Summary
The β-sympathomimetic effect of prenalterol was investigated on the electrically driven left atrium as well as on the tracheal chain of the guinea pig.
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1.
On the atrium driven at 2 Hz prenalterol caused a positive inotropic effect with a pD2-value of 7.0±0.08 (N=4). Compared to isoprenaline (1.0) its intrinsic activity amounted to 0.3.
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2.
On the tracheal chain prenalterol caused very little relaxation. Its intrinsic activity was virtually negligible when compared with those of fenoterol (1.0) or noradrenaline (1.0); it amounted to 0.07 only.
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3.
On the atrium the positive inotropic effect of prenalterol vanished after 1 hour of incubation. At this time the concentration-response curve for isoprenaline was shifted dose-dependently to the right. The pD2-value for isoprenaline was significantly diminished (P<0.001) by prenalterol, 10−6 M, from 8.36 to 7.14.
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4.
Likewise, on the trachea prenalterol caused a pronounced, dose-dependent shift of the concentrationresponse curves for fenoterol as well as for noradrenaline to the right.
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5.
The results presented here show that on β-adrenoceptors of the guinea pig prenalterol is acting like a partial agonist in the left atrium, but as full antagonist in the trachea.
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This work was supported by Deutsche Forschungsgemeinschaft
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Rohm, N., Wagner, J. & Schümann, H.J. The lack of a pronounced preference of prenalterol for the beta-l-adrenoceptor subtype. Naunyn-Schmiedeberg's Arch. Pharmacol. 315, 85–88 (1980). https://doi.org/10.1007/BF00504235
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DOI: https://doi.org/10.1007/BF00504235