Adenosine modulation of adrenergic neurotransmission in the human fallopian tube

The effects of adenosine and adenosine analogues on nerve-induced contractile responses and [3H]noradrenaline ([3H]NA) release, were studied in the isthmic part of human oviducts. Adenosine and L-N6-phenylisopropyladenosine (L-PIA) could enhance neurogenic contractile responses in preparations obtained mainly in the proliferative phase. At higher concentrations, adenosine derivatives inhibited contractile responses to nerve stimulation in both proliferative and secretory phase, with the potency order: 5'-N-ethylcarboxamideadenosine (NECA) greater than or equal to L-PIA much greater than D-PIA. This indicated actions at both stimulatory A1- and inhibitory A2-receptors. Adenosine, L-PIA and NECA but not D-PIA inhibited [3H]NA release during nerve stimulation. The relative potency order for the prejunctional inhibition was compatible with an action at A1-receptors. Furthermore, adenosine was found to modulate nerve-induced contractions via postjunctional stimulatory A1- and inhibitory A2-like receptors. The postjunctional effects may be influenced by cyclic hormonal changes. The adenosine antagonist 8-p-sulfophenyltheophylline (PSøT) reversibly antagonized the stimulatory and inhibitory effects by adenosine and analogues.