Cumulative Concentration-effect Curves Research Articles

Role of the iNOS isoform in the cardiovascular dysfunctions of male rats with 6-OHDA-induced Parkinsonism

IntroductionAvailable studies have shown the involvement of nitric oxide (NO) in the processes that lead to neurodegeneration in Parkinson's disease (PD). Also, the use of inhibitors of the inducible isoform of NO-synthase (iNOS) promotes neuroprotection and attenuates dopamine (DA) loss in experimental models of Parkinsonism. In addition, NO also appears to be involved in cardiovascular changes in 6-hydroxydopamine (6-OHDA)-induced Parkinsonism. The current study aimed to evaluate the effects of iNOS inhibition on cardiovascular and autonomic function in animals that were subjected to Parkinsonism by the administration of 6-OHDA. Materials and methodsThe animals underwent stereotaxic surgery for bilateral microinfusion of the neurotoxin 6-OHDA (6 mg/mL in 0.2% ascorbic acid in sterile saline solution) or vehicle solution for the Sham group. From the day of stereotaxis until the day of femoral artery catheterization, the animals were treated with the iNOS inhibitor, S-methylisothiourea (SMT; 10 mg/kg; i. p.) or saline solution (0.9%; i. p.) for 7 days. The animals were divided into four groups: Sham-Saline, Sham-SMT, 6-OHDA-Saline, and 6-OHDA-SMT. Subsequent analyses were performed on these four groups. After 6 days, they underwent catheterization of the femoral artery, and 24 h later, mean arterial pressure (MAP) and heart rate (HR) were recorded. Another group of animals (the 6-OHDA and Sham groups) was assessed for aortic vascular reactivity after 7 days of bilateral infusion of 6-OHDA or vehicle, in which cumulative concentration-effect curves (CCEC) were made for phenylephrine (Phenyl), acetylcholine and sodium nitroprusside (NPS). Also, CCEC in the presence of Nw-nitro-arginine-methyl-ester (l-NAME) (10-5 M), SMT (10-6 M), and indomethacin (10-5 M) blockers were made. ResultsThe effectiveness of the 6-OHDA lesion was confirmed with the reduction of DA in 6-OHDA animals. However, treatment with SMT could not reverse the loss of DA. Concerning the baseline parameters, SBP and MAP values were lower in 6-OHDA animals compared to their Sham control, with no effect of treatment with SMT. In the analysis of SBP variability, a decrease in variance, the VLFabs component, and the LFabs component were observed in the 6-OHDA groups when compared to their controls, regardless of treatment with SMT. It was also observed that intravenous injections of SMT resulted in an increase in BP and a decrease in HR. However, the response was not different between the Sham and 6-OHDA groups. In vascular function, there was a hyporeactivity to Phenyl in the 6-OHDA group, and when investigating the mechanisms of this hyporeactivity, it was seen that the Rmax to Phenyl increased with incubation with SMT, indicating that iNOS could be involved in the vascular hyporeactivity of animals with Parkinsonism. ConclusionThus, the set of results presented in this study suggests that part of the cardiovascular dysfunction in animals subjected to 6-OHDA Parkinsonism may be peripheral and involve the participation of endothelial iNOS.

Congenital diaphragmatic hernia increases the sensitivity of pulmonary arteries to nitric oxide

Left congenital diaphragmatic hernia (CDH) can lead to pulmonary arteries abnormalities in the contralateral and ipsilateral sides of the diaphragm. Nitric oxide (NO) is the main therapy used to attenuate the vascular effects of CDH, but it is not always effective. We hypothesized that the left and right pulmonary arteries do not respond similarly to NO donors during CDH. Therefore, vasorelaxant responses of the left and right pulmonary arteries to sodium nitroprusside (SNP, a NO donor) were determined in a rabbit experimental model of left CDH. CDH was surgically induced in the fetuses of rabbits on the 25th day of pregnancy. On the 30th day of pregnancy, a midline laparotomy was performed to access the fetuses. The fetuses’ left and right pulmonary arteries were isolated and mounted in myograph chambers. Vasodilation was evaluated by cumulative concentration-effect curves to SNP. Protein expression of guanylate cyclase isoforms (GCα, GCβ) and the α isoform of cGMP-dependent protein kinase 1 (PKG1α), and the concentration of NO and cGMP were determined in the pulmonary arteries. The left and right pulmonary arteries of newborns with CDH exhibited increased vasorelaxant responses to SNP (i.e. the potency of SNP was increased) compared to the control group. GCα, GCβ, and PKG1α expression were decreased, while NO and cGMP concentrations were increased in the pulmonary arteries of newborns with CDH compared to the control group. The increased cGMP mobilization may be responsible for the increased vasorelaxant responses to the SNP in the pulmonary arteries during left CDH.

