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Keywords:

  • beta-adrenoceptor;
  • beta-agonist;
  • catecholamines;
  • detrusor relaxation;
  • human;
  • organ bath;
  • pig;
  • smooth muscle

Abstract

Aim:  Relaxant effects of different β-adrenoceptor agonists on porcine and human detrusor were examined. Thus, the β-adrenoceptor subtype mainly responsible for relaxation in the detrusor muscle of pigs was characterized. Additionally, different effects of several β-agonists in both species were shown.

Methods:  Experiments were performed on muscle strips of porcine and human detrusor suspended in a tissue bath. The relaxant effects of the non-selective β-agonist isoprenaline, the selective β2-agonists procaterol, salbutamol and the selective β3-agonists BRL 37344, CL 316 243 and CGP 12177 on potassium-induced contraction were investigated. The inhibitory effect of different substances on the maximum contraction and the rank order of potency for endogenous catecholamines was determined in pigs. Furthermore, concentration-relaxation curves were performed for pigs and humans.

Results: Pigs: In the pre-treatment experiments isoprenaline and procaterol showed similar effects. The concentration–response experiments showed that the maximum relaxation induced by procaterol and salbutamol was more than 90%, not significantly different from isoprenaline, whereas the maximum relaxations of CL 316 243, BRL 37344 and CGP 12177 amounted to 68, 70 or 30%, respectively. Rank order of potencies was isoprenaline ≥ adrenaline > noradrenaline. Humans: Isoprenaline, procaterol, salbutamol and CL 316 243 showed a maximum relaxation of 80, 41, 24 and 35% and pD2 values of 6.24, 5.65, 5.48 and 5.55, respectively.

Conclusion: β2-receptors play a main functional role in mediating relaxation of porcine detrusor. Selective β2- and β3-agonists similarly relax the human detrusor. Effects were smaller compared with the pig.