Ring Preparations Of Arteries Research Articles

The effect of temperature on vascular smooth muscle: cooling-induced vasodilation in deep arteries and veins.

Blood vessels in the cardiovascular system include arteries and veins, which are responsible for moving blood to and from tissues around the body. Our previous studies showed that cooling induces relaxation of arteries. The aim of this study is to investigate the effect of cooling on both arteries and veins pairs. Isometric tension was recorded in rat artery ring preparations (aorta, carotid, pulmonary arteries) and their vein pairs (vena cava, jugular, pulmonary veins) in organ baths during stepwise cooling from 37 to 4°C. Cooling responses were tested before and after the addition of various standard agents. The possibility of the presence of a cooling-relaxed substance and the influence of endothelium were also examined. Cooling-induced relaxation of both arteries and veins and the degree of relaxation were inversely proportional to the temperature. The cooling response was highest in arteries than their respective paired veins. The relaxation response was not endothelium dependent or affected with neurogenic mechanism (autonomic blockers or tetrodotoxin). Additionally, it was not changed by alterations of extra- or intra-cellular calcium transfer, and no relaxant substance was released from vascular smooth muscles during cooling. The study showed that cooling induces relaxation of both arteries and veins. Our results suggested that the effect of cooling could be through a thermal receptor in the vascular smooth muscle. Therefore, cold temperature can act as an agonist and increase in cooling temperature behaves as increase in concentration of the agonist. This study contributes to a better understanding of the mechanisms behind cooling-induced relaxation of blood vessels, which may have implications for the treatment of cardiovascular diseases.

Abstract 931: Compensatory Response of Perivascular Adipose Tissue to Vascular Dysfunction in Metabolic Syndrome Rats Involves Apelin

Perivascular adipose tissue (PVAT) regulates vascular homeostasis including vascular tone via release of adipokines. Using SHRSP.Z- Lepr fa /IzmDmcr (SHRSP.ZF) rats, an animal model of metabolic syndrome (MetS), we have demonstrated that mesenteric PVAT enhances vasodilation under impaired vasodilation, in response to nitric oxide. We have also shown that the compensatory effect of PVAT disappears later in the course of MetS. Apelin is an adipokine that is produced at high levels in obesity and acts as a vasorelaxing factor. In this study, we evaluated the role of apelin in the enhancing effect of mesenteric PVAT on relaxations in SHRSP.ZF rats, by examining whether apelin canenhance vasorelaxation in the mesenteric arteries of SHRSP.ZF rats without PVAT, as it does in those with PVAT. Furthermore, we investigated whether apelin expression changes with increasing age. SHRSP.ZF rats at 17, 20, 23, and 30 weeks old were used. The mesenteric artery and surrounding adipose tissue were isolated from each rat; PVAT samples were isolated from surrounding adipose tissue; and the mRNA transcript level of apelin was examined by quantitative real-time PCR assays. Mesenteric arterial ring preparations with and without PVAT were made, and after a stable contraction was obtained by adding phenylephrine, relaxation was elicited using acetylcholine in the presence or absence of apelin (100 ng/mL, 20 min). There was no significant difference in apelin mRNA levels between 17 and 20 weeks, but there was a decrease at 23 and 30 weeks of age, which was when the enhancing effect of PVAT on vasodilation in SHRSP.ZF rats was impaired. In the presence of apelin, acetylcholine-induced relaxation in arteries without PVAT was significantly increased to the level of the response in arteries with PVAT in SHRSP.ZF rats at 20 weeks. These findings suggest that apelin is involved in the enhancing effect of PVAT in MetS rat mesenteric artery, and decreases in the level is associated with deterioration of PVAT function. Further study to investigate the mechanisms underlying the decrease in apelin production with increasing age in metabolic syndrome is needed, butthe apelin level could be one of the predictors for development of cardiovascular complications in patients with MetS.

