THE RELATIONSHIP BETWEEN BLOOD-FLOW AND DIAMETER IN THE ILIAC ARTERY OF THE ANESTHETIZED DOG - THE ROLE OF ENDOTHELIUM-DERIVED RELAXING FACTOR AND SHEAR-STRESS

The quantitative relationship between increase in blood flow and arter ial diameter was determined in an anaesthetized dog preparation (pento barbitone, induction 30 mg kg(-1) I.V., maintenance 3 mg kg(-1) I.V. e very 30 min). Changes in external iliac artery diameter were measured using piezoelectric ultrasound transducers capable of measuring diamet ers within the range of 2-20 mm with a resolution of +/-0.005 mm. The diameter of the artery was measured at two sites, at one of which the endothelium was damaged using a balloon angioplasty catheter. Increase s in blood flow were brought about by a combination of vasodilatation and cardiac stimulation (intra-arterial administration of acetylcholin e, downstream to the sites of diameter measurement, and electrical sti mulation of the left ansa subclavia), thereby preventing large changes in blood pressure. The effects of both transient and maintained incre ases in blood flow on mean arterial diameter in the section of artery with intact endothelium were measured. Transient increases in mean flo w from 147+/-0.21 to 611+/-80.0 ml min(-1) caused increases in diamete r of 0.12+/-0.02 mm from a control of 5.42+/-0.19 mm. The mean delay b etween maximum flow and maximum diameter was 24.51+/-1.1 s and the hal f-time for the return to control diameter was 82.0+/-9.6 s, compared w ith 12.1+/-1.5 s for the return to control flow. Maintained (3-4 min) increases in mean blood flow (from 104.7+/-15.1 to 694.7+/-135.1 ml mi n(-1)) produced larger increases in diameter of 0.48+/-0.30 mm from a control diameter of 4.89+/-0.12 mm. These changes in diameter were abo lished by N-omega-nitro-L-arginine methyl eater (L-NAME, 10-100 mg kg( -1) I.V.). In the section of artery with damaged endothelium, changes in diameter were relatively small and associated with small changes in blood pressure. This effect of a nearly 7-fold increase in flow on ar terial diameter is dependent upon the integrity of the endothelium and the release of endothelium-derived relaxing factor and causes a 29% r eduction in calculated boundary wall shear stress.