CUTANEOUS PERMEABILITY RESPONSES TO BRADYKININ AND HISTAMINE IN THE GUINEA-PIG - POSSIBLE DIFFERENCES IN THEIR MECHANISM OF ACTION

1 Plasma protein extravasation (PPE) responses in guinea-pig skin have been measured using accumulation of intravenously injected I-125-labelled human serum albumin (I-125-HSA). 2 The nitric oxide (NO) synthase inhibitor, N-G-nitro-L-arginine methyl ester (L-NAME; 0.1 mu mol/site) significantly reduced responses to bradykinin (BK; 0.5 nmol/site) or histamine (4.5 nmol/site) when co-injected with the inflammatory mediators. D-NAME (0.1 mu mol/site) had no significant effect. 3 L-NAME (0.01-0.1 mu mol/site) appeared to produce greater shifts of the dose-response curve to BK (0.1-3 nmol/site) than of that to histamine (2.3-27 nmol/site). Both 0.01 and 0.1 mu mol L-NAME/site significantly reduced the response to BK (0.5 nmol/site) whereas only the higher dose of L-NAME produced a significant reduction in the response to histamine (4.5 nmol/site). 4 The inhibitory effect of L-NAME (0.1 mu mol/site) on the response to BK but not on that to histamine was significantly reversed by L-arginine (L-Arg; 10 mu mol/site). D-arginine (D-Arg; 10 mu mol/site) had no significant effect in either case. 5 L-Arg (10 mu mol/site) significantly enhanced the response to BK but inhibited that to histamine. D-Arg (10 mu mol/site) had no significant effect on BK but significantly inhibited histamine. L-Lysine (L-Lys: 10 mu mol/site) had no significant effect on the response to either BK or histamine. 6 L-Arg (100 mM) had a significant inhibitory effect on isometric contractions to histamine, but not BK in guinea-pig ileum in vitro. D-Arg (100 mM) also significantly inhibited histamine responses whereas L-Lys (100 mM) had no effect. 7 The alpha-adrenoceptor agonist, phenylephrine (0.3 or 6 nmol/site) inhibited matched responses to BK (0.5 nmol/site) or histamine (5.4 nmol/site) to comparable degrees, but gave significant inhibition only at the higher dose. 8 The beta-adrenoceptor agonist, isoprenaline (0.5 or 10 nmol/site) had a significant inhibitory effect on the response to histamine (5.4 nmol/site) whereas a comparable response to BK (0.5 nmol/site) was significantly reduced by the higher:dose only. 9 Our results with L-NAME suggest that local production of NO is involved in the modulation of mediator-induced vascular permeability. It is possible that NO may play a greater role in the extravasation response to BK than to that induced by histamine. 10 The differential effects of L-NAME and isoprenaline on BK- and histamine-induced PPE raise the possibility that BK and histamine may induce vascular permeability via different mechanisms in guinea-pig skin.