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

1 In the present study we investigated the role of mast cells during inflammation in rat skin. As the release of several pro-inflammatory mediators, such as histamine and tumour necrosis factor alpha (TNF alpha), occurs following mast cell activation we studied whether mast cell degranulation and the release of both histamine (H) and TNF alpha occurred in a model of lipopolysaccharide (LPS)-induced plasma leakage in rat skin. 2 Plasma leakage in the rat skin was measured over a period of 2 h as the local 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 compared to saline (9.0+/-3.2 mu l site(-1)). Histological analysis of rat tissue 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 stabilizer, 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 histamine receptor antagonist only partially inhibited LPS-induced plasma leakage 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 skin by 15+/-2.0%, 24+/-2.1% and 50+/-3.0% respectively. 6 Taken together these results suggest that LPS-induced plasma leakage in rat skin is mediated, at least in part, by mast cell degranulation and by the release of histamine and TNF alpha from these cells.