Dietary potassium and laxatives as regulators of colonic potassium secretion in end-stage renal disease.
BACKGROUND
In end-stage renal disease (ESRD), colonic potassium (K+) secretion increases as renal K+ excretion declines. The nature of this adaptive process is poorly understood, but post-prandial increases in plasma K+ concentration may be a determining factor. In addition, even though colonic K+ secretion increases in ESRD, interdialytic hyperkalaemia is a serious problem in haemodialysis patients, which might be reduced by stimulating colonic K+ secretion still further using laxatives.


METHODS
Plasma K+ concentrations were measured in the fasting state, and for 180 min after the oral administration of 30 mmol of K+ to nine control subjects and 16 normokalaemic patients with ESRD (eight "predialysis" patients and eight patients undergoing continuous ambulatory peritoneal dialysis (CAPD)). Plasma K+ concentrations were also monitored for 180 min in fasting controls and ESRD patients who were not given the oral K+ load. To study the effect of laxatives on interdialytic hyperkalaemia, plasma K+ concentrations were measured in eight control subjects and 13 haemodialysis patients before and during 2 weeks treatment with bisacodyl (a cAMP-mediated laxative) and in five haemodialysis patients before and during 2 weeks treatment with lactulose (an osmotic laxative).


RESULTS
Oral K+ loading caused plasma K+ concentration to rise within the normal range (3.5-5.1 mmol/l) in control subjects, while significantly higher concentrations were achieved in the "predialysis" patients and sustained hyperkalaemia developed in the CAPD patients. Bisacodyl treatment had no effect on plasma K+ concentrations in control subjects, but significantly decreased the mean interdialytic plasma K+ concentration (from 5.9+/-0.2 to 5.5+/-0.2 mmol/l, P<0.0005) in haemodialysis patients, whereas plasma K+ concentration did not change during lactulose treatment.


CONCLUSIONS
Higher plasma K+ concentrations after food may help to maintain K+ homeostasis in ESRD by enhancing colonic K+ secretion. Bisacodyl may be useful for reducing interdialytic hyperkalaemia in patients undergoing haemodialysis.
Mathialahan
Thiriloganathan
T
Molecular Medicine Unit, St James's University Hospital, Beckett Street, Leeds LS9 7TF, UK.
Sandle
Geoffrey I
GI
D000328:Adult; D000368:Aged; D001726:Bisacodyl / Q000494:pharmacology*; D016022:Case-Control Studies; D002400:Cathartics / Q000494:pharmacology*; D003106:Colon / Q000378:metabolism*; D005215:Fasting / Q000097:blood; D005260:Female; D005765:Gastrointestinal Agents / Q000494:pharmacology; D006706:Homeostasis; D006801:Humans; D007676:Kidney Failure, Chronic / Q000097:blood / Q000378:metabolism* / Q000628:therapy; D007792:Lactulose / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D009994:Osmolar Concentration; D010531:Peritoneal Dialysis, Continuous Ambulatory; D011188:Potassium / Q000097:blood / Q000378:metabolism*; D017419:Potassium, Dietary / Q000494:pharmacology*
D002400:Cathartics; D005765:Gastrointestinal Agents; D017419:Potassium, Dietary; D001726:Bisacodyl; D007792:Lactulose; D011188:Potassium