Vaccine-derived Pasteurella haemolytica alter the responses of ovine pulmonary artery and vein to drugs acting on adenylate cyclase.

Sheep were vaccinated with a live, vaccine-derived strain of Pasteurella haemolytica. The ex vivo response of isolated pulmonary artery and vein to isoproterenol, cholera toxin, sodium fluoride and calcium were examined three days after vaccination. In the pulmonary artery (endothelium intact), vaccination did not alter the response to isoproterenol, or sodium fluoride whereas the relaxation response to cholera toxin was impaired. In the pulmonary artery (endothelium removed), the maximum relaxation attained in response to isoproterenol was reduced and the response to exogenous calcium, sodium fluoride and cholera toxin not altered. In the pulmonary vein (endothelium intact), the response to isoproterenol and sodium fluoride was unchanged whereas the response to cholera toxin was impaired. In the pulmonary vein (endothelium removed), the response to isoproterenol and sodium fluoride was not altered following P haemolytica vaccination whereas the relaxation response to cholera toxin was enhanced and the response to exogenous calcium slightly impaired. These experiments suggest that vaccination with live strains of P haemolytica cause subclinical disturbances in the pulmonary circulation and may potentially alter the animals' response to pathogens.