Royal jelly increases peripheral circulation by inducing vasorelaxation through nitric oxide production under healthy conditions

AimsRoyal jelly (RJ) has a variety of reported biological activities, including vasorelaxation and blood pressure–lowering effects. Although functional foods are positively used for health, the effects of RJ on the cardiovascular system in healthy individuals have not been well studied. Therefore, we investigated the mechanisms underlying the vasorelaxation effects of RJ in healthy control rats to evaluate whether the peripheral circulation was increased. Main MethodsWe used fresh RJ to examine the vasorelaxation effects and related mechanisms in Wistar rats using organ bath techniques. Furthermore, we measured changes in tail blood circulation, systolic blood pressure (sBP), and heart rate (HR) after the oral administration of RJ to control rats and nitro-l-arginine methyl ester (l-NAME)–treated rats (0.5 mg/ml dissolved in distilled drinking water for 1 week). Concentrations of acetylcholine (ACh) in the RJ were measured using a commercial kit. Key findingsRJ caused vasorelaxation of isolated rat aortas and superior mesenteric arteries, and this effect was inhibited by atropine (10−5 M, 15 min) or L-NAME (10-4 M, 20 min) and endothelium-denuded arterial ring preparations. Oral RJ increased tail blood flow and mass in control rats 1 h after treatment without affecting velocity, sBP, or HR. These effects were not observed in L-NAME–treated rats. RJ contained approximately 1000 μg/g of ACh. SignificanceThe present study demonstrated that RJ is composed of muscarinic receptor agonist(s), likely ACh, and induces vasorelaxation through nitric oxide (NO) production from the vascular endothelium of healthy rats, leading to increased tail blood circulation. Thus, fresh RJ may improve peripheral circulation in healthy individuals.

Resveratrol's initial transient enhancement of adrenergic contractions of rat tail arterial tissues involves a mechanism limiting its ability to exert a later sustained relaxation

We have reported that resveratrol can enhance as well as relax adrenergic contractions of arterial tissue rings prepared from both proximal (conductance) and distal (resistance) segments of the long ventral tail artery of the rat (Stom, JSMR 2016; 52:18–35). While the enhancing action only occurred in approximately half of our ring preparations (from proximal and distal segments alike), it always appeared immediately after administration before the later, more sustained relaxing effect (which occurred in all preparations) became apparent. Thus, the enhancing effect seemed to be only transient in duration. However, that does not rule out the possibility of its mechanism lasting long enough to limit the degree to which resveratrol eventually causes relaxation. To determine if that were true, we re‐examined data from our original arterial ring preparations to see if the half in which early transient enhancement occurred showed less eventual relaxation compared to the half in which they did not occur. Indeed, that was the case. This provides a novel explanation for why long‐term administration of resveratrol in vivo is reported to lower arterial blood pressures in some clinical studies but not in others, as highlighted in recent reviews (e.g. Liu, Clin Nutr 2015; 34: 27–34).Support or Funding InformationMWU Biomedical Masters Program

Time-Dependent Differences in the Influence of Perivascular Adipose Tissue on Vasomotor Functions in Metabolic Syndrome

Metabolic syndrome (MetS) facilitates the development of cardiovascular disease due to atherosclerosis, which is accelerated by defects of the vascular endothelium. Vascular dysfunction in response to nitric oxide (NO) occurs in the mesenteric arteries of an animal model of MetS, SHRSP.Z-Leprfa/IzmDmcr (SHRSP.ZF) rats. Vascular responses to vasodilators are affected by perivascular adipose tissue (PVAT) that surrounds the outsides of arteries. In this study, we assessed the role of PVAT in vascular dysfunction observed in SHRSP.ZF. To determine the effects of PVAT on vasodilators in SHRSP.ZF and control Wistar-Kyoto (WKY) rats, we used organ bath bioassay techniques to assay acetylcholine and nitroprusside-induced relaxations of isolated mesenteric arterial ring preparations with PVAT intact or removed. A PVAT-mediated enhancement of relaxations induced by acetylcholine and nitroprusside occurred in SHRSP.ZF at 20 weeks of age, but not at 10 and 30 weeks, and did not occur in WKY. Furthermore, the enhancing effects of PVAT from SHRSP.ZF at 20 weeks could not be substituted by replacement with PVAT from either WKY or 30-week-old SHRSP.ZF, was inhibited by NO synthase inhibitor, and abolished by removal of the arteries' endothelium. Cyclic guanosine monophosphate (cGMP) accumulation elicited by nitroprusside was higher in SHRSP.ZF arteries with PVAT than arteries without PVAT at 20 weeks, but the enhancement of cGMP accumulation did not occur at 30 weeks. PVAT may regulate arterial tone by releasing diffusible vasorelaxing factor(s), which, through endothelium-derived NO production, compensates for impaired vasodilations at early stages of MetS.

