Under ordinary circumstances the elaboration of a dilute urine is dependent upon suppression of the secretion of antidiuretic hormone (ADH). Even when ADH secretion is maximally suppressed, however, a concentrated urine may be formed. Berliner The present experimiients were designied to examine the role of GFR, solute excretion, and sodium excretion on urinary tonicity when ADH activity is negligible. To determine whether acute reductions in GFR produce effects that are then obscured by adaptative changes, studies in which GFR was reduced for periods up to three months were also undertakeni.
Materials and MethodsFemale mongrel dogs, weighing 10 to 17 kg and fed regular commercial diets, were used in all studies.The effects of acute and chronic reductions in GFR on the excretion of water and solutes were studied during water diuresis and during hypotonic saline diuresis.Acute reductions in GFR were produced in four dogs by inflating a balloon in the thoracic aorta. After the dogs were anesthetized with sodium pentobarbital, a balloon connected to an arterial catheter was inserted througlh the right brachial artery into the thoracic aorta to a point just above the renal arteries. Inflation of the balloon so that femoral arterial pressure was reduced byabout 50% reproducibly depressed GFR by about 30%.Urine was collected from an indwelling bladder catheter. Blood was collected with a Cournand needle in the femoral artery through which blood pressure was also monitored.The studies were then carried out in the following order (Table I)