Hemodynamic and myocardial effects of long-lasting venodilation in the conscious dog: analysis of molsidomine in comparison with nitrates

Can preload-reducing therapy prevent disease progression in arrhythmogenic right ventricular cardiomyopathy? Experimental evidence and concept for a clinical trial

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy and a leading cause of sudden cardiac death in a young population. ARVC is especially common in young athletes. Mutations in different desmosomal genes have been identified causing dysfunctional cell-cell contacts. Reduced myocardial expression of plakoglobin in cell-cell contact complexes appears to associate with disease manifestation in patients harbouring mutations within other cell-cell contact genes. Experimental data suggest that preload reduction may be a simple and effective intervention to prevent disease progression and ventricular arrhythmias in ARVC. This review discusses the potential effects of this innovative approach and describes the design of the first controlled trial of preload-reducing therapy in patients with ARVC.

The nitric oxide donor molsidomine rescues cardiac function in rats with chronic kidney disease and cardiac dysfunction

We recently developed a rat model of cardiorenal failure that is characterized by severe left ventricular systolic dysfunction (LVSD) and low nitric oxide (NO) production that persisted after temporary low-dose NO synthase inhibition. We hypothesized that LVSD was due to continued low NO availability and might be reversed by supplementing NO. Rats underwent a subtotal nephrectomy and were treated with low-dose NO synthase inhibition with N(ω)-nitro-l-arginine up to week 8. After 3 wk of washout, rats were treated orally with either the long-acting, tolerance-free NO donor molsidomine (Mols) or vehicle (Veh). Cardiac and renal function were measured on weeks 11, 13, and 15. On week 16, LV hemodynamics and pressure-volume relationships were measured invasively, and rats were killed to quantify histological damage. On week 15, blood pressure was mildly reduced and creatinine clearance was increased by Mols (both P < 0.05). Mols treatment improved ejection fraction (53 ± 3% vs. 37 ± 2% in Veh-treated rats, P < 0.001) and stroke volume (324 ± 33 vs. 255 ± 15 μl in Veh-treated rats, P < 0.05). Rats with Mols treatment had lower end-diastolic pressures (8.5 ± 1.1 mmHg) than Veh-treated rats (16.3 ± 3.5 mmHg, P < 0.05) and reduced time constants of relaxation (21.9 ± 1.8 vs. 30.9 ± 3.3 ms, respectively, P < 0.05). The LV end-systolic pressure-volume relationship was shifted to the left in Mols compared with Veh treatment. In summary, in a model of cardiorenal failure with low NO availability, supplementing NO significantly improves cardiac systolic and diastolic function without a major effect on afterload.

The effect of a nitric oxide donor and an inhibitor of nitric oxide synthase on blood flow and vascular resistance in feline submandibular, parotid and pancreatic glands

The aim was to examine whether (1) blood flow and vascular resistance are altered in response to exogenous nitric oxide and (2) whether endogenous synthesis of nitric oxide participates in the haemodynamic regulation of the submandibular, parotid and pancreatic glands. Experiments were performed on anaesthetized, artificially ventilated cats. Mean arterial blood pressure, heart rate, blood gases, cardiac output and tissue blood flow were determined before and 15 min after intravenous administration of either the nitric oxide donor SIN-1 (3-morpholinosydnonimine, 1 mg/kg, n = 10) or the competitive nitric oxide synthase inhibitor NOLA (NG-nitro-L-arginine, 30 mg/kg, n = 9) blood flow was measured by a radioactive-labelled microsphere method. In the SIN-1 group, in spite of a serious decrease in mean arterial blood pressure (p < 0.001), the blood flow in the glands remained unchanged. The vascular resistance decreased after SIN-1 in the submandibular and pancreatic glands (p < 0.001 and p < 0.05, respectively), and was slightly reduced in the parotid. The NOLA increased mean arterial blood pressure (p < 0.01) and reduced the blood flow in the submandibular and pancreatic glands (p < 0.01 and p < 0.001, respectively), but the decrease in the parotid was not significant. Vascular resistance increased after NOLA in all three glands (p < 0.05, p < 0.001 and p < 0.05). These findings suggest that basal nitric oxide production in these exocrine glands is sufficient to modulate vascular resistance. Moreover, the release of endogenous NO from the nerves and/or endothelium is probably involved in the regulation of vascular tone. The nitric oxide-dependent component of blood-flow regulation, however, seems to be less pronounced in the parotid gland.

