[Adrenergic regulation of contractile activity of smooth muscles in umbilical vessels]

The effect of agonists and antagonists of alpha- and beta-adrenoreceptors on mechanical properties of the smooth muscle was studied in the isolated muscle strips of the human umbilical artery and vein. Noradrenaline was shown to cause the contraction of smooth muscles of the umbilical vein. Tonic and phase components in the contraction process were observed. Isoprenaline caused tonic contraction of the muscle strip. Phentolamine, and alpha-adrenoblocker did not inhibit the stimulating activity of noradrenaline. In presence of obsidane (beta-adrenoblocker) noradrenaline triggered the contraction with lesser tonic component as compared to the initial one. So the selective stimulation of beta-adrenoreceptors of smooth muscles of the umbilical vein by isoprenaline and blocking of the same receptors by obsidane have proved that activation of alpha-adrenoreceptors is responsible for the phasic component of contraction, while that of beta-adrenoreceptors--for the tonic component of contraction. As both alpha- and beta-adrenoblockers in smooth muscles of the umbilical artery inhibit the noradrenaline-induced contraction, it was concluded that the differentiation of adrenoreceptors of the vessel is rather low.