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

1 The effects of noradrenaline, ATP, adenylyl-imidodiphosphate (AMP-PN P), adenosine, alpha,beta-methylene-ATP and the P-2-purinoceptor antag onist, suramin on N'-acetyl-5-hydroxytryptamine production were studie d in cultured denervated rat pineal glands. 2 Noradrenaline (3 nM-1 mu M) increased N'-acetyl-5-hydroxytryptamine production as measured bot h in the, gland and the culture medium. 3 In noradrenaline (10 nM)-sti mulated pineal glands, ATP (0.03 nM-1 mM) or AMP-PNP (0.1 mu M-1 mM) i ncreased N'-acetyl-5-hydroxytryptamine production in a concentration-d ependent 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 no radrenaline (10 nM)-induced N'-acetyl-5-hydroxytryptamine production. 5 Suramin (0.1 mM) blocked the potentiating effect of ATP (0.1 mM), bu t not the potentiating effect of adenosine (0.1 mM) in glands incubate d with noradrenaline (10 nM). 6 These findings suggest that the rat pi neal gland possesses P-2-purinoceptors which when stimulated potentiat e the effect of noradrenaline but do not, by themselves, induce an inc rease in N'-acetyl-5-hydroxytryptamine production.