Evidence for the role of nitric oxide in the circulation of the dental pulp

Many authors have studied the hemodynamics of the dental pulp; however, there are scarcely any data regarding the involvement of the L-arginine/nitric oxide pathway in the regulatory mechanism. Thus, we have examined the physiological effects of (1) NG-nitro-L-arginine as an inhibitor of nitric oxide synthesis and (2) the nitric oxide donor 3-morpholinosydnonimine on blood flow and vascular resistance in the canines of anesthetized cats to study the potential involvement of nitric oxide in the regulation of dental vascular homeostasis. Mean arterial blood pressure, heart rate, blood gases, pH, cardiac output, and tissue blood flow were determined prior to and 15 min after i.v. administration of either NG-nitro-L-arginine (30 mg/kg, n = 9) or 3-morpholinosydnonimine (1 mg/kg, n = 7). Blood flow was measured by radioactive-labeled microspheres. There were no significant differences in baseline parameters between the two groups of cats. The dental pulp blood flow decreased to 53 +/- 13% (p < 0.01) of the control level after NG-nitro-L-arginine administration, while it decreased only slightly (to 82 +/- 12%) after 3-morpholinosydnonimine administration. The dental pulp's vascular resistance increased to 367 +/- 69% (p < 0.01) of the control level after NG-nitro-L-arginine, while it decreased to 73 +/- 10% (p < 0.05) of control after 3-morpholinosydnonimine. We found that the L-arginine/nitric oxide pathway plays an important role in the regulation of pulpal blood circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of SIN-1 on peripheral hemodynamics and viscoelastic properties of aorta in anesthetized rabbits

In closed-chest, non-barbiturate-anesthetized rabbits, we have used a computer-based parameter estimation method to evaluate the effects of a slow intravenous infusion of SIN-1 (15 micrograms/kg/min for 20 minutes) upon hemodynamic, geometric, viscoelastic, and energetic characteristics of the hindlimb arterial bed from the measurement of abdominal aortic diameter, blood flow, and blood pressure. To evaluate intrinsic effects of SIN-1 upon arterial wall characteristics, a moderate arterial bleeding (3 ml/kg) was performed to achieve a -10% lowering of arterial pressure, i.e., to reach an equivalent blood pressure reference threshold in the absence of the drug. The SIN-1 IV infusion induced a marked blood pressure lowering (-10.0 +/- 2.1%), resulting from a relaxing action on smooth muscle vasculature both in capacitive and resistive components of the hindlimb vascular tree, thereby eliciting a lowering in peripheral resistance (-22.8 +/- 3.1%) and an increased blood flow (+11.7 +/- 3.6%). SIN-1 enhanced vascular compliance (+28.0 +/- 2.2%) and lowered vascular input impedance (-31.2 +/- 8.9%), as confirmed by modulus and phase spectra. SIN-1 IV infusion contrasted bleeding effects by increasing blood flow and maintaining constant or increasing aortic diameter, both of them being lowered by bleeding. The relaxing effect elicited by SIN-1 was further demonstrated by changes in viscoelastic characteristics, and it was further associated with a decreasing energetic demand as well. The present results demonstrated that SIN-1, administered as a slow IV infusion, exhibits vasodilating properties by acting both on capacitive and resistive vessels of the systemic circulation.

