Histamine release, complement consumption, and microvascular changes after radiographic contrast media infusion in rabbits

The intravenous injection of RCM into rabbits produced dose-dependent changes in SAP, MVP, and RBCV, as well as plasma histamine and complement concentrations. After infusion of 8 ml/kg Hypaque-50, SAP dropped from 86 ± 3 mm Hg to 50 ± 3, MVP from 42 ± 2 cm H₂O to 26 ± 3, and RBCV from 0.98 ± 0.11 mm/sec to 0.37 ± 0.13. The microvascular changes appeared 10 sec after injection and persisted for 10 to 40 min. During the course of the reaction it was observed that leukocytes adhered to the endothelial walls and red blood cells shrank and finally aggregated in the microvessels. The microvascular changes were accompanied by an increase in plasma histamine concentration, with an average of 44 ng/ml after 2 min, and a drop in total plasma CH₅₀ by an average of 46%. Infusion of 8 ml/kg hyperosmolar saline solution (4.1 gm/dl or 1324 mOsm/L) produced initial changes in microvascular parameters which returned to normal within a few seconds. At the same time plasma histamine concentration increased slightly without changes in complement. It is concluded that the hyperosmolar properties of RCM may contribute to the initial hemodynamic changes observed after RCM infusion. However, the prolonged microcirculatory disturbances produced by RCM in rabbits appear to be a direct effect of the chemotoxicity of these compounds. Part of this chemotoxicity might result from initial release of vasoactive mediators such as histamine and activation of the complement system.