Relaxation Of Guinea-pig Aorta Research Articles

The effects of vasodilators on the relaxation of guinea-pig aorta during acute recoil

Background: We have investigated the effects of various vasodilators on smooth muscle relaxation during acute recoil with guinea-pig aorta to find effective therapies to prevent acute recoil at percutaneous transluminal coronary angioplasty (PTCA). Methods: Muscle strips from guinea-pig aorta without endothelium were placed in a bath filled with modified Krebs solution. The strip was isotonically stretched with a tension of 9 mN for 1 min, and then isometric tension was measured until the tension reached a steady state. Various vasodilators were applied during isometric tension measurement. Results: When no drug was applied (control), isometric tension reached a steady state within 20 min. The steady state was approximately 10% lower (more relaxed) than the stretched level. When isosorbide dinitrate (ISDN, 1 mM) was applied during isometric measurement, 18.7±5.3% greater relaxation occurred than in control relaxation ( P<0.05, n=5). When nicorandil (1 mM) was applied, the following relaxation was 18.6±5.7% greater than control ( P<0.05, n=8). The simultaneous application of glibenclamide (1 mM) completely inhibited such additional relaxation by nicorandil. Application of nifedipine (10 μM) caused a 12.9±2.5% greater relaxation than control ( P=0.066, n=4). The first metabolite of sarpogrelate (BP984, 10 μM) caused much greater relaxation than control (23.7±7.9%, P<0.05, n=6). Amlodipine (10 μM), phentolamine (10 μM), and sarpogrelate (10 μM) had no influence on the relaxation of the strip. Conclusions: ISDN, nicorandil and BP984 significantly increase relaxation of the muscle strips after stretching compared to the control. These vasodilators may reduce acute recoil of the smooth muscle after PTCA.

NO-mediated MaxiK Ca channel activation produces relaxation of guinea pig aorta independently of voltage-dependent L-type Ca 2+ channels

(1) The role of L-type Ca 2+ channels in the relaxation to nitric oxide (NO)-mediated MaxiK Ca channel activation was examined in guinea pig aorta. (2) Acetylcholine (ACh) produced an endothelium-dependent relaxation of guinea pig aorta precontracted with noradrenaline (NA), which was abolished by an NO synthase inhibitor, N G-nitro- l-arginine ( l-NNA). (3) Both endothelium-dependent relaxation by ACh and endothelium-independent relaxation by an NO donor, (±)-( E)-ethyl-2-[( E)-hydroxyimino]-5-nitro-3-hexeneamide (NOR3), were strongly suppressed by a soluble guanylate cyclase (sGC) inhibitor, 1 H-[1,2,4]-oxadiazolo-[4,3- a]-quinoxalin-1-one (ODQ), suggesting that increased intracellular cGMP plays the key role in both responses. (4) ACh- and NOR3-induced relaxations were significantly suppressed by iberiotoxin (IbTX), a selective blocker of MaxiK Ca channels. (5) ACh- and NOR3-induced relaxations were greatly attenuated when arteries were precontracted with high KCl instead of NA, supporting the idea that K + channel activation mediates the relaxant responses. (6) NOR3-induced relaxations were not affected by a L-type Ca 2+ channel blocker, diltiazem. Furthermore, endothelium-independent relaxation by a K ATP channel opener, (+)-7,8-dihydro-6,6-dimethyl-7-hyroxy-8-(2-oxo-1-piperidinyl)-6 H-pyrano[2,3- f]benz-2,1,3-oxadiazole (NIP-121) was not affected by diltiazem and nicardipine. (7) These findings suggest that blockade of L-type Ca 2+ channels is not a major mechanism responsible for the vascular relaxation due to NO-mediated MaxiK Ca channel activation in guinea pig aorta.

Evidence for a contribution of store-operated Ca2+ channels to NO-mediated endothelium-dependent relaxation of guinea-pig aorta in response to a Ca2+ ionophore, A23187.

