The effect of water and of isotonic saline administration on the renal plasma and glomerular filtrate flows in the dog, with incidental observations of the effects on these flows of compression of the carotid and renal arteries

Abstract

The effects of water and of isotonic saline administration on the renal plasma and glomerular filtrate flows of the living dog are described. The plasma extraction ratio forp-amino-hippurate (PAH) during renal passage has been directly determined under the conditions of our experiments; and it is shown that this ratio gives, at low arterial plasma levels of PAH, a reliable measure of plasma flow. This also holds after water administration and during the large rise in blood pressure produced by bilateral carotid occlusion. In control experiments, serial determinations of renal plasma and filtrate flows over a period of about 2 h showed that these flows remained remarkably constant. After water administration the renal plasma and filtrate flows increased, the increases being related to the dose of water given. The filtration fraction was little altered in animals with intact renal nerve supply. Isotonic saline, in the same dosage as water, also increased the filtrate flow, but the increase in plasma flow was minimal or absent in animals with intact renal nerve supply. The filtration fraction therefore rose. When the renal nerve supply had been interrupted the plasma flow increased after saline was given, and the plasma-flow response to water was greater than it was when the renal nerve supply was intact. Renal denervation had no significant effect on the filtrate-flow response to water, but increased that to saline. Renal denervation, therefore, had no significant effect on the filtration fraction after saline administration, but caused a fall in the filtration fraction after water administration. The increases in plasma and filtrate flows preceded the increases in urine flow. They were not the result of alterations in blood pressure, nor was their trend affected by antidiuretic hormone in a dosage sufficient to inhibit the diuresis. Any immediate changes in the plasma and filtrate flows that may have occurred when the blood pressure to the kidney was suddenly and reversibly altered by bilateral occlusion of the common carotid arteries or by partial obstruction of the renal artery, were rapidly neutralized by vascular readjustment within the kidney. Large variations in plasma and filtrate flows between successive fifteen minute periods were observed in one animal made hypertensive by chronic partial constriction of the artery to one kidney at a time when, the arterial pressure being normal, the other kidney had become grossly shrunken and fibrotic as a result of arterial thrombosis. Denervation of the kidney with the mechanically constricted artery largely abolished these variations. The results are discussed, and a hypothesis is advanced which, in order to account for the changes observed in plasma and filtrate flows after water and saline administration to ‘innervated’ and ‘denervated’ animals, postulates a functioning relationship between the intratubular pressure at some undetermined site and the resistance of the preglomerular vessels.