In focus: Fe3O4 nanoparticles and human mesenteric artery interaction in vitro.

The growing implementation of iron oxide nanoparticles in medicine requires a thorough investigation of their physiological influence. Therefore, effects of Fe3O4 nanoparticles on isometric contractions of healthy human mesenteric artery in vitro were investigated. The effect of increasing concentrations (0.023, 0.069, 0.23, 0.69 and 2.31 μg/μl) of Fe3O4 nanoparticles (50-100 nm) on the contractility of mesenteric artery ring preparations was studied using wire myography technique. A lack of effects of Fe3O4 nanoparticles (50-100 nm) on isometric contractions of human mesenteric artery segments both in conditions of basal tension and precontraction was found. The observed unresponsiveness of human mesenteric arteries in vitro to Fe3O4 nanoparticles could be attributed to their safe mode of use in biomedicine.

Resveratrol can both enhance and relax adrenergic contractions of the rat tail artery.

Our aims were to determine 1) if resveratrol's vasorelaxant action is greater in the distal (resistance) versus proximal (conductance) portion of the rat tail artery, and 2) if it can be blocked by agents known to block different potassium (K) channels in arterial smooth muscle. We found that its half-maximally effective concentration values were essentially identical (25 ± 3 versus 27 ± 3 μM) for relaxing adrenergically-precontracted rings prepared from distal versus proximal tissues. This does not confirm a previous report of greater relaxation in resistance versus conductance arteries. We also found that its relaxation could not be blocked by any of seven different K channel blockers. However, we uncovered a novel unanticipated action not yet reported. In half our arterial ring preparations, resveratrol transiently enhanced adrenergically-induced precontractions beginning well before its sustained relaxant effect became apparent. This action provides the first reasonable explanation for previously unexplained increases in arterial pressures observed during acute intravenous administration of resveratrol to animal models of traumatic ischemic tissue injury, in which hypotension is often present and in need of correction. Also unanticipated, this same transient enhancement of adrenergic contraction was notably inhibited by some of the same K channel blockers (particularly tetraethylammonium and glibenclamide) that failed to influence its relaxant effect. Although we do not rule out smooth muscle as a possible site for such a paradoxical finding, we suspect resveratrol could also be acting on K-selective mechano-sensitive ion channels located in the endothelium where they may participate in release of contracting factors.

Inhibitory effects of sertraline in rat isolated perfused kidneys and in isolated ring preparations of rat arteries

Sertraline is often prescribed to patients suffering with end stage renal disease, but its action on kidney has not been investigated. We aimed to investigate the pharmacological action of sertraline on rat kidney with emphasis on the underlying mechanisms involved in the vascular actions of the drug. The effects of sertraline were evaluated in rat isolated perfused kidneys and on ring preparations of mesenteric or segmental rat renal artery. In kidneys, sertraline prevented the effects of phenylephrine on perfusion pressure, glomerular filtration rate, urinary flow and renal vascular resistance. In mesenteric rings sertraline inhibited phenylephrine-induced contractions with potency 30-times lower than verapamil. Sertraline reversed sustained contractions induced by phenylephrine or 60mm K(+) within a similar concentration range. In segmental isolated rings, sertraline also reversed contractions induced by phenylephrine or 60mm K(+) with the same concentration range, but with higher potency compared with mesenteric preparations. Under Ca(2+) -free conditions, sertraline did not change the intracellularly-mediated phasic contractions induced by phenylephrine or caffeine. Sertraline was ineffective against contractions induced by extracellular Ca(2+) restoration after thapsigargin treatment and Ca(2+) store depletion with phenylephrine. Conversely, sertraline decreased the contractions induced by Ca(2+) addition in tissues under high K(+) solution or phenylephrine plus verapamil. In rat isolated kidneys and in rat ring preparations of mesenteric or renal vessels, sertraline had antispasmodic effects that appeared to be caused by a direct action on vascular smooth muscle cells. Its actions were ineffective against Ca(2+) -releasing intracellular pathways, but appeared to interfere with sarcolemmal Ca(2+) influx with reduced permeability of both receptor- and voltage-gated Ca(2+) channels.

