Mesenteric Resistance Blood Vessels Research Articles

Angiotensinergic neurons in sympathetic coeliac ganglia innervating rat and human mesenteric resistance blood vessels

In contrast to the current belief that angiotensin II (Ang II) interacts with the sympathetic nervous system only as a circulating hormone, we document here the existence of endogenous Ang II in the neurons of rat and human sympathetic coeliac ganglia and their angiotensinergic innervation with mesenteric resistance blood vessels. Angiotensinogen - and angiotensin converting enzyme-mRNA were detected by using quantitative real time polymerase chain reaction in total RNA extracts of rat coeliac ganglia, while renin mRNA was untraceable. Cathepsin D, a protease responsible for cleavage beneath other substrates also angiotensinogen to angiotensin I, was successfully detected in rat coeliac ganglia indicating the possibility of existence of alternative pathways. Angiotensinogen mRNA was also detected by in situ hybridization in the cytoplasm of neurons of rat coeliac ganglia. Immunoreactivity for Ang II was demonstrated in rat and human coeliac ganglia as well as with mesenteric resistance blood vessels. By using confocal laser scanning microscopy we were able to demonstrate the presence of angiotensinergic synapses en passant along side of vascular smooth muscle cells. Our findings indicate that Ang II is synthesized inside the neurons of sympathetic coeliac ganglia and may act as an endogenous neurotransmitter locally with the mesenteric resistance blood vessels.

Vasoconstricting and vasodilating actions of halothane are unrelated to Ser19 MLC phosphorylation

Contraction or relaxation in smooth muscle is primarily dependent on Ser19 phosphorylation/dephosphorylation of the 20 kDa regulatory myosin light chain (MLC). In isolated mesenteric resistance blood vessels, halothane has a transient vasoconstricting action related to Ca2+release from ryanodine-sensitive intracellular Ca2+ stores, and a long-lasting vasodilating action. Whether these vasoconstricting and vasodilating actions of halothane depend on Ser19 phosphorylation/dephosphorylation of MLC has not been fully elucidated. Methods Vessels are cannulated and held at a constant transmural pressure (40mmHg) and image analysis is used to measure vessel diameter. Ser19 phosphorylation of MLC is quantified using the Western blotting technique and an Odyssey Infrared Imaging System. Results In physiologic saline solution (PSS), halothane (4.5 vol%) produced transient contraction to 51% of maximal and an increase in Ser 19 phosphorylation of MLC. Following a 30 min. incubation in PSS containing 0Ca2+ + 2mM EGTA, both halothane contraction and Ser19 phosphorylation were reduced. After incubation for 10 min in the kinase inhibitor wortmannin (10-6M), halothane contraction was reduced but Ser19 phosphorylation was not affected. After a 15 min incubation with the phosphatase inhibitor calyculin A (3 X 10-8M), halothane contraction was 52% of maximal with an increase in Ser19 phosphorylation, but a small contraction persisted in calyculin while MLC phosphorylation decreased below baseline. With halothane in PSS alone, the vessel diameter returned to baseline after approx. 20 sec, however the Ser19 phosphorylation decreased only a small amount. Conclusion The vasoconstricting and vasodilating actions of halothane appear to be poorly correlated with changes in MLC Ser19 phosphorylation levels.

Endogenous calcitonin gene-related peptide (CGRP) mediates adrenergic-dependent vasodilation induced by nicotine in mesenteric resistance arteries of the rat.

