Influences of exercise-stress and adrenaline upon intra- and extracellular acid-base status, electrolyte composition and respiratory properties of blood in tench (Tinca tinca) at different seasons

Summary Exercise-stress in tench resulted in severe acidoses in both the red cells and the extracellular fluid in vivo. These coincident pH decreases conformed to the in vitro pH_i-pH_e relationship for tench blood in the oxygenated state. The extracellular acidosis was primarily respiratory in winter and metabolic in spring and summer. This was due to more effective buffering of metabolic protons in winter by an elevation in [HCO ⁻₃ ] levels, rather than to differences in the lactic- and carbonic acid loads. A good correspondence was found between buffered metabolic protons and increases in [lactate]. There was no evidence for β-adrenergic red cell swelling and associated red cell pH changes in tench both after exercise and adrenaline infusion. Arterial O₂ transport was, however, improved in exercise by pronounced increases in\(P_{O_2 } \). Large increases in plasma potassium concentration and small elevations of chloride and calcium levels occurred in exercise. Hematocrit and blood [Hb] also increased, probably due to an adrenergic release of erythrocytes from the spleen, but these increases were small and appeared unimportant for blood O₂ transport. Seasonal differences were found in exercise-induced changes in [lactate], in the magnitude of electrolyte and\(P_{O_2 } \) changes, as well as in resting values for pH_e, pH_i, [HCO ⁻₃ ], [Cl⁻] and [Ca⁺⁺]. The origin and importance of these are discussed.