Abstract
Blanching skin reaction induced by topical corticosteroids has been employed for the estimation of their anti-inflammatory effect for the last two decades, yet the mechanisms responsible for this reaction are still controversial. Therefore, we studied vascular constriction following the application of dexamethasone and clobetasol propionate, utilizing pharmacological and fine structural techniques both in vivo and in vitro.
1: Mechanical responses of isolated ear arteries to the corticosteroids, measured isometrically, revealed that steroids facilitated neither vascular constriction induced by electrical stimulation, by noradrenalin stimulation and by a high concentration of extracellular potassium, nor had inhibitory effect on EDRF (endothelium derived relaxing factor) on the vascular smooth muscle cell.
2: The clinical observation that the blanching reaction developed in the skin area without any nerve reflexes implied the lack of involvement of substance P.
3: A chronological analysis revealed that the topical application of steroids gave immediate rise to vascular dilatation and successively to edema and was followed by vascular constriction by 60 to 90 minutes.
4: Electron microscopic observation demonstrated the immediate release of mast cell granule content, of which matrix (heparan proteoglycans) deposited and persisted for hours in the interspaces of the connective tissue in the dermis.
Since proteoglycans can hold a considerable amount of free water as their constitute, the present findings suggest the possibility that the matrix of degranulated mast cell content may play an important role in narrowing the vessels embedded in the connective tissue spaces by increasing the pressure of the surrounding tissue, and thus produce the skin blanching phenomenon.