Muscarinic Receptor Activation Reduces Force and Arrhythmias in Human Atria Independent of IK,ACh.

In human hearts, muscarinic receptors (M-R) are expressed in ventricular and atrial tissue, but the acetylcholine-activated potassium current (IK,ACh) is expressed mainly in the atrium. M-R activation decreases force and increases electrical stability in human atrium, but the impact of IK,ACh to both effects remains unclear. We used a new selective blocker of IK,ACh to elaborate the contribution of IK,ACh to M-R activation-mediated effects in human atrium. Force and action potentials were measured in rat atria and in human right atrial trabeculae. Cumulative concentration-effect curves for norepinephrine-induced force and arrhythmias were measured in the presence of carbachol (CCh; 1 µM) or CCh together with the IK,ACh -blocker XAF-1407 (1 µM) or in time-matched controls. To investigate the vulnerability to arrhythmias, we performed some experiments also in the presence of cilostamide (0.3 µM) and rolipram (1 µM), inhibiting PDE3 and PDE4. In rat atria and human right atrial trabeculae, CCh shortened the action potential duration persistently. However, the direct negative inotropy of CCh was only transient in human, but stable in rat atria. In rat and human atria, the negative inotropic effect was insensitive to blockage of IK,ACh by XAF-1407. In the presence of cilostamide and rolipram about 40% of trabeculae developed arrhythmias when exposed to norepinephrine. CCh prevented these concentration-dependent norepinephrine-induced arrhythmias, again insensitive to XAF-1407. Maximum catecholamine-induced force was not depressed by CCh. In human atrium, the direct and the indirect negative inotropic effect of CCh are independent of IK,ACh. The same applies to the CCh-mediated suppression of norepinephrine/PDE-inhibition-induced arrhythmias.

Effects of omecamtiv mecarbil on failing human ventricular trabeculae and interaction with (-)-noradrenaline.

Omecamtiv mecarbil (OM) is a novel medicine for systolic heart failure, targeting myosin to enhance cardiomyocyte performance. To assist translation to clinical practice we investigated OMs effect on explanted human failing hearts, specifically; contractile dynamics, interaction with the β1–adrenoceptor (AR) agonist (−)‐noradrenaline and spontaneous contractions. Left and right ventricular trabeculae from 13 explanted failing hearts, and trabeculae from 58 right atrial appendages of non‐failing hearts, were incubated with or without a single concentration of OM for 120 min. Time to peak force (TPF) and 50% relaxation (t 50%) were recorded. In other experiments, trabeculae were observed for spontaneous contractions and cumulative concentration‐effect curves were established to (−)‐noradrenaline at β1‐ARs in the absence or presence of OM. OM prolonged TPF and t 50% in ventricular trabeculae (600 nM, 2 µM, p < .001). OM had no significant inotropic effect but reduced time dependent deterioration in contractile strength compared to control (p < .001). OM did not affect the generation of spontaneous contractions. The potency of (−)‐noradrenaline (pEC50 6.05 ± 0.10), for inotropic effect, was unchanged in the presence of OM 600 nM or 2 µM. Co‐incubation with (−)‐noradrenaline reduced TPF and t 50%, reversing the negative diastolic effects of OM. OM, at both 600 nM and 2 µM, preserved contractile force in left ventricular trabeculae, but imparted negative diastolic effects in trabeculae from human failing heart. (−)‐Noradrenaline reversed the negative diastolic effects, co‐administration may limit the titration of inotropes by reducing the threshold for ischemic side effects.

