Potentiation by substance P of contractions of the isolated vas deferens of the mouse elicited by electric field stimulation and by drugs.

1 Isolated vasa deferentia from the mouse were opened longitudinally and suspended in Krebs solution at 37 degrees C in an organ bath. Contractions of the muscle were elicited by electric field stimulation, noradrenaline (10(-6) M) and acetylcholine (10(-6) M). Continued transmural stimulation evoked a biphasic response comprising a rapid twitch followed about 10 s later by a smaller, sustained rise in muscle tone.2 The amplitudes of nerve-mediated and drug-induced responses were considerably potentiated by substance P (SP) in the dose range 10(-12) to 10(-7) M. Higher concentrations of SP were directly spasmogenic. The sensitizing property of SP was dose-dependent and was usually well maintained, but always disappeared quickly on washing the preparation. In some experiments SP facilitated the twitch, but not the subsequent phase of the electrically-induced contraction or the response to externally applied noradrenaline.3 Phentolamine (10(-6) M) failed to block this effect of SP, but itself potentiated the nerve-mediated twitch, and completely abolished the sustained secondary contraction.4 Desmethylimipramine (10(-6) M) enhanced the delayed contraction but not the immediate contraction.5 The uptake of tritiated noradrenaline (3 x 10(-7) M) by vasa was inhibited by desmethylimipramine (10(-6) M) and increased by nialamide (3 x 10(-5) M), but was not modified by SP (10(-6) M).6 Nerve-mediated release of accumulated radioactivity was accelerated by phentolamine, but not by SP or desmethylimipramine.7 These findings suggest that SP sensitizes the muscle cells to depolarizing stimuli but that it has no facilitatory effect on sympathetic neural elements.