EFFECTS OF AN ENDURANCE TRAINING-PROGRAM ON THE PASSIVE AND NORADRENALINE-ACTIVATED COMPLIANCES OF RAT AORTA

The effects of a 12-week endurance training programme (treadmill) upon the passive and the noradrenaline-activated properties of the aorta w ere studied in 15 trained and 24 sedentary rats. Aortic compliance was studied by measuring the length-tension curves of rings of the descen ding aorta without (passive properties) and with noradrenaline (noradr enaline activated) in a bubbling Krebs bath kept at a temperature of 3 7 degrees. The training effect on aortic volume compliance was studied by transforming the tension-length curves into a cross-sectional area -pressure curve according to Laplace's law. The noradrenaline responsi veness was studied by the dose-effect curve. The mechanical data were correlated with the results of a histomorphometric study which measure d the aortic wall thickness and the percentages and amounts of elastic , connective and muscle components. Passive aortic compliance and volu me compliance were higher in endurance-trained rats whose tunica media presented a lower percentage of collagen and a larger amount of elast ic tissue. The dose-effect curve showed that the maximal aortic respon se to noradrenaline was stronger in trained rats but that the half max imal effective dose was not different. As a consequence, the length-te nsion curves of the noradrenaline fully activated aorta were similar i n trained and sedentary rats except at the highest tensions where coll agen is the main factor determining aortic stiffness. The increased no radrenaline response in trained rats was probably the result of the hy pertrophy of the smooth muscle cells as maximal active strain (Newtons per square metre) was similar in trained and sedentary rats.