Foreman and Garland from the Department of Pharmacology of the University College of London and the Pharmacology Laboratory of Welcome Research Laboratories, respectively, found that antiallergic drugs inhibit cAMP phosphodiesterase and have ability to inhibit the release of histamine in anaphylactic episodes. The enzyme has been isolated from the human lung tissue, where the cells are mostly non-mast, while histamine has been released in rat peritoneal mast cells.
Camp metabolism seems to be differently controlled in the two tissues. It is of difficult interpretation, unless we obtain pure mast cells from a single species. Cromoglycate, doxantrazole, and theophylline have shown a time course of inhibition of histamine release very similar to that provoked by antihistaminic drugs. 3-adrenergic receptor stimulants and anti-allergist in rat mast cell studies are not synergic, because of the relative insensitivity of these cells to 5-agonists .
Anti-allergic do not seem to inhibit histamine release by maintaining a high level of cAMP within the cell, but its high level inhibits calcium transport across the cell membrane. Other studies made by Mr Vardey and Dr Skidmore were not conclusive either, and show more disparity between the time course of inhibition of histamine release y anti-allergic drugs and phosphodiesterase inhibitors. Also, these studies are incomplete, and the mechanism of action anti-allergic drugs remains unrevealed.
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