The effectiveness of beta-adrenoceptor stimulation and the contribution of beta 1-adrenoceptors increase from the proximal to the distal part of the canine saphenous vein.

The present study was undertaken to characterize beta-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 mumol.l-1 dobutamine was larger than that to 2.7 mumol.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.(ABSTRACT TRUNCATED AT 250 WORDS)