A23187 (6S-[6alpha,8beta,9beta,11alpha]-5-(methylamino) -2-[[3,9,11-trimethyl-8-[1-methyl-2-oxo-2-(1H-pyrrol-2-yl)ethyl]-1,7- dioxaspiro[5.5]undec-2-yl]methyl]-4-benzoxazolecarboxylic acid, calcimycin), an antibiotic Ca2+ ionophore, produces an endothelium-dependent vascular relaxation. In the present study, pharmacological features were functionally characterized of endothelium-dependent relaxant response of guinea-pig aorta to A23187, especially focusing on the possible Ca2+ source and Ca2+ mobilization mechanisms in endothelial cells responsible for the vasorelaxant response to the Ca2+ ionophore. A23187-induced endothelium-dependent relaxation was suppressed profoundly by N(G)-nitro-L-arginine (L-NNA; 3 x 10(-4) M) or calmidazolium (3 x 10(-5) M), suggesting that nitric oxide (NO) produced by the enhanced activation of Ca2+/calmodulin-dependent endothelial NO synthase (eNOS) is largely responsible for the relaxant response of this artery to A23187. In the Ca2+-free solution without EGTA, NO-mediated endothelium-dependent relaxation induced by A23187 was almost abolished, which suggests that Ca2+ entry from extracellular space into endothelial cells plays the key role in the A23187-induced functional vasorelaxation. On the other hand, SK&F96365 (1-[beta-[3-(4-methoxyphenyl)propoxy]-4-methoxyphenethyl]-1H-imidazole; 5 x 10(-5) M) and Ni2+ (3 x 10(-4) M), both of which inhibit capacitative Ca2+ influx through store-operated Ca2+ channels (SOCCs), attenuated significantly NO-mediated endothelium-dependent relaxation by A23187. Furthermore, A23187-induced endothelium-dependent relaxation was suppressed more strongly than endothelium-independent relaxation induced by SIN-1 (3-morpholino-sydnonimine), an NO donor, when aortic preparation was preconstricted with high KCl instead of agonistic stimulation (prostaglandin F2alpha). These findings suggest that NO-mediated endothelium-dependent relaxant response of guinea-pig aorta to A23187 is preceded by the increase in endothelial cytosolic free Ca2+ concentration ([Ca2+]cyt) due to the enhanced Ca2+ influx from extracellular space. In the enhanced Ca2+ entry leading to the stimulation of eNOS and NO-mediated functional relaxant response of guinea-pig aorta to A23187, activation of SOCCs but not the Ca2+ entry through plasma membrane Ca2+-specific routes made by A23187 seems to play the predominant role. It is most likely that A23187 acts primarily at the Ca2+ store sites in endothelial cells, which subsequently depletes stored Ca2+ to activate SOCCs via unidentified mechanisms.

Pharmacological characterization of AMP 579, a novel adenosine A1/A2 receptor agonist and cardioprotective

AMP 579 1S-[1α,2β,3β,4α(S*)]-4-[7-[[1 -[(3-chloro-2-thienyl)methyl]propylamino]-3H-imidazo[4,5-b]pyridin-3-yl]-N-ethyl-2,3-dihydroxy cyclopentanecarboxamide) is a novel cardioprotective adenosine agonist with the following order of affinity at adenosine receptors: A 1 > A 2A > A 3 . Agonism at A 1 receptors was demonstrated in vitro in three different systems: 1) inhibition of lipolysis in rat and human isolated adipocytes, 2) restoration of insulin-dependent glucose transport in rat adipocytes, and 3) reduction of heart rate in spontaneously beating rat right atria. Agonism at A 2A receptors was reflected in vasorelaxation of porcine coronary arterial rings (IC 50 = 0.3 μM); in comparison, agonism at A 2B receptors was ∼100-fold weaker, as reflected in relaxation of guinea pig aorta (IC 50 = 28 μM). When given iv to conscious Sprague-Dawley (SD) rats, AMP 579 dose-dependently lowered free fatty acids (FFA), heart rate (HR), and mean arterial pressure (MAP), but was 25-fold more potent at reducing FFA than at decreasing HR and MAP. In anesthetized rats undergoing myocardial ischemia-reperfusion injury, AMP 579 (3 μg/kg + 0.3 μg/kg/min iv and 10 μg/kg + 1 μg/ kg/min iv) was able to reduce infarct size by 55% and 63%, respectively, compared to control animals, when given 10 min prior to and throughout the first hour of reperfusion. These cardioprotective doses of AMP 579 caused no significant change in blood pressure or coronary blood flow. In summary, AMP 579 is a novel adenosine A 1 /A 2A receptor agonist which causes long-lasting reductions in FFA in vivo and has cardioprotective effects in a rat model of myocardial ischemia-reperfusion injury at doses which have minimal hemodynamic effects. Thus, AMP 579 has significant potential for the therapy of acute myocardial infarction.

PPADS and extracellular ATP both mediate endothelial dependent relaxation of guinea pig aorta.

PPADS and extracellular ATP both mediate endothelial dependent relaxation of guinea pig aorta.

MECHANISMS OF TENSION DEVELOPMENT INDUCED BY MONENSIN IN GUINEA-PIG AORTA : EFFECTS OF VERAPAMIL, OUABAIN, PRAZOSIN AND GLIBENCLAMIDE

The influence of monensin (10 µmol/L) alone and in the presence of verapamil (3 µmol/L) or ouabain (1 mmol) and prazosin (1 µmol/L) or glibenclamide (10 µmol/L) were studied on the muscle tension of guinea pig aorta. Changes in tissue sodium, potassium and calcium ion contents of the aortic muscle produced by monensin in the presence of prazosin were evaluated. Monensin in normal Tyrode's solution containing prazosin caused an increase in the resting tension followed by a decrease and returned to normal values. Verapamil reduced the muscle tension induced by monensin. After ouabain, monensin induced sustained increase in the resting tension. Glibenclamide partially reversed the relaxant phase of monensin in presence of norepinephrine. The findings of the present study indicate that the contraction induced by monensin in guinea Pig aorta is due to the increased influx of calcium through voltage-dependent calcium Channels as well as through Na+ - Ca2+ exchange mechanisms. Monensin produced relaxation of guinea pig aorta in part through the increase in K+ permeability via opening of K+-ATP channels.