The aim of the study was to demonstrate the effect of xylazine and selected antagonists of α2 -adrenergic receptors on the contractility of the human aneurysmal abdominal aorta compared with the contractility of the abdominal aorta of healthy pigs in vitro. The study was conducted on 34 aneurysmal human abdominal aorta sections and 28 unchanged porcine abdominal aorta sections. The pigs weighed between 50 and 70 kg. The influence of xylazine was investigated. The experiments also examined the impact of xylazine on sections preincubated with α2 -antagonists (BRL 44408, RX 821002, yohimbine). The application of xylazine in the incubation chamber evoked a similar relaxant response in human and porcine material. However, the increasing concentration of the α2 -agonist applied to sections preincubated with α2 -antagonists (BRL 44408, RX 821002) caused their contraction, and this reaction was much stronger in the porcine material. The results demonstrate that after the inhibition of α2 -receptors, xylazine induces contraction due to non-specific α1 -adrenergic receptor activation. The much weaker reaction in the human sections may indicate a reduced number of α1 -adrenergic receptors resulting from their decreased expression and/or the thinning of the smooth muscle layer. The application of yohimbine at a concentration of 10 µM and then of xylazine in the chamber with the porcine material induced a decrease in muscle tonus. This phenomenon is not entirely clear, but it appears that yohimbine at a high concentration behaves like a non-specific α1 -antagonist and causes a relaxant response.
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