Determining the Properties of Omecamtiv Mecarbil on Human Explanted Cardiac Trabeculae and Its Interaction with Current Inotropes via the Beta 1-Adrenoceptor

Omecamtiv mecarbil (OM) is a first in class selective myosin activator, developed to increase contractile force without altering intracellular calcium concentrations in patients with advanced heart failure (AHF). We sought to investigate the effect of OM on contractility, arrhythmia genesis and interaction with Beta 1-adrenoceptor (B1AR) inotropes directly on explanted human failing heart. Trabeculae from 7 explanted hearts with AHF were dissected and set up to contract at 1 Hz. Trabeculae were incubated with or without OM (600 nM or 2 µM) for 120 mins. Cumulative concentration-effect curves were established to (-)-noradrenaline at B1ARs in the presence of the B2AR blocker (50 nM ICI 118,551) and phenoxybenzamine to block α1ARs and neuronal uptake. Contractile force and duration were recorded and observed for spontaneous contractions. OM prevented time dependent reduction (fade) in contractile force (Fig A, P=0.013 at 120mins). Trabeculae exhibited a concentration dependent increase in systolic ejection time (SET), associated with increased stroke volume, but this reduces the time for diastole. (Fig B). The concentration of (-)-noradrenaline required for 50% of maximal contractile force, the LogEC50, remained unchanged in the presence of OM (Mean LogEC50: -6.1 (control), -6.2 (600 nM), -6.1 (2 µM); P=0.7). (-)-Noradrenaline reversed OM mediated increases in SET. There was no significant increase in spontaneous contractions with OM concentrations up to 2 µM. OM maintains contractile force, independent of a B1AR mediated mechanism, without an increase in spontaneous contraction. In isolation OM increases SET at the cost of diastolic performance. Concomitant B1AR activation by (-)-noradrenaline normalises SET, improving ventricular filling. This finding may prove clinically relevant, especially when titrating traditional inotropes which increase metabolic demand.

025 Determining the Effects of Omecamtiv Mecarbil on Human Failing Ventricular Trabeculae and Interaction With (-)-Noradrenaline Via the β1-adrenoceptor

Omecamtiv mecarbil (OM) is a novel medicine for systolic heart failure, targeting myosin to enhance cardiomyocyte performance. However, OM had negative diastolic effects and evidence of ischaemia at supratherapeutic doses. To assist translation to clinical practice we investigated OMs effect on ventricular trabeculae from explanted human failing hearts, specifically; contractile dynamics, interaction with the β1–adrenoceptor (AR) agonist (-)-noradrenaline and arrhythmia genesis. Ventricular trabeculae from explanted failing hearts were paced under tension and incubated with or without a single concentration of OM for 120 mins. Time to peak force (TPF) and 50% relaxation (t50%) were recorded. Cumulative concentration-effect curves were established to (-)-noradrenaline at β1-ARs in the absence or presence of OM, whilst β2-AR, α1-ARs and neuronal uptake were blocked. Stimulators were switched off and trabeculae observed for arrhythmic contractions. OM prolonged TPF and t50% in ventricle (600 nM, 2 mM, p<0.001) but had no effect on inotropic force. OM did not affect the generation of arrhythmic contractions. The potency of (-)-noradrenaline (pEC50 6.05±0.10), for inotropic effect, was unchanged in the presence of OM 600 nM or 2 μM. (-)-Noradrenaline reversed the negative diastolic effects of OM at maximal β1-AR effect. In ventricular trabeculae from explanted human failing hearts, OM prolonged TPF and t50%, but had no effect on contractile force, generation of arrhythmic contractions or potency of (-)-noradrenaline at β1-ARs. The competing diastolic effects of OM and (-)-noradrenaline may prove clinically important. If used together in patients with cardiogenic shock.

In Endothelial Cells, the Activation or Stimulation of Soluble Guanylyl Cyclase Induces the Nitric Oxide Production by a Mechanism Dependent of Nitric Oxide Synthase Activation.

In endothelial cells, investigate if the soluble guanylate cyclase (sGC) activation or stimulation is able to potentiate the relaxation in vessels. Aortic and coronary rings with and without endothelium were placed in a myograph and cumulative concentration-effect curves for DETA-NO or ataciguat were performed. Nitric oxide (NO) were measured by fluorescence or by selective electrode in human umbilical endothelial cells (HUVECs) in response to some treatments, including ataciguat, 8-Br-cGMP and A23187. The presence of the endothelium potentiated the relaxation induced by DETA-NO in aortic and coronary rings. In addition, in aortic rings the endothelium potentiated the relaxation induced by ataciguat. In the presence of nitric oxide synthase (NOS) inhibitor, the endothelium effect was abolished to DETA-NO or ataciguat, in both vessels. Ataciguat, 8-Br-cGMP and A23187 were able to induce NO production in HUVECs cells. In the presence of NOS inhibitor, the NO production induced by ataciguat and 8-Br-cGMP was abolished. Our results suggest that in aortic and coronary rings the endothelium potentiates the relaxation induced by activation or stimulation of sGC through a mechanism dependent of NOS activation.This article is open to POST-PUBLICATION REVIEW. Registered readers (see "For Readers") may comment by clicking on ABSTRACT on the issue's contents page.

