Prevention of acute hyponatremia by mannitol: an unanticipated mechanism.
OBJECTIVE
To evaluate the effectiveness and mode of action of the osmotic diuretic mannitol to prevent the development of acute hyponatremia in a setting designed to mimic the acute hyponatremia observed on the day of surgery.


RESULTS
Hyponatremia (129+/-1 mM, fall of 10+/-1 mM, p <0.01) was induced by the intraperitoneal administration of half-isotonic saline plus DDAVP to rats (n = 8); hyponatremia was due to a positive balance of electrolyte-free water (EFW). Rats given mannitol (10 mmol/kg body wt) in addition to the hypotonic saline plus DDAVP had only a minor degree of hyponatremia (plasma [Na+] 136+/-1 mM, fall 3+/-2 mM, p >0.05). All the mannitol given was excreted over the 16 h of observation, but the urine volume was not higher in these rats. The higher rate of excretion of EFW was due to a marked reduction in the rate excretion of Na+ with mannitol. This antinatriuresis was also present when mannitol was given intravenously.


CONCLUSIONS
Although mannitol increased the excretion of EFW, the mechanism required an enhanced renal reabsorption of Na+ rather than an increase in the urine flow rate.
Gowrishankar
M
M
Division of Nephrology, St. Michael's Hospital, University of Toronto, Ontario, Canada.
Chen
C B
CB
Cheema-Dhadli
S
S
Halperin
M L
ML
D000818:Animals; D003894:Deamino Arginine Vasopressin / Q000494:pharmacology; D004234:Diuretics, Osmotic / Q000494:pharmacology*; D007010:Hyponatremia / Q000503:physiopathology / Q000517:prevention & control*; D008297:Male; D008353:Mannitol / Q000494:pharmacology*; D009318:Natriuresis / Q000187:drug effects / Q000502:physiology; D011183:Postoperative Complications / Q000503:physiopathology / Q000517:prevention & control; D051381:Rats; D017208:Rats, Wistar; D012076:Renal Agents / Q000494:pharmacology
D004234:Diuretics, Osmotic; D012076:Renal Agents; D008353:Mannitol; D003894:Deamino Arginine Vasopressin