Pulmonary pharmacology

Effects of milrinone, sulmazole and theophylline on adenosine enhancement of antigen-induced bronchoconstriction and mediator release in rat isolated lungs.

PMID 1725275


The effects of adenosine and some of its analogues on bronchoconstriction and mediator release were studied in isolated lungs of actively sensitized rats. The influence of two novel cardiotonic drugs, milrinone and sulmazole on these adenosine-induced effects was compared with that of theophylline, a well known adenosine antagonist. Adenosine (ADO) and its analogues N-ethyl-carboxamide-adenosine (NECA) and R-phenyl-isopropyladenosine (R-PIA), dose-dependently enhanced antigen-induced bronchoconstriction. The enhancement of anaphylactic bronchoconstriction by adenosine and its analogues was accompanied by a rise in histamine release. The rank order of potency for adenosine and analogues with respect to enhancement of anaphylactic bronchoconstriction, was NECA greater than or equal to R-PIA greater than ADO. An unequivocal classification of the adenosine receptor involved, was therefore not possible. Dipyridamole and S-(p-nitrobenzyl-6-thioinosine) (NBTI), both inhibitors of adenosine uptake, had no inhibitory influence on the adenosine-induced enhancement of anaphylactic bronchoconstriction, indicating that this enhancement is mediated by an extra-cellular receptor. Theophylline, milrinone and sulmazole inhibited the enhancement of anaphylactic bronchoconstriction, without affecting preformed mediator release. Theophylline and sulmazole were both more effective as inhibitors of adenosine-enhanced bronchoconstriction than as inhibitors of antigen-induced bronchoconstriction, suggesting adenosine antagonism. Milrinone was equi-effective as inhibitor of both types of bronchoconstriction. Since adenosine antagonism has been associated with the side effects of theophylline it will be interesting to further investigate the therapeutic merits of novel cyclic nucleotide phosphodiesterase inhibitors in the treatment of asthma.