DIRECT OBSERVATIONS OF SYMPATHETIC CHOLINERGIC VASODILATATION OF SKELETAL-MUSCLE SMALL ARTERIES IN THE CAT

1. The aim of this study was to examine the actual changes of the inte rnal diameter (i.d.) of arterial vessels of skeletal muscle evoked by activation of sympathetic cholinergic nerve fibres during stimulation of the hypothalamic defence area in anaesthetized cats. 2. For this pu rpose, ave have used our novel X-ray TV system for visualizing small a rteries (100-500 mu m i.d.) of the triceps surae muscle and larger ext ramuscular arteries (500-1400 mu m i.d.) of the hindlimb (the femoral (FA), popliteal (PA) and distal caudal femoral (DCFA) arteries). The p assage of a contrast medium from the large extramuscular arteries to t he smaller intramuscular arteries was serially measured before and dur ing hypothalamic stimulation. 3. Hypothalamic stimulation increased me an arterial blood pressure, heart rate and femoral vascular conductanc e. The i.d. of FA, PA, and DCFA did not change during the hypothalamic stimulation, whereas the i.d. of small arteries in the triceps surae muscle increased by 48 +/- 2% (mean +/- S.E.M.) and the cross-sectiona l area increased concomitantly by 118%. The maximum increase in i.d. o f 78 +/- 6%, was observed in arteries of 100-200 mu m. These increases in diameter were markedly reduced by intra-arterial injection of atro pine or by cutting the sciatic nerve, but not by phentolamine and prop ranolol given together. 4. The vasodilatation evoked by hypothalamic s timulation was seen in almost all the sections of the small arteries o bserved under control conditions and was distributed along the entire length of the vessel. In addition, the number of arterial vessels that could be detected increased by 42% during hypothalamic stimulation. T he newly detected arterial branches, which ranged from 100 to 300 mu m in diameter, mostly arose from the branching points. 5. It is conclud ed that stimulation of sympathetic cholinergic nerve fibres dilates th e small arteries of skeletal muscle ranging from 100 to 500 mu m, but not the larger extramuscular arteries.