1. The mechanisms underlying vasodilator effect of nicotine on mesenteric resistance blood vessels and the role of calcitonin gene-related peptide (CGRP)-containing (CGRPergic) vasodilator nerves were studied in the rat. 2. Mesenteric vascular beds isolated from Wistar rats were perfused with Krebs solution, and perfusion pressure was measured with a pressure transducer. 3. In preparations with intact endothelium and contracted by perfusion with Krebs solution containing methoxamine, perfusion of nicotine (1 - 100 microM) for 1 min caused a concentration-dependent vasodilator response without vasoconstriction. 4. The nicotine-induced vasodilation was markedly inhibited by hexamethonium (nicotinic cholinoceptor antagonist, 10 microM) and blocked by guanethidine (adrenergic neuron blocker, 5 microM). 5. Either denervation by cold storage (4 degrees C for 72 h) or adrenergic denervation by 6-hydroxydopamine (toxin for adrenergic neurons, 2 mM for 20 min incubation, twice) blocked the nicotine-induced vasodilation. 6. Neither endothelium removal with perfusion of sodium deoxycholate (1.80 mg ml(-1), for 30 s) nor treatment with N(omega)-nitro-L-arginine (nitric oxide synthase inhibitor, 100 microM), atropine (muscarinic cholinoceptor antagonist, 10 nM) or propranolol (beta-adrenoceptor antagonist, 100 nM) affected the nicotine-induced vasodilation. 7. In preparations without endothelium, treatment with capsaicin (depleting CGRP-containing sensory nerves, 1 microM) or human CGRP[8 - 37] (CGRP receptor antagonist, 0.5 microM) markedly inhibited the nicotine-induced vasodilation. 8. These results suggest that, in the mesenteric resistanc artery of the rat, nicotine induces vasodilation, which is independent of the function of the endothelium and is involved in activation of CGRPergic nerves. It is also suggested that nicotine stimulates presynaptic nicotinic cholinoceptors on adrenergic nerves to release adrenergic neurotransmitters, which then act on CGRPergic nerves to release endogenous CGRP from the nerve.

O-197 - Involvement of thromboxane A2 (TXA2) in bradykinin-induced vasoconstriction in rat mesenteric resistance blood vessels

O-197 - Involvement of thromboxane A2 (TXA2) in bradykinin-induced vasoconstriction in rat mesenteric resistance blood vessels

Endogenous calcitonin gene-related peptide suppresses vasoconstriction mediated by adrenergic nerves in rat mesenteric resistance blood vessels

The role of perivascular calcitonin gene-related peptide (CGRP)-containing nerves in the modulation of adrenergic nerve-mediated vasoconstrictions was studied in the rat perfused mesenteric vascular bed. A frequency-dependent vasoconstriction induced by periarterial nerve stimulation (1–6 Hz) of the bed was significantly potentiated by perfusion of 1 μM CGRP-(8–37) (CGRP receptor antagonist) or to a similar extent after treatment with 500 nM capsaicin. In the preparations treated with capsaicin, CGRP-(8–37) caused a small potentiation of periarterial nerve stimulation-induced vasoconstriction. Exogenous CGRP (0.1–1 nM) concentration-dependently attenuated the augmented vasoconstriction in response to periarterial nerve stimulation after treatment with capsaicin. However, exogenous CGRP (1 nM) did not attenuate the periarterial nerve stimulation-induced vasoconstriction in the bed untreated with capsaicin. These results suggest that endogenous CGRP, which is released from CGRP-containing nerves, suppresses the adrenergic nerve function involved in mechanisms regulating the tone of resistant blood vessels.

Neuronal control of mesenteric circulation

The mesenteric circulation plays an important role in maintenance of systemic blood pressure and regulation of tissue blood flow. The tone of the mesenteric artery and resistance blood vessels are mainly regulated by sympathetic adrenergic nerves through the release of neurotransmitter noradrenaline and also controlled by nonadrenergic noncholinergic (NANC) nerves and possibly by parasympathetic cholinergic nerves. Noradrenaline and adrenergic cotransmitters including neuropeptide Y and adenosine triphosphate act as a vasoconstrictor neurotransmitter for sympathetic nerves. While, dopamine, calcitonin gene-related peptide and acetylcholine act as a vasodilator neurotransmitter for adrenergic, NANC and cholinergic nerves, respectively. In the mesenteric circulation, these nerves containing various neurotransmitters and cotransmitters interact and modulate each other via feedback autoregulatory mechanisms and neuromodulation of various vasoactive substance to regulate vascular resistance.

