Pharmacological studies of sensitized canine pulmonary blood vessels

Pulmonary artery and vein from an ovalbumin sensitized canine model of allergic asthma showed hypersensitivity (leftward shift of dose-response curve) and hyper-reactivity (upward shift) to histamine when compared to those from a littermate control in vitro. Dose-response studies showed that only sensitized pulmonary veins exhibited hypersensitivity, but not hyper-reactivity, to norepinephrine. However, sensitized pulmonary arteries showed neither hypersensitivity nor hyper-reactivity to norepinephrine. Both sensitized and control pulmonary arteries and veins displayed no difference in serotonin dose-response curves. The Schultz-Dale reaction was only observed in the sensitized pulmonary veins; it could be blocked (25-45%) by pyrilamine maleate (10(-7) M) and (5-15%) by phentolamine (5 X 10(-6) M). We concluded that anaphylaxis develops only on the venous side of the pulmonary circulation, but that increase in sensitivity or reactivity to agonists develops in both arteries and veins. Histamine appears to be the major, but not the only, mediator released and we have obtained data to suggest it exerts its contractile effect on the muscle via both postsynaptic (directly) and presynaptic (indirectly) effects.