The new long-acting coronary artery dilator molsidomine and its metabolite SIN-1

The effects of the nitric oxide donor SIN-1 on ischemia-reperfused cutaneous and myocutaneous flaps

Ischemia-reperfusion injury causes tissue damage that leads to a decrease in bioavailability of nitric oxide. The authors hypothesized that an exogenous supply of nitric oxide will have beneficial effects on survival of skin and skeletal muscle subjected to ischemia-reperfusion injury. By using the nitric oxide donor SIN-1 (3-morpholino-sydnonimine) the effects of direct intraarterial infusion of an exogenous source of nitric oxide in reperfused flaps was studied. Bilateral island buttock skin flaps and latissimus dorsi myocutaneous flaps were elevated in eight pigs, for a total of 32 flaps. Flaps were subjected to 6 hours of ischemia followed by 18 hours of reperfusion. Flaps on one side of each animal were randomized to be treated with the nitric oxide donor (treatment group). The contralateral side was treated with an equivalent volume of saline vehicle (infusion control) SIN-1, or saline was administered as a continuous direct intraarterial infusion at the onset of reperfusion and continued during the observation period. Outcomes measured were tissue neutrophil accumulation by using myeloperoxidase assay and tissue survival (intravenous fluorescein and nitroblue tetrazolium for skin and muscle, respectively). In both skin and myocutaneous flaps, SIN-1 treatment caused a significant improvement in survival and a decrease in neutrophil accumulation. Nitric oxide may play an important role in the pathophysiologic process of ischemia-induced reperfusion injury in skin and skeletal muscle. Nitric oxide donors may be a promising family of therapeutic agents for the prevention of ischemia-induced reperfusion injury in cutaneous and myocutaneous flaps.

SIN-1 has no direct myocardial anti-ischemic action

Anti-ischemic drugs may develop their cardiac activity via peripheral (reduction in preload and/or afterload) or cardiac (coronary vasculature, myocardial cell metabolism) effects. The aim of the study was to investigate whether SIN-1, the active metabolite of molsidomine, develops a direct myocardial anti-ischemic property. Three groups of seven patients each were treated with 0.4 mg SIN-1 administered via either the intracoronary (IC) or intravenous (IV) route, or with placebo in a double-blind randomized investigation. SIN-1 had no influence on either the ischemic parameters in the surface electrocardiogram (ECG) or the intracoronary ECG. There was also no change in peripheral or central hemodynamics or in the severity of angina following this low IC or IV dosage. There is no evidence of a direct myocardial anti-ischemic response of SIN-1. The well known anti-ischemic activity of SIN-1 or molsidomine has to be attributed to the proven peripheral and cardiac vascular responses.

Response of coronary arteries to nitrates, the EDRF-donor SIN-1, and calcium antagonists

Intracoronary drug administration is an important tool to study coronary effects without interaction of systemic effects. The difficult methodological aspects and the results of clinical trials in which the effects of vasodilating drugs were evaluated with respect to coronary dilatation are reviewed. Major (coronary substrate, study design) and minor (measuring devices, methods of evaluation) methodological problems make it difficult to precisely evaluate pharmacological effects such as dose-response relationship, duration of action, and selective responses, and to compare the effects of different drugs. From a clinical point of view, knowledge of the maximal effect (EDmax) in coronary stenoses and the duration of action is essential. NO-donors tend to act stronger than CA-channel blockers which may be attributable to their different modes of action. Among those NO-donors investigated, SIN-1 showed stronger effects than nitroglycerin. Only with SIN-1 were maximal effects obviously achieved. The additional administration of nitroglycerin or nisoldipine never led to a more prominent dilatation. In coronary stenoses, the underlying morphology causes a wider range of responses than is seen in normal segments: deendothelialized stenoses with high coronary tone show a larger dilatation, while fully sclerotic stenoses may not react.

Reproducible uniform coronary vasomotor tone with nitrocompounds: prerequisite of quantitative coronary angiographic trials

In quantitative analysis of repeated coronary angiograms, a variable vasomotor tone of the epicardial coronary arteries may influence the accuracy of the results. Therefore, we evaluated the extent and reproducibility of coronary artery dilation with nitrocompounds. In 32 patients with coronary artery disease, the vasodilatory response of angiographically normal coronary segments to different nitrocompounds was analyzed with the computer-assisted contour detection system CAAS. Twenty patients received 5 mg or 10 mg of isosorbide dinitrate sublingually. After 10 to 15 min, a maximal diameter increase was measured with an average of 16 +/- 11% (5 mg: P less than 0.01) and 28 +/- 13% (10 mg: P less than 0.001) from control. Another 12 patients received 0.025 mg per kg body weight of SIN-1, the active metabolite of molsidomine, as an intravenous infusion over 5 min. A comparable maximal dilation (29 +/- 5%; P less than 0.001) occurred after 10 to 15 min and could not be enhanced further with 0.8 mg nitroglycerin administered sublingually (28 +/- 7%; n.s.). One hour after square root of Sin-1, coronary dilation was still 24 +/- 8% (P less than 0.001 compared with control), and 0.8 mg of nitroglycerin sublingually reestablished the previous maximal dilation of 28 +/- 8%. We conclude that high doses of nitrocompounds induce a reproducible maximal coronary dilation that eliminates a substantial source of error in quantitative analysis of repeated coronary angiograms. At present, sublingual administrations of either 10 mg isosorbide dinitrate once or 0.8 mg nitroglycerin repeatedly seem to represent the easiest practicable modes to achieve maximal coronary vasodilation for an adequate period.