Molsidomine: alternative approaches to treat myocardial ischemia

The long-acting antianginal drug molsidomine has been shown experimentally to reduce myocardial infarct size when administered prior to or after cardiac insult. This is due to several drug actions. Dilation of postcapillary capacitance vessels diminishes venous return, preload, heart dimensions, and myocardial oxygen consumption. Relaxation of stenosed conductive coronary arteries increases the perfusion of myocardial areas at risk of infarction due to enhanced collateral circulation. Increased regional blood supply nourishes predominantly subendocardial cardiac muscles as a result of reduction of extravascular coronary pressure, and resistance. The stable heart rate and cardiac contractility favor improved heart performance. The inhibition of platelet aggregation in vivo by molsidomine or its active metabolites, SIN-1 and SIN-1A, is linked to the stimulation of prostacyclin synthesis, inhibition of thromboxane release with induction of thrombosis and vasoconstriction, and enhanced concentrations of cyclic guanosine monophosphate. Dilation of coronary arteries after intracoronary administration of SIN-1, with inhibition of platelet aggregation by restrained release of adenosine diphosphate and stabilization of platelet membranes, facilitates the recanalization of stenosed arteries and reduces coronary muscle tone at the site of thrombosis. Activation of the human fibrinolytic system and drug-induced release of a plasminogen activator favor dysaggregatory effects. The drug's inhibiting actions on lipoxygenase products of arachidonate (e.g., 12-hydroperoxy-eicosatetraenoic acid and leukotrienes) may shift prostaglandin catabolism to cyclooxygenase products (e.g., prostacyclin) that protect against the expansion of ischemia and the induction of coronary spasm. Experimentally, the hemodynamic effectiveness of molsidomine can be antagonized by catecholamines (afterload effects) and dihydroergotamine (preload and afterload effects) respectively. Further clinical investigations will clarify the application of these mechanisms for the therapeutic success of the drug in human myocardial infarction.

Molsidomine on cardiovascular leukotriene D4 actions

Anaesthetized open-chest dogs were used to study the effects of intracoronary leukotriene D4 (LTD4; 0.5 micrograms/kg) on haemodynamics, the electrocardiogram (ECG), coronary blood flow in the left circumflex artery and coronary resistance in the absence or presence of the antianginal drug molsidomine (500 micrograms/kg i.v.). LTD4 increased left ventricular (LV) filling pressure from 6.5 +/- 3.8 to 14.7 +/- 3.2 mm Hg (P less than 0.01), decreased LV dP/dtmax from 2,500 +/- 200 to 1,240 +/- 205 mm Hg/s (P less than 0.05), elevated the S-T segment of the ECG from 0.3 +/- 0.2 to 2.4 +/- 0.6 mV (P less than 0.01), and coronary resistance from 3.4 +/- 0.9 to 33.7 +/- 4.8 mm Hg X min X ml-1 (P less than 0.001). Coronary artery blood flow fell from 33.8 +/- 2.7 to 3 +/- 3 ml/min (P less than 0.001). Molsidomine treatment 15 min prior to repeated intracoronary LTD4 application attenuated vasoconstrictor response to LTD4 and the subsequent elevation in total coronary vascular resistance. The negative inotropic actions of the eicosanoid were counteracted by molsidomine. Filling pressure decreased and no temporary signs of ischaemia were noted in the ECG. Inhibition of the cyclooxygenase enzyme activity by i.v. indomethacin (5 mg/kg) had no effects on the LTD4-induced haemodynamic alterations, the ECG, and coronary flow and resistance. The antagonistic molsidomine actions on haemodynamic and electrocardiographic LTD4 effects were not influenced by previous indomethacin treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of molsidomine on cardiac preload, coronary artery diameter, and coronary resistance

The vascular and hemodynamic effects of a single intravenous bolus injection of molsidomine (100 micrograms/kg) were studied in six chronically instrumented, conscious dogs. At this dose only a minimal, short-term effect on peripheral resistance was observed. However, there was a pronounced dilation of peripheral veins and a simultaneous increase of effective vascular compliance of more than 60%. At the same time, central blood volume decreased significantly (17%). Because of preload reduction, left ventricular end-diastolic volume and pressure decreased significantly for more than 1 hour. A significant increase of large coronary artery diameter (up to 7% occurred simultaneously. Coronary resistance vessels were not affected. All effects reached a maximum between 15 and 30 minutes and were observed for at least 4 hours. We conclude that molsidomine exerts a long-lasting effect on the large coronary arteries and on the peripheral venous system. As a result of the combined effects on cardiac preload and on epicardial artery conductance, the myocardial oxygen supply and the supply/demand ratio will be improved.

