A novel approach to maintaining cardiovascular stability after hemorrhagic shock: Beneficial effects of adrenomedullin and its binding protein

Vascular responsiveness to adrenomedullin (AM), a recently discovered vasodilator peptide, is depressed after hemorrhage and resuscitation. Downregulation of AM binding protein-1 (ie, AMBP-1) appears to be responsible for this hyporesponsiveness. Therefore, we hypothesize that administration of AM/AMBP-1 improves cardiovascular responses after hemorrhagic shock and resuscitation. Male rats were bled to and maintained at a mean blood pressure of 40 mm Hg for 90 minutes. The animals were then resuscitated with 4 times the volume of shed blood with Ringer's lactate over 60 minutes. At 15 minutes after the beginning of resuscitation in hemorrhaged animals, AM alone, AMBP-1 alone, AM in combination with AMBP-1, or vehicle (phosphate-buffered saline solution) was administered intravenously over 45 minutes. At 4-hour postresuscitation, in vivo left ventricular contractility parameters, maximal rates of ventricular pressure increase (+dP/dt _max) and decrease (-dP/dt _max), were determined. Cardiac output and organ blood flow were measured with the use of radioactive microspheres. In an additional group of animals, cardiac tumor necrosis factor-alpha (TNF-α) levels were measured by an enzyme-linked immunosorbent assay. Four hours after resuscitation, +dP/dt _max, -dP/dt _max, cardiac output, and organ blood flow in the liver, small intestine, and kidneys were decreased while treatment with AM/AMBP-1 increased these parameters (P <.05). Moreover, cardiac TNF-α levels were elevated at 4 hours after hemorrhage and resuscitation, while AM/AMBP-1 treatment reduced them to sham levels (P <.05). Administration of AM/AMBP-1 appears to be a useful approach for restoring and maintaining cardiovascular stability after severe hemorrhagic shock and crystalloid resuscitation.