Influence of beta-adrenoceptor-mediated relaxation on alpha-adrenoceptor-mediated contraction of rat pulmonary artery to adrenaline or noradrenaline.

Concentration-response (contraction) curves to either adrenaline or noradrenaline were obtained on isolated ring preparations of pulmonary artery from rats. In preparations from young rats the curve for adrenaline was bell-shaped, unless beta-adrenoceptors were blocked with propranolol (1 X 10(-6) M). The maximum contraction to adrenaline was less in the absence than in the presence of propranolol. In preparations from aged rats the adrenaline curve was no longer bell-shaped, even in the absence of propranolol. This reflected a decrease in the beta-adrenoceptor-mediated relaxant responses of preparations from aged rats, seen as a separation between the concentration-response (relaxation) curves to adrenaline on preparations (phenoxybenzamine-treated, KCl-contracted) from young and aged rats. In preparations from young rats the noradrenaline curve was not bell-shaped, but if the preparations were from young rats treated with thyroxine (T4), then a bell-shaped curve for noradrenaline was obtained, unless beta-adrenoceptors were blocked by propranolol. These data could be explained by an increase in beta-adrenoceptor-mediated relaxant responses of preparations from T4-treated rats, seen as a separation in the concentration-response (relaxation) curves to noradrenaline on preparations from control and T4-treated rats, respectively. Thus alpha-adrenoceptor-mediated contractile responses of rat pulmonary artery preparations, to adrenaline or noradrenaline, can be attenuated by activation of beta-adrenoceptors, mediating relaxation, and the extent of this attenuation changes under the influence of factors, such as ageing or T4-treatment, which modify beta-adrenoceptor-mediated relaxation in this blood vessel type.

Diaphragm muscle and its feed artery after chronic respiratory airway obstruction in rats

A chronic respiratory load was produced in Wistar rats by tracheal binding to produce a twofold increase of pleural pressure oscillation amplitude during respiration. Eight weeks after the surgery, a higher proportion of type-I muscle fibers (MFI) in the costal diaphragm along with a greater MFI cross-section area and a higher succinate dehydrogenase activity in MFII in the lumbar diaphragm were observed. During recording the mechanical activity of ring preparations of diaphragm arteries under isometric conditions, an increase in endothelium-dependent relaxation was found, whereas endothelium-independent relaxation and arterial reactivity to noradrenaline did not change. Tracheal binding did not produce any changes of MF in the gastrocnemius muscle, but endothelium-dependent relaxation of gastrocnemius feed arteries was reduced. We conclude that chronic respiratory load affects the endothelial function in diaphragm arteries in a manner favorable for blood flow control in the diaphragm. Functional alterations in gastrocnemius arteries may be associated with the reduced locomotor activity of operated rats.

