A CIRCULATING PROTEIN THAT DEPOLARIZES CELLS INCREASES AFTER HEMORRHAGE IN DOGS

Recent evidence suggests that a circulating factor or factors may medi ate cell membrane depolarization after hemorrhage in rats. To test for the presence of a similar factor in dogs, conscious adult splenectomi zed dogs with chronic arterial cannulae were either (1) bled 30% of me asured blood volume over 3 minutes (HEM, n = 8); (2) bled 30% of measu red blood volume over 3 minutes and reinfused with the shed blood 10 m inutes later (HEM + REINF, n = 6); or (3) observed without hemorrhage (CONTROL, n = 5). Treatments were applied in random order, 72 hours ap art. Arterial blood was sampled at rest and for 1 hour. Depolarizing a ctivity of the plasma was measured in an in vitro bioassay using resti ng dog RBCs and a membrane potential-sensitive oxonol dye (DIBAC). Flu orescence was measured by spectrofluorometry and the percentage of cha nge from resting values was calculated. Fluorescence intensity increas ed after hemorrhage in the HEM and the HEM + REINF groups. Fluorescenc e intensity decreased to CONTROL values in the HEM + REINF group by 10 minutes after reinfusion of shed blood, but remained greater than CON TROL values in the HEM group. The magnitude of early cell membrane dep olarization was approximately 20 mV. Similar depolarization was observ ed in cultured canine skeletal myocytes and pre-adipocytes. Changes in fluorescence intensity correlated with changes in mean arterial press ure at all times after hemorrhage except at 15 minutes (5 minutes afte r reinfusion in the HEM + REINF group). The depolarizing activity in d og plasma after hemorrhage shares several physical chemical properties with a similar substance identified in rats after hemorrhage. We conc lude that a circulating protein mediates cell depolarization in dogs a fter 30% hemorrhage, and that reinfusion of shed blood may block relea se of this substance. Attenuation of circulating depolarizing activity may be a useful index of the success of resuscitation.