Dual effects of adenosine and adenosine analogues on motor activity of the human fallopian tube.

Effects of adenosine and adenosine analogues on spontaneous contractility of the human fallopian tube during different phases of the menstrual cycle were studied. In isthmic preparations, a stimulatory effect by L-N6-phenylisopropyladenosine (L-PIA), with preference for adenosine A1-receptors, was seen mainly during the proliferative phase. In ampullary preparations, stimulation by L-PIA was seen both in the secretory and proliferative phases. Adenosine and 2-chloroadenosine exerted similar stimulatory effects. 5'-N-ethylcarboxamide-adenosine (NECA), with selectivity for adenosine A2-receptors, or D-PIA never showed a stimulatory effect. At concentrations above those needed for stimulation, adenosine, 2-chloroadenosine and L-PIA inhibited spontaneous contractions, in common with NECA and D-PIA. Here, NECA was more potent than L-PIA. The D-PIA and L-PIA were equipotent. The inhibition was seen during the whole menstrual cycle. The competitive adenosine antagonist 8-p-sulphophenyltheophylline (PSøT) reversibly antagonized the stimulatory and inhibitory effects elicited by adenosine and the analogues. The PSøT alone could exert a stimulatory or an inhibitory action on spontaneous contractility. We suggest that adenosine can modulate contractile activity in the human fallopian tube via stimulatory A1-and inhibitory A2-receptors. These receptors are located on the smooth muscle cells, and might act via cAMP. The relative receptor dominance may be influenced by cyclic hormonal changes.