Noradrenaline modulates smooth muscle activity of the isolated intravesical ureter of the pig through different types of adrenoceptors

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Abstract
We have studied the effects of α‐ and β‐adrenoceptor agonists and antagonists on both phasic peristaltic activity and basal tone of the isolated intravesical ureter of the pig by means of isometric techniques in vitro. Spontaneous phasic activity was exhibited by 21% of pig intravesical ureter preparations manifested as rhythmic contractions with average frequency and amplitude of 2.54 ± 0.18 min−1 and 1.48 ± 0.16 g (n = 31), respectively. Adrenaline, noradrenaline and phenylephrine induced concentration‐dependent increases in both phasic activity and basal tone of ureteral preparations, all three agonists being more potent in modifying ureteral phasic activity than baseline tone. B‐HT 920, B‐HT 933 and clonidine had no significant effect. Phentolamine (10−9 − 10−7 m) and prazosin (3 × 10−11 − 3 × 10−8 m) significantly inhibited increases in both frequency of phasic activity and baseline tone induced by a submaximal dose of noradrenaline. Rauwolscine (10−9 − 10−7 m) affected only the tone evoked by noradrenaline and higher concentrations of this antagonist were needed to block phasic activity. Pretreatment of ureteral strips with the β‐adrenoceptor antagonist, propranolol (10−6 m), significantly increased the maximum contraction evoked by noradrenaline. After incubation with phentolamine (10−6 m), noradrenaline (10−7 − 10−6 m) decreased phasic activity induced by prostaglandin F2α (10−5 m). Isoprenaline and salbutamol also abolished PGF2α‐induced phasic activity. Pafenolol (10−6 m) and butoxamine (10−6 m) blocked the inhibitory effect of noradrenaline, isoprenaline, and salbutamol on PGF2α‐induced phasic activity. These results suggest that noradrenaline may modulate both phasic peristaltic activity and basal tone of pig intravesical ureter through both α‐ and β‐adrenoceptors.