Facilitation of reflex micturition by intravesical administration of [beta Ala8]-neurokinin A (4-10), a selective NK-2 tachykinin receptor agonist.

We have determined the ability of [beta Ala8]-NKA(4-10), a selective agonist for NK-2 tachykinin receptors to stimulate micturition in anesthetized rats and guinea-pigs. In both species, the intravesical instillation of the peptide at microM concentrations reduced bladder capacity and residual volume, indicating a facilitatory effect on reflex micturition. At these concentrations, no plasma extravasation was produced as determined by the Evans blue content of the organ. In experiments on the isolated rat or guinea-pig bladder strips, the NK-2 receptor agonist induced powerful contractions. In a in vitro model of the guinea-pig whole bladder the intravesical instillation of the NK-2 agonist facilitated the occurrence of rhythmic contractile activity. It is concluded from these studies that intravenous administration of [beta Ala8]-NKA(4-10) exerts a facilitatory effect on the micturition reflex, presumably involving the ability of the NK-2 receptor agonist to cross the urothelium and stimulate smooth muscle contraction.