Isolated Rat Atria Research Articles

Cholinergic–adrenergic antagonism in the induction of tachyarrhythmia by electrical stimulation in isolated rat atria

Atrial tachyarrhythmias (AT) are the most common cardiac rhythm disturbance. In the present study, we analyzed the cholinergic–adrenergic interaction in the in vitro induction of cholinergic-dependent tachyarrhythmia by high-frequency electric stimulation. Tachyarrhythmia was evoked in isolated rat right atria by trains of electric stimuli. Atrial response was expressed as the tachyarrhythmia induction index (ATI, i.e. the fraction of applied trains that resulted in arrhythmia induction). ATI was reversibly increased by 0.6 μM carbachol (CCh), which also decreased atrial spontaneous rate (ASR). In contrast, 10 nM isoproterenol (ISO), 100 μM tyramine and the phosphodiesterase inhibitor isobutyl-methylxanthine (IBMX, 100 μM) increased ASR and decreased ATI. Amiodarone (AMI, 10 μM) reduced ATI in the presence and absence of CCh. Further CCh addition restored ATI in atria treated with either IBMX or AMI, but not when both compounds were present. Increase in ATI by CCh in atria pretreated with IBMX plus ISO was significantly attenuated by 3 mM NaF. The antagonism between cholinergic muscarinic and β-adrenergic receptor stimulation (the former facilitating and the latter inhibiting tachyarrhythmia installation) possibly involves regulation of the phosphorylation status of adenosine cyclic 3′-5′-monophosphate (cAMP)-dependent protein kinase substrates. Additionally, cAMP-independent, AMI-sensitive mechanism stimulated by CCh (possibly muscarinic-dependent K + current activation) seems to contribute to AT facilitation.

Mitogen-activated Protein Kinases p38 and ERK 1/2 Mediate the Wall Stress-induced Activation of GATA-4 Binding in Adult Heart

The zinc finger transcription factor GATA-4 has been implicated as a critical regulator of inducible cardiac gene expression and as a potential mediator of the hypertrophic program. However, the precise intracellular mechanisms that regulate the DNA-binding activity of GATA-4 are not fully understood. The aim of the present study was to examine the role of mitogen-activated protein kinases (p38 kinase, extracellular signal-regulated protein kinase, and c-Jun N-terminal protein kinase) in the left ventricular wall stress-induced activation of GATA-4 DNA binding in adult heart. Isolated perfused rat hearts were subjected to increased left ventricular wall stress by inflating a balloon in the ventricle. Gel mobility shift assays were used to analyze the transacting factors that interact with the GATA motifs of the B-type natriuretic peptide promoter. The left ventricular wall stress rapidly activated GATA-4 DNA binding and significantly increased the levels of phosphorylated p38 kinase, extracellular signal-regulated protein kinase, and c-Jun N-terminal protein kinase. The wall stress-induced increase in the DNA-binding activity of GATA-4 was abolished both in the presence of the p38 inhibitor SB239063 and MEK1/2 inhibitor U0126. In contrast, the inhibition of c-Jun N-terminal protein kinase by CEP11004 had no effect on the baseline or stretch-induced GATA-4 DNA binding. Moreover, GATA-4 DNA binding was up-regulated by mechanical stretch in the isolated rat atria via p38 and extracellular signal-regulated protein kinase. In conclusion, the present study demonstrates that both p38 and extracellular signal-regulated protein kinase are required for the stretch-induced GATA-4 binding in intact heart.

Cardiac and vascular effects of diltiazem, dobutamine and amrinone, drugs used after myocardial revascularization.

