DEGRANULATION OF RAT OMENTAL MAST-CELLS BY A(1) RECEPTOR AGONISTS IN-VITRO

THE haemodynamic effects of adenosine are thought to result in part fr om a release of mast cell amines via A(3) receptor stimulation, To inv estigate the nature of the receptors involved in adenosine-induced mas t cell degranulation in the rat isolated omentum we have used adenosin e analogues with varying specificities as activators of the A(1), A(2) and A(3) receptors, and antagonists with differing specificities for A(1) and A(2) receptors, Analogues which act predominantly as A(1) (e. g. N-6-cyclopentyladenosine) or as mixed A(1)/A(2) receptor agonists ( e.g. adenosine, inosine, 5'-(N-ethylcarboxamido)adenosine) caused mast cell degranulation, whereas a predominantly A(3) receptor agonist (IB -MECA) was inactive. Pre-treatment of the omentum with the A(1)/A(2) r eceptor antagonist 8-phenyltheophylline or with the more specific A(1) receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine significantly reduced agonist-induced degranulation. Pre-treatment disodium cromogly cate or with BN52021 reduced degranulation of mast cells in response t o N-6-cyclopentyladenosine. In the rat isolated omental mast cell we c onclude that degranulation is an indirect result of A(1) receptor stim ulation, Platelet-activating factor release appears to mediate at leas t part of the degranulation.