Effects of isosmotic and hyperosmotic glycine solutions on the fluid balance in conscious sheep.

Glycine 0.55 g.kg-1 was given as an isosmotic (285 mosmol.kg-1) and a hyperosmotic (approx. 3,000 mosmol.kg-1) solution by intravenous infusion during 30 min to six euhydrated ewes. Urine and blood samples were collected, and the distribution of the administered water between the intra- and extracellular fluids (ICF and ECF) was calculated for up to 150 min after the infusions. Both solutions produced an osmotic diuresis with a marked increase of the urinary excretion of sodium, potassium, and amino acids. A paradoxical increase of the plasma vasopressin concentration occurred from the isosmotic but not from the hyperosmotic glycine solution. At the end of the follow-up period, the isosmotic glycine solution had resulted in hyperhydration of the ICF and the hyperosmotic solution in dehydration of the ICF, whereas with both fluids, the ECF resumed the same volume as before the experiments.