The skin hyperaemic response to local injection of substance P and capsaicin in diabetes mellitus

Abstract

Recent studies have demonstrated impaired skin hyperaemia to local injury in diabetes mellitus. In order to gain insight into the mechanisms of impaired hyperaemia, dose-response curves to intradermal substance P (25, 50, 100 pmol) and capsaicin (1.0, 2.5, 5.0 nmol) were examined before and after histamine blockade with chlorpheniramine, in 6 patients with uncomplicated Type 1 diabetes and 9 matched control subjects. Skin hyperaemia was measured indirectly as the peak laser Doppler flow in proximity to the area of hyperaemia. The response to the three doses of substance P was significantly lower in diabetic patients (0.37 +/- 0.12 (+/- SD), 0.51 +/- 0.12, 0.67 +/- 0.09 V) than in control subjects (0.57 +/- 0.15, 0.70 +/- 0.19, 0.84 +/- 0.21 V; p less than 0.01). In contrast there was no significant difference in skin hyperaemia to capsaicin between diabetic patients (0.41 +/- 0.07, 0.50 +/- 0.09, 0.59 +/- 0.09 V) and control subjects (0.41 +/- 0.06, 0.52 +/- 0.08, 0.63 +/- 0.07 V). Following chlorpheniramine, the response to capsaicin remained unaltered (0.39 +/- 0.07, 0.51 +/- 0.05, 0.60 +/- 0.07 in diabetic patients and 0.43 +/- 0.08, 0.50 +/- 0.10, 0.63 +/- 0.07 V in control subjects), but there was a significant reduction in hyperaemia to substance P in both patients (20.4 +/- 12.3% reduction, p less than 0.05) and control subjects (20.6 +/- 14.1% reduction, p less than 0.05). It is suggested that impaired skin hyperaemia may represent decreased vascular reactivity to locally released substance P from peripheral nerve fibres.