Evidence for large intestinal control of potassium homoeostasis in uraemic patients undergoing long-term dialysis.

1. The role of the large intestine in the maintenance of K+ balance in uraemic patients established on long-term dialysis was studied with a rectal dialysis technique in 14 normal subjects, ten normokalaemic patients undergoing chronic ambulatory peritoneal dialysis (CAPD), and seven patients undergoing haemodialysis. Dietary K+ intakes in the normal subjects, CAPD patients and haemodialysis patients were 80-100 mmol/24 h, 70-80 mmol/24 h and 60-70 mmol/24 h, respectively. 2. At an initial intraluminal K+ concentration of 45 mmol/l, rectal K+ secretion in the CAPD patients (2.4 +/- 0.4 mumol h-1 cm-2) was greater than in normal subjects (1.2 +/- 0.2 mumol h-1 cm-2, P less than 0.02). Under similar conditions, rectal K+ secretion was also greater in the haemodialysis patients than in normal subjects, both predialysis (3.7 +/- 0.4 mumol h-1 cm-2, P less than 0.001) and postdialysis (2.4 +/- 0.5 mumol h-1 cm-2, P less than 0.05), even though haemodialysis decreased plasma K+ concentration from 5.3 +/- 0.1 mmol/l to 3.5 +/- 0.2 mmol/l (P less than 0.001). 3. There were no significant differences in rectal Na+ absorption, rectal potential difference, plasma aldosterone concentration, or total body K+ content (measured by whole-body counting of 40K), between the normal subjects and either the CAPD or the haemodialysis patients. 4. These results indicate that K+ homoeostasis is maintained in uraemic patients undergoing long-term dialysis by a combination of K+ losses during dialysis, and enhanced large intestinal K+ excretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Enhanced rectal potassium secretion in chronic renal insufficiency: evidence for large intestinal potassium adaptation in man.

The role of the large intestine in K+ excretion in chronic renal insufficiency was studied with a rectal dialysis technique in 14 normal subjects and eight normokalaemic, normotensive patients with chronic renal insufficiency. At initial intraluminal K+ concentrations of 10, 20, 30 and 45 mmol/l, net K+ secretion in patients with renal insufficiency was significantly greater than in normal subjects by approximately 1.8 mumol h-1 cm-2. The increase in net K+ secretion was more marked in those patients with creatinine clearances of less than 10 ml/min. In contrast, there were no significant differences in net Na+ and water transport, transmucosal potential difference and plasma aldosterone concentrations between the two groups. With an initial intraluminal K+ concentration of 30 mmol/l, the addition of amiloride (final concentration 1 mmol/l) to the rectal lumen decreased net Na+ absorption and transmucosal potential difference in normal subjects by 69% (P less than 0.005) and 31% (P less than 0.005) respectively, and in patients with renal insufficiency by 75% (P less than 0.05) and 36% (P less than 0.05) respectively, but there was no change in net K+ secretion in either group. These results indicate that the K+ secretory capacity of the rectal mucosa increases in chronic renal insufficiency, and the large intestine may therefore contribute to the maintenance of K+ homoeostasis as renal K+ excretion declines. Increased rectal K+ secretion in renal insufficiency occurs independently of changes in plasma K+ and aldosterone concentrations, net Na+ absorption and transmucosal potential difference, and may reflect stimulation of an active K+ secretory process.

Effect of storage on measurement of ionized calcium in serum of uremic patients.

We studied, in 70 acidotic and non-acidotic uremic patients, the analytical variance in serum ionized calcium as related to duration and temperature of storage. Storage of serum or whole blood at 4 degrees C for as long as 6 h did not significantly alter the measured concentration of ionized calcium in the serum. Storage at room temperature for 6 h, or longer at 4 degrees C or -20 degrees C, resulted in inaccuracies in 39 to 79% of the samples of serum and in 38 to 92% of the samples of whole blood. These errors were not negated by correcting the values for ionized calcium to a pH of 7.40. Indeed, corrected values for calcium were even more unreliable in acidotic patients. We conclude that samples from uremic patients should be analyzed for ionized calcium within 2 h, or within 6 h if stored at 4 degrees C.