Purinergic and noradrenergic cotransmission in the rat pineal gland

ATP is coreleased with noradrenaline in several noradrenergic synapses, and P2-like receptors were shown to be present in rat pineal glands. A new method of functional investigation was developed to assess the importance of both transmitters (noradrenaline and ATP) in eliciting the synthesis of melatonin and its precursor N'-acetyl-5-hydroxytryptamine (N'-acetyl-5-HT) through transmural electrical field stimulation of cultured pineal glands. Incubation with the beta-adrenoceptor antagonist propranolol (> 10(-7) M) blocked almost completely the production of N'-acetyl-5-HT, whilst the P2 receptor antagonists pyridoxalphosphate-6 azophenyl-2',4'-disulfonic acid (PPADS, > 3 x 10(-6) M) and suramin (> 10(-6) M) blocked it partially. These findings indicate a physiologically relevant role for the purinegic cotransmission in this system. (C) 2000 Published by Elsevier Science B.V.