Regulation of cardiac function in the horn shark by changes in pericardial fluid volume mediated through the pericardioperitoneal canal

Abstract

The California horn shark (Heterodontus francisci), instrumented with a pericardial catheter and a ventral-aortic flow probe, was studied to determine the effect of complete pericardial chamber evacuation on the time course for restitution of pericardial fluid-volume and pressure, and the effects of both fluid removal and its restitution on cardiac output. Prior to evacuation, pericardial pressure was −0.02±0.02 kPa, and cardiac output was 18±2 ml min⁻¹ kg⁻¹. Evacuation reduced pericardial pressure to −0.73±0.14 kPa, and increased cardiac output to 23±4 ml min⁻¹ kg⁻¹. The time course for restoration of post-evacuation pressure is described by a non-linear asymptotic function. A large percentage of the pericardial pressure and volume recovery occurred within the first hour, while, complete restoration of pre-withdrawal conditions required about 11 h. Pericardial pressure-volume relationships, determined by incremental infusion of small volumes of elasmobranch saline into the pericardium, confirm previous findings that the operating pericardial pressure in the horn shark is at or near ambient pressure and that both pericardial fluid volume and cardiac stroke volume influence horn shark pericardial pressure.