Treatment with sodium nitroprusside improves the endothelial function in aortic rings with endothelial dysfunction

PurposeVerify if sodium nitroprusside (SNP) is able to improve endothelial function and if this effect is independent of nitric oxide (NO) release of the compound. MethodsNormotensive (2K) and hypertensive (2K-1C) wistar rats were used. Intact endothelium aortas were placed in a myograph and incubated with SNP: 0.1nM; 1nM or 10nM during 30min. Cumulative concentration-effect curves for acetylcholine (Ach) were realized to measure the relaxing capacity. Intracellular NO were measured (by DAF-2DA probe) in HUVEC treated with SNP 0.1nM or DETA/NO 0.1μM. The detection of intracellular superoxide radical (O2•-) was obtained by using DHE probe. ResultsTreatment of 2K-1C aortic rings with SNP (0.1; 1.0 and 10nM) improved endothelium dependent relaxation induced by acetylcholine. This improvement induced by SNP was verified at the concentration of 0.1nM, which does not release NO, suggesting that this effect was not induced due to NO release by SNP compound. Besides, we show that the cell treatment with 0.1nM of SNP decreased the fluorescence intensity to DHE in cells stimulated with angiotensin II. These results indicate that SNP decreases the concentration of O2•- in HUVEC cells. ConclusionsThe SNP at a concentration that does not release NO inside the cells is able to attenuate endothelial dysfunction. Drugs and chemicalsAcetylcholine (Ach) (PubChem CID:6060); angiotensin II human (Ang II) (PubChem CID: 16211177); diethylenetriamine/nitric oxide (DETA-NO) (PubChem CID 4518); dihydroethidium (DHE) (PubChem CID: 128682); phenylephrine (Phe) (PubChem CID: 5284443); sodium nitroprusside (SNP) (PubChem CID: 11963579); Thiazolyl Blue Tetrazolium Bromide (MTT) (PubChem CID: 64965); 4,5-diaminofluorescein diacetate (DAF-2DA); 4-hidroxy-Tempo (Tempol) (PubChem CID: 137994), were purchased from Sigma–Aldrich (St. Louis, MO, USA).

Would calcium or potassium channels be responsible for cardiac arrest produced by adenosine and ATP in the right atria of Wistar rats?

Autonomic nerves release ATP, which is processed into adenosine in the synaptic cleft. Adenosine and ATP exert a negative chronotropic effect in the heart. This study aims to evaluate adenosine and P2 receptors and cellular signalling in cardiac arrest produced by purines in the heart. Right atria of adult Wistar rats were used to evaluate the effects of adenosine, ATP and CPA (an adenosine A1 receptor agonist), in the presence and absence of DPCPX, an adenosine A1 receptor antagonist. Effects of adenosine A2 and A3 receptors agonists and antagonists were also investigated. Finally, involvement of calcium and potassium channels in these responses was assessed using BayK 8644 and 4-Aminopyridine. Cumulative concentration–effect curves of adenosine and CPA resulted in a negative chronotropic effect culminating in cardiac arrest at 1000μM (adenosine) and 1µM (CPA). Furthermore, ATP produced a negative chronotropic effect at 1–300µM and cardiac arrest at 1000μM in the right atrium. ATPγS (a non-hydrolysable analogue of ATP) reduced chronotropism only. The effects of adenosine, CPA and ATP were inhibited by DPCPX, a selective adenosine A1 receptor antagonist. The selective adenosine A2 and A3 receptors antagonists did not alter the chronotropic response of adenosine. 4-Aminopyridine, a blocker of potassium channels at 10mM, prevented the cardiac arrest produced by adenosine and ATP, while BayK 8644, activator of calcium channels, did not prevent cardiac arrest. Adenosine A1 receptor activation by adenosine and ATP produces cardiac arrest in the right atrium of Wistar rats predominantly through activation of potassium channels.