Mechanism of Nicotine-Induced Vasodilation in Mesenteric Resistance Blood Vessels of the Rat

Mechanism of Nicotine-Induced Vasodilation in Mesenteric Resistance Blood Vessels of the Rat

P–384 - Vascular effect of bradykinin in mesenteric resistance blood vessels of the rat

P–384 - Vascular effect of bradykinin in mesenteric resistance blood vessels of the rat

Involvement of calcitonin gene-related peptide (CGRP) receptors in insulin-induced vasodilatation in mesenteric resistance blood vessels of rats.

1. The vascular effect of insulin in the mesenteric resistance blood vessel and the role of calcitonin generelated peptide (CGRP)-receptor in insulin-induced vascular responsiveness were investigated in rats. 2. The mesenteric vascular beds isolated from Wistar rats were perfused with Krebs solution, and perfusion pressure was measured with a pressure transducer. In preparations contracted by perfusion with Krebs solution containing methoxamine in the presence of guanethidine, the perfusion of insulin (from 0.1 to 3000 nM) caused a concentration-dependent decrease in perfusion pressure due to vasodilatation. The pD2 value and maximum relaxation (%) were 6.94+/-0.22 and 43.9+/-5.2, respectively. 3. This vasodilator response to insulin was unaffected by 100 nM propranolol (beta-adrenoceptor antagonist) plus 100 nM atropine (muscarinic cholinoceptor antagonist), 100 microM L-NG-nitroarginine (nitric oxide synthase inhibitor), 1 microM ouabain (Na+-K+ ATPase inhibitor), or 1 microM glibenclamide (ATP sensitive K+-channel inhibitor). 4. In preparations without endothelium, perfusion of insulin produced a marked vasodilatation. The pD2 value and maximum relaxation (%) were 7.62+/-0.21 and 81.0+/-4.6, respectively, significantly greater than in preparations with intact endothelium. 5. The vasodilator responses to insulin in the preparations without endothelium were significantly inhibited by CGRP[8 37], a CGRP receptor antagonist, whereas pretreatment with capsaisin, a toxin for CGRP-containing nerves, did not affect insulin-induced vasodilatation. 6. These results suggest that insulin induces non-adrenergic, non-cholinergic and endothelium-independent vasodilatation, which is partially mediated by CGRP receptors.

P-329 - Insulin acts on calcitonin gene-related peptide (CGRP) receptors in mesenteric resistance blood vessels of rats

P-329 - Insulin acts on calcitonin gene-related peptide (CGRP) receptors in mesenteric resistance blood vessels of rats

Endothelium-independent vasoconstricting and vasodilating actions of halothane on rat mesenteric resistance blood vessels.

Whether volatile anesthetics produce changes in vascular resistance and blood flow because of direct effects on vascular tissue is unclear. Direct vasoconstricting and vasodilating actions have been demonstrated in isolated conductance arteries in vitro, but there is little information regarding direct effects on the small vessels that mediate resistance and flow changes in vivo. We investigated the actions of halothane on 50-200 microM branches of the rat mesenteric artery that were cannulated and studied in vitro. The vessels were pressurized to 60 mmHg, and vascular dimensions were continuously monitored using a computer-based real-time image analysis system. The vessel bath was perfused with HCO3(-)-buffered saline (37 degrees C) equilibrated with 95% O2/5% CO2 (+/- halothane). The vascular endothelium was mechanically removed before cannulation in some vessels. In unstimulated vessels, halothane had a concentration-dependent vasoconstricting action (EC50 = 0.45 mM approximately 1.5 vol% at 37 degrees C) that was largely transient and was similar to that produced by caffeine. Both halothane and caffeine constrictions were unaffected by bath [Ca2+], nifedipine (1 microM) or Cd2+ (100 microM) and were abolished by ryanodine (10 microM). In addition, caffeine responses were attenuated by halothane in a concentration-dependent manner (EC50 = 1.6 mM). In vessels preconstricted with KCl (40 mM) or phenylephrine (10(-6) M), halothane produced transient constriction followed by concentration-dependent vasodilation. Ryanodine, which abolished halothane constrictions, had little effect on the amplitude of KCl- or phenylephrine-induced constrictions or the vasodilating action of halothane. Removal of the endothelium likewise had little effect on the vasoconstricting or the vasodilating actions of halothane in unstimulated, KCl- or phenylephrine-constricted vessels. Halothane completely relaxed KCl and phenylephrine constrictions with EC50 values of 0.36 mM (1.2% at 37 degrees C) and 0.75 mM (2.5%), respectively, in intact vessels before ryanodine; 0.25 mM (0.8%) and 0.59 mM (1.9%) in intact vessels after ryanodine; and 0.52 mM (1.7%) and 0.67 mM (2.2%) in endothelium-denuded vessels. Halothane has endothelium-independent vasoconstricting and vasodilating actions in isolated mesenteric resistance blood vessels. The vasoconstricting action appears to involve halothane-induced Ca2+ release from caffeine/ryanodine-sensitive intracellular store(s). The vasodilating action in phenylephrine- or KC1-constricted vessels is independent of the Ca(2+)-releasing action and most likely involves an effect(s) on sarcolemmal-dependent Ca2+ signaling (e.g., extracellular Ca2+ influx) and/or Ca2+ activation of contractile proteins. The magnitude of both the vasoconstricting and the vasodilating actions of halothane in these vessels at clinically relevant concentrations suggests these direct actions contribute to the overall cardiovascular effects of halothane in vivo.

