PRESSURE-FLOW RELATIONSHIPS IN THE PERFUSED POST-SYSTEMIC CIRCULATION OF THE SQUID, LOLIGO-PEALEI

An artificially perfused preparation of the posterior systemic circulation of the squid, L. pealei, was developed to permit examination of some physical and chemical factors affecting pressure-flow relationships. A preparation took .apprx. 30 min to stabilize when perfused by vigorously oxygenated, filtered seawater. Stability was maintained for 1-2 h, after which the preparation decayed rapidly. The decay was characterized by increasing vascular resistance and edema. When flow was plotted against pressure, a curve which obeyed a power function was obtained that indicated the posterior systemic vasculature possessed very little autoregulatory capacity. Marked passive distensibility was also observed in this region of the vascular system. A critical closing pressure of 0.54 kPa [Pascal] was measured. The posterior systemic vasculature was sensitive to O2 tension and decreased its vascular resistance in response to hypoxia. Acetylcholine also caused marked vasodilation. This response to acetylcholine was dose-dependent and had a threshold of 10-12 M.