Abstract 665: Endothelial Nitric Oxide Negatively Modulates Phenylephrine-induced Contraction In Matrix Metalloproteinase 2 (mmp-2)-filled Rabbit Aortic Rings

Endothelial nitric oxide negatively modulates Phenylephrine-induced contraction in Matrix metalloproteinase 2 (MMP-2)-filled rabbit aortic rings The present study aimed to evaluate the vascular function of aortic rings after intraluminal injection of matrix metalloproteinase 2 (MMP-2) and contribution of endothelial nitric oxide (NO) in this response. METHODS: thoracic aorta isolated from New Zealand rabbits (3.0 Kg) was isolated and were performed in situ gelatinolytic assay (intraluminal exposure with Krebs solution or MMP-2 1.2 μg/mL, at 37° C for 30 minutes, with measure of fluorescence intensity - FI) or vascular reactivity. Cumulative concentration-effect curves for phenylephrine (PE, 0.1 nM - 10 μM/L) were performed in endothelium-intact (E+) or denuded (E-) aortic rings, in the absence or presence of L-NAME (non-selective inhibitor of NOS, 100 μM) or Hydroxycobalamine (scavenger of intracellular NO), 30 min before the PE curves on E+ rings. The vascular contraction was normalized by grams of tension by dry tissue (g/g) and were analyzed the agonist maximum effect (Emax) and potency (pD2). Data represent mean ± S.E.M and the results were statistically analyzed using Student t test, one-way or two-way ANOVA with Bonferroni pos-hoc (p&lt;0,05). Results: In situ gelatinolytic activity was increased in the vessels filled with MMP-2 (19.19+0.93U,n=5) compared to vehicle (10.75+0.45U,n=5). In the vascular reactivity, E- aortic rings filled with MMP-2 increased Emax of PE (1893,28+122,40g/g,n=9) versus vehicle E- (1485.73+76.82g/g,n=9), but no differences were observed on Emax of E+ aortic rings (vehicle: 1416.13+120.87g/g,n=7; MMP-2: 1893.28+122.40g/g,n=9). The presence of L-NAME induced an increase in Emax of E+ aortic rings filled with vehicle (1817.60+76.37g/g,n=7) or MMP-2 (2340.50+130.43g/g,n=5). Hydroxycobalamine also increased the Emax of E+ aortic rings with vehicle (1889,81+129,17,n=6) or MMP-2 (2480,12+192,57,n=5). No difference of pD2 value was observed in this study. Conclusion: Data suggest this protease cross the aorta layers from the lumen. An increased vasoconstriction in E- vessels suggests a vascular smooth muscle activity of MMP-2. In the presence of L-NAME and Hydroxycobalamine, vessels filled with MMP-2 shows a greater maximum effect suggesting that NO exerts a negative modulation of the PE-induced vasoconstriction on MMP-2 aortic rings.

The character of the antagonism by polyphloretin phosphate of contractions to prostaglandins E1 and F 2alpha in guinea-pig ileum.

Polyphloretin phosphate (PPP) produced a dose-dependent decrease in the tone and reduction of the spontaneous phasic contactions of the longitudinal muscle of guinea-pig isolated ileum. PPP (100 microgram ml-1) after a 2 min contact with the ileum decreased the contractile effects of PGE1 0.1 micron by 40.6 +/- 7.4%, of PGE1 0.01 micron by 86.7 +/- 3.3% and of PGE2alpha 0.1 micron by 62.2 +/- 8.6%. After 10 min contact of PPP the contractile effect of PGE1 0.1 micron was decreased by 47.7 +/- 4.7% and that of PGE2alpha 0.1 micron by 89.6 +/- 1.7%. When the contact was longer, PPP showed a pronounced after-effect in respect to the effects of PGE1 and particularly of PGF2alpha. PPP signicantly reduced contractions to 5-HT and BaCL2, but not to acetylcholine, histamine or substance P. The type of antagonism of PGE1 by PPP was examined using cumulative concentration-effect curves for PGE1 in the presence of increasing concentrations of PPP. We conclude that on guinea-pig ileum PPP acts as a non-competitive antagonist of PGE1 and PGF2alpha.

