In vitro diameter response of rat femoral artery to flow in the presence and absence of endothelium

We have examined the diameter response of rat femoral artery segments in th e presence and absence of endothelium to changes in flow rate. The segments were isolated, mounted on microcannulae, maintained at 37 degreesC, and pe rfused at 90 mmHg with Tyrode's solution. The external arterial diameter wa s measured using video-microscopy. The mean control diameter was 741 +/- 22 mum (mean +/- SEM,n = 7). The arteries were preconstricted to 75 +/-1% of the control diameter with a superfusion of 1 muM norepinephrine (NE). Endot helial function was verified by perfusion of 1 muM acetylcholine (ACh). Two different flow protocols were employed: step changes in flow (n = 7) and l ow-frequency sinusoidal flow changes (0.01 Hz <f <0.05 Hz,n = 3). The endot helium was then removed by perfusion of the artery with 0.3% CHAPS (n = 7) and the flow protocol repeated. All arteries contracted with increasing flo w. For rapid step changes in flow, contractions and relaxations were modell ed with an exponential fit where characteristic time constants were 34 +/-2 and 40 +/- 3s, respectively (functional endothelium) and 35 +/-2 and 37 +/ - 2s, respectively (non-functional endothelium). The time constants in the presence and absence of endothelium were not significantly different (paire d t-test, p > 0.05). Sinusoidal flow oscillations resulted in sinusoidal di ameter oscillations, whose amplitude and phase lag were inversely proportio nal to the frequency of the flow oscillations. A first-order low-pass filte r, with a time constant of 28 +/-3 and 30 +/-5 s for arteries with and with out functional endothelium, respectively, was used to describe the relation between oscillatory flow and diameter. The response of the rat femoral art eries to changes in flow was not found to be different whether the endothel ium was intact or removed. (C) 2001 Elsevier Science Ltd. All rights reserv ed.