Central venous pressure and mean circulatory filling pressure in the dogfishSqualus acanthias: adrenergic control and role of the pericardium

Abstract

Subambient central venous pressure (Pven) and modulation of venous return through cardiac suction (vis a fronte) characterizes the venous circulation in sharks. Venous capacitance was estimated in the dogfish S qualus acanthias by measuring the mean circulatory filling pressure (MCFP) during transient occlusion of cardiac outflow. We tested the hypothesis that venous return and cardiac preload can be altered additionally through adrenergic changes of venous capacitance. The experiments involved the surgical opening of the pericardium to place a perivascular occluder around the conus arteriosus. Another control group was identically instrumented, but lacked the occluder, and was subjected to the same pharmacological protocol to evaluate how pericardioectomy affected cardiovascular status. Routine Pvenwas negative (−0.08 ± 0.02 kPa) in control fish but positive (0.09 ± 0.01 kPa) in the pericardioectomized group. Injections of 5 μg/kg body mass ( Mb) of epinephrine and phenylephrine (100 μg/kg Mb) increased Pvenand MCFP, whereas isoproterenol (1 μg/kg Mb) decreased both variables. Thus, constriction and relaxation of the venous vasculature were mediated through the respective stimulation of α- and β-adrenergic receptors. α-Adrenergic blockade with prazosin (1 mg/kg Mb) attenuated the responses to phenylephrine and decreased resting Pvenin pericardioectomized animals. Our results provide convincing evidence for adrenergic control of the venous vasculature in elasmobranchs, although the pericardium is clearly an important component in the modulation of venous function. Thus active changes in venous capacitance have previously been underestimated as an important means of modulating venous return and cardiac performance in this group.