In vitro, exogenous adrenaline reduced the Bohr and Root shifts caused by elevated PaCO2 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 (pHi) fell only slightly after exercise (0.07 units) at 0 h, 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 PaO2. The reduction in [O2]/[Hb] was less than predicted from in vitro O2-dissociation curves at low (0.5 nmol l-1) catecholamine levels, but similar to that predicted at high (90 nmol l-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 pHi fell significantly (0.10 units) after exercise in the face of a large plasma acidosis (0.4 units) and remained depressed until 4 h, although RBC swelling did occur. These factors in addition to the increased PaCO2 may have contributed to the reduction in arterial [O2]/[Hb], in the face of a constant PaO2. However, [O2]/[Hb] was restored to resting levels prior to the correction of RBC pHi and PaCO2. 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.

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