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The study was conducted on 30 New Zealand rabbits weighing 3-4 kg from which sample strips of the abdominal aorta were collected. The study investigated the in vitro reaction of rabbit aorta smooth muscle to ligands binding to beta-adrenergic receptors. The response of aortic strips to beta-adrenergic receptor agonists (dobutamine, isoproterenol, salbutamol) and the influence of beta-adrenergic receptor antagonists (propranolol, betaxolol) on contractile activity was determined. All tested agonists induced contraction of the rabbit abdominal aorta muscle in a concentration-dependent manner (dobutamine >> isoproterenol > salbutamol). Enhanced reaction to low concentrations of agonists (dobutamine, isoproterenol) after administration of propranolol and inhibition of contractility in the presence of high concentrations thereof (dobutamine, salbutamol) was observed. Maximal reaction to agonists decreased after betaxolol pretreatment. The results indicate that all the substances with beta-agonist activity also possess contracting properties (presumably by acting at alpha-adrenergic receptors), but are much weaker in the case of isoproterenol and salbutamol than for dobutamine. Propranolol and betaxolol reduce the contractile response of smooth muscle using probably other mechanisms than those associated with adrenergic receptors.

The aim of the study was to demonstrate the effect of selected agonists and antagonists of alpha-adrenergic receptors on muscle contractility of the rabbit abdominal aorta in vitro with particular emphasis on alpha2-adrenergic receptor subtypes. The study was conducted on 30 New Zealand breed rabbits from which specimens of the abdominal aorta were collected. The sections were set up in an automatic water bath in a Krebs-Henseleit buffer at 37 degrees C. The experiments showed that alpha1-adrenergic receptors played the main role in the contractile response ofthe rabbit abdominal aorta. Stimulation of alpha1-adrenergic receptor by administration ofphenylephrine resulted in an increase in smooth muscle tonus ofthe rabbit abdominal aorta by an average of 4.75 mN. The reaction after stimulation of alpha2-adrenergic receptors by similar doses of their agonists was much weaker. Prolonged tissue response time and time needed to reach maximum tonus for alpha2-adrenergic receptor agonists were observed. The obtained results confirm the thesis that the alpha1-adrenergic receptor is the most important factor controlling the contractility of the rabbit abdominal aorta, but the alpha2-adrenergic receptor is also involved in maintaining muscle tissue tonus.