Plasma catecholamines in rainbow trout (Salmo gairdneri) during hypoxia

Plasma catecholamines (CAs) were assayed radioenzymatically in normoxic and variably hypoxic rainbow trout (Salmo gairdneri). Results were grouped according to four levels of progressively deeper hypoxemia. Only in animals where PaO2 fell below 6.7 kPa, were both adrenaline (A) and noradrenaline (NA), slightly, but significantly, increased. In contrast, substantial increases of plasma CAs occurred when PaO2 was reduced below 3.99 kPa (increment factor: A = 3.8, NA = 3.4). Comparisons between dose/response data from the literature and the present results suggest that plasma CAs might have a functional role during deep hypoxia. The regulatory role during mild hypoxia remains uncertain due to the lack of data concerning plasma CA prebranchial concentrations and of more precise dose/response relationships.