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The modulatory effects of exogenous applications of adenosine on luminous organs (photophores) of the fish Porichthys were studied. Pretreatment of photophores with adenosine (10(-7) to 10(-3) M) potentiated both phases of adrenaline induced luminescence. The first peak of light (Lmax1) showed a 3-fold increase following 10(-7) M adenosine treatment; a maximal increase of 12-fold was observed with 10(-3) M adenosine. The second peak of light (Lmax2) exhibited a similar dose-response curve, but the maximal increase was attained with 10(-4) M adenosine. The potentiating effect of 1 muM adenosine on light emission triggered by adrenaline increased for adrenaline concentrations ranging from 10(-7) to 10(-4) M for Lmax1, but it remained stable for Lmax2. All 4 P1-purinergic agonists tested at the final concentration of 10(-4) M induced a potentiation of adrenaline luminescence with the following rank of potency: L-PIA > NECA > CADO greater-than-or-equal-to CHA = ADO for Lmax1 and NECA > CADO > ADO > CHA > L-PIA for Lmax2. The potentiating effect of adenosine was antagonized with the following rank of potency by the P-1 purinergic antagonists: CPT > DPMX greater-than-or-equal-to AMINO > THEO for Lmax1 and CPT > AMINO > THEO greater-than-or-equal-to DPMX for Lmax2. According to the classification of purinergic receptors, our results suggest that P1-purinergic receptors might be implicated in the adenosine potentiation of Porichthys adrenaline luminescence. Experiments also showed that noradrenaline luminescence is inhibited by 1 muM adenosine pretreatment. Further work will be necessary to elucidate the mechanism involved in the modulatory roles played by the purinergic receptors on adrenaline and noradrenaline luminescence in Porichthys photophores.