PRESENCE OF P-2-PURINOCEPTORS IN THE RAT PINEAL-GLAND

1 The effects of noradrenaline, ATP, adenylyl-imidodiphosphate (AMP-PNP), adenosine, alpha,beta-methylene-ATP and the P-2-purinoceptor antagonist, suramin on N'-acetyl-5-hydroxytryptamine production were studied in cultured denervated rat pineal glands. 2 Noradrenaline (3 nM-1 mu M) increased N'-acetyl-5-hydroxytryptamine production as measured both in the, gland and the culture medium. 3 In noradrenaline (10 nM)-stimulated pineal glands, ATP (0.03 nM-1 mM) or AMP-PNP (0.1 mu M-1 mM) increased N'-acetyl-5-hydroxytryptamine production in a concentration-dependent manner. 4 alpha,beta-Methylene-ATP at the concentration of 0.1 mM, but not 3 mu M, attenuated the enhancement by ATP (0.1 mM) of noradrenaline (10 nM)-induced N'-acetyl-5-hydroxytryptamine production. 5 Suramin (0.1 mM) blocked the potentiating effect of ATP (0.1 mM), but not the potentiating effect of adenosine (0.1 mM) in glands incubated with noradrenaline (10 nM). 6 These findings suggest that the rat pineal gland possesses P-2-purinoceptors which when stimulated potentiate the effect of noradrenaline but do not, by themselves, induce an increase in N'-acetyl-5-hydroxytryptamine production.