Evidence that mast cell degranulation, histamine and tumour necrosis factor alpha release occur in LPS-induced plasma leakage in rat skin

1 In the present study we investigated the role of mast cells during inflam mation in rat skin. As the release of several pro-inflammatory mediators, s uch as histamine and tumour necrosis factor alpha (TNF alpha), occurs follo wing mast cell activation we studied whether mast cell degranulation and th e release of both histamine (H) and TNF alpha occurred in a model of lipopo lysaccharide (LPS)-induced plasma leakage in rat skin. 2 Plasma leakage in the rat skin was measured over a period of 2 h as the l ocal accumulation of intravenous injection of I-125-human serum albumin (I- 125-HSA) in response to intradermal injection of LPS. LPS (10 mu g site(-1) ) produced an increase of plasma leakage (50.1+/-2.3 mu l site(-1)) as comp ared to saline (9.0+/-3.2 mu l site(-1)). Histological analysis of rat tiss ue showed that LPS induced a remarkable mast cell degranulation (59.8+/-2.1 %) as compared to saline (13.5+/-2.2%). 3 Ketotifen (10(-9)-10(-7) mol site(-1)), a well-known mast cell-membrane s tabilizer, produced a dose-related inhibition of LPS-induced plasma leakage by 36+/-3.5%, 47+/-4.0%, 60+/-3.3% respectively. In addition, ketotifen(10 (-7) mol site(-1)) inhibited mast cell degranulation by 59.2+/-2.7%. 4 Chlorpheniramine maleate (CPM) (10(-9)-10(-7) mol site(-1)), an H-1 hista mine receptor antagonist only partially inhibited LPS-induced plasma leakag e in rat skin (38+/-1.1% at the highest dose). Furthermore, CPM (10(-7) mol site(-1)) did not prevent mast cell degranulation. 5 A polyclonal antibody against TNF alpha (1 : 500, 1 : 100, 1 : 50 v v(-1) dilution), locally injected, decreased LPS-induced plasma leakage in the s kin by 15+/-2.0%, 24+/-2.1% and 50+/-3.0% respectively. 6 Taken together these results suggest that LPS-induced plasma leakage in r at skin is mediated, at least in part, by mast cell degranulation and by th e release of histamine and TNF alpha from these cells.