[Absence of the inhibitory effect of ATP and adenosine on adrenergic neurotransmission in the portal vein in guinea pigs].

Influence of purin substances ATP and adenosine on the magnitude of contractile response induced by transmural nerve stimulation (TNS) and exogene norepinephrine (NE) has been investigated on isolated segments of v.portae of a foetus, newborn and grown guinea pig. ATP and adenosine had no inhibitory effect on adrenergic contractions of v.portae of the guinea pig of all three investigated groups. In concentrations of 0.03-0.3 mol/l which inhibit neurogene contractions of v.portae in rabbits and in rats they potentiated contractions in response to TNS and exogene NE in newborn as well as grown animals. Absence of an inhibitory effects indicates lack of presynaptic P1 purinergic receptors in the area of adrenergic terminals of guinea pig's v.portae. Potentiation is probably caused by activation of postsynaptic purinergic receptors.