Hemodynamic care during postoperative management of myocardial revascularization should include vasorelaxing drugs to insure adequate graft and coronary flow, and stimulation of stroke volume to maintain vascular perfusion pressure. We tested the cardiac (inotropic and lusitropic) and vascular (relaxant) effects of diltiazem (0.1 nM to 0.1 mM), dobutamine (10 microM to 10 mM) and amrinone (10 microM to 1 mM) on isolated rat atria and thoracic aorta, and also on isolated human saphenous vein (HSV) and human mammary artery (HMA). Dobutamine produced a maximal positive inotropic effect (+dF/dt max = 29 +/- 7%) at its ED50 for aortic relaxation (88 +/- 7 microM). Conversely, at their ED50 for aortic relaxation diltiazem depressed myocardial contractility and amrinone did not exhibit myocardial effects. In HSV and HMA contracted with 80 mM potassium, diltiazem and dobutamine (but not amrinone) had a vasorelaxant activity similar to that in rat aorta. Norepinephrine-contracted human vessels were significantly more sensitive than potassium-contracted vessels to the relaxant effect of amrinone (ED50 HMA = 15 +/- 5 microM, ED50 HSV = 72 +/- 31 microM, P < 0.05). We conclude that at concentrations still devoid of myocardial effects dobutamine and amrinone are effective dilators in graft segment vessels and rat aorta contracted by membrane depolarization. If the difference between aortic and myocardial tissue still holds in human tissues, at the appropriate concentrations these drugs should be expected to improve cardiac performance while still contributing to the maintenance of graft patency.

Optical mapping of tachycardia-like excitation evoked by pacing in the isolated rat atrium

Multiple-site optical recording of membrane potential activity using a voltage-sensitive dye was employed to monitor action potentials in the rat atrium. Electrical pacing at 1 Hz evoked the events of tachycardia-like excitation (TE). Optical mapping revealed that a coupling of spontaneous and evoked action potentials resulted in the initiation of TE.

Optical Mapping of Tachycardia-Like Excitation Evoked by Pacing in the Isolated Rat Atrium

Multiple-site optical recording of membrane potential activity using a voltage-sensitive dye was employed to monitor action potentials in the rat atrium. Electrical pacing at 1 Hz evoked the events of tachycardia-like excitation (TE). Optical mapping revealed that a coupling of spontaneous and evoked action potentials resulted in the initiation of TE.

Optical mapping of the spread of excitation in the isolated rat atrium during tachycardia-like excitation.

Multiple-site optical recording of membrane potential activity, using the voltage-sensitive merocyanine-rhodanine dye NK2761 and a multiple-element photodiode array, was employed to monitor action potentials in an isolated rat atrial preparation. The events of tachycardia-like excitation (TE) were evoked by electrical stimulation. The conduction pattern of excitation was assessed optically by timing the feet of optical action potentials, then maps of excitation spread patterns were made. The excitatory waves often rotated around the blocked area including the ostium of the superior vena cava. Other patterns, such as reentry without anatomical obstacles, ectopic pacemaker and more complex patterns, were sometimes observed. Optical mapping during the initiation phase of TE indicated that the decrease of the conduction velocity and the appearance of blocked areas contributed the establishment of TE. On the basis of the characteristics of TE, it is suggested that TE is a metastable state of atrial rhythm. TE appears to be analogous to atrial flutter.

The influence of endogenously generated reactive oxygen species on the inotropic and chronotropic effects of adrenoceptor and ET-receptor stimulation.

Reactive oxygen species (ROS) play a role in cardiovascular diseases such as heart failure and hypertension. Furthermore, increasing evidence has accumulated suggesting that ROS can also be formed subsequent to the stimulation of various receptors, thus functioning as second messengers. The objective of the present study was to elucidate the role of intracellular-generated ROS in the inotropic and chronotropic effects of the alpha1- and beta-adrenoceptor and the ET-receptor stimulation in isolated rat atria. In addition, we investigated whether the MAPKerk pathway is involved in the ROS-provoked rise of contractile force. For this purpose hydrogen peroxide was applied, which is known to serve several endogenous functions as a second messenger. Moreover, hydrogen peroxide readily crosses cell membranes, which thus allows to mimic the intracellular formation. Preincubation of atria with EUK 8 (400 microM), a cell permeable superoxide dismutase- and catalase-mimetic, reduced the positive inotropic effect upon alpha1-adrenoceptor and ET-receptor stimulation. The responsiveness to beta-adrenoceptor stimulation remained unaffected by this pretreatment. The chronotropic effects were not altered by preincubation with EUK 8. In contrast to the MAPK(p38) inhibitor SB203580 (2 and 10 microM), the two MKKmek inhibitors PD98059 (30 and 100 microM) and U0126 (10 microM) significantly attenuated the positive inotropic response to hydrogen peroxide in isolated rat left atria. In addition, inhibition of the Na+/H+ exchange (NHE) by cariporide (1 microM) counteracted ROS-provoked increase of contractile force. From the present study we conclude that the inotropic responses to alpha1-adrenoceptor and ET-receptor stimulation are, at least partially, caused by intracellular-formed ROS, that subsequently may activate the MAPKerk pathway and the NHE.

