Effect of glucagon on gastrointestinal blood flow of dogs in hypovolemic shock.

A microsphere technique was used to study the effect of glucagon on blood flow to the different tissue layers of the stomach, small bowel, and colon of the dog in hypovolemic shock. In normal dogs, glucagon caused a twofold rise in flow to all layers of the stomach and colon, and a threefold increase to all layers of the small bowel. After administration of glucagon, a larger fraction of cardiac output was diverted to the gut microcirculation. In acute hypovolemic shock, intestinal perfusion was preserved relative to cardiac output inasmuch as cardiac output and gastric blood flow fell 75% and flow to the small bowel and colon fell by only about 50%. Glucagon markedly increased the fraction of cardiac output passing to the gut circulation in hypovolemic shock and, most importantly, sustained flow to the areas most prone to ischemic necrosis; gastric mucosa, colonic mucosa, and small intestinal villi. In more prolonged shock, however, glucagon precipitated fatal cardiovascular collapse unless part of the lost blood volume first was replaced. Glucagon, therefore, should not be used in patients in hypovolemic shock without prior replacement of at least part of the lost blood volume.