Figure 6.
Perceived pain during iontophoresis of acid before and after topical application of glyceryl trinitrate. Recordings were made by iontophoresis of acid solution, pH 2.0, or saline at a current of 0.3 mA. A, Topical application of GTN significantly increased the perceived acid mediated-pain compared with application of vehicle or to untreated skin (naive). B, Time course of the mean VAS with application of GTN, vehicle or no treatment (naive). The effect of GTN was most prominent in the first 2 min after beginning iontophoresis. C, D, Treatment of the skin with GTN did not affect heat pain threshold (C) or mechanical pain threshold (D).