Regulation Of Blood Oxygen Transport and Red Cell pH_i After Exhaustive Activity in Rainbow Trout (Salmo Gairdneri) and Starry Flounder (Platichthys Stellatus)

In vitro, exogenous adrenaline reduced the Bohr and Root shifts caused by elevated ⁠, and depressed plasma pH in rainbow trout blood, but not in starry flounder blood. In vivo immediately after exercise, plasma adrenaline (Ad) and noradrenaline (NAd) increased about 12-fold in rainbow trout. Associated with this catecholamine mobilization was a significant haemoconcentration, red blood cell (RBC) swelling and a reduction in RBC [NTP]; the latter was larger than that explained by cell swelling alone, indicating metabolic degradation of nucleoside triphosphate (NTP). RBC intracellular pH (pH_i) fell only slightly after exercise (0·07 units) at 0h, but was restored by 0·5 h in the face of a large plasma acidosis (0·4 units). [O₂]/[Hb] fell significantly, but this decline may have been due in part to the significant reduction in ⁠. The reduction in [O₂]/[Hb] was less than predicted from in vitro O₂-dissociation curves at low (0·5 nmol 1⁻¹) catecholamine levels, but similar to that predicted at high (90 nmol 1⁻¹) catecholamine levels. In flounder, resting Ad and NAd levels were about 10 times those in trout and did not change significantly after exercise. As a consequence, there was no reduction in RBC [NTP], and RBC pH, fell significantly (0·10 units) after exercise in the face of a large plasma acidosis (0·4 units) and remained depressed until 4h, although RBC swelling did occur. These factors in addition to the increased ⁠, may have contributed to the reduction in arterial [O₂]/[Hb], in the face of a constant ⁠. However, [O₂]/[Hb] was restored to resting levels prior to the correction of RBC pH_i and ⁠. This, in conjunction with the observation that catecholamines did not affect the in vitro blood-O₂ dissociation curve, suggests that additional factors may be involved in regulating O₂ transport after exercise in flounder.