Characterization of prostanoid receptors present on adrenergic neurons innervating the porcine uterine longitudinal muscle

The cyclooxygenase–prostanoid pathway regulates myometrial contractility through activation of prostanoid receptors on uterine smooth muscles. However, the possible expression of prostanoid receptors on autonomic nerves cannot be excluded completely. The aim of the present study was to clarify the presence