カルシトニン遺伝子関連ペプチド（ＣＧＲＰ）による血管緊張調節について

Rat mesenteric resistance blood vessels are innervated by nonadrenergic, noncholinergic (NANC) vasodilator nerves. In vitro pharmacological, biological and immunohistochemical studies have provided evidence that the calcitonin gene related peptide (CGRP), a 37 amino acid peptide translated by the calcitonin gene, has a potent vasodilator effect and acts as a vasodilator neurotransmitter for NANC vasodilator nerves. The CGRP-containing vasodilator nerves inhibit adrenergic nerve-mediated vasoconstriction through direct relaxation of vascular smooth muscle, while adrenergic nerves suppress the neurotransmision of CGRP-containing nerves by inhibiting CGRP release from the nerve. Thus, CGRP-containing nerves and adrenergic nerves control vascular tone with reciprocal interferences. In in vivo studies, spinal cord (T9-12) stimulation of pitched rats produced a NANC depressor response mediated by endogenous CGRP, suggesting that CGRP-containing nerves are regulated by the central nervous system. The malfunction of CGRP-containing vasodilator nerves may be involved in cardiovascular diseases such as essential hypertension, coronal vasospasm, cerebral vasospasm and Renaud's phenomenon. It is suggested that the CGRP-containing vasodilator nerves play an important role in the regulation of vascular tone.

Age-related decrease of calcitonin gene-related peptide-containing vasodilator innervation in the mesenteric resistance vessel of the spontaneously hypertensive rat.

We previously demonstrated that the mesenteric resistance blood vessels have nonadrenergic, noncholinergic vasodilator innervation in which calcitonin gene-related peptide (CGRP) is a possible neurotransmitter. The role of CGRP-containing vasodilator nerves in hypertension was investigated in perfused mesenteric vascular beds isolated from spontaneously hypertensive rats (SHR). The adrenergic vasoconstrictor responses to perivascular nerve stimulation in both SHR (8-, 15-, and 30-week-old) and age-matched Wistar-Kyoto (WKY) rat preparations increased with aging, but the response was greater in SHR than in WKY rats at all ages. The preparation isolated from SHR and WKY rats was precontracted by continuous perfusion of Krebs' solution containing 7 x 10(-6) M methoxamine plus 5 x 10(-6) M guanethidine. In both SHR and WKY rats, perivascular nerve stimulation (1-8 Hz) produced frequency-dependent vasodilation, which was blocked by 1 x 10(-7) M tetrodotoxin, pretreatment with 5 x 10(-7) M capsaicin, and denervation by cold storage (4 degrees C for 72 hours). The vasodilation induced by perivascular nerve stimulation in SHR greatly decreased with age, whereas a slight decrease in the response with age was found in WKY rats. The neurogenic vasodilation in the young SHR preparation was similar in magnitude to the vasodilation in age-matched WKY rats, whereas the vasodilation in 15- and 30-week-old SHR was significantly smaller than that in age-matched WKY rats. In both SHR and WKY rats, perfusion of rat CGRP (1 x 10(-10) to 3 x 10(-8) M) produced marked vasodilation in a concentration-dependent manner. The CGRP-induced vasodilation in SHR increased with age, whereas an age-related decrease in vasodilation was found in WKY rats. Perivascular nerve stimulation (4 and 8 Hz) of the perfused mesenteric vascular bed evoked an increased release of CGRP-like immunoreactive substance in the perfusate, which was significantly less in 15-week-old SHR than in age-matched WKY rats. Immunohistochemical studies showed an age-related decrease in CGRP-like immunoreactive fibers in SHR but not in WKY rats. These results suggest that CGRP-containing vasodilator innervation is greatly decreased when SHR develop and maintain hypertension. It is also suggested that the decreased vasodilator mechanism by CGRP-containing nerves contributes to the development and maintenance of hypertension.

