrine Ang II. Endocrine Ang II controls and communicates with its paracrine counterparts solely through endothelial receptors.
Assuntos
Angiotensina II/metabolismo , Endotélio Vascular/metabolismo , Losartan/farmacologia , Receptor Tipo 1 de Angiotensina/metabolismo , Angiotensina II/administração & dosagem , Angiotensina II/química , Bloqueadores do Receptor Tipo 1 de Angiotensina II/administração & dosagem , Bloqueadores do Receptor Tipo 1 de Angiotensina II/química , Bloqueadores do Receptor Tipo 1 de Angiotensina II/farmacologia , Animais , Biotina/química , Vasos Coronários/metabolismo , Dextranos/química , Difusão , Losartan/administração & dosagem , Losartan/química , Comunicação Parácrina , Polímeros/química , Ratos , Ratos WistarRESUMO
Coronary blood flow applied to the endothelial lumen modulates parenchymal functions via paracrine effectors, but the mechanism of flow sensation is unknown. We and others have demonstrated that coronary endothelial luminal membrane (CELM) oligosaccharides and lectins are involved in flow detection, and we proposed that cardiac effects of coronary flow result from a reversible flow-modulated lectin-oligosaccharide interaction. Recently, glycosylated and amiloride-sensitive Na(+)/Ca(++) channels (ENaCs) have been proposed to be involved in the flow-induced endothelial responses. Because N-acetylglucosamine (GlcNac) is one of the main components of glycocalyx oligosaccharides (i.e., hyaluronan [-4GlcUAbeta1-3GlcNAcbeta1-](n)), the aim of this article is to isolate and define CELM GlcNac-binding lectins and determine their role in cardiac and vascular flow-induced effects. For this purpose, we synthesized a 460-kDa GlcNac polymer (GlcNac-Pol) with high affinity toward GlcNac-recognizing lectins. In the heart, intracoronary administration of GlcNac-Pol upon binding to CELM diminishes the flow-dependent positive inotropic and dromotropic effects. Furthermore, GlcNac-Pol was used as an affinity probe to isolate CELM GlcNac-Pol-recognizing lectins and at least 35 individual lectinic peptides were identified, one of them the beta-ENaC channel. Some of these lectins could participate in flow sensing and in GlcNac-Pol-induced effects. We also adopted a flow-responsive and well-accepted model of endothelial-parenchymal paracrine interaction: isolated blood vessels perfused at controlled flow rates. We established that flow-induced vasodilatation (FIV) is blocked by endothelial luminal membrane (ELM) bound GlcNac-Pol, nitro-l-arginine methyl ester and indomethacin, amiloride, and hyaluronidase. The effect of hyaluronidase was reversed by infusion of soluble hyaluronan. These results indicate that GlcNac-Pol inhibits FIV by competing and displacing intrinsic hyaluronan bound to a lectinic structure such as the amiloride-sensitive ENaC. Nitric oxide and prostaglandins are the putative paracrine mediators of FIV.
Assuntos
Acetilglucosamina/metabolismo , Circulação Coronária/fisiologia , Endotélio Vascular/fisiologia , Lectinas/metabolismo , Miocárdio/metabolismo , Animais , Cromatografia de Afinidade , Cobaias , Masculino , Contração Miocárdica/fisiologia , Vasodilatação/fisiologiaRESUMO
Diverse intracoronary agonists cause cardiac effects while acting on coronary endothelial luminal membrane (CELM) receptor. Our data show: a) the presence of AT(1)R in isolated CELM and in all cardiac cell types and b) sustained intracoronary infusions of Ang II-POL, a large sized molecule (approximately 15,000 kDa) confined to the vessel lumen that can only act on CELM's AT(1)R or Ang II (approximately 1 kDa); both exert the same maximum positive inotropic (PIE) and coronary constriction (CPP). The effects of these two agonists are blocked by Losartan and by Sar-POL; a large size antagonist (approximately 15,000 kDa) that acts only on CELM. Ang II effects are transient due to desensitization and cause tachyphylaxis to Ang II and toward Ang II-POL suggesting that both Ang II and Ang II-POL act on the same receptor group. In contrast, Ang II-POL effects are sustained and do not cause tachyphylaxis. The results show that intravascular Ang II and Ang II-POL act differentially by an unknown mechanism on CELM's AT(1)R and suggest that intravascular Ang II and Ang II-POL cause PIE and CCP by activation limited to CELM's AT(1)R through an unknown mechanism that is space-confined to the CELM's AT(1)R.
Assuntos
Vasos Coronários/efeitos dos fármacos , Endotélio Vascular/efeitos dos fármacos , Receptor Tipo 1 de Angiotensina/agonistas , Angiotensina II/farmacologia , Animais , Vasos Coronários/fisiologia , Endotélio Vascular/fisiologia , Losartan/farmacologia , Ratos , Ratos Wistar , Receptor Tipo 1 de Angiotensina/análise , Receptor Tipo 1 de Angiotensina/efeitos dos fármacos , Saralasina/farmacologia , Vasoconstrição/efeitos dos fármacosRESUMO
The coronary endothelial luminal membrane (CELM) glycocalyx has diverse molecules involved in blood flow signal transduction. Evidence suggests that some of these structures may be lectinic. To test this, we synthesized two monosaccharide polymers (Mon-Pols) made of Mannose (Man-Pol) or Galactose (Gal-Pol) covalently coupled to Dextran (70 kDa) and used them as lectin affinity probes. In situ intracoronary infusion of both polymers resulted in CELM-binding but only Man-Pol caused a reduction in flow-induced positive inotropism and dromotropism. To demonstrate that our lectinic probes could bind to CELM lectins, a representative CELM protein fraction was isolated via intracoronary infusion of a cationic silica colloid and either Mannose- or Galactose-binding lectins were purified from the CELM protein fraction using the corresponding Mon-Pol affinity chromatography resin. Resin-bound CELM proteins were eluted with the corresponding monosaccharide. 2D-SDS-PAGE (pH 4-7) revealed 9 Mannose- and approximately 100 Galactose-selective CELM lectins. In summary, the CELM glycocalyx contains Mannose- and Galactose-binding lectins that may be involved in translating coronary flow into a cardiac parenchymal response.