The effect of noradrenaline, angiotensin II and vasopressin on blood flow and sensitivity to heat in capsaicin-treated skin

Drummond, P.D. (1998) The effect of noradrenaline, angiotensin II and vasopressin on blood flow and sensitivity to heat in capsaicin-treated skin. Clinical Autonomic Research, 8 (2). pp. 87-93.

Abstract

The effect of iontophoretically applied noradrenaline, angiotensin II and vasopressin on blood flow and sensitivity to heat was investigated in the capsaicin-treated forearms of 52 healthy volunteers. Non-specific effects of a 4-min saline iontophoresis were investigated in another 19 subjects. Pretreatment with phentolamine inhibited vasoconstriction and thermal hyperalgesia to noradrenaline, indicating that α-adrenoceptors mediated these responses. The intensity of thermal hyperalgesia differed significantly across the following treatments: saline (heat pain threshold 1.1°C lower than at control sites), angiotensin II (3.4°C), noradrenaline (6.4°C) and vasopressin (9.0°C). Decreases in skin blood flow were significantly greater after the iontophoresis of noradrenaline (65% reduction from baseline) and vasopressin (68%) than after the iontophoresis of angiotensin II (45%). In contrast to the other two drugs, angiotensin II induced thermal hyperalgesia in proportion to the intensity of vasoconstriction. The findings suggest that iontophoretic currents induce minor non-specific thermal hyperalgesia. Angiotensin II appears to increase sensitivity to heat by an ischaemic mechanism, whereas an additional non-vascular influence contributes to thermal hyperalgesia induced by noradrenaline and vasopressin. These mechanisms could contribute to hyperalgesia in chronic inflammatory or neuropathic pain syndromes.