Glycerol hyperhydration in resting horses

To determine whether administration of glycerol-containing solutions induce s a state of transient hyperhydration in resting euhydrated horses, changes in plasma and urine constituents were measured in four horses for 1 h befo re and 5 h after nasogastric administration of each of four treatments (Exp eriment 1). Treatments were applied in a randomized fashion and included: ( I) 1.0 g.kg(-1) glycerol in 8 L of water (G); (2) 8 L of water (W); (3) 8 L of 9.9% NaCl solution (8); and (4) 1.0 g.kg(-1) glycerol in 8 L of 0.9% Na Cl solution (GS). In a subsequent study, voluntary water intake was measure d hourly for 5 h after nasogastric administration of each treatment (Experi ment 2). All treatments produced mild plasma volume expansion ranging from 3.2 to 5.8% in Experiment 1. Administration of glycerol containing solution s increased serum glycerol concentration approximate to 100-fold and plasma osmolality ((osm)) by approximate to 10 mOsm/kg and resulted in a tendency towards increased renal water conservation despite increased osmole excret ion. In contrast, W treatment decreased plasma and urine osmolality and was accompanied by increased urine production and decreased renal water conser vation. Plasma and urine osmolality, as well as renal osmole and water excr etion, were unchanged after 8 administration. In Experiment 2, horses treat ed with GS voluntarily drank an additional 5.2 +/- 0.9 L of water during th e initial hour following nasogastric administration of 8 L of solution. Vol untary water intake with the other treatments was less than 1.0 L for the e ntire 5 h observation period. Collectively, the results of both experiments suggest that administration of glycerol in saline would produce transient hyperhydration in resting euhydrated horses by enhancing renal water conser vation and stimulating voluntary water intake. (C) 2001 Harcourt Publishers Ltd.