Effects of hypervolemia and hypovolemia on cardiac and posterior lymph heart function in the toad Bufo marinus (L.)

Cardiac and posterior lymph heart function in the toad Bufo marinus (L.) were measured in response to hemorrhage and both systemic and lymphatic volume loading to evaluate the role of the amphibian lymphatic system in fluid regulation. In every animal, systemic volume loading elicited an initial sharp rise in mean arterial blood pressure, corresponding to an immediate cessation of lymph heart contraction lasting approximately 12 min. This was followed by a short-term decrease in blood pressure, to 36% below normal. While stroke volume and lymph flow for the individual animals increased variably over a 6-h period, mean lymph heart rate and pressure varied little. Lymphatic volume loading elicited only minor changes in blood heart and lymph heart rate. Again, stroke volume and lymph flow increased variably, with the effect lasting about 13 h. Hypovolemia caused a sharp drop in blood pressure and a corresponding rise in blood heart rate. Lymph heart variables changed little, with the exception of rate, which, in some animals, was elevated for approximately 20 min following hemorrhage.