Summary
The present study was undertaken to characterize β-adrenoceptors of the canine saphenous vein and their distribution along this vessel. In a first series of experiments, concentration-response curves to isoprenaline and forskolin were compared on strips taken from proximal and distal portions of the vein. The tone of the strip was previously increased by phenylephrine to one of the three levels: about 85, 70 and 55% of the maximum, which corresponds to 3.08±0.16 and 2.96±0.17 (n = 6) N·g−1, for proximal and distal strips, respectively. The maximal relaxation to isoprenaline was significantly larger in the distal than in the proximal portion, for responses starting at 85 and 70% of the maximum tone. In contrast, forskolin caused 100% relaxation, both proximally and distally, irrespective of the previous tone.
In a second series of experiments, the relaxation to dobutamine and terbutaline was compared in proximal and distal portions after the tone had been elevated by adrenaline, noradrenaline and phenylephrine to about 70% of the maximum. When the tone was increased by adrenaline, the relaxation in response to 2.7 μmol·l−1 dobutamine was larger than that to 2.7 μmol·l−1 terbutaline both in proximal and distal portions, while when it was increased by noradrenaline, the relaxation to terbutaline was larger than that to dobutamine in the proximal portion; in the distal portion, dobutamine and terbutaline were equieffective. When the tone was increased by phenylephrine, dobutamine and terbutaline caused equivalent relaxations proximally, but distally the relaxation to dobutamine was larger than that to terbutaline.
In a third series of experiments, the antagonism exerted by atenolol and by the compound ICI-118,551 on the relaxation to dobutamine and terbutaline was compared proximally and distally. Both proximally and distally atenolol was more effective against dobutamine than against terbutaline, while the compound ICI-118,551 was effective only against terbutaline.
It is concluded that β1- and β2-adrenoceptors exist in the canine saphenous vein and that the effectiveness of β-adrenoceptor stimulation increases from the proximal to the distal portion of this vessel due to a progressive increase in the density of β1-adrenoceptors.
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Guimaraes, S., Mota, A. & Begonha, R. The effectiveness of β-adrenoceptor stimulation and the contribution of β1-adrenoceptors increase from the proximal to the distal part of the canine saphenous vein. Naunyn-Schmiedeberg's Arch Pharmacol 347, 596–600 (1993). https://doi.org/10.1007/BF00166942
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DOI: https://doi.org/10.1007/BF00166942