Agonist-induced periodic vasomotion in rat isolated pulmonary artery

Vasomotion is linked to the rapid oscillations of intracellular calcium levels. In rat pulmonary artery, this activity can manifest as a slow periodic on-off pattern, the timing of which depends on the type and intensity of pharmacological stimuli employed. In this study, we have sought to characterize a slow-wave vasomotor activity pattern induced in isolated arterial ring preparations by simultaneous exposure to the α(1) -adrenoceptor agonist phenylephrine (1-10 nm) and the L channel agonist S(-)-Bay K 8644 (3-20 nm). Treated tissues responded with a stable on-off pattern of vasomotion persisting for >5 h at 5-6 cycles/h. In intact rings, this response was suppressed by methacholine and restored or enhanced by N(ω) -nitro-l-arginine methyl ester. Analogous inhibitory effects were obtained with high Mg(2+) , 8-Br-cGMP (but not 8-Br-cAMP), riluzole, ryanodine, chelerythrine, and fasudil. Pinacidil (30 nm) increased off-cycle length without change in slow-wave amplitude. Conversely, tetraethylammonium (1.0-3.0 mm) augmented the latter without affecting periodicity. Carbenoxolone (10 μm) abolished slow-wave activity, while raising basal tone and inducing random phasic activity. In endothelium-denuded rings, the threshold of agonist-induced slow-wave vasomotion was lowered and a similar inhibitory effect obtained with carbenoxolone. In conclusion, the slow-wave pattern of vasomotion described here is (i) subject to inhibitory modulation by endothelial NO and an array of voltage-gated and leak K conductances yet to be fully characterized; (ii) dependent on Ca(2+) from both extracellular and sarcoendoplasmatic sources; (iii) controlled by kinase (Rho and PKC)-mediated regulation of myosin light chain phosphatase; and (iv) synchronized via intermyocyte gap junctions.

L-arginine-induced dilatation of goat coronary artery involves activation of K ATP channels

In the present study, the mechanism of relaxant response of nitric oxide precursor, l-arginine, was investigated in goat isolated coronary artery. l-arginine (1 mM) reversed the U-46619 (1 µM)-induced contraction both in endothelium-intact and endothelium-denuded arterial ring preparations. l-arginine analogues, l-NAME, l-NNA and l-NMMA and the guanylyl cyclase inhibitor, methylene blue failed to attenuate the relaxant response of l-arginine. These observations negate the involvement of nitric oxide in mediating the relaxation by l-arginine. K ATP channel blocker, glibenclamide (3 µM), abolished the vasorelaxant responses of l-arginine in endothelium-denuded preparations, thereby suggesting the involvement of K ATP channels. Further, l-arginine also failed to induce relaxation of the coronary arterial rings constricted with K + (80 mM)-PSS. Taken together, the results of the present study suggest that l- arginine relaxes goat isolated coronary artery through activation of K ATP channels.

Vardenafil, but not sildenafil or tadalafil, has calcium‐channel blocking activity in rabbit isolated pulmonary artery and human washed platelets

Phosphodiesterase type-5 (PDE5) inhibitors constitute a novel and important therapeutic option for the treatment of pulmonary hypertension. The effects of the PDE5 inhibitors sildenafil, tadalafil and vardenafil on rabbit isolated pulmonary artery ring preparations and on intracellular Ca2+ concentration of thrombin-stimulated human platelets were investigated. Rabbit pulmonary artery rings were mounted in 10 mL organ bath containing Krebs solution. Tissues were connected to force-displacement transducers, and changes in isometric force were recorded. Ca2+ flux in human washed platelets was measured. Sildenafil, tadalafil and vardenafil (0.0001-10 microM) concentration-dependently relaxed endothelium-intact and endothelium-denuded pulmonary artery rings. Endothelium denudation caused rightward shifts in the concentration-response curves to sildenafil, tadalafil and vardenafil (9-, 12- and 123-fold, respectively). Incubation with N(omega)-nitro-L-arginine methyl ester (100 microM) or ODQ (1H-[1,2,4] oxadiazolo [4,3,-a]quinoxalin-1-one) (10 microM) caused similar reductions of PDE5-induced vasorelaxations in intact rings. Sildenafil and tadalafil did not affect the phenylephrine-induced contractions, whereas vardenafil reduced the maximal responses, and shifted the phenylephrine-induced contraction curves to the right in endothelium-denuded rings (5- and 19-fold for 1 and 10 microM, respectively). Vardenafil (but neither sildenafil nor tadalafil) caused a marked rightward shift and a decrease of maximal contractile response to CaCl2. Vardenafil, but neither sildenafil nor tadalafil, significantly reduced the Ca2+ mobilization and Ca2+ influx in thrombin-stimulated washed platelets. Our results indicate that vardenafil, in contrast to sildenafil or tadalafil, also blocked Ca2+ fluxes, thus enhancing its vasorelaxation of the pulmonary artery.