The contribution of guanylyl cyclase and potassium channels to the relaxation induced by the NO donors [Ru(terpy)(bdq)NO+]3+ (Terpy) and sodium nitroprusside (SNP) in rat mesenteric resistance arteries

This study aimed to verify the mechanisms of vasodilatation induced by Terpy and SNP in resistance mesenteric arteries isolated from normotensive (2K) and renal hypertensive rats (2K‐1C). We also studied the inhibitory effects of the guanylyl‐cyclase (GC) with ODQ and K+ channel with TEA. Cumulative concentration‐effect curves to Terpy (0.01 μM‐ 0.01mM) and sodium nitroprusside (SNP 1nM‐0.1mM) were constructed in the third branch of mesenteric arteries pre‐contracted with phenylephrine. We have analyzed the efficacy (ME) and the potency (pD2) of the NO donors. Both SNP and Terpy induced relaxation with similar efficacy in 2K (Terpy 93.8±1.2%, n=7 SNP 96.1±0.7% n=6) and 2K‐1C rats (Terpy 93.7±1.4% n=8, SNP 90.2±4.2% n=5). However, Terpy was less potent (pD2) (2K 4.45±0.3; 2K‐1C 4.51±0.3) than SNP (2K: 6.60±0.2, 2K‐1C: 7.28±0.01), although the relaxation induced by Terpy and SNP, were not different in mesenteric resistance arteries from 2K and 2K‐1C. The incubation with ODQ (1μM) almost abolished the response induced by Terpy and SNP. TEA (1mM) reduced the effect of Terpy in a similar way in 2K (ME: Terpy 73.1±7.3% n=5; SNP 69.2±6.2% n=7) and 2K‐1C rats (Terpy 71.7±8.2% n=5; SNP 77.1±6.6% n=7). In conclusion, in mesenteric resistance arteries from hypertensive and normotensive rats the NO donors Terpy and SNP induce relaxation in a similar way, which involves GC and K+ channels activation. Supported by FAPESP and CNPq.

Methyl-β-cyclodextrin Prevents Angiotensin II-Induced Tachyphylactic Contractile Responses in Rat Aorta

Tachyphylaxis or desensitization is frequently observed following angiotensin II type I (AT1) receptor activation by angiotensin II. One of the possible mechanisms contributing to receptor desensitization involves receptor internalization. In addition to clathrin-coated pits/vesicles, caveolae, small invaginations in the plasma membrane rich in cholesterol, may also be involved in receptor internalization. After activation, AT1 receptor partially redistributes to lipid-enriched domains. We hypothesize that AT1 receptor internalization via caveolae contributes to the tachyphylactic response observed to angiotensin II. Endothelium-denuded rat aortic rings were exposed to increasing concentrations of angiotensin II or phenylephrine, generating two cumulative concentration-effect curves (CCEC) with a 90-min interval separating each curve (CCEC-I and CCEC-II). CCEC-II was performed in the presence of either vehicle or methyl-beta-cyclodextrin (CD), a drug that depletes cholesterol from the membrane and disassembles caveolae. CCEC-II to angiotensin II, but not to phenylephrine, was blunted in aortic rings treated with vehicle. In the presence of CD, CCEC-II did not differ significantly from CCEC-I for both agonists. CCEC-I to angiotensin II was abolished when in the presence of the AT1 receptor antagonist. The presence of AT1 receptors at the aortic smooth muscle cells' membrane treated with angiotensin II was observed by immunofluorescence only in the presence of CD. In addition, caveolin-1 coimmunoprecipitated with AT1 receptor after agonist stimulation, and this interaction was inhibited by CD. Our data suggest that caveolae are involved in the tachyphylactic contractile response induced by angiotensin II in rat aorta, and this effect is related to receptor internalization.