Hemodynamic effects of molsidomine, isosorbide dinitrate, and nifedipine at rest and during exercise

In the first study the hemodynamic effects of standard doses of molsidomine (2 mg intravenously), isosorbide dinitrate (ISDN) (5 mg sublingually), and nifedipine (20 mg sublingually) were assessed at rest and under exercise conditions in a group of 30 patients with coronary heart disease. With the patients at rest both molsidomine and ISDN were associated with prompt reductions in left ventricular end-diastolic pressure and mean pulmonary artery pressure, whereas nifedipine was associated with slight reductions in left ventricular end-diastolic pressure and mean pulmonary artery pressure that did not attain statistical significance. Nifedipine and ISDN caused a decrease in mean aortic blood pressure, which resulted in a reactive increase in heart rate that was only significant with nifedipine. After administration of molsidomine, there was no significant change in mean aortic pressure at rest. There were reductions in stroke volume index and cardiac index after administration of molsidomine and ISDN. Nifedipine, however, was associated with significant increases in stroke volume index and cardiac index. None of the three test substances caused changes of contractility parameters. Under exercise conditions reductions in left ventricular end-diastolic pressure, mean pulmonary pressure, and mean aortic pressure were documented following administration of molsidomine, ISDN, and nifedipine. There were no major changes in maximum heart rate or stroke volume index during exercise with any of the three drugs. However, nifedipine was associated with a significant increase in cardiac index, whereas molsidomine and ISDN produced no major changes.(ABSTRACT TRUNCATED AT 250 WORDS)

The activity of molsidomine in experimental models of ischemic cardiac disease

The cardioprotective and antithrombotic activity of molsidomine, a novel therapeutic agent for the treatment of coronary heart disease, was investigated in a series of animal models of myocardial ischemia. Molsidomine given to dogs with marked ST segment elevation (epicardial electrogram), induced by a reduction of left descending coronary artery (LAD) flow to 20% to 30% of the original value, resulted within 40 minutes in complete normalization of ECG changes. In another animal model molsidomine given either before or after occlusion of the LAD significantly reduced infarct size. All these molsidomine effects were accompanied by a marked lowering of preload, resulting in a reduction of extravascular coronary artery resistance and in increased blood flow toward the ischemic zones. In a model of myocardial ischemia and reperfusion in the anesthetized dog, molsidomine had a marked protective effect against the incidence of spontaneous ventricular fibrillation. This effect could also be attributed to the anti-ischemic activity of molsidomine, which would reduce the disparity between the refractory periods in normal and ischemic areas and thus increase ventricular stability. The antithrombotic activity of molsidomine was investigated in dogs in which the left circumflex coronary artery was electrically stimulated, a procedure that leads to thrombotic occlusion. Molsidomine in a dose-dependent manner prevented coronary thrombotic occlusion and reduced thrombus wet weight and the size of the resulting infarction. These effects of molsidomine were not related to its hemodynamic activity, since nitroglycerin and isosorbide dinitrate had similar hemodynamic effects but did not prevent coronary thrombosis. The antithrombotic activity of molsidomine is probably related to its ability to lower coronary venous blood thromboxane levels.

Unloading effects of molsidomine on peripheral circulation and cardiac hemodynamics in patients with acute myocardial infarction

