Urine and papilla concentrations during transition from hypotonic to hypertonic urine

Dogs in water diuresis, with high urine flow and low urine osmolality and sodium concentration, had papilla fluid osmolality of 398 milliosmols/kg H2O and papilla fluid sodium concentration of 116 millimolal. At 5.5 min after laparotomy and 100 mU of vasopressin intravenously, papilla fluid osmolality and sodium concentration showed no significant rise, but urine osmolality and sodium concentration had risen greatly. At longer intervals, up to 13 min, papilla osmolality rose to above 600 mM with a further rise in urine osmolality; osmotic equilibration between urine and papilla fluid was attained at about 10 min Papilla fluid sodium concentration rose after 5.5 min Cortex fluid remained isosmolal with plasma.