Analysis of ouabain-induced contractions in isolated coronary arteries

Conformational flexibility of serotonin1A receptor ligands from crystallographic data. Updated model of the receptor pharmacophore

Preparation and affinity to 5-HT1A and 5-HT2A receptors of new buspirone analogues 7-17 are reported. The compounds possess high to low affinity to 5-HT1A and moderate to low to 5-HT2A receptors. The crystal structures have been determined for compounds 11, 12, 13, and 14. For low affinity ligand (15) of 5-HT1A receptor conformational analysis was performed and compared with similar analyses performed for know high (buspirone 1) and very high (WY-48,723 2) affinity ligands of the receptor. Structure-activity relationship is discussed for the affinity to 5-HT1A receptor. A three-point pharmacophore explaining interactions of buspirone-like molecules with the receptor binding site is proposed.

Nifedipine antagonizes ouabain-induced ST-segment changes and derangement of epicardial activation pattern in isolated rabbit hearts

Isolated rabbit hearts, perfused according to the Langendorff technique were treated with 0.2 mumol/l ouabain or with a combination of 0.2 mumol/l ouabain and 3 nmol/l nifedipine. In a second series of experiments, a combination of 0.2 mumol/l ouabain with 0.2 mumol/l nitroglycerin was examined. Under this treatment, coronary flow and left ventricular pressure were continuously measured and, furthermore, the epicardial potential distribution was mapped with high temporal (4 kHz/channel) and spatial resolution (256 electrodes, arranged in 4 plates with 64 electrodes each, 8 x 8 matrix with 1 mm mesh size). Ouabain led to the expected positive inotropy of 10%, but also to a decrease in coronary flow of 15%. Besides these changes a nearly generalized ST-segment elevation could be observed. Moreover, the epicardial activation pattern was disturbed by changes in the location of epicardial breakthrough-points. Concomitantly, the epicardial activation vector field was deranged. Under the additional influence of nifedipine, coronary flow was reduced by only 5%, whereas the positive inotropic effect remained unchanged. The epicardial ST-elevation was diminished significantly and there was no derangement in the process of epicardial activation. Nitroglycerin led to an increase in relative coronary flow comparable to that observed under nifedipine but did not antagonize the disturbances of the process of activation by ouabain and only partially inhibited ST-elevation. Hence, it is concluded that ouabain already provokes coronary vasoconstriction in therapeutic concentrations leading to ST-elevation and prearrhythmic changes in the process of excitation. These changes could be diminished by additional treatment with nifedipine, but not with nitroglycerin.

Ouabain-induced contraction of vascular smooth muscle in spontaneously hypertensive rats and the effect of hydralazine

The effect of ouabain (10(-3) M) on contractile responses of SHR (spontaneously hypertensive rat) and WKY (Wistar-Kyoto rat) aortas and mesenteric arteries was studied. Ouabain addition caused a rapid contraction of aortic strips with a steeper rate of rise and a larger maximal force development in strips from SHR than WKY. This difference in contractile response is known to occur in the prehypertensive period of SHR (4-week-old). Phentolamine (10(-6) M) pretreatment had no effect on the ouabain-induced contraction but partially suppressed it in both SHR and WKY aortas when diltiazem (10(-5) M) was also added. The difference in the ouabain-induced contractions of SHR and WKY aortas was more apparent in the residual contraction during suppression by diltiazem. The 45Ca uptake in the presence of ouabain was significantly larger in the early period of incubation in SHR aorta than in WKY aorta. The ouabain-induced contraction of hydralazine-treated SHR aorta from the prehypertensive period was very similar to that of non-treated WKY aorta. These results suggested that the abnormality of the ouabain-induced contraction in SHR arterial smooth muscle could have arisen from an increased Ca2+ movement due to Ca2+ leakage when ouabain inhibited the Na+-pump in the membrane. This abnormality seems to start during the prehypertensive period and continue in the hypertensive stage.