Elimination of variable vasomotor tone in studies with repeated quantitative coronary angiography

In quantitative coronary angiographic studies, unintentional changes of coronary vasomotor tone may have a significant influence on the coronary artery diameters, thereby increasing the variability in the measurements. To obtain objective data on these measurement variabilities, two protocols were designed to assess the influences of ionic and nonionic radiographic contrast media on the mean diameters of angiographically normal coronary arteries. The vessel sizes were determined with the CAAS using automated edge detection techniques. In 21 patients (study no. I), coronary angiograms were taken in identical angiographic projections before (control), and immediately following several (at average 7) subsequent diagnostic dye injections administered over a period of about 7 min. The ionic contrast agent diatrizoate 76% induced a coronary dilation of 19 +/- 7% (mean +/- s.d., p less than 0.001; n = 10); the nonionic agent iopromide 370 increased the coronary artery diameters by only 6 +/- 4% (p less than 0.01; n = 11). In another 11 patients (study no. II) coronary angiograms were obtained using the nonionic contrast medium iopamidol 300 at 5, 8, 10 and 11 min after the control acquisition; this protocol was repeated in the same patients with diatrizoate 76%. With iopamidol, coronary diameter changes were not significant at any time; with diatrizoate, however, coronary dilation was measured at 10 min (2 +/- 2%; p less than 0.01) and at 11 min (10 +/- 3%; p less than 0.001). In a third study it was tested, whether standardization of coronary vasomotor tone (e.g. in coronary angiographic follow-up studies) is possible by the induction of a reproducible maximum coronary dilation with nitrocompounds. In 12 patients, the mean diameters of angiographically normal coronary segments were analyzed before and at various times after i.v. administration (over 4 min) of 0.025 mg SIN-1/kg bodyweight. Coronary dilation was maximal at 10 or 15 min after the onset of the SIN-1-infusion (29 +/- 5%; p less than 0.001). 0.8 mg nitroglycerin given s.l. at 15 min did not further dilate the coronary arteries (28 +/- 7%). One hour after SIN-1, coronary dilation still amounted to an average of 24 +/- 8% (p less than 0.001) and became 'maximal' again, when 0.8 mg nitroglycerin was again administered sublingually (28 +/- 8%; p less than 0.001). In conclusion, short-term variability of coronary vasomotor tone induced by ionic radiographic contrast media can be eliminated by the use of nonionic contrast agents and observation of injection intervals of at least 2 min. In quantitative coronary angiographic follow-up studies, as well as during acute interventions (e.g., PTCA), identical baseline vasomotor tone can be achieved by induction of the maximal coronary dilation using nitrocompounds.

Comparison of haemodynamic effects of nifedipine and molsidomine in patients with coronary artery disease

The haemodynamic effects of oral nifedipine 20 mg and molsidomine 4 mg were compared in 24 patients with coronary artery disease. Molsidomine unlike nifedipine caused a significant fall in mean pulmonary artery pressure and left ventricular end-diastolic pressure. Both drugs caused a significant and comparable reduction in systolic and diastolic blood pressure. Although only nifedipine significantly reduced systemic vascular resistance the difference between the drugs was not significant. The heart rate was significantly increased by nifedipine but not by molsidomine. The ejection phase indices were all increased by molsidomine and the increment in the mean normalized systolic ejection rate was significantly greater than that due to nifedipine. The left ventricular end-systolic volume index decreased significantly after molsidomine but not nifedipine. Neither drug significantly affected left ventricular end diastolic volume index, stroke volume index, maximal rate of rise of left ventricular pressure or left ventricular stroke work index.

Nonresponsiveness to antianginal therapy--a frequent problem?

Nonresponsiveness to anginal treatment varies greatly and may be due to either the pathophysiology of the patients or the special pharmacology of different antianginal drugs. Therefore, individualized therapy, taking all aspects of patient and drug into account to improve responsiveness, seems desirable. Patients may vary--thus influencing the outcome of antianginal therapy--with respect to the severity of the disease, vasospastic components, and the pattern of organic vessel involvement. Drugs differ with respect to the ease of dose-finding, tolerance, the extent of spasmolytic activity, side effects, and paradoxical effects. In no patient with coronary artery disease is the outcome to treatment predictable, even if a full diagnostic evaluation of the patient has been performed. For example, the individual relevance of angiographically documented vasospastic components in patients with underlying organic multivessel disease can hardly be predicted, and therefore the appropriate choice of an antianginal drug is difficult. In addition, a full invasive evaluation of all coronary patients, only to find arguments for the optimal drug therapy, is not feasible. Therefore, the empiric approach is recommended for daily routine. Drugs are preferred that usually provide a high response rate and the smallest cause for concern.

[Molsidomine in the treatment of coronary insufficiency]

Molsidomine, a predominantly venous vasodilator, has been coronary disease. The basic mechanism of its anti-anginal effect is a reduction in myocardial oxygen consumption due to a fall in left ventricular end-diastolic pressure resulting from the vasodilator action of the drug. To this may be added direct dilatation of the main coronary vessels on the surface of the heart, which may account for part in its therapeutic effects in unstable and vasospastic angina. The effectiveness of molsidomine has been evaluated by controlled drug versus placebo or drug versus reference anti-anginal drug studies in 3 types of angina pectoris: exertion, unstable and vasospastic. The usefulness of the drug has also been established in acute and chronic left ventricular failure of ischaemic origin. Because of its high bioavailability when administered orally, molsidomine shows little inter-individual variations in its pharmacodynamic effects. Unlike nitrates, it can be administered for long period without gradual loss of activity with time. Finally, on several experimental models molsidomine has been shown to exert an antiplatelet effect, but the therapeutic implications of this finding have yet to be evaluated.