INTRADERMAL ACTIONS OF HYPERTONIC SALINE INVOLVE NEURAL AND VASCULAR MECHANISMS

The aim of this study was to investigate whether the wheal and flare r esponses to intradermal injection of hypertonic (4.5%) saline (HTS) we re inhibited by local injection of 1% lignocaine. Eight normal subject s were studied on one occasion. Lignocaine (0.125 mi) was infiltrated at four sites on one forearm and normal saline on the other, Five minu tes later, duplicate intradermal injections of 30 mu l of histamine (2 2.5 nmol ml(-1)), substance P (1 nmol ml(-1)), HTS and normal saline w ere given coded and in random order, one of each pair to each forearm. Lignocaine inhibited flare responses to histamine, substance P and HT S by 56% (P < 0.01), 78% (P < 0.01) and 77% (P < 0.05) respectively su ggesting similar involvement of an axon reflex. Wheal to histamine was inhibited by 31% (P < 0.02) and to substance P by 33% (P < 0.05) but not to HTS. This suggests that the mechanism of wheal response to HTS differs from that of histamine and substance P.