Changes in arterial, mixed venous and intraerythrocytic concentrations of ions in supramaximally exercising horses.

Autor:	Bayly WM; Department of Veterinary Clinical Sciences, College of Veterinary Medicine. Washington State University, Pullman, Washington 99164-6610, USA., Kingston JK, Brown JA, Keegan RD, Greene SA, Sides RH
Jazyk:	angličtina
Zdroj:	Equine veterinary journal. Supplement [Equine Vet J Suppl] 2006 Aug (36), pp. 294-7.
DOI:	10.1111/j.2042-3306.2006.tb05556.x
Abstrakt:	Reasons for Performing Study: Horses experience major perturbations in acid-base balance during supramaximal exercise. Ion movement in and out of erythrocytes (RBCs) is believed to be important in maintaining acid-base balance but it is unclear as to the extent to which this happens, nor how it affects single measurements of ion concentrations in arterial and venous blood. Objectives: To clarify the role RBCs play in mitigating perturbations in acid-base balance during high speed exercise in horses, and to describe associated differences in arterial (a) and mixed venous (v) concentrations of key ions. Methods: Six exercise-trained Thoroughbreds galloped to fatigue at speeds calculated to have an oxygen demand that was 115% of the VO2max. Blood samples (a and v) were collected pre-exercise, during warm-up, at fatigue, and immediately post exercise. Packed cell volume (PCV), pH, PCO2, and plasma concentrations of bicarbonate (HCOP3-), chloride (Cl-), sodium (Na+), potassium (K+), and lactate (Lac-) and strong ion difference (SID) were determined, and RBC concentrations of Lac- and electrolytes calculated for each sample. Data were analysed using a 2-way ANOVA for repeated measures testing for effects of sampling time and site (P<0.05). Results: Plasma and RBC [Cl-] were increased with hypercapnoea and acidaemia. [HCO3-]v was greater than pre-exercise values at fatigue, although [HCO3l]a was lower. Hyperkalaemia and decreased RBC [K+] were evident at fatigue, as was an increased RBC [Na+]. Plasma [K+] started to decrease as soon as exercise ceased and Na+ began to move back onto RBCs in exchange for K+. Concentrations of all measures of Lac- rose from fatigue to post exercise. The SID decreased with exercise and was higher in v at fatigue and post exercise, reflecting the decrease in pH. Conclusions: RBCs act as a repository for lactate, and therefore the increase in PCV facilitates the maintenance of the muscle to plasma Lac- diffusion gradient during exercise. Potential Relevance: This serves to keep intramuscular [Lac-] lower than it would otherwise be and, because of the link between Lac- accumulation, pH decrease and the onset of fatigue, may help delay the onset of fatigue.
Databáze:	MEDLINE
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