Journal of Applied Physiology, Vol 68, Issue 1 309-315, Copyright © 1990 by American Physiological Society

ARTICLES

Plasma [H+] regulation and whole blood [CO2] in exercising ponies

H. V. Forster, C. L. Murphy, A. G. Brice, L. G. Pan and T. F. Lowry
Medical College of Wisconsin, Milwaukee 53226.

The major objective was to determine in ponies whether factors in addition to changes in blood PCO2 contribute to changes in plasma [H+] during submaximal exercise. Measurements were made to establish in vivo plasma [H+] at rest and during submaximal exercise, and CO2 titration of blood was completed for both in vitro and acute in vivo conditions. In 19 ponies arterial plasma [H+] was decreased from rest 4.5 neq/l (P less than 0.05) during the 7th min of treadmill running at 6 mph, 5% grade (P less than 0.5). A 5.6-Torr exercise hypocapnia accounted for approximately 2.9 neq/l of this reduced [H+]. The non-PCO2 component of this alkalosis was approximately neq/l, and it was due presumably to a 1.7-meq/l increase from rest in the plasma strong ion difference (SID). Despite the arterial hypocapnia, mixed venous PCO2 was 2.7 Torr above rest during steady-state exercise. Nevertheless, mixed venous plasma [H+] was 1.2 neq/l above rest during exercise, which was presumably due to the increase in SID. Also studied was the effect of submaximal exercise on whole blood CO2 content (CCO2). In vitro, at a given PCO2 there was minimal difference in CCO2 between rest and exercise blood, but plasma [HCO3-] was greater for exercise blood than for rest blood. In vivo, during steady-state exercise, arterial plasma blood. In vivo, during steady-state exercise, arterial plasma [HCO3-] was unchanged or slightly elevated from rest, but CaCO2 was 4 vol% below rest.(ABSTRACT TRUNCATED AT 250 WORDS)

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