[Effect of pulsed excimer laser on arterial smooth muscle]

The effect of pulsed lasers on vasomotricity was measured on 22 segments of isolated rabbit thoracic aorta. The segments were isometrically suspended in a bath of Krebs-bicarbonate buffer and irradiated with two excimer lasers (XeCl and XeF) emitting at 308 and 351 nm respectively and coupled with a 400 mu optical fibre. The 10 to 120 seconds irradiations were performed at frequencies ranging from 10 to 100 Hz and pulse energies comprised between 1 and 7 mJ. These parameters were on both sides of the tissue ablation threshold. On the 22 segments studied the irradiation induced in every case (n = 118) relaxation of the vascular smooth muscle. The presence or absence of an anatomically and functionally intact endothelium was checked by scanning electron microscopy and by induction of relaxation with acetylcholine. Identical results were observed on specimens that had been subjected to deliberate endothelial abrasion. Relaxation was increased by drug-induced precontraction. The rise in arterial wall temperature, as measured by thermistor microprobe, never exceeded 5 degrees C, and histological examination of the specimens never showed thermal damage. It is concluded that on the isolated rabbit aorta pulsed excimer laser irradiation induces an endothelium-independent smooth muscle relaxation most probably due to photorelaxation combined with a lack of significant heating of the arterial wall. These experimental data support the use of pulsed sources for laser angioplasty.