Bernd Muller-Beckmann

Pharmacological characteristics of the stereoisomers of carvedilol

SummaryThe racemic compound carvedilol possesses two complementary pharmacological effects, vasodilation and β-blockade. TheR- andS-enantiomers of carvedilol and the racemate were investigated with respect to the β-blocking, vasodilating, and hypotensive actions. In agreement with results obtained with other β-blockers, only theS-enantiomer of carvedilol exerts β-blocking effects. In contrast, no substantial difference between the enantiomers could be seen with respect to α-blockade. The greater hypotensive activity ofS-carvedilol may be attributed to β-blockade, which inhibits counter-regulatory mechanisms provoked by vasodilation. From these results it is concluded that there is a rationale for using carvedilol as the racemate. Using theS-enantiomer would lead to relatively strong β-blockade with only a weak vasodilating effect. TheR-enantiomer alone would act only as a hypotensive agent without β-blockade.

Ca2+-sensitizing effect of BM 14.478 on skinned cardiac muscle fibres of guinea-pig papillary muscle.

A concentration-dependent increase in force development was obtained with BM 14.478 (10(-9)-5 X 10(-4) M) in skinned fibres of guinea-pig papillary muscles. Guinea-pig papillary muscles are standard preparations for evaluating inotropic effects and they were also used in the present case for evaluating the positive inotropic effect of BM 14.478. We therefore conclude that a marked calcium-sensitizing effect contributes to the positive inotropic effect obtained with BM 14.478 even at very low concentrations.

Haemodynamic profile of an inhibitor of phosphodiesterase III, adibendan (BM 14.478): comparison with nitroprusside and dobutamine in conscious dogs

1 This study was performed to investigate whether cardiac positive inotropic as well as peripheral vasodilator properties of adibendan contribute to its overall haemodynamic profile in conscious dogs. 2 Haemodynamic measurements were carried out in conscious chronically instrumented dogs after administration of adibendan, sodium nitroprusside or dobutamine. 3 The cardiovascular changes induced by adibendan (0.01 and 0.03 mg kg−1) resembled those of dobutamine (1.0–4.0 μg kg−1 min−1): left ventricular dP/dt60 (LV dP/dt60), stroke volume (SV) and cardiac output (CO) increased to a similar extent, but mean arterial pressure (MAP) and heart rate (HR) remained unchanged. 4 In contrast to dobutamine, higher doses of adibendan (0.1–1.0 mg kg−1) decreased MAP and LVEDP. These effects were of a similar magnitude to those observed following nitroprusside administration (0.5–12.5 μg kg−1 min−1). In contrast to nitroprusside, adibendan still showed additional effects on LV dP/dt60 and CO. 5 From these results, it is concluded that both the peripheral vasodilator and the cardiac positive inotropic action of adibendan contribute to its overall haemodynamic profile.

Differences in the nitrite ion formation and the toxicological findings between isosorbide dinitrate and isosorbide-5-mononitrate.

In the metabolism of isosorbide dinitrate (ISDN), fast denitration with the formation of nitrite ions and a mononitrate plays an important role. In contrast, the denitration of isosorbide-5-mononitrate (IS-5-MN) to isosorbide is very slow. Accordingly po administration of high doses of ISDN (92.5 and 236 mg/kg) in conscious dogs led to maximum nitrite concentrations in the blood of 0.9 and 3.3 mg/liter, respectively. In contrast, with equimolar doses of IS-5-MN (75 and 191 mg/kg) we were able to detect nitrite ions reliably only at the higher dose and this gave a maximum blood concentration of 0.4 mg/liter. The rise in nitrite ion concentration is followed by the formation of methemoglobin. As is known from the literature, there is a rise in the activity of alkaline phosphatase in the serum of rabbits in addition to methemoglobin formation following repeated administration of sodium nitrite. So we have specifically investigated whether this is also the case following ISDN and IS-5-MN administration. On po administration of 236 mg/kg ISDN/day to dogs, there was a continuous rise in alkaline phosphatase from about the 20th day onward which we did not observe after the equimolar dose of IS-5-MN (191 mg/kg). NaNO2, 35 mg/kg po, led to a comparable maximal rise in methemoglobin to that obtained with 236 mg/kg ISDN. Repeated po administration of 35 mg/kg NaNO2/day also caused a rise in alkaline phosphatase. It is concluded that the formation of nitrite ions from ISDN is the reason for the rise in methemoglobin and alkaline phosphatase. The lower formation of nitrite ions from IS-5-MN can also be of clinical importance, at least in certain cases.