Mechanisms of the vasorelaxant effect of 1-hydroxy-2, 3, 5-trimethoxy-xanthone, isolated from a Tibetan herb, Halenia elliptica, on rat coronary artery

1-Hydroxy-2, 3, 5-trimethoxyxanthone (HM-1) is a xanthone isolated from Halenia elliptica, a Tibetan medicinal herb. HM-1 (0.33–42.1 μM) produced a concentration-dependent relaxation in rat coronary artery rings pre-contracted with 1 μM 5-hydroxytryptamine (5-HT), with an EC 50 of 1.67 ± 0.27 μM. Removal of the endothelium significantly affected the vasodilator potency of HM-1, resulting in 46% decrease in E max value. The endothelium-dependent effects of HM-1 was confirmed when its vasorelaxant effect was inhibited after addition of nitric oxide synthase (NOS) inhibitor N ω-nitro- l-arginine methyl ester (100 μM) or the soluble guanylate cyclase inhibitor 1H-[1, 2, 4] oxadiazolo [4,3-α] quinoxalin-1-one (ODQ, 10 μM). Atropine (100 nM), flurbiprofen (10 μM), propranolol (100 μM), pyrilamine (10 μM), cimetidine (10 μM) and SQ22536 (100 μM) had no effect on the vasorelaxant activity of HM-1 indicated the non-involvement of other receptor/enzyme systems. In endothelium-denuded coronary artery rings, the vasorelaxant effect of HM-1 was unaffected by potassium channel blockers such as tetraethylammonium (10 mM), iberiotoxin (100 nM), barium chloride (100 μM) and 4-aminopyridine (1 mM). The involvement of Ca 2+ channel in 5-HT-primed artery ring preparations incubated with Ca 2+-free buffer was confirmed when HM-1 (9.93 μM) partially abolished the CaCl 2-induced vasoconstriction (87% inhibition in intact-endothelium artery rings; 50% inhibition in endothelium-denuded rings). In the KCl-primed preparations incubated with Ca 2+-free buffer, HM-1 (9.93 μM) produced a 27.3% inhibition in endothelium-denuded rings. HM-1 (3.31–33.1 μM) had minimal relaxant effects (14.4%–20.3%) on the contractile response generated by 10 μM phorbol 12,13-diacetate (PDA) in Ca 2+-free solutions, suggesting minimal effects on intracellular Ca 2+ mechanisms. These findings suggest the vasodilator action of HM-1 involved both an endothelium-dependent mechanism involving NO and an endothelium-independent mechanism by inhibiting Ca 2+ influx through L-type voltage-operated Ca 2+ channels; a minor contribution to the effects of HM-1 may be related to inhibition of the protein kinase C-mediated release of intracellular Ca 2+ stores.

Acetylcholine stimulated dilatation and stretch induced myogenic constriction in mesenteric artery of rats with chronic heart failure

Rats with chronic heart failure (CHF) develop increased myogenic constriction in mesenteric resistance arteries. Here we investigated increased myogenic constriction in relation to alterations in EDHF- and NO-mediated dilatation in CHF-rats. Male Spraque-Dawley rats were subjected to myocardial-infarction or sham-surgery. At 9-10 weeks after surgery, isolated mesenteric artery ring preparations were studied in a wire-myograph. Stretch-induced myogenic constriction was obtained by stepwise increase of the internal circumference diameter (0.5-1.2 L100). Cyclooxygenase- and eNOS-inhibitors were employed to study NO- and EDHF-mediated dilatation in response to acetylcholine. Rats with CHF (n=8), but not sham-rats (n=6), developed significant myogenic constriction. In addition, the contribution of endothelial dilator mediators was significantly altered in CHF-rats, with increased dependency on NO and decreased EDHF-mediated dilatation. Moreover, EDHF-mediated dilatation was inversely correlated with myogenic constriction in individual CHF-rats (r=-0.74, p=0.04). These data demonstrate increased myogenic constriction in mesenteric arteries of rats with CHF post-MI to be correlated to decreased EDHF-mediated dilatation. These findings extend the previous observation that myogenic constriction antagonizes EDHF-mediated dilatation in rat coronary artery under normal conditions, and suggests this relationship also to become functional in mesenteric arteries under pathophysiological conditions of CHF.