The unloading mechanisms and side of peripheral action of the new antianginal drug molsidomine was compared with isosorbide dinitrate (ISDN) in 14 patients with acute myocardial infarction using a Swan-Ganz catheter and venous occlusion plethysmography. Sublingual molsidomine (2-4 mg) increased calf venous capacitance (CVC) (0.42 +/- 0.18 to 0.64 +/- 0.09 ml/100 ml, p less than 0.05) from 30 to 240 minutes, while simultaneously lowering of PCWP (25.9 +/- 4.9 to 15.8 +/- 7.3 mmHg, p less than 0.05) and CVP (9.3 +/- 3.7 to 5.8 +/- 3.5 cmH2O, p less than 0.05). Calf blood flow (CBF), calf vascular resistance (CVR), CI, TSPR and SWI were not affected significantly. Molsidomine reduced preload more than 240 minutes after its administration. Sublingual ISDN increased CBF into the initial 15 minutes (1.19 +/- 0.49 to 1.83 +/- 0.98 ml/100ml/min, p less than 0.05) and CVC from 5 to 60 minutes (0.42 +/- 0.19 to 0.68 +/- 0.24 ml/100ml p less than 0.01) while simultaneously lowering PCWP (24.3 +/- 2.2 to 14.6 +/- 4.5 mmHg, p less than 0.01) and CVP (9.0 +/- 2.8 to 5.5 +/- 3.5 cmH2O, p less than 0.05). Neither drug affected cardiac index, blood pressure or systemic vascular resistance. These data suggest that molsidomine significantly lowered elevated preload (PCWP/PCP) by dilating venous capacitance vessels. Its length of action was 240 minutes compared with 60 minutes obtained with ISDN, which suggests this new agent may be of marked benefit in the AMI patients suffering from backward failure uncomplicated by forward failure in whom continued preload reduction is necessary. (Results are expressed as the mean +/- standard deviation).

The effect of repeated intravenous and oral doses of molsidomine (N-carboxy-3-morpholino-sydnonimine-ethylester) on plasma renin activity and plasma catecholamine levels in conscious dogs

The responses of plasma renin activity (PRA) and plasma catecholamine levels to molsidomine, administered both intravenously and orally, were investigated in conscious trained dogs. Intravenous administration of molsidomine at increasing dosage up to 0.4 mg/kg with a constant dose interval of 4 hours did not lead to a sustained increase in PRA. By contrast, a significant increase in PRA was still present after 4 hours on administration of 0.4 mg/kg molsidomine by the oral route. This longer-lasting increase in PRA following oral administration is discussed in relation to the conversion of molsidomine to an active metabolite in the liver. A reduction of dose interval to 3 hours or less led to a marked cumulative increase in PRA. It appears that substances acting via venous pooling lead to persistent activation of the renin angiotensin aldosterone system (RAA system), which counteracts its primary therapeutic effect. A slight increase in plasma noradrenaline levels was observed in response to repeated oral administration of 0.4 mg/kg molsidomine at a dose interval of 2 hours, indicating participation of the sympathetic nervous system in the counterregulatory process.

Anti-ischemic effects of molsidomine in an experimental model of coronary artery stenosis

The effect of molsidomine, a novel antianginal agent, on the epicardial electrographic changes induced by reduced perfusion of the left anterior descending coronary artery (LAD) was investigated in the anesthetized dog. The LAD was cannulated and perfused at a constant volume with blood taken from a carotid artery. The perfusion volume was than reduced by approximately 75%. The sum of the ST-segment changes obtained from six unipolar epicardial leads was taken as a measure of myocardial hypoxia. Simultaneously, heart rate, blood pressure, left ventricular end-diastolic pressure, pulmonary arterial pressure, and heart contractility were also recorded. In control animals, reduction of the perfusion volume of the LAD resulted in a dramatic elevation of the ST segments lasting more than 4 hr. Molsidomine administered after the induction of the ischemia at a dose of 0.05 mg/kg i.v. resulted within 40 min in a complete normalization of the electrographic changes. This effect was evident for over 4 hr in spite of the continuous reduced perfusion of the LAD. The beneficial effect of molsidomine on the electrical changes paralleled the reduction of the left ventricular end-diastolic pressure. It is suggested that the effect of molsidomine on the ischemic electrographic changes is brought about by a reduction of the preload, resulting in a better perfusion of the ischemic zones.

Effect of molsidomine on spontaneous ventricular fibrillation following myocardial ischemia and reperfusion in the dog

The effect of the novel antianginal agent molsidomine on the incidence of spontaneous ventricular fibrillation during myocardial ischemia and reperfusion was investigated in the anesthetized dog. Molsidomine was administered as an intravenous bolus at the dose of 0.05 mg/kg. Twenty minutes later, the left anterior descending coronary artery was occluded for 90 min. During the occlusion period, molsidomine was given as a continuous intravenous infusion at the dose of 0.5 micrograms/kg per ml per min. After release of the occlusion, the animals that survived were monitored for another 30 min. Control animals received saline. In the control animals, coronary occlusion was accompanied by an increase in heart rate, heart contractility, left ventricular end-diastolic pressure, and blood pressure as well as by ventricular arrhythmias. Molsidomine either abolished or reduced both hemodynamic and electrical changes. During the reperfusion period, 10 out of 12 control animals died, and the deaths were from ventricular fibrillation; one out of eight molsidomine-treated animals also died of ventricular fibrillation. It is postulated that the protective effect of molsidomine rests on its hemodynamic effects resulting in a shift in blood flow toward the ischemic zones and, consequently, in an increase in ventricular electrical stability.

