Effects of hypoxia on blood pressure and heart rate in three marine teleosts.

Ventral aortic blood pressure (Pva) and heart rate (HR) responses to rapidly (within 1 min) induced hypoxia (PWO2=4-5.3 kPa) were investigated in vivo in three species of marine teleosts (shorthorn sculpin, Myoxo-cephalus scorpius; eel-pout, Zoarces viviparus; and five-bearded rockling, Ciliata mustela). Fish were exposed to hypoxia for 4 min (M.scorpius) or 5 min (Z.viviparus and C.mustela).Pva was unaffected in M.scorpius, decreased in Z.viviparus and increased in C.mustela in response to hypoxia.Untreated M.scorpius and Z. viviparus responded with a characteristic bradycardia during hypoxia, whereas C.mustela developed no bradycardia. Injection of atropine followed by the β-adrenoceptor antagonist sotalol in M.scorpius and Z. viviparus, revealed that both the inhibitory (cholinergic) and the excitatory (adrenergic) influence on the heart increase during hypoxia. The inhibitory influence dominates, resulting in the observed bradycardia.