Vascular recovery following hemorrhage in the dogfish shark Squalus acanthias

Cardiovascular regulatory systems were examined in the dogfish shark after hemorrhage of 1% of body weight. An immediate 45% decrease in mean dorsal aortic pressure and delayed increases in plasma epinephrine concentration and plasma norepinephrine concentration were noted. During the recovery period following hemorrhage, the catecholamine levels peaked (epinephrine 203% of control, norepinephrine 148% of control) and then returned toward control values. Hematocrit, however, continued to decline as blood pressure recovered. Phentolamine pretreatment, which in itself caused a 55% decrease in dorsal aortic pressure, did not prevent the recovery of blood pressure after hemorrhage. This study indicates that 1) hemorrhage causes an increase in circulatory catecholamine concentration, possibly by a baroreceptor reflex; 2) volume recruitment, as indicated by the drop in hematocrit, is a major mechanism contributing to the recovery of dorsal aortic pressure after hypotension; and 3) alpha-adrenergic receptors are not necessary for the recovery of dorsal aortic pressure after hemorrhage.