The effects of molsidomine on intracranial pressure in anaesthetized dogs

Measurements of intracranial liquor pressure were made during i.v. molsidomine administration in pentobarbital anaesthetized beagle dogs without thoracotomy, and compared with those after nitroglycerin. The administration of 100 micrograms/kg molsidomine decreased blood pressure by 14 mmHg and increased intracranial pressure by 3.7 cm H2O (P less than 0.05). No changes in heart rate and the alveolar end-tidal CO2 concentration were noted. The i.v. administration of 5 micrograms/kg nitroglycerin, however, decreased systolic blood pressure by 41 mmHg (p less than 0.05), increased heart rate by 40 bpm (p less than 0.01), elevated intracranial pressure by 3.2 cm H2O (p less than 0.05), and caused marked hyperventilation indicated by increased end-tidal CO2 concentration. Larger increases in intracranial pressure were related to larger pressure reductions. Thus, molsidomine produced significant increase in intracranial liquor pressure of longer duration (60 to 90 min of observation time). Nitroglycerin increased liquor pressure with a short duration of action and was about twenty time more effective with respect to intracranial pressure increase. In contrast to molsidomine, this was accompanied by significant decrease in systolic peripheral blood pressure.

Effects of molsidomine on the coronary circulation in anesthetized dogs

The intravenous effects of molsidomine on the coronary circulation, myocardial oxygen consumption, and hemodynamics were investigated in anesthetized, open-chest dogs. Left coronary artery flow was reduced after drug administration, while coronary resistance remained unaffected. The coronary arteriovenous oxygen difference did not change after molsidomine. Myocardial oxygen consumption was significantly reduced. Stroke work of the heart was diminished. Molsidomine caused a dose-dependent decrease in aortic and left ventricular pressures (after-load) as well as a sustained fall in left ventricular end-diastolic and mean pulmonary artery pressures (preload). Heart rate and contractility were only moderately affected. Stroke volume and cardiac output decreased significantly for the experimentation time, while total peripheral resistance increased after 0.25 mg/kg molsidomine. All observed effects of the drug can be explained by extracardiac effects: an increase in venous capacity. No direct effects of molsidomine on myocardial function could be noted. The fall in blood pressure was not induced by vasodilatation of peripheral arteriolar vessels but occurred as sequel of the reduced cardiac output following decreased ventricular filling. Molsidomine improved the oxygen supply-demand balance by decreasing external work of the heart and hence myocardial oxygen demand.

[Effect of molsidomine on hemodynamics and myocardial ischemia in patients with acute myocardial infarction (author's transl)]

The effect of molsidomine on hemodynamics and myocardial ischemia were studied in 48 patients with acute myocardial infarction. Between 8 and 12 mg of orally and intravenously administered molsidomine led to a significant reduction in left ventricular filling pressure. In response to 2 x 4 mg p.o., diastolic pulmonary arterial pressure fell from 12.1 to 8.8 mm Hg in patients with filling pressure below 20 mm Hg. Patients with left heart failure and left ventricular filling pressure above 20 mm Hg (Group 2) displayed a decline in filling pressure from 23.8 to 17.4 mm Hg following 12 mg i.v. In addition, right atrial pressure dropped significantly across the entire range of dosages. Although patients without left ventricular failure (Group I) showed a decline in cardiac output (5.7 to 4.7 l/min), this parameter remained unchanged in Group 2. Heart rate in Group 2 fell from 85 to 81 per min. Arterial blood pressure was reduced by a mean of only 10 mm Hg at high dosages and remained unchanged at lower dosages. No change was observed in peripheral resistance. The maximum effect was seen 30 min after oral administration. Three hours later, the effect was reduced by half. Only minimal activity could be observed after 8 h. The incidence of side effects was low, with transient headaches occurring in 8% of the patients. An intraindividual comparison with 1.6 mg of sublingually administered nitroglycerin demonstrated no significant difference in hemodynamic effectiveness (n = 11). Molsidomine, not unlike nitroglycerin, exerts a favorable effect on hemodynamics and myocardial ischemia. It acts primarily to reduce preload. The additional moderate effect on afterload with a slight decline in arterial pressure at high dosages may also be considered advantageous.