Pharmacological effects of (+)-nantenine, an alkaloid isolated from Platycapnos spicata, in several rat isolated tissues.

In this work, the potential activity of (+)-nantenine (a natural aporphin alkaloid) in several rat isolated tissues was studied. In rat isolated intact aorta, (+)-nantenine (0.05 - 0.5 microM) competitively antagonized with almost equal effectiveness the contractions produced by phenylephrine (PE) and 5-hydroxytryptamine (5-HT) in normal Krebs solution. However, at higher concentrations (2 microM), the alkaloid also reduced the maximal effect induced by these two agonists. In depolarizing Ca2+-free high KCl 50 mM solution, (+)-nantenine (1.5 - 6 microM) inhibited, in a non-competitive way, the increase in tension evoked by Ca2+ with depression of the maximum response. On the other hand, (+)-nantenine (3 - 30 microM) did not affect the contractile effect caused by okadaic acid (OA, 1 microM) while, however, this alkaloid totally relaxed, in a concentration-dependent fashion, the contractions produced by phorbol 12-myristate 13-acetate (PMA, 1 microM) in endothelium-containing rat aortic rings. (+)-Nantenine (1 - 30 microM) reversed and competitively antagonized the inhibitory action induced by B-HT 920 in electrically-stimulated rat vas deferens. In isolated rat atria, (+)-nantenine (3 - 10 microM) diminished the contraction frequency. (+)-Nantenine (3 microM) significantly reduced the depolarization (voltage)-activated transient (T-type) and sustained (long-lasting, L-type) barium inward currents [ IBa(T) and IBa(L) ] recorded in whole cell-clamped rat aortic myocytes. These results indicate that the pharmacological effects of (+)-nantenine observed at concentrations lower than 1 microM can be attributed to alpha 1 -adrenergic and 5-HT 2A receptor blocking properties whereas at higher concentrations (> 1 microM) the pharmacological activity of this natural compound may be also due to a decrease of Ca2+ influx through transmembrane calcium channels (calcium antagonist activity), to an inhibition of PKC actions and/or to an alpha 2 -adrenoceptor blockade.

Hypotensive activity of the ethanol extract of Pavetta crassipes leaves.

Pavetta crassipes leaf is routinely used locally in Nigeria for the management of respiratory disorders and hypertension. The hypotensive and other cardiovascular effects of Pavetta crassipes were investigated in cats and rats. The effects of the extract on rat and cat blood pressures, isolated rat atria, rat portal vein, isolated rat aorta and rat vas deferens were studied. Specific receptor antagonists (atropine, mepyramine, phentolamine, propranolol) were used to elucidate the underlying mechanism(s) involved in the cardiovascular changes induced by P. crassipes. The results revealed that the ethanolic extract of Pavetta crassipes lowered the blood pressures of cats and rats in a dose dependent manner. The extract also caused a concentration-dependent decrease in the force of contraction of the isolated rat atria and rat portal vein. The decreases in blood pressure values were attenuated in the presence of a beta-adrenoceptor antagonist, propranolol. The extract also attenuated isoprenaline-induced contraction of the rat atria. However, the extract did not affect contractions evoked by KCl, norepinephrine and 5-HT on the rat aorta. Pavetta crassipes contains biologically active substances that may be useful in the management of hypertension.

Cardiovascular Effects of Isorhamnetin and Quercetin in Isolated Rat and Porcine Vascular Smooth Muscle and Isolated Rat Atria

Isorhamnetin and quercetin produced endothelium-independent vasodilator effects in rat aorta, rat mesenteric arteries, rat portal vein and porcine coronary arteries. The effects of the two flavonoids were similar in arteries stimulated by noradrenaline, KCl, U46619 or phorbol esters but the two flavonoids were more potent in the coronary arteries than in the aorta. At high concentrations, they also induced a positive inotropic effect in isolated rat atria. Therefore, at least part of the in vivo effects of quercetin may result from its conversion to isorhamnetin which is the main metabolite of quercetin found in plasma. The arterial, venous and coronary vasodilator effects may contribute to the protective effects of flavonoids in ischaemic heart disease observed in epidemiological studies.

