Effect of volume expansion induced by Ringer's solution or plasma on the natriuretic response of the kidney.

Studies were carried out in anaesthetized dogs, to determine the effects of volume expansion induced by Ringer's solution, plasma taken from non-hydrated or previously volume expanded animals on the natriuretic response of the kidney. When the animals were infused with Ringer's solution (0.25 ml/kg/min iv.) water and sodium excretion increased gradually reaching a peak value at about 70 min. after starting the infusion (3.01 +/- 0.21 ml/min and 329 +/- 23.9 mmol/min, respectively). Infusing the dogs with plasma taken from non-hydrated animals (0.25 ml/kg/min iv.) water and sodium excretion showed a small increase in the first 15 min, but afterwards there was hardly any change in them, and water and sodium excretions were significantly less in the remaining part of the experiment than in with Ringer's solution expanded animals. (Peak values 1.44 +/- 0.53 ml/min and 193 +/- 85.3 mmol/min.) In animals infused with plasma taken from previously hydrated dogs (0.25 ml/kg/min iv.) water and sodium excretion were already after the first 15 min significantly higher than in the two other groups, they increased further in the following 15 to 30 minutes and remained elevated during the time of the study. (Peak values for water and sodium excretion being 3.30 +/- 0.58 ml/min and 344 +/- 73.5 mmol/l.) Blood pressure, CPAH and glomerular filtration rate were the same and did not change in either of the experimental series. We concluded, that besides the physical forces playing certainly a role mainly in the Ringer's solution hydrated dogs, some humoral natriuretic factor liberated in the volume expanded animals plays also a role in the diuretic-natriuretic response. This humoral factor can be released from the atria or other organs, but its production is not primarily regulated by intravasal volume/or pressure changes.