GREENE, H.M.*; COGGER, E.A.; MILTENBERGER, T.L.; KOCH, A.K.; BRAY, R.E.; WICKLER, S.J.: Hypoxic effects on metabolic function and fluid/electrolyte balance in exercising horses

Physiological adjustments to altitude include not only respiratory and cardiovascular adjustments, but also renal and endocrine responses. In addition, hypoxia alters energy balance and metabolic function. Four horses and a pony were studied at 225m (P_b=743 mmHg) and 10 days at 3800m (P_b=487 mmHg). Metabolic adjustments were assessed by measuring changes in glucose, insulin, cortisol, thyroxine and fluid/electrolyte balance by measuring osmolality, sodium, potassium, and total protein. Blood samples were taken after 15-min of sub-maximal exercise, prior to high altitude (HA), during HA, and post-HA. Data were analyzed with repeated measures ANOVA and significance at P&lt0.10. Insulin but not thyroxine increased at HA (8.7 to 11.3 &microU/ml and 1.8 to 2.4 &microg/dL, respectively). Coritsol and glucose increased at HA (5.0 to 6.6 &microg/dL and 5.1 to 6.8 mM, respectively). The hyperglycemic effects of cortisol may provide increased substrates for an increased dependence on anaerobic metabolism associated with hypoxia. Osmolality increased at HA (296.0 to 312.9 mOsm). Total protein was significantly increased on day 2 at HA and remained slightly increased during HA (7.5 to 8.2 g/dl). Based on osmolality and protein the animals were likely dehydrated at HA. The animals experienced a hypokalemia (6.48 to 5.16 mEq/L) and hyponatremia (131.76 to 116.58 mEq/L) in response to Ex at HA. Shifts in electrolytes can be explained by: 1) sweat that occurs with exercise (not likely a cause); 2) decreased food intake (well-documented in altitude studies); and/or 3) metabolic acidosis induced as a result of respiratory alkalosis (based on strong ion difference). Supported by grants: RSCA, Cal Poly Pomona; CEH, UC Davis; WMRS, UC San Diego