Safety of Dietary Supplements: Chronotropic and Inotropic Effects on Isolated Rat Atria.

We investigated the effects of dietary supplements on atria isolated from male Wistar rats. The examined supplements, which are increasingly used in Japan, those were Ginkgo biloba extract (GBE), catechins, isoflavones, sodium iron chlorophyllin and sodium copper chlorophyllin. GBE at 100-1000 microg/ml significantly increased the beat rate and the contractile force. Catechins at 1-100 microg/ml significantly potentiated the contractile force but did not effect the beat rates. However, isoflavones, sodium iron and sodium copper chlorophyllins did not change the contractile force or the beat rates. To identify the active ingredient of GBE, ginkgolide B, quercetin and amentoflavone on the atria were tested. Ginkgolide B weakened the contractile force. Quercetin potentiated the contractile force at only 30 microg/ml. Amentoflavone significantly increased the beat rate. From these findings, amentoflavone and quercetin were considered to be the principal ingredients of GBE producing the positive chronotropic and inotropic actions, respectively. In the case of catechins, (-)-epigallocatechin gallate (EGCg), one of the principal ingredients, produced inotropic actions. These findings suggest that there are some dietary supplements which affect cardiac function, such GBE and catechins.

Effects of chronic atrial fibrillation on gap junction distribution in human and rat atria

OBJECTIVESTo elucidate the structural basis for the electrophysiologic remodeling induced by chronic atrial fibrillation (AF), we investigated connexin40 and connexin43 (Cx40 and Cx43) expression and distribution in atria of patients with and without chronic AF and in an animal model of AF with additional electrophysiologic investigation of anisotropy (ratio of longitudinal and transverse velocities).BACKGROUNDAtrial fibrillation is a common arrhythmia that has a tendency to become persistent. Since gap junctions provide the syncytial properties of the atrium, changes in expression and distribution of intercellular connections may accompany the chronification of AF.METHODSAtrial tissues isolated from 12 patients in normal sinus rhythm at the time of cardiac surgery and from 12 patients with chronic AF were processed for immunohistology and immunoblotting for the detection of the gap junction proteins. The functional study of the cardiac tissue anisotropy was performed in rat atria in which AF was induced by 24 h of rapid pacing (10 Hz).RESULTSImmunoblotting revealed that AF did not induce any significant change in Cx43 content in human atria. In contrast, a 2.7-fold increase in expression of Cx40 was observed in AF. Immunohistologic analysis indicated that AF resulted in an increase in the immunostaining of both connexins at the lateral membrane of human atrial cells. A similar spatial redistribution of the Cx43 signal was seen in isolated rat atria with experimentally-induced AF. In addition, AF in rat atria resulted in decreased anisotropy with slightly enhanced transverse conduction velocity.CONCLUSIONSThis experimental study showed that AF is accompanied by spatial remodeling of gap junctions that might induce changes in the biophysical properties of the tissue.

Reactive oxygen species potentiate the negative inotropic effect of cardiac M2-muscarinic receptor stimulation.

The aim of the present study was to investigate the influence of reactive oxygen species (ROS) on the contractile responses of rat isolated left atria to muscarinic receptor stimulation. ROS were generated by means of electrolysis (30 mA, 75 s) of the organ bath fluid. Twenty minutes after the electrolysis period, the electrically paced atria (3 Hz) were stimulated with the adenylyl cyclase activator forskolin (1 microM). Subsequently, cumulative acetylcholine concentration-response curves were constructed (0.01 nM-10 microM). In addition, phosphoinositide turnover and adenylyl cyclase activity under basal and stimulated conditions were measured. For these biochemical experiments we used the stable acetylcholine analogue carbachol. The atria exposed to reactive oxygen species were influenced more potently (pD2 control: 6.2 vs. 7.1 for electrolysis-treated atria, P<0.05) and more effectively (Emax control: 40% vs. 90% reduction of the initial amplitude, P<0.05) by acetylcholine. In contrast, ROS exposure did not alter the responses to adenosine, whose receptor is also coupled via a Gi-protein to adenylyl cyclase. The basal (40% vs. control, P<0.05) as well as the carbachol-stimulated (-85% vs. control, P<0.05) inositol-phosphate formation was reduced in atria exposed to ROS. The forskolin-stimulated adenylyl cyclase activity was identical in both groups but carbachol stimulation induced a more pronounced reduction in adenylyl cyclase activity in the electrolysis-treated atria. Accordingly we may conclude that ROS enhance the negative inotropic response of isolated rat atria to acetylcholine by both a reduction of the positive (inositide turnover) and increase of the negative (adenylyl cyclase inhibition) inotropic components of cardiac muscarinic receptor stimulation. This phenomenon is most likely M2-receptor specific, since the negative inotropic response to adenosine is unaltered by ROS exposure.

