EFFECT OF A NITRIC-OXIDE DONOR (GLYCERYL TRINITRATE) ON NOCICEPTIVE THRESHOLDS IN MAN

Several animal studies suggest that nitric oxide (NO) plays a role in central and peripheral modulation of nociception. Glyceryl trinitrate (GTN) exerts its physiological actions via donation of NO. The purpose of the present study was to examine the effect of this NO donor on no ciceptive thresholds in man. On two different study days separated by at least a week 12 healthy subjects received a staircase infusion of G TN (0.015, 0.25, 1.0, 2.0 mu g/kg/min, 20 min each dose) or placebo in a randomized double-blind crossover design. Before the infusion and a fter 15 min of infusion on each dose, pressure pain detection and tole rance thresholds were determined by pressure algometry (Somomedic AB, Sweden) in three different anatomic regions (finger, a temporal region with interposed myofascial tissue and a temporal region without inter posed myofascial tissue). Relative to placebo, the three higher GTN do ses induced a decrease in both detection and tolerance thresholds in t he temporal region with interposed myofascial tissue (p=0.003 detectio n and p=0.002 tolerance thresholds, Friedman). No such changes were ob served in the other two stimulated regions. These results could reflec t central facilitation of nociception by NO. However, we regard conver gence of nociceptive input from pericranial myofascial tissue and from cephalic blood vessels dilated by NO as a more Likely explanation of our findings.