RESPONSES TO PRESSURE AND VASOACTIVE AGENTS BY ISOLATED PULMONARY-ARTERIES FROM MONOCROTALINE-TREATED RATS

Intralobar and side branch pulmonary arteries removed from rats 7, 14, and 21 days after injection with monocrotaline (MCT) were cannulated and pressurized, and their responses to potassium chloride, norepineph rine, acetylcholine, and angiotensin II were measured. Static pressure -diameter curves were also performed, and arterial distensibility was calculated. Arteries from all three MCT-treated groups showed reduced responses to potassium chloride and angiotensin II compared with contr ol arteries (P < 0.05). The norepinephrine response was significantly reduced in arteries from the 14- and 21-day groups (P < 0.05). Dilatio ns in response to acetylcholine were similar in arteries from the cont rol and 7-day groups but were reduced compared with those in control v essels from the 14- and 21-day groups (P < 0.05). Compared with contro l values, the slopes of the pressure-diameter curves and the arterial distensibility decreased significantly with time after MCT treatment ( P < 0.05). Values for arterial distensibilities obtained in the isolat ed pulmonary arteries support the theory that structural changes that occur as a result of MCT administration contribute to vessel stiffness . The acetylcholine-induced dilation of vessels from MCT-treated rats indicates that endothelium-derived factors are still produced, but dim inished vasodilation coupled with decreased distensibilities after MCT suggest that abnormal vascular remodeling rather than a change in ago nist sensitivity may be responsible for the reduced responsiveness see n in these arteries.