Pressor and hemodilution responses compensate for acute hemorrhage in bluefish

1. After hemorrhage of 21% blood volume (0.9% body weight) blood pressure (BP) and heart rate (H.R.) of unanesthetized bluefish (Pomatomus saltatrix) recovered within 5 min. 2. Phentolamine blocked this recovery. 3. Atropine increased control H.R. from 48 to 87 per min, and to 108 after hemorrhage, with delay of BP recovery to 10 min. 4. With small, repeated hemorrhages every 20 min, hemodilution and recovery of BP occurred between hemorrhages. Removal of 27% blood volume resulted in only temporary recovery. 5. Thirty min after hemorrhage, plasma epinephrine was 5 x and norepinephrine 8 x control. 6. Thus, bluefish tolerate hemorrhage with initial vasoconstriction via alpha-adrenergic pathways, and hemodilution.