Contractile Effects of Some Polypeptides on the Isolated Urinary Bladder of Guinea‐pig, Rabbit, and Rat

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Abstract
In isolated detrusor from guinea pigs and rats substance P (SP) induced concentration-dependent phasic contractions. Rabbit detrusor strips responded to SP with an initial phasic and an ensuing tonic contraction. The concentration-response curve to SP in this preparation had a biphasic appearance. Eledoisin (E) caused contractile responses similar to those of SP when tested on the guinea pig detrusor. Somatostatin was tested on the rabbit urinary bladder; it caused a concentration-dependent rise in basal tone, but no phasic contraction. The responses to SP and E were not affected by tetrodotoxin or physostigmine. They were only partly inhibited by high concentrations of atropine and the anticholinergic drug PR 197. Noradrenaline [norepinephrine] and isoprenaline caused a concentration-dependent inhibition of the peptide induced responses in guinea pig bladder; at high concentrations of the amines this inhibition was almost complete. Indomethacin did not affect the SP induced contractions in the guinea pig bladder, reduced the responses in the rabbit detrusor, but increased them in the rat bladder. Contractions elicited by SP and E were rapidly diminished or abolished after 30 min treatment in a Ca-free medium. The responses were also inhibited by the Ca antagonist nifedipine. In guinea pig, preparations depolarized by K+ (127 mM) both SP and E caused a contractile response .apprx. 20% of that obtained in normal Tyrode solution. Evidently, SP and E cause contraction of detrusor by a direct effect on the smooth muscle cells, and this response is dependent on the extracellular Ca concentration. Prostaglandins may be involved in the SP-induced response of the rabbit detrusor.