Increase in the sensitivity of the vascular smooth muscle to constrictor factors after denervation and with a decrease in blood pressure

The effect of denervation on the contractile activity of the saphenous artery in normotensive rats and rats with regional hypotension was studied. Hypotension was caused by partial occlusion of the abdominal aorta distally from the renal arteries, and then, in four weeks, to denervate the saphenous artery, a portion of the femoral nerve in one of the limbs was resected. In two more weeks, the contractile responses of ring preparations of the saphenous artery (after removal of the endothelium and block of neuronal uptake and β-adrenoreceptors) were investigated under isometric conditions. In normotensive rats, the denervation led to an increase in the vascular sensitivity to norepinephrine, phenylephrine, serotonin, and KCl. Similar changes in contraction were caused by chronic hypotension; however, rats with hypotension exhibited no additional denervation-induced increase in the vascular sensitivity. After treatment with glyoxylic acid, the fluorescence intensity of the vascular adrenergic fibers adapted to a reduced pressure was lower than that in the norm. It was assumed that the vascular hypersensitivity in hypotension is caused by impairment of sympathetic innervation.

Akrinor-induced Relaxation of Pig Coronary Artery In Vitro is Transformed into α1-Adrenoreceptor-mediated Contraction by Pretreatment With Propranolol

Akrinor (AKR), a mixture of theodrenaline (TDR) and cafedrine (CDR), is a sympathomimetic agent used to counter transitory hypotension. Although some cases of vascular complications associated with AKR have been reported there are no experimental data about its direct effects on coronary arteries. The effects of AKR, TDR, CDR, and ephedrine (EDR) were studied on the isometric contraction of the ring preparations of pig coronary arteries precontracted with KCl. The influence of endothelium removal and preincubation with nonselective beta-adrenoreceptor antagonist propranolol (PROP), alpha(1)-adrenoreceptor antagonist prazosin, dopamine receptor antagonist SCH 23390, and adenosine receptor antagonist CGS 15943 were also tested. AKR, TDR, and CDR produced relaxation of the preparations. Preparations without endothelium were more sensitive to AKR relaxing effects. EDR produced an increase of vascular ring tonus. AKR, TDR, and EDR produced contraction in preparations pretreated with PROP. Higher concentrations of AKR relaxed PROP-pretreated preparations. AKR-induced contraction could be prevented by pretreatment with prazosin. Dopamine and adenosine receptor antagonists did not influence relaxing effects of AKR. In conclusion, AKR and its constituents induce the relaxation of pig coronary artery preparations precontracted with KCl. The observed contraction in the preparations pretreated with PROP was probably due to stimulation of unmasked alpha(1)-adrenoreceptors.