Postsynaptic alpha-adrenoreceptor populations in several vascular systems of the anaesthetized rat.

The contribution of postsynaptic alpha 1- and alpha 2-adrenoreceptors to vasoconstrictor responses was investigated in several vascular systems of pentobarbital-anaesthetized rats pretreated with atropine and propranolol. In the intact circulatory system of the anaesthetized rat, pressor responses were obtained to noradrenaline and phenylephrine. The pressor responses to noradrenaline were only partially blocked by prazosin and the responses which remained after prazosin were significantly reduced further by the subsequent addition of yohimbine. However, the responses to phenylephrine were largely antagonized by prazosin alone. In the blood-perfused hindquarter of the anaesthetized rat, a differential blocking activity of prazosin against noradrenaline and phenylephrine was also demonstrated. Prazosin, as observed in the intact circulatory system of the anaesthetized rat, was a more potent antagonist against phenylephrine than against noradrenaline. In the blood-perfused mesentery of the anaesthetized rat, sympathetic nerve stimulation, noradrenaline and phenylephrine produced a marked vasoconstrictor response whilst B-HT 920 hardly induced a pressor response. The pressor responses to nerve stimulation, noradrenaline and phenylephrine were largely blocked by prazosin alone. However, only the responses to all frequencies of nerve stimulation were enhanced by yohimbine pretreatment. These results obtained from the intact animal and blood-perfused hindquarter indicate that the pressor responses to exogenous noradrenaline result from the activation of both postsynaptic alpha 1- and alpha 2- adrenoreceptors. However, the result obtained from the blood-perfused mesentery indicates that the vasoconstrictor responses to neuronally released noradrenaline are largely mediated by activation of postsynaptic alpha 1-adrenoreceptors. Consequently, these results suggest that, in rats, the postsynaptic alpha-adrenoreceptor population in the mesenteric resistance blood vessels differs from that in other tissues.

Effect of sodium-potassium-dependent ATPase inhibition on noradrenaline-activated calcium sensitivity of mesenteric resistance vessels in adult spontaneously hypertensive rats.

1. We have investigated the noradrenaline-activated calcium sensitivity of 150 micrometer mesenteric resistance blood vessels from spontaneously hypertensive and control Wistar-Kyoto rats. 2. Under control conditions the spontaneously hypertensive rat blood vessels had a greater calcium sensitivity than the Wistar-Kyoto rat vessels. 3. In the presence of 1 mmol of ouabain/l, a treatment known to inhibit the sodium-potassium-dependent ATPase, the responses of the spontaneously hypertensive rat blood vessels were reduced more than those of the Wistar-Kyoto rat blood vessels, so that the responses of spontaneously hypertensive rat and Wistar-Kyoto rat blood vessels were then similar. 4. Similar results were obtained by removing external potassium, a procedure which should also inhibit the sodium-potassium-ATPase. 5. The results suggest that the greater noradrenaline-activated calcium sensitivity of spontaneously hypertensive rat blood vessels may be associated with an increased sodium-potassium-ATPase activity.