1 The possibility that tachykinin NK, receptors

1. Increased expression of inducible nitric oxide synthase (iNOS) and subsequent elevation of nitric oxide (NO) levels at inflammatory sites have led to the suggestion that peroxynitrite (the reaction product of superoxide and NO) is involved in pro-inflammatory processes. The present study has investigated the ability of peroxynitrite to induce oedema formation in the rat cutaneous microvasculature. 2. Peroxynitrite was synthesized from hydrogen peroxide and acidified nitrite. Spectrophotometry was used to measure the concentration and breakdown of peroxynitrite. It was also used to determine maximum amounts of hydrogen peroxide and sodium nitrite remaining after synthesis. 3. Oedema formation in response to intradermally (i.d.) injected peroxynitrite, hydrogen peroxide and sodium nitrite was measured by the extravascular accumulation of i.v. [125I]-albumin in the anaesthetized rat. 4. Peroxynitrite (40, 100 and 200 nmol/site) acted in a dose-dependent manner to cause a mean (+/- SEM) increase in plasma extravasation of 24 +/- 2, 55 +/- 5 and 69 +/- 6 microL, respectively (n = 4), with resulting inflammatory oedema. Peroxynitrite induced significantly larger plasma extravasation than equivalent vehicle controls at doses of 100 (P > 0.05) and 200 nmol (P > 0.001). This increased extravasation appears to be a direct microvascular response to peroxynitrite administration and not due to either a raised pH, necessary to stabilize the peroxynitrite, or contaminating concentrations of hydrogen peroxide or sodium nitrite from which peroxynitrite is formed. 5. These results suggest that peroxynitrite acts to increase microvascular permeability and oedema formation. Therefore, peroxynitrite may mediate vascular pro-inflammatory effects in addition to its direct cytotoxic activity.

Calcitonin gene-related peptide produces dose-related vasodilatation after intradermal injection in several species. In the present study, CGRP increased blood flow in rabbit skin but had no direct effect on edema formation in rat or rabbit skin or in the rat knee joint. However, CGRP produced significant potentiation of edema formation when co-injected with histamine, a potent mediator of increased vascular permeability. Therefore, release of CGRP from stimulated C-fiber nerves may contribute to the vascular changes that are an integral part of the inflammatory process. The activity of the putative CGRP antagonist CGRP8-37 (300 pmol) against CGRP was also investigated in rabbit and rat skin. Whereas it was found to selectively antagonize the effects of CGRP in rabbit skin, the antagonist produced edema in rat skin at the same dose. Thus, CGRP8-37 may be used in the rabbit to study the effects of endogenously released CGRP, but caution is required when this antagonist is used in the rat.

1 The relative contribution of ETA and ETB receptors in the response of rat skin to endothelins was investigated by use of the selective ETB agonist IRL-1620 and the selective ETA antagonist BQ-123.2 Binding data suggest the presence of ETA and ETB receptors as preincubation with [Ala3""',18Nle7]-endothelin-1 reduced ET-1 binding by approximately 40%. 3 Intradermal injection of endothelin-1 (ET-1, 1-10 pmol/site) and ET-3 (3-100 pmol/site) induced a dose-dependent decrease in local blood flow assessed by '33Xe clearance at test sites in rat skin.4 The endothelin analogue [Ala3" "'18NMe7]-ET-1 (30-1000 pmol/site) induced significant vasoconstriction (P<0.05) at the highest doses used and the selective ETB receptor agonist, IRL-1620 [Suc-[Glu9,Ala"l "5] endothelin (8-2 1)], (0.01-100 pmol/site) acted in a potent manner to induce a significant (P<0.01) dose-dependent decrease in '33Xe clearance. 5 Co-injection with the selective ETA receptor antagonist, BQ-123 (1 nmol/site), completely abolished the vasoconstriction to ET-1 and partially to ET-3, but had no effect on IRL-1620-induced vasoconstriction. In addition, IRL-1620 responses were not altered at sites treated with submaximal doses of a nitric oxide synthase inhibitor or a prostaglandin synthase inhibitor.6 ET-1 and IRL-1620 (100 fmol-1 pmol/site) did not induce oedema formation as measured by [125I]I albumin accumulation in the presence or absence of the vasodilator, calcitonin gene-related peptide (CGRP). ET-1 (1-3 pmol/site) inhibited substance P-induced oedema formation and this effect, suggested to be secondary to a vasoconstrictor effect, was significantly reversed by BQ-123 (1 nmol/site). 7 The findings in this study indicate that there are ETA and ETB receptors in rat skin and agents which activate either receptor act to mediate a decrease in cutaneous blood flow, but have no effect on increased microvascular permeability.

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