Changes in arterial, mixed venous and intraerythrocytic ion concentrations during prolonged exercise.
BACKGROUND
Prolonged equine exercise can cause hypochloraemic alkalosis and hypokalaemia secondary to the loss of hypertonic sweat. Movement of ions in and out of erythrocytes during exercise may help regulate acid-base balance and changes in plasma ion concentrations. The extent to which this happens during prolonged equine exercise has not been reported.


OBJECTIVE
To measure changes in blood gases and major plasma and intraerythrocytic (iRBC) ion concentrations of horses undergoing prolonged submaximal exercise.


METHODS
Six horses were trotted at ∼ 30% VO2max on a treadmill for 105 min. Arterial ((a)) and mixed venous ((v)) blood samples were collected every 15 min, and pre- and post exercise. Blood gases and plasma (pl) concentrations of sodium, potassium, chloride and protein were measured and their iRBC concentrations calculated and compared (P < 0.05).


RESULTS
P(a)CO(2) decreased in all horses. pl[Cl(-)]v decreased and [HCO(3)(-)]v increased. Due to the exhalation of CO(2) and chloride shifting, [HCO(3)(-)]a<[HCO(3)(-)]v, pl[Cl(-)]a>pl[Cl(-)]v)and iRBC[Cl(-)]a<iRBC[Cl(-)]v. pl[K(+)]a and pl[K(+)](v) both initially increased then decreased and horses were hypokalaemic post exercise. Both iRBC[Cl(-)](a) and iRBC[Cl(-)](v) decreased over the course of exercise but there was no change in the arteriovenous difference between them. There was no arteriovenous difference in pl[K(+)]. iRBC[K (+)]a>iRBC[K(+)]v. Conversely, iRBC[Na(+)]a<iRBC[Na(+)]v). pl[Na(+)]a<pl[Na(+)]v and [TP]a<[TP]v.


CONCLUSIONS
Significant arteriovenous differences in iRBC and plasma concentrations of chloride, potassium and sodium reflect the role that movement of ions across erythrocyte cell membranes play in regulating acid-base balance and plasma concentrations of these ions. Exhalation of CO(2) has a major influence on this ion flux.
College of Veterinary Medicine, Washington State University, Washington, USA. ndmeyer@vetmed.wsu.edu
N D
ND
Meyer
W M
WM
Bayly
R H
RH
Sides
K J
KJ
Wardrop
B K
BK
Slinker
D000818:Animals; D001784:Blood Gas Analysis / Q000662:veterinary; D001831:Body Temperature / Q000502:physiology; D004912:Erythrocytes / Q000378:metabolism*; D005080:Exercise Test; D006863:Hydrogen-Ion Concentration; D007477:Ions / Q000097:blood* / Q000378:metabolism*; D010805:Physical Conditioning, Animal / Q000502:physiology*; D005082:Physical Exertion; D013997:Time Factors
D007477:Ions