ALTERED ENDOTHELIUM-DEPENDENT ALPHA-ADRENERGIC VASCULAR REACTIVITY FOLLOWING EXPOSURE TO PASTEURELLA-HAEMOLYTICA ANTIGENS

Rats were injected with sterile saline (controls), 10(5) cfu of Pasteu rella haemolytica (biotype A) obtained from a commercial vaccine, or a commercial Pasteurella leukotoxoid vaccine. Three days after vaccinat ion, the animals were killed and the thoracic aorta was removed. In so me experiments the vascular endothelium was mechanically removed. Each isolated aorta was placed in a tissue bath and the biophysical respon ses to methoxamine (alpha-1 agonist) were determined. In separate expe riments the endothelial surface was examined by scanning electron micr oscopy. In endothelium-intact vessels both vaccines appeared to enhanc e the contractile response to methoxamine. On the other hand, in endot helial-denuded vessels, the methoxamine-mediated contractile response was enhanced in the P. haemolytica-treated group but not in animals va ccinated with leukotoxoid. Furthermore, scanning electron microscopy r evealed deposition of a fibrin-like material on the endothelial surfac e of vaccinated animals. These results suggest that exposure to vaccin e-derived P. haemolytica antigens alters the morphology and adrenergic responsiveness of vascular smooth muscle.