Vasopressin excitatory action on smooth muscle from human renal calyx and pelvis

The motor response to vasopressin, a neuropeptide promoting the reabsorption of water, was isometrically investigated in vitro in human renal calyces and pelvis in relation to possible modulation of urinary flow by these tubular structures. Kidneys were obtained from nine male patients who underwent nephrectomy for either renal or ureteral cancer. Minor calyces and pelvis were carefully removed. Strips (10 mm x 3 mm) were cut from infundibular region of minor calyces and from renal pelvis and placed in 10 ml organ bath for isometric tension recordings. Calyceal and pelvic smooth muscle strips exhibited spontaneous phasic contractions which occurred with regular frequency and amplitude. Vasopressin induced a dose-dependent [10(-10) to 10(-6) M] enhancement of basal tone (P <0.01) and a decrease of spontaneous contractions on isolated strips from minor calyces and pelvis. The effect of vasopressin was inhibited by prior administration of D(CH2)5Tyr(Me)2-Arg8-Vasopressin antagonist [10(-7) M]. The excitatory response to vasopressin was Tetrodotoxin [TTX]-resistant and was not affected by pre-treatment with phentolamine [10(-5) M], atropine [10(-5) M], and hexamethonium [10(-5) M]. After incubation of the specimens in Ca2+-free medium containing EGTA [0.5 mM] or after treatment with nifedipine [10(-5) M], both spontaneous and vasopressin-induced contractions [10(-10) to 10(-6) M] were completely inhibited in all specimens. Our results can be interpreted to imply that the tonic contractions induced by vasopressin facilitate the reabsorption of water by increasing the hydraulic resistance of the tubular structures below collecting ducts.