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For anybody interested, you can set up a RSS feed on pubmed on any topic 
that interests you.  The main page link is 
here:  http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed   The 
following are a couple of things I found by typing in hyponatremia, 
horse.  There's lots more, though nothing really recent.  Karen


Equine Vet J Suppl. 1999 Jul;30:425-9.
Electrolyte vs. glucose-electrolyte isotonic solutions for oral rehydration 
therapy in horses.
Facultat de Veterinaria, Universitat Autonoma de Barcelona, Spain.

An isotonic electrolyte solution with a composition similar to equine sweat 
was compared to an isotonic glucose-glycine-electrolyte solution for oral 
rehydration therapy in exercising horses. Ten horses were dehydrated by 
using frusemide and allocated randomly to receive 4 different oral 
solutions: isotonic sweat-like electrolyte solution, half-strength 
hypotonic electrolyte solution, isotonic glucose-glycine-electrolyte 
solution, and plain water. Solutions were given by nasogastric tube using 
the same volume as the bodyweight lost by each horse. Blood samples were 
collected before and throughout 6 h of the rehydration period. Results 
showed that all solutions recovered pre-frusemide values of packed cell 
volume (PCV) and total plasma protein (TP) in a similar fashion. No changes 
for Na+ values were observed during the rehydration period when the 
isotonic sweat-like solution was used. However, a significant hyponatraemia 
was induced throughout rehydration when the other 3 solutions were given, 
especially when hypotonic solution and water were used. Osmolality values 
did not change when both isotonic solutions were administered; but a 
significant hypotonicity was observed when hypotonic solution and water 
were given. When the isotonic sweat-like solution was used, plasma Cl-, K+ 
and creatinine values recovered to premedication values significantly 
faster than the other 3 solutions. In conclusion, the isotonic sweat-like 
electrolyte was the best solution because it restored rapidly the fluid and 
plasma electrolyte imbalances. In contrast, the isotonic 
glucose-glycine-electrolyte solution impaired the plasma electrolyte 
imbalances.


Equine Vet J Suppl. 2002 Sep;(34):513-8.
Drinking salt water enhances rehydration in horses dehydrated by frusemide 
administration and endurance exercise.
Department of Large Animal Clinical Sciences, Michigan State University, 
East Lansing 48824-1314, USA.

Because the primary stimulus for thirst is an increase in plasma tonicity, 
we hypothesised that dehydrated horses would drink a greater total volume 
of fluid voluntarily during the first hour of recovery when they were 
initially offered salt water. To test this hypothesis, bodyweight (bwt), 
fluid intake (FI) and [Na+] were measured in 6 Arabian horses offered 3 
rehydration solutions. After dehydration was induced by frusemide 
administration (1 mg/kg bwt, i.v.) followed by 45 km treadmill exercise, 
water (W), 0.45% NaCl and 0.9% NaCl were offered, in a randomised order, 
during the initial 5 min after completing exercise. Horses were 
subsequently placed in a stall and further intake of plain water during the 
first hour of recovery was measured. By the end of exercise, horses lost 
5.2 +/- 0.2, 5.6 +/- 0.3 and 5.7 +/- 0.2% (P>0.05) bwt and FI during the 
first 5 min of recovery was 10.5 +/- 0.7, 11.6 +/- 0.8 and 11.6 +/- 1.5 l 
(P>0.05) for W, 0.45% NaCl and 0.9% NaCl, respectively. After 20 min of 
recovery, [Na+] had decreased with W but remained unchanged from the end 
exercise values for both saline solutions. During the initial hour of 
recovery, further water intake was 0.9 +/- 0.4, 5.0 +/- 0.5 and 6.9 +/- 0.7 
l (P<0.05) for W, 0.45% NaCl and 0.9% NaCl, respectively. Therefore, total 
FI was 11.4 +/- 0.5, 16.6 +/- 0.7 and 18.5 +/- 1.7 l (P<0.05) for W, 0.45% 
NaCl and 0.9% NaCl, respectively, and persisting bwt loss after 60 min of 
recovery was greater (P<0.05) for W (3.5%) than for the 2 saline solutions 
(24% for 0.45% NaCl and 1.9% for 0.9% NaCl). In conclusion, providing salt 
water as the initial rehydration fluid maintained an elevated [Na+] and 
resulted in greater total FI and recovery of bwt loss during the first hour 
of recovery, in comparison to offering only plain water.

Equine Vet J Suppl. 1996 Jul;(22):108-12.
Restoration of water and electrolyte balance in horses after repeated 
exercise in hot and humid conditions.
Agricultural Research Centre, Ypaja, Finland.

Nine adult riding horses performed on a treadmill a competition exercise 
test (CET) and 24 h later a standardised exercise test (SET) at mean 
temperature 28 degrees C and relative humidity 58%. Each horse performed 
the tests 5 times at 2 week intervals. The horses were given isotonic 
glucose-electrolyte solution via a nasogastric tube 30 min after the CET, 
except after the last trial when water was given. Blood lactate, plasma 
concentration of aldosterone, arginine vasopressin, protein, sodium, 
potassium, chloride, magnesium and calcium were measured. Heart rate at 
blood lactate concentration 4 mmol/l (PLa4) in the SET, plasma volume (PV) 
and red cell volume (CV) were determined. Mean weight loss after CET was 
3.1% and did not change significantly during the study. Bodyweight loss 
(BWL2) before SET (-1.8% after the first trial) decreased linearly with 
time (P < 0.05) and was -0.8% after the fourth trial. After the fifth 
trial, when only water was given, the weight loss was -2.5%. PLa4 
correlated significantly (P < 0.001) with BWL2 when BWL2 was greater than 
-1.2%. The horses acclimated to exercise in hot and humid conditions as 
indicated by better recovery of bodyweight, increased PV, lower peak 
lactate concentrations and heart rate and attenuated decrease in the 
concentrations of sodium and chloride. It is concluded that changes in 
bodyweight provide a good indication of recovery of horses after exercise 
in hot and humid conditions; and administration of an isotonic 
glucose-electrolyte rehydration solution after exercise helps to overcome 
dehydration better than water alone.  

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