Labedipinedilol-A: A vanilloid-based ?/?-adrenoceptor blocker with calcium entry blocking and long-acting antihypertensive properties

The combination of β-adrenoceptor blockade and vasodilator action have proved highly useful in antihypertensive therapy. Studies of the mechanisms of action of labedipinedilol-A that combine these effects within a single molecule are described in this report. Intravenous labedipinedilol-A (0.1–1.0 mg/kg) produced dose-dependent hypotensive and bradycardia responses for above 1.0 h, significantly different from nifedipine (0.5 mg/kg, i.v.)-induced hypotensive and reflex tachycardia activities in pentobarbital-anesthetized Wistar rats. Pretreatment with labedipinedilol-A also inhibited phenylephrine (20 μg/kg, i.v.)-induced hypertensive and (-)isoprenaline (0.5 μg/kg, i.v.)-induced tachycardia effects. Oral administration of labedipinedilol-A (5–50 mg/kg) in spontaneously hypertensive rats (SHR) reduced the blood pressure and heart rate for 24 h but did not increase heart rate. Labedipinedilol-A (10–7–10–5 M) competitively antagonized (-)isoprenaline (10–10–10–4M)-induced positive chronotropic and inotropic effects of the isolated rat atria and tracheal relaxation responses of the isolated guinea pig tissues. Labedipinedilol-A also prevented the rate-increasing effects of increased extracellular Ca2+ (3.0–9.0 mM) in a concentration-dependent manner. In the isolated rat aorta, labedipinedilol-A competitively antagonized CaCl2 and norepinephrine-induced contractions with pKCa–1 and pA2 values of 8.46 ± 0.05 and 8.28 ± 0.03 and had a potent effect of inhibiting high K+-induced vasocontraction. Furthermore, labedipinedilol-A, in an equal antagonist activity, inhibited norepinephrine-induced phasic and tonic contraction. In the cultured blood vessel smooth muscle cell (A7r5 cell line), KCl, norepinephrine, and Bay K 8644-induced intracellular calcium changes were decreased after application of labedipinedilol-A (10–9–10–6 M). The binding characteristics of labedipinedilol-A were evaluated in [3H]CGP-12177 binding to ventricle and lung and [3H]nitrendipine and [3H]prazosin binding to brain membranes in rats. The -logIC50 values of labedipinedilol-A for β1-, β2-, and α1-adrenoceptor and calcium channel, were 8.17 × 10–7 M, 8.20 × 10–7 M, 2.20 × 10–8 M, and 2.46 × 10–8 M, respectively. Labedipinedilol-A-induced sustained depressor effect was mainly attributed to its calcium entry and α-adrenoceptor blocking activities in the blood vessel. Sustained bradycardia effect resulted from β-adrenoceptor and calcium entry blocking, which deleted the sympathetic activation-associated reflex tachycardia in the heart. Drug Dev. Res. 49:94–108, 2000. © 2000 Wiley-Liss, Inc.

Intracellular acidosis modulates the stretch-induced changes in E-C coupling of the rat atrium.

