INFLUENCE OF VASCULAR SMOOTH-MUSCLE HETEROGENEITY ON ANGIOTENSIN CONVERTING ENZYME-ACTIVITY IN CHICKEN EMBRYONIC AORTA AND IN ENDOTHELIAL-CELLS IN CULTURE

The smooth muscle of the abdominal region of the chicken aorta derives from locally recruited mesenchyme (mesenchymal smooth muscle), whereas that of the thoracic region derives from the neural crest (ectomesenchymal smooth muscle). We hypothesized that this smooth muscle heterogencity might affect important enzymatic functions of the vessel wall. Therefore, we measured angiotensin converting enzyme (ACE) activity in homogenates of chicken thoracic and abdominal aorta at different embryonic stages (days 10, 14, and 18 of gestation). ACE activity increased in both regions over the time of gestation (p<0.001 in both cases); the increase was steeper and ACE activity was higher in thoracic than in abdominal segments (p<0.001). K(m) values were similar (almost-equal-to 7-mu-M) at all times and between the two segments, whereas changes in V(max) values closely paralleled those in enzyme activity, indicating gestation-dependent increases in the amount of enzyme. Neural crest ablation at an early developmental stage resulted in an increase of ACE activity in thoracic homogenates (p<0.001), predictably leaving that in abdominal homogenates unaffected. Bovine pulmonary artery endothelial cell monolayers exposed to media conditioned with cultured mesenchymal or ectomesenchymal smooth muscle cells exhibited elevated ACE activity (46% and 83%, respectively, relative to control medium, with p<0.01 in both cases; p<0.05 between the two media). Increases in endothelial cell ACE activity corresponded to proportional increases in ACE protein determined by enzyme-linked immunosorbent assay (r=0.99) and were interpreted as indicative of enhanced enzyme synthesis subsequent to exposure of endothelial cells to smooth muscle-conditioned media. We conclude that, in addition to mechanical and humoral factors, smooth muscle ontogeny may differentially influence vascular ACE activity.