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 Pasteurel la 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 (endot helium intact), vaccination did not alter the response to isoprotereno l, or sodium fluoride whereas the relaxation response to cholera toxin was impaired. In the pulmonary artery (endothelium removed), the maxi mum relaxation attained in response to isoproterenol was reduced and t he response to exogenous calcium, sodium fluoride and cholera toxin no t 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 remo ved), the response to isoproterenol and sodium fluoride was not altere d following P haemolytica vaccination whereas the relaxation response to cholera toxin was enhanced and the response to exogenous calcium sl ightly impaired. These experiments suggest that vaccination with live strains of P haemolytica cause subclinical disturbances in the pulmona ry circulation and may potentially alter the animals' response to path ogens.