By inducing a small reduction of the intracellular pH (0.18 units) with 20 mmol L-1 propionate we demonstrated that acidification changed the responses of isolated rat atria to stretch. Stretch (increase of the intra-atrial pressure) in normal pH increased the Ca2+ transients' amplitude (Indo-1 fluorescence) from 0.26 +/- 0.09 in 1 mmHg to 0.36 +/- 0.13 in 4 mmHg (P < 0.05, n=6), without affecting the diastolic [Ca2+]i level (n.s. n=6). The changes in Ca2+ balance during stretch were accompanied by a biphasic increase in the contraction force. Five minutes of continuous stretch increased the action potential duration (APD90%, P < 0.01, n=13) and decreased the APD15% (P < 0.001, n=13). During acidosis, the stretch-induced increase of the Ca2+ transient amplitude (0.4 +/- 0. 13 vs. 0.3 +/- 0.08, P < 0.05, n=6) was accompanied by the increase of the diastolic [Ca2+]i (1.16 +/- 0.07, P < 0.05, n=6) compared with non-acidotic control (1.06 +/- 0.06, n=6). Acidic intracellular pH also inhibited the stretch-induced changes in the action potentials (n=10) and slowed down the development of the contractile force during stretch. The results showed that acidosis modulates the mechanotransduction. It does this by interfering with the intracellular Ca2+ balance, inhibiting the Ca2+ extrusion mechanisms and reducing the Ca2+-buffering power of the cells. The physiological and pathological processes associated with stretch are therefore modulated by intracellular pH owing to its concerted effects on intracellular Ca2+ handling caused by a competitive inhibition of various Ca2+-binding molecules.

Cardiac effects of non-depolarizing neuromuscular blocking agents pancuronium, vecuronium, and rocuronium in isolated rat atria

Pancuronium, vecuronium, and rocuronium produce different cardiac effects. Using spontaneously beating right and electrically stimulated left rat atria, while measuring developed force, effective refractory period, and heart rate, we determined and compared the concentration-dependent cardiac effects of the compounds. The preparations were exposed to five progressively increasing concentrations of these compounds (10 −9, 10 −8, 10 −7, 10 −6, and 10 −5 mol/L). Pancuronium increased heart rate; vecuronium and rocuronium produced positive inotropic effects; and vecuronium shortened refractoriness. These effects may be the result of a blockade of the M 2 muscarinic receptors. However, the concentrations required to produce changes were higher than those observed in patients under neuromuscular blockade.

Synthesis and cardiovascular evaluation of N-substituted 1-aminomethyl-2-naphthols

Aseries of 1-alkylaminomethylnaphthols have been prepared. These compounds were readily prepared in good yields by addition of 2-naphthol to formalin and alkylamines. The hypotensive and bradycardiac effects of these compounds in normotensive rats as well as their in vitro inotropic and aortic contraction effects in isolated rat left atria and aorta have been evaluated. A higher depressor and bradycardiac activity was found for compounds substituted on nitrogen by naphthol with primary amines, i.e., ethylamine, propylamine, isopropylamine, or butylamine and with a cyclic secondary amine, i.e., pyrrolidinyl. These compounds produced biphasic changes in contractile force in isolated rat atria which was correlated to blood pressure and heart rate activity. 1-Isopropylaminomethyl-2-naphthol hydrochloride relaxed isolated rat aortic rings precontracted with high extracellular K + (80 mM) and Ca 2+ (1.9 mM). The suppressive effects of the compounds may involve a direct inhibition of Ca 2+ channels. The biological activity of these compounds can be explained in terms of substitution on nitrogen.

Potentiation of stretch-induced atrial natriuretic peptide secretion by intracellular acidosis.

We sought to investigate whether atrial myocyte contraction and secretion of the atrial natriuretic peptide (ANP) are affected in the same manner by intervention in intracellular Ca(2+) handling by acidosis. The effects of propionate (20 mM)-induced intracellular acidosis on the stretch-induced changes in ANP secretion, contraction force, and intracellular Ca(2+) concentration ([Ca(2+)](i)) were studied in the isolated rat atrium. The stretch of the atrium was produced by increasing the intra-atrial pressure of the paced and superfused preparation. Contraction force was estimated from pressure pulses generated by the contraction of the atrium. Intracellular Ca(2+) was measured from indo 1-AM-loaded atria, and ANP was measured by radioimmunoassay from the perfusate samples collected during interventions. Intracellular pH of the atrial myocytes was measured by a fluorescent indicator (BCECF)-based imaging system. Intracellular acidification caused by 20 mM propionic acid (0.18 pH units) potentiated the stretch-induced (intra-atrial pressure from 1 to 4 mmHg) ANP secretion, causing a twofold secretion compared with nonacidotic controls. Simultaneously, the responsiveness of the atrial contraction to stretch was reduced (P < 0.05, n = 7). Stretch augmented the systolic indo 1-AM transients in acidic (P < 0.05, n = 6) and nonacidic atria (P < 0.05, n = 6). However, during acidosis this was accompanied by an increase of the diastolic indo 1-AM ratio (P < 0.05, n = 6). Cooccurrence of stretch and acidosis caused an increase in systolic and diastolic [Ca(2+)](i) and potentiated the stretch-induced ANP secretion, whereas the contraction force and its stretch sensitivity were decreased. This mechanism may be involved in ischemia-induced ANP secretion, suggesting a role for ANP secretion as an indicator of contractile dysfunction.

