Effect of dehydration and hyperosmolality on thermoregulatory water losses in exercising dogs

Publisher Website
Google Scholar
Abstract
In 6 dogs, rectal temperature (Tre), respiratory evaporative water loss (Eresp) and water lost by drooling were measured during 30 min of rest, 30 min of heavy exercise (7.5 km/h at a 20% slope) and 30 min of postexercise recovery at 25.degree. C ambient temperture under 3 conditions: hydrated ad lib; dehydrated by removal of drinking water; and after i.v. infusion of hypertonic NaCl. In hydrated animals, mean body weight was 28.3 kg, plasma osmolality (Posmol) was 297 mOsmol/kg H2O, and plasma volume (PV) was 1430 ml. Dehydration resulted in a reduction in body weight to 25.6 kg, an elevation in Posmol to 324 mOsmol/kg H2O (P < 0.001 compared with hydrated state), and a reduction in PV to 1182 ml (P < 0.05). Hypertonic NaCl infusion elevated Posmol to 328 mOsmol/kg H2O (P < 0.001) and did not change PV. Tre at the end of exercise was 42.06.degree. C in hydrated dogs, 42.50.degree. C (P < 0.02) in dehydrated dogs, and 42.34.degree. C (P< 0.05) in hypertonic dogs. Eresp in hydrated dogs in the preexercise period (29 g) and the exercise period (146 g) was not different from Eresp in dehydrated and hypertonic dogs. Eresp in the postexercise period was 122 g in hydrated dogs, 90 g (P < 0.01) in dehydrated dogs and 116 g (NS) in hypertonic dogs. Water drooled from the lips and tongue during exercise was 105 g in hydrated dogs, 10 g (P < 0.01) in dehydrated dogs and 51 g (P < 0.01) in hypertonic dogs. The slope of the regression line relating Tre to rate of water loss during exercise was lower in hypertonic than in hydrated animals (P < 0.05) and lower in dehydrated than in hypertonic animals (P < 0.01). Dehydrated dogs performing heavy exercise can save water by reducing the rate of oral-salivary secretions. Elevated osmolality of body fluids with no reduction in plasma volume leads to some reduction of these secretions, but the greatest reduction occurs in dehydrated animals in which osmolality is elevated and plasma volume is decreased.

This publication has 11 references indexed in Scilit: