DIRECT MEASUREMENT OF FLOW FROM THE POSTERIOR LYMPH HEARTS OF HYDRATED AND DEHYDRATED TOADS (BUFO-MARINUS)

Flow from the posterior lymph hearts of Bufo marinus was measured usin g Doppler how probes. These probes were placed on the posterior verteb ral vein and recorded flow as lymph was ejected from the heart. In res ting, hydrated toads, mean lymph flow from one of the paired posterior lymph hearts was 25.9+/-1.9 ml kg(-1) h(-1), stroke volume was 8.9+/- 1.41 mu l kg(-1) and lymph heart rate was 47.5+/-3.7 beats min(-1). We estimate that, together, the paired posterior lymph hearts are capabl e of generating flows that are approximately one-sixtieth of the resti ng cardiac output. Mean peak systolic pressure developed by the poster ior lymph hearts was 1.62+/-0.08 kPa. Simultaneous measurements of lym ph heart pressure development and flow revealed that the outflow pore of the heart opened at a pressure of 0.71+/-0.04 kPa, approximately 11 3+/-5 ms into systole. When toads were moderately disturbed, stroke vo lume increased by as much as fourfold with little change in lymph hear t rate (<5 beats min(-1)). When toads were dehydrated, lymph how decre ased by 70 % at 12 h and by 80 % at 24 h. Since there was only a modes t non-significant decrease in lymph heart rate (30 %), this reduction in flow was attributed to decreases in stroke volume (approximately 80 %). Lymph heart flow and stroke volume returned to control values 30 min after adding water back into the experimental chamber. Stroke volu me was clearly more important in regulating lymph flow than lymph hear t rate under these conditions in Bufo marinus.