Enantioselective synthesis and pharmacological evaluation of a new type of verapamil analog with hypotensive and calcium antagonist activities.

The syntheses and evaluation for cardiovascular activity in the rat of both enantiomers of a verapamil analog in which the cyano group has been replaced by hydroxyl. (+)- and (-)-alpha-[3-[[2-(3,4-Dimethoxyphenyl)ethyl]methylamino]propyl]- 3,4-dimethoxy-alpha-(1-methyl ethyl)benzyl alcohol were prepared from chiral sulfoxides produced by microbial biotransformations using Mortierella isabellina ATCC 42613 or Helminthsporium species NRRL 4671, and were examined for hypotensive and calcium antagonist activity using anaesthetized normotensive rats and isolated rat aorta and atria. The analogs showed a pharmacological profile similar to that exhibited by verapamil, possessing a remarkable hypotensive activity, accompanied by a significant bradycardia, in anaesthetized normotensive rats. In vitro, these analogs displayed clear inhibitory effects: in isolated rat aorta they inhibited, in a concentration-dependent fashion, the contractions and 45Ca2+ uptake induced by norepinephrine and high KCl, and in isolated rat atria the analogs considerably decreased the rate of contraction (negative chronotropic effects). No significant differences between the quantitative cardiovascular effects produced by the two enantiomers of the verapamil analogs were observed. The results suggest that, like that of verapamil, the cardiovascular activity exhibited by the new compounds seems to be due, at least in part, to a blockage of transmembrane calcium channels present in vascular smooth muscle cells.

Endotoxin-induced atrial natriuretic factor release: In vivo and in vitro studies

OBJECTIVE: We evaluated the effects of coliform endotoxin on the circulating levels of atrial natriuretic factor and renal function. To understand the direct effects of endotoxin in the release of atrial natriuretic factor by cardiac tissue, studies in isolated rat atria were performed. STUDY DESIGN: In vivo studies were used. Anesthetized dogs were studied, with one group receiving isotonic saline solution ( n = 6) and the other group receiving 50 μg/kg of coliform endotoxin ( n = 7) as a continuous infusion over a 4-hour period. Cardiovascular parameters, renal function, and circulating levels of atrial natriuretic factor were measured at specified time intervals. In another set of experiments with in vitro studies left atria from Sprague-Dawley rats were isolated and perfused. In the control group ( n = 9) the standard Krebs perfusate was used. In the endotoxin group ( n = 9) coliform endotoxin was added at a concentration of 250 μg/mL to the standard perfusate. Atrial pressure was used as an index of stretch, and atrial natriuretic factor was measured from the perfusate. RESULTS: Administration of endotoxin resulted in decreased blood pressure ( P < .05) with a concomitant increase in heart rate. Renal artery flow, however, showed an increase ( P < .05) initially followed by a return to its baseline value, with a sustained increase occurring in the saline solution control group. A significant ( P < .05) and sustained increase in the circulating levels of atrial natriuretic factor after endotoxin infusion did not prevent the decrease in fractional sodium excretion ( P < .05) and creatinine clearance despite an increase in the urinary output. Serum sodium, serum potassium, and osmolalities, however, remained relatively stable. The study pertaining to isolated atria showed that in the presence of low atrial pressures, addition of endotoxin had no significant effect on the release of atrial natriuretic factor. With the increase in atrial pressure atrial natriuretic factor release was significantly higher in the group directly exposed to endotoxin compared with the control group. CONCLUSIONS: These studies demonstrate that the slow infusion of coliform endotoxin results in increased circulating levels of atrial natriuretic factor. This increase is in part due to the direct effect of endotoxin on the heart as indicated by studies in isolated atria. Our data suggest that atrial natriuretic factor in endotoxemia acts in an integrative manner with other hormones on a variety of target organs to modulate cardiovascular function and fluid balance. (Am J Obstet Gynecol 1998;179:21-7.)