The contribution of the lymph hearts in compensation for acute hypovolemic stress in the toad Bufo marinus

Abstract

The Marine Toad Bufo marinus was used as a model for an investigation of the rate and volume pumping capacity of the amphibian lymph heart. B. marinus is a widely studied terrestrial toad which would be expected to experience a hypovolemic stress as a consequence of evaporative water loss when it is away from water.Currently published data on the role of the lymphatic system in amphibians are inadequate and contradictory. Estimates of the rate of formation of lymph and the role of the lymph hearts in returning this fluid to the circulation are not based on actual volume determinations :2 but rather estimates derived from changes in hematocrit using published values of plasma and blood volume. The lymph hearts are known to be vital to the maintainence of normal fluid compartment physiology and to increase their rate of activity during episodes of hypovolemic stress.Yet, significant redistribution of body fluids following hemorrage appears to occur in animals without lymph hearts.In this study, plasma and blood volumes were determined by the dye dilution technique using injected Evan's blue dye to label the plasma.Eight intact and 6 animals with their lymph hearts destroyed were hemorrhaged to 78% and 75% of their initial blood volumes, respectively.Changes in blood volume were measured following the hemorrhage by analysis of Evan's blue washout and hemodilution.