INVOLVEMENT OF ENDOTHELIAL CYCLO‐OXYGENASE METABOLITES IN NORADRENALINE‐INDUCED CONTRACTION OF RAT CORONARY ARTERY

1. Noradrenaline (NA; 0.3 micromol/L) caused a contraction of the rat coronary artery that markedly increased in the presence of the nitric oxide synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (L-NAME; 100 micromol/L) and arachidonic acid (1 micromol/L; P < 0.05). 2. The present experiments attempted to elucidate the endothelium dependency of the contraction and to pharmacologically characterize the factors involved in the contraction induced by NA (0.3 micromol/L) in the presence of L-NAME and arachidonic acid in ring preparations of the rat coronary artery. 3. The NA (0.3 micromol/L)-induced contraction was attenuated by a chemical remover of the endothelium (saponin at concentrations of 0.1 and 0.4 mg/mL) in a concentration-dependent manner (P < 0.05). 4. The cyclo-oxygenase (COX)-1 inhibitor flurbiprofen (0.01-1 micromol/L) and the COX-2 inhibitor nimesulide (0.01-1 micromol/L) attenuated the NA-induced contraction in a concentration-dependent manner and the inhibitory effect of flurbiprofen was significantly more potent than that of nimesulide (P < 0.05). The 5-lipoxigenase inhibitor ZM-230487 (1 micromol/L) did not affect the NA-induced contraction. 5. The thromboxane A2 (TXA2) synthetase inhibitor OKY-046 (30 micromol/L) and the TXA2 antagonist S-1452 (0.1-10 micromol/L) did not attenuate the NA-induced contraction. 6. These results indicate that the contraction induced by NA in the rat coronary artery in the presence of L-NAME and arachidonic acid is endothelium dependent and is due to endothelial COX metabolites of arachidonic acid.

Fetal origins of adult vascular dysfunction in mice lacking endothelial nitric oxide synthase

Epidemiological studies have shown increased incidence of hypertension and coronary artery disease in growth-restricted fetuses during their adult life. A novel animal model was used to test the hypothesis regarding the role of an abnormal uterine environment in fetal programming of adult vascular dysfunction. Mice lacking a functional endothelial nitric oxide synthase (NOS3-/-KO, where KO is knockout) and wild-type (WT) mice (NOS3+/+WT) were crossbred to produce homozygous NOS3-/-KO, maternally derived heterozygous (NOS3+/-mat, mother with NOS3 deficiency), paternally derived heterozygous (NOS3+/-pat, normal mother), and NOS3+/+WT litters. Number of fetuses per litter was smaller in NOS3-/-KO and NOS3+/-mat compared with NOS3+/-pat and NOS3+/+WT mice. Adult female mice from these litters (7-8 wk old) were killed, and ring preparations of carotid and mesenteric arteries were mounted in a wire myograph to evaluate the passive and reactive vascular characteristics. Slope of the length-tension plot (a measure of vascular compliance) was increased, and optimal diameter (as calculated by Laplace equation) was decreased in NOS3-/-KO and NOS3+/-mat compared with NOS3+/-pat and NOS3+/+WT mice. Acetylcholine caused vasorelaxation in NOS3+/-pat and NOS3+/+WT and contraction in NOS3-/-KO and NOS3+/-mat mice. Responses to phenylephrine and Ca2+ were increased in NOS3-/-KO and NOS3+/-mat compared with NOS3+/-pat and NOS3+/+WT mice. Relaxation to isoproterenol was decreased in NOS3-/-KO and NOS3+/-mat vs. NOS3+/-pat and NOS3+/+WT mice. Abnormalities in the passive and reactive in vitro vascular properties seen in NOS+/-mat that developed in a NOS3-deficient maternal/uterine environment compared with the genetically identical NOS3+/-pat mice that developed in a normal environment are the first direct evidence in support of a role for uterine environment in determining vascular function in later life.

CORONARY VASODILATORY RESPONSE TO A NOVEL PEPTIDE, ADRENOMEDULLIN 2

1. Adrenomedullin-2 (AM2) is a novel peptide originally found in a fish and it is structurally related to mammalian AM or fish AM1. Cloning of AM2 cDNA in the mouse, rat and human has been successful. In the present study, the vasodilatory effect of synthetic human AM2 was analysed in isolated artery ring preparations of porcine. 2. Vasodilatory effect of AM2 was the most potent in the coronary artery, followed by the carotid and supramesenteric arteries, but absent in the femoral, pulmonary and renal arteries. 3. The effect of AM2 was equipotent with that of human AM/AM1 in these arteries. 4. AM2-induced relaxation was inhibited by human CGRP (8-37), but not by human AM/AM1 (22-52), suggesting that the vasodilatory response to AM2 is mediated through the CGRP1 receptor. 5. AM2 may share the same receptor (complex) with AM/AM1 for the vasorelaxation. This is the first report of the vasodilatory responses to AM2 in isolated vasculature.