Ion-osmotic hyperthermia during exercise in dogs

Abstract

The influence of intravenous infusions of various concentrations of NaCl solutions on temperature regulation was investigated in dogs at rest and during moderate exercise for 1 h on a treadmill. Infusion of hypertonic solutions either before and during exercise resulted in elevated (P less than 0.05) plasma Na+ and osmotic concentrations and produced higher equilibrium levels (P less than 0.05) of rectal temperature (Tre) during exercise (prehypertonic 40.9 degrees C vs. no infusion 40.4 degrees C; hypertonic 40.8 degrees C vs. isotonic infusion 40.4 degrees C), but not at rest. Increasing the [Na+] and osmotic concentrations above 170 meq/liter and 325 mosmol/kg, respectively, resulted in no additional increase in exercise Tre. Water consumption during exercise decreased (P less than 0.05) plasma [Na+], osmolality, and the equilibrium level of Tre to control levels. There was no effect of changes in plasma volume (PV) of +/- 8% on the time course, equilibrium level, or change in Tre during exercise. At the end of exercise, there were moderate correlations (P less than 0.01) between Tre and [Na+] (r = 0.51) and Tre and osmoti (r = 0.52) concentrations. It was concluded that a) the exercise Tre responses of the dog respond quantitatively like man to elevated plasma [Na+] and osmolality, b) the Tre levels are not influenced by changes in PV, and c) water intake significantly reduces the ion-osmotic hyperthermia.

Control of evaporative heat loss during changes in plasma osmolality in the cat

“…Since infusion of water alone adds no excess ions and is unlikely to alter the equilibrium between bound and unbound calcium ions significantly, this is further evidence that the changes in body temperature regulation observed in our experiments are not the result of an ambient temperature-independent alteration in set point produced by changing hypothalamic ionic ratios. The dependence ofelevation of body temperature in hyperosmotic states upon either exercise or ambient heat loads has been reported uniformly in many studies (Turlejska-Stalmasiak, 1974;Maskrey & Nichol, 1975;Greenleaf et al 1976;Baker, Kolb & Weitzman, 1978;Taylor, 1979;Kozlowski et at. 1980) and it must be concluded that such elevations can be independent of the influence of ionic ratios.…”

“…Similar elevations in deep body temperature and inhibition of evaporation occur in most other mammals examined under these conditions (Taylor, 1970;Turlejska-Stelmasiak, 1974;Doris & Baker, 1981). Ingestion or infusion of hypertonic fluids has been associated similarly with the changes in temperature regulation observed in dehydrated subjects (Nielsen, Hansen, Jorgenson & Nielsen, 1971;Nielsen, 1974;Greenleaf, Kozlowski, Nazar, Kacuiba-Uscilko, Brzezinska & Ziemba, 1976;Kozlowski, Greenleaf, Turlejska & Nazar, 1980). Replacement ofwater losses reverses these changes in dehydrated subjects (Senay & Christensen, 1965) as does water consumption in animals made hyperosmotic by hypertonic saline infusion (Greenleaf et al 1976).…”

“…Ingestion or infusion of hypertonic fluids has been associated similarly with the changes in temperature regulation observed in dehydrated subjects (Nielsen, Hansen, Jorgenson & Nielsen, 1971;Nielsen, 1974;Greenleaf, Kozlowski, Nazar, Kacuiba-Uscilko, Brzezinska & Ziemba, 1976;Kozlowski, Greenleaf, Turlejska & Nazar, 1980). Replacement ofwater losses reverses these changes in dehydrated subjects (Senay & Christensen, 1965) as does water consumption in animals made hyperosmotic by hypertonic saline infusion (Greenleaf et al 1976). Prior hyperhydration is associated with lower levels of equilibrium rectal temperature and higher evaporative heat loss during exercise than if water losses are replaced (Moroff & Bass, 1965;Nielsen et al 1971).…”

Working Dogs Drinking a Nutrient-Enriched Water Maintain Cooler Body Temperature and Improved Pulse Rate Recovery After Exercise

“…More specifically, dehydrated dogs at rest maintain higher rectal and hypothalamic temperatures (17). Dogs that commence exercise in a dehydrated state develop higher BT rec at the end of a 30 min exercise compared to adequately hydrated dogs (7, 16, 19). In addition, dehydrated dogs have a lower carotid blood flow and lower cardiac output during exercise (7), as well as lower rate of evaporative water loss during 30-min after exercise (16), which will contribute to greater hyperthermia, but will aid in reducing water loss.…”

“…Although a variety of canine exercise studies have examined hyperthermia and water loss, they have largely focused on physiological changes while dogs were dehydrated or provided a hypertonic solution (model to increase plasma osmolality and not change plasma volume) compared to “hydrated” dogs with free access to tap water (4, 5, 7, 16, 17, 19). Only a few nutrition studies have examined the use of a water supplement to enhance hydration or reduce the risk of dehydration in dogs on exercise-related dehydration (20) or physiological changes (21).…”