Vasodilator Effects of Bis-Dihydropyridines Structurally Related to Nifedipine

Calcium channel blockers are widely used in therapy for hypertension and angina pectoris, and among these blockers some 1,4-dihydropyridines (e.g. amlodipine, nitrendipine and nifedipine) have had widespread clinical use. In this work we investigated the vascular effects of four bis-1,4-dihydropyridines (bis-DHPs: 01-04), structurally related to nifedipine, in which a second 1,4-dihydropyridinic moiety was incorporated in the corresponding arylic moiety in para and meta position. Of these four bis-DHPs, the meta regioisomers (bis-DHP-03 and bis-DHP-04; 0.01-3.16 mg kg(-1)) and nifedipine induced a greater decrease on diastolic and systolic blood pressure than the para isomers (bis-DHP-01 and bis-DHP-02), as shown in two experimental models: normotensive and spontaneously hypertensive rats. Complementarily, bis-DHPs action was examined in intact and endothelium-denuded rat aorta, depolarized by KCl [80 mM] in one group and stimulated by noradrenaline (1 x 10(-7) M) in another and the corresponding IC(50) values were obtained (1.5 x 10(-6)-2. 4 x 10(-7)M). Later, the relaxing action of bis-DHP-03,04 and nifedipine on the contraction evoked by Ca(2+) in K(+)-depolarized rat aorta was analyzed and the corresponding EC(50) values for the meta isomers and nifedipine were obtained. The results showed a concentration dependent vasodilating activity in both KCl precontracted and noradrenaline stimulated aorta rings. The apparent order of potency with and without endothelium in both experimental models was nifedipine >bis-DHP-04 >bis-DHP-03. The cumulative concentration-effect curves for Ca(2+) in the presence of the bis-DHPs tested show the same potency order. Unlike nifedipine, the tested compounds are not photosensitive, which makes them more attractive in therapy for hypertension related diseases.

The Aortic Reactivity to Nitric Oxide after Cardiopulmonary Bypass in Rats

Background: We evaluated whether vessel reactivity to nitric oxide changed after cardiopulmonary bypass, which would play an inportant role in temporary vital organ perfusion. Methods: We used the distal aortas of five rats weighing 400-500 g after cardiopulmonary bypass in experimental group. We also used the distal aortas of five rats before cardiopulmonary bypass under sham operation in control group. All cumulative concentration-effect curves were performed in the aortic rings and and maximal response () were calculated by using nonlineal logistic regression analysis with the software PRISM (Graphpad, Mountain View, CA). Results: CPB inhibited acetylcholine induced relaxation in aortic rings and also inhibited sodium nitroprusside (SNP) induced relaxation in ones. It was similar to depression of acetylcholine induced relaxation. Conclusions: The depression of aortic rings relaxation after CPB may be associated with attenuated sensitivity of them to NO in rats.

The Pulmonary Arterial Reactivity to Nitric Oxide after Cardiopulmonary Bypass and Reperfusion in Pigs

Background: We hypothesized that the decreased nitric oxide after cardiopulmonary bypass and reperfusion would play an important role in temporary pulmonary hypertension. Methods: We used the pulmonary arteries of three pigs weighing 40-50 kg after cardiopulmonary bypass and reperfusion in experimental group. We also used the pulmonary arteries of five pigs before cardiopulmonary bypass under sham operation in control group. All cumulative concentration-effect curves were performed on vessel rings beginning at their optimum resting zone. and maximal response () were calculated by using nonlineal logistic regression analysis with the software PRISM (Graphpad, Mountain View, CA). Results: CPB inhibited endothelium-dependent relaxation to acetylcholine in pulmonary arterial rings, but did not affect SNP induced relaxation in ones. Conclusions: The Ability of pulmonary arterial relaxation after CPB and reperfusion in pigs was decreased without attenuated pulmonary arterial sensitivity to NO.

Effect of histamine on lung contractile elements in growing cattle.

To determine the effect of histamine on the contractile elements of the respiratory tract in neonatal calves and young adult cattle. Samples of trachealis muscle, bronchi, and intrapulmonary arteries and veins dissected from the respiratory tracts of healthy bovids (2 to 8 days and 16 to 20 months old). Histamine cumulative concentration-effect curves (10(-6) to 10(-3) M) were constructed in duplicate smooth muscle samples mounted in organ baths. Contractile responses to histamine were compared with reference contractions elicited by methacholine (10(-5) M) for airways or KCl (127 mM) for vessels. In young adult cattle, trachealis muscle had a substantial contractile response to histamine (84% of methacholine-induced contraction), whereas bronchi reacted slightly (15 and 20% for large and small bronchi, respectively). Although contractile responses to KCl were comparable in arteries and veins, histamine-induced contractions were greater for intrapulmonary veins than for arteries (202 vs 48% of KCl-induced contraction). In neonatal calves, histamine-induced contraction of veins also exceeded that of arteries (230 vs 54% of KCl-induced contraction); however, unlike in young adult cattle, histamine produced notable contraction of large and small bronchi (48 and 60% of methacholine-induced contraction, respectively). Compared with intrapulmonary arteries, intrapulmonary veins have greater contractile responses to histamine in neonatal and young adult cattle. Data suggest loss of histamine responsiveness in bronchial smooth muscle as neonatal calves grow to young adults. Venodilation may be useful in treatment of lung edema in cattle.

Effects of Rocuronium on Smooth Muscle Tension of Isolated Rat Thoracic Aorta

Background: The cardiovascular effects of muscle relaxants may be produced by a muscarinic receptor block, ganglion block, increased noradrenaline release and blockage of it's reuptake or histamine liberation. However certain analogues of steroidal muscle relaxants directly cause relaxation of isolated vascular smooth muscles. Rocuronium is the 2-morpholino, 3-desacetyl, 16-N-allyl-pyrrolidino derivative of vecuronium, known to have a relative lack of ganglion blocking, sympathomimetic effects or histamine release. The aim of this study was to investigate the effect and action mechanism of rocuronium on isolated aortic smooth muscle in rats. Methods: The ability of rocuronium to elicit a direct relaxant effect on vascular smooth muscle has been studied using isolated rat thoracic aortic rings contracted with phenylephrine (PE). Each ring of aortic arteries was suspended on wire supports in a 20 ml tissue bath under 2 g of resting tension. All tissues were bathed in Tris Tyrode solution at 37 and 100% oxygen was supplied. Results: Rocuronium M and M shifted the cumulative concentration-effect curves of PE to the right significantly (P

Spontaneous contractions of myometrium from humans, non-human primate and rodents are sensitive to selective oxytocin receptor antagonism in vitro.

To determine whether: 1. oxytocin receptor antagonists influence spontaneous contractions of myometrium from humans, non-human primates and rodents (in vitro), and 2. vasopressin V1a receptor antagonism is important for inhibition of spontaneous contractions in human myometrium. In vitro pharmacology of spontaneous contractions of myometrium from humans and animals. The research laboratories of a university department of obstetrics and gynaecology and a pharmaceutical industry research centre. Samples of human myometrium were obtained at caesarean section. Tissue strips were suspended in organ baths for isometric force recording. Cumulative concentration effect curves to a selective oxytocin receptor antagonist (L-371,257) and a mixed oxytocin/vasopressin V1a receptor antagonist (atosiban) were obtained. The effect of L-371,257 was also determined in myometrium from non-pregnant rats and marmosets. The inhibition of spontaneous myometrial contractions in vitro. L-371,257 and atosiban significantly inhibited spontaneous activity of human myometrium in a concentration-related manner (P < 0.05), although the effect was more pronounced with L-371,257. Spontaneous contractions of myometrium from non-pregnant rats and marmosets were also inhibited by L-371,257 (atosiban was not tested). Spontaneous contractions of myometrium from humans, marmosets and rats are, at least in part, dependent on oxytocin receptor activity, in vitro. L-371,257 and atosiban may be inverse agonists. Selective non-peptide oxytocin receptor antagonists may be effective tocolytics.

Spontaneous contractions of myometrium from humans, non-human primate and rodents are sensitive to selective oxytocin receptor antagonism in vitro

Objectives To determine whether: 1. oxytocin receptor antagonists influence spontaneous contractions of myometrium from humans, non-human primates and rodents ( in vitro), and 2. vasopressin V 1a receptor antagonism is important for inhibition of spontaneous contractions in human myometrium. Design In vitro pharmacology of spontaneous contractions of myometrium from humans and animals. Setting The research laboratories of a university department of obstetrics and gynaecology and a pharmaceutical industry research centre. Interventions Samples of human myometrium were obtained at caesarean section. Tissue strips were suspended in organ baths for isometric force recording. Cumulative concentration effect curves to a selective oxytocin receptor antagonist (L-371,257) and a mixed oxytocin/vasopressin V 1a receptor antagonist (atosiban) were obtained. The effect of L-371,257 was also determined in myometrium from non-pregnant rats and marmosets. Main outcome measures The inhibition of spontaneous myometrial contractions in vitro. Results L-371,257 and atosiban significantly inhibited spontaneous activity of human myometrium in a concentration-related manner ( P<0.05), although the effect was more pronounced with L-371,257. Spontaneous contractions of myometrium from non-pregnant rats and marmosets were also inhibited by L-371,257 (atosiban was not tested). Conclusions Spontaneous contractions of myometrium from humans, marmosets and rats are, at least in part, dependent on oxytocin receptor activity, in vitro. L-371,257 and atosiban may be inverse agonists. Selective non-peptide oxytocin receptor antagonists may be effective tocolytics.