Renal and Salivary Responses to Infusion of Potassium Chloride, Bicarbonate and Phosphate in Merino Sheep

Abstract

The excretion of electrolytes was measured during infusion of isosmotic NaCl and hyperosmotic NaCl, KCl, KHCO3 and KH2PO4. The increases in G.F.R., urine flow and urinary excretion of potassium, sodium, chloride, bicarbonate and solute during the infusion ofpotassium saltswere significantly greaterthan those duringthe isosmotic and hyperosmotic NaCl infusions; this finding excludes the rate of infusion and hyperosmolality of infusate as major contributors in the response to potassium infusion. The renal clearance ofpotassium was significantly higher in the sheep receiving the bicarbonate salt than in the animals receiving the chloride or the phosphate salts. Potassium bicarbonate loading was associated with low chloride excretion and potassium phosphate loading with low bicarbonate excretion. Potassium loading resulted in high rates of bicarbonate excretion in some experiments, which indicates a reduction in solute reabsorption in the proximal tubule. During the potassium infusions, the urinary calcium excretion rate and urinary pH were inversely correlated, renal magnesium excretion was not altered significantly and phosphate excretion was increased only when phosphate was infused. Salivary potassium secretion was highest in the phosphate-loaded sheep and potassium retention was lowest in the sheep receiving KCI infusions.Both oral and parenteral loading with potassium salts have been shown to increase the renal excretion of water, potassium, sodium, chloride and bicarbonate in a number of mammalian species including man, but the magnitudes of these effects vary considerably [Bassett, Elden and McCann, 1932;Keith and Binger, 1935;Laragh, 1954;Laragh and Capeci, 1955; Kahn and Bohrer, 1967]. The effect of potassium loading on the renal excretion of calcium, magnesium and phosphate ions has rarely been examined and the data available frequently conflict [Miller, 1926;Bassett et al., 1932;Winkler and Smith, 1942].This variability of the responses to potassium administration may be due to differences in the experimental design. The main areas of difference are the routes of administration, rates of infusion, solution osmolalities, potassium salts used and the mineral and hormonal status of the experimental animals.In this study an attempt has been made to separate the effects of potassium loading on urine formation and composition from the effects attributable to the rate of fluid infusion, the solution osmolality and the species of potassium salt. The potassium salts compared were chloride, bicarbonate and phosphate, these being the salts most frequently studied in the past.Since the high rate of production of saliva in the sheep could provide an alternative site for sequestration of potassium during potassium loading, parotid saliva was collected to give a measure of salivary potassium secretion.

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.…”

“…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.…”

Plasma Insulin Concentrations During Infusion of Potassium and Sodium Chloride Solutions Into Conscious Splenectomized Sheep

“…In these splenectomized sheep the haematocrit can be used as an indicator of changes in extracellular volume. During the potassium infusion the maximum increase in haematocrit ranged from 0·2 to 2·5 % which indicates a small fall in extracellular volume owing to redistribution of fluid between the extracellular and intracellular compartments and to the diuretic action of hyperkalaemia in the sheep (Beal et al 1973). At the same time the plasma insulin concentration was augmented 1·9-5·4 times.…”

The Effect of Vasopressin Upon the Excretion of Calcium by the Sheep

“…Blood samples were drawn at the mid-point of each urine collection throughout the entire experiment. Blood and urine samples were analysed as described by Beal, Budtz-Olsen, Clark, Cross and French [1973]. In addition total calcium was estimated by atomic absorption spectrometry and free ionized Ca++ was estimated by method of French, Cham and Cross [1972].…”