Increased effective vascular compliance and venous pooling of intravascular volume during sustained venodilation in conscious dogs

The hemodynamic effects of the long-acting antianginal drug molsidomine were studied in 8 chronically instrumented conscious dogs by measuring the partition of the intravascular volume and the effective compliance of the total vascular bed. The blood volume of the resting dogs was varied by +/- 4 ml/kg in a cycle of blood infusion, withdrawal and reinfusion within 12 minutes. Relating the observed alterations in mean right atrial pressure to the induced changes in intravascular volume, an effective compliance of 2.9 +/- 0.4 ml. mm Hg-1 . kg -1 (mean +/- SD) was found. Heart rate, total peripheral vascular resistance and the local capacity of the distal femoral vein did not change significantly during the cycle of volume alterations. Following 0.1 mg/kg molsidomine i.v., mean right atrial pressure was lowered by 1.6 mm Hg and mean left atrial pressure by 3.4 mm Hg; the effective compliance was elevated to 4.7 +/- 0.6 ml . mm Hg-1. kg -1 (p less than 0.001), and the central blood volume was lowered from 17.8 +/- 3.1 to 14.8 +/0 3.3 ml/kg (p less than 0.01), while the total blood volume remained constant. The decline in stroke volume and the reflexly induced increase in heart rate correlated with the control heart rate. Mean arterial pressure declined from 101 +/- 7 to 91 +/- 14 mm Hg (p less than 0.05) and total peripheral vascular resistance remained unaffected. It is concluded that molsidomine exerts exerts its hypotensive effect by dilation within the vascular low-pressure system and that this dilation can be described quantitatively in conscious animals by the analysis of the total effective vascular compliance.

Effects of molsidomine on coronary artery thrombosis and myocardial ischemia in acute canine experiments

Antithrombotic and hemodynamic properties of molsidomine (0.10 mg/kg i.v.) were evaluated in an in-vivo model of coronary artery thrombosis initiated by electrical stimulation for 6 h. Molsidomine prolonged time to vessel occlusion and prevented heart rate and end-diastolic pressure increase and contractility decrease. Infarct size was smaller after drug treatment related either to left ventricle (P less than 0.02) or to vessel area-at-risk (P less than 0.01). It is suggested that molsidomine has antithrombotic effects which might prevent acute coronary infarction.

Effect of molsidomine on coronary collateral blood flow in acute myocardial ischemia

The actions of molsidomine, a new antianginal agent, on coronary collateral blood flow and myocardial oxygen consumption were studied in anesthetized dogs with acute ligation of the distal third of the left anterior descending coronary artery. Molsidomine (50 and 100 microgram/kg, i.v.) produced a significant decrease in myocardial oxygen consumption, however no change occurred in collateral blood flow. These results suggest that the beneficial actions of molsidomine in myocardial ischemia are primarily due to a decrease in oxygen demand.

Determination of left ventricular dimensions with ultrasound

A new ultrasonic measuring system (UM 3) is described. In addition, the construction of simple piezoelectric transducers is outlined. These can be implanted either in the epicardium or in the endocardium of the left ventricle in anesthetized or conscious dogs. The total system has a high accuracy and linearity, and zero drift is small. An automatically controlled floating window excludes most artifacts due to unwanted echoes. Together with a modified delay-time measuring circuit, better recordings of dimensions are obtained. Sources of error due to the technique of implantation or due to electrical disturbances are described. A modified technique of implantation of endocardial transducers is presented.