Effect of minor surgery on urinary flow and electrolyte excretion in the awake dog

Spontaneous variations in urinary flow and electrolyte excretion are well known to occur both in man and in the non-human primate. Data on these spontaneous variations is scarce in the dog, an animal which is widely used in physiological investigations. Our study was designed to characterize the spontaneous pattern of renal hemodynamics, urine flow and electrolyte excretion in the awake dog both under conditions of minimal surgical stress (group I), and after routine preparatory surgery (group II). Our results show significant spontaneous variation for urine flow and urinary excretion of Na, K, Cl, HCO3, Ca, PO4 and Mg for both groups of dogs. Urinary excretion of Na, K, PO4 and Mg was significantly higher for group II than for group I (p less than 0.05). Glomerular filtration rate and effective renal plasma flow (estimated from the clearance of p-aminohippurate) were measured in group II and showed no spontaneous variation. Our study shows that there is diurnal urinary electrolyte excretion variation in the dog which is exaggerated by small changes in the experimental protocol. These variations need to be considered when evaluating experimental maneuvers that induce changes in the renal handling of electrolytes in the dog.