Genistein, an inhibitor of protein tyrosine kinase, is also a competitive antagonist for P1-purinergic (adenosine) receptor in FRTL-5 thyroid cells.

Genistein, a potent inhibitor for protein tyrosine kinase, remarkably inhibited the stimulatory action of N6-(L-2-phenylisopropyl)adenosine (PIA), an A1-adenosine receptor agonist, on thyrotropin (TSH)-induced phospholipase C activation in FRTL-5 thyroid cells. This drug also suppressed both the A1-receptor-mediated inhibition of cAMP accumulation in the cells and binding of [3H]8-cyclopentyl-1,3-dipropylxanthine, a specific antagonist for A1-receptor, to the cell membranes in a competitive manner. Adenosine-induced cAMP accumulation through A2-receptor in pertussis toxin-treated cells was also competitively antagonized by genistein. We conclude that genistein is also a competitive antagonist for P1-purinergic receptors.