A circulating protein that depolarizes cells increases after hemorrhage in dogs

Recent evidence suggests that a circulating factor or factors may mediate cell membrane depolarization after hemorrhage in rats. To test for the presence of a similar factor in dogs, conscious adult splenectomized dogs with chronic arterial cannulae were either (1) bled 30% of measured blood volume over 3 minutes (HEM, n = 8); (2) bled 30% of measured blood volume over 3 minutes and reinfused with the shed blood 10 minutes later (HEM + REINF, n = 6); or (3) observed without hemorrhage (CONTROL, n = 5). Treatments were applied in random order, 72 hours apart. Arterial blood was sampled at rest and for 1 hour. Depolarizing activity of the plasma was measured in an in vitro bioassay using resting dog RBCs and a membrane potential-sensitive oxonol dye (DIBAC). Fluorescence was measured by spectrofluorometry and the percentage of change from resting values was calculated. Fluorescence intensity increased after hemorrhage in the HEM and the HEM + REINF groups. Fluorescence intensity decreased to CONTROL values in the HEM + REINF group by 10 minutes after reinfusion of shed blood, but remained greater than CONTROL values in the HEM group. The magnitude of early cell membrane depolarization was approximately 20 mV. Similar depolarization was observed in cultured canine skeletal myocytes and pre-adipocytes. Changes in fluorescence intensity correlated with changes in mean arterial pressure at all times after hemorrhage except at 15 minutes (5 minutes after reinfusion in the HEM + REINF group). The depolarizing activity in dog plasma after hemorrhage shares several physical chemical properties with a similar substance identified in rats after hemorrhage.(ABSTRACT TRUNCATED AT 250 WORDS)