Renal Excretion of Potassium and Potassium Tolerance in the Pig

Abstract

Young pigs given supplements of KCI in the food excreted the additional KCI in the urine indicating the importance of the kidney in the regulation of potassium excretion.Intravenous infusion of KCI increased the concentration of potassium in the plasma and the rate of excretion of potassium in the urine. This increase was proportional to infusion rate and in some experiments the amount of potassium excreted in the urine exceeded the amount filtered at the glomerulus, demonstrating net secretion ofpotassium by the renal tubule. Urinary excretion of sodium was markedly increased during KCI infusion.After pigs had been given a diet containing supplementary KCI for 6 days their ability to excrete potassium in the urine in response to intravenous KCI infusion was not altered although the sodium diuresis was much reduced.Intravenous infusion of KC1 into acidotic pigs resulted in a rise in the rate of excretion of potassium in the urine of less than half that seen in pigs in normal acid-base balance given the same rate of infusion. Glomerular filtration rate and the amounts of potassium filtered at the glomerulus during KOl infusion were unaffected by acidosis, which suggests that the lowered excretion of potassium in urine seen in acidotic pigs was the result of reduced tubular secretion.There is considerable evidence to show that the renal tubular cells can secrete potassium and that distal regions of the nephron are responsible. In small mammals such as the rat this has been demonstrated using the technique of micropuncture [Malnic, Klose and Giebisch, 1964] while in larger mammals such as the dog [Berliner, Kennedy and Hilton, 1950] sheep [Scott, 1969] or the cow [Anderson and Pickering, 1962] demonstration of this secretory function depends upon loading experiments in which potassium salts are infused intravenously. Ifthe rate of infusion is sufficiently high then the amount of potassium excreted in the urine can be shown to exceed the amount filtered at the glomerulus and as such indicates net secretion.Workers who have studied this response in the dog agree that its tolerance to intravenous potassium infusion is much improved if supplements of potassium are given in the food for several days prior to infusion [Berliner et al., 1950;Mudge, Ames, Foulks and Gilman, 1950]. Improved tolerance to potassium after increased potassium intake has also been shown in the rat but cattle and sheep fed diets naturally rich in potassium are able to withstand intravenous. infusion of potassium salts without dietary supplementation [Anderson and Pickering, 1962;Scott, 1969].The purpose of the experiments described below was to examine renal excretion of potassium in the pig and to see if its renal response to intravenous potassium loading was influenced by the level of potassium in the diet or by acidosis.393

The Effect of Plasma Potassium in Determining Normal Rates of Excretion of Potassium in Dogs

“…Injection of K into the renal artery has been shown to cause increase in K excretion, with a small increase in Na excretion [Beal and Harrison, 1975;Harrison et al, 1970]. Several authors [Anderson and Pickering, 1962;Scott, 1969;Mason and Scott, 1972;Beal et at., 1973] have described immediate increase in K excretion and increased Na excretion on intravenous injection of K salts in larger doses than those used here. Mills [1955] found changes in K excretion when plasma K was altered by an injection of insulin or ingestion of KHCO3.…”

“…Na excretion also increased with the same time course as the increase in K excretion, to reach a maximum of 20-25,mol/min in comparison with 6-8 ,mol/min in control experiments. Increased excretion of Na after K salts has been reported with larger doses given to cattle, sheep and pigs [Anderson and Pickering, 1962;Harrison, McDonald and Olsson, 1970;Beal, Budtz-Olsen, Clark, Cross and French, 1973;Mason and Scott, 1972].…”

“…Increased excretion of Na after K salts has been reported with larger doses given to cattle, sheep and pigs [Anderson and Pickering, 1962;Harrison, McDonald and Olsson, 1970;Beal, Budtz-Olsen, Clark, Cross and French, 1973;Mason and Scott, 1972]. In the middle frames of Fig.…”

Effluent from grass silage for finishing pigs

“…The depression in performance indicates that additional water should be made available with effluent diets. The acidity of silage effluent may have increased the mineral stress in relation to water supply, as rats and pigs in an acidotic state have been shown to have impaired ability to excrete potassium by the renal route (Malnic et al 1971;Mason & Scott 1972).…”

Renal Regulation of Phosphate Excretion in the Pig

“…Glomerular fitration rate (GFR) was measured using inulin as a marker substance. The solution and procedure used have both been previously described [Mason and Scott, 1972].…”