The pivotal role of adrenomedullin in producing hyperdynamic circulation during the early stage of sepsis

Background: Initial cardiovascular responses during sepsis are characterize d by hyperdynamic circulation. Although studies have shown that a novel pot ent vasodilatory peptide, adrenomedullin (ADM), is up-regulated under such conditions, it remains unknown whether ADM is responsible for initiating th e hyperdynamic response. Objective: To determine whether increased ADM release during early sepsis p lays any major role in producing hyperdynamic circulation. Design, Intervention, and Main Outcome Measure: Synthetic rat ADM (8.5 mu g /kg of body weight) was infused intravenously in normal rats for 15 minutes at a constant rate. Cardiac output, stroke volume, and microvascular blood flow in various organs were determined immediately as well as 30 minutes a fter ADM infusion. At 30 minutes after infusion, plasma ADM level was also measured. In additional groups, rats were subjected to sepsis by cecal liga tion and puncture. At 1.5 hours after cecal ligation and puncture, specific anti-rat ADM antibodies were infused, which completely neutralized the cir culating ADM. Various hemodynamic variables were measured 5 hours after cec al ligation and puncture (ie, the early stage of sepsis). Results: Cardiac output, stroke volume, and microvascular blood flow in the liver, small intestine, kidney, and spleen increased, and total peripheral resistance decreased 0 and 30 minutes after ADM infusion. In addition, pla sma levels of ADM increased from the preinfusion level of 92.7 +/- 5.3 to 6 91.1 +/- 28.2 pg/mL 30 minutes after ADM infusion, which was similar to ADM levels observed during early sepsis. Moreover, 5 hours after the onset of sepsis, cardiac output, stroke volume, and microvascular blood flow in vari ous organs increased and total peripheral resistance decreased. Administrat ion of anti-ADM antibodies, however, prevented the occurrence of the hyperd ynamic response. Conclusions: The results suggest that increased ADM production and/or relea se plays a major role in producing hyperdynamic responses during early seps is. Since our previous studies have shown that vascular responsiveness to A DM decreases in late sepsis, maintenance of ADM vascular responsiveness by pharmacological agents during the course of sepsis may prevent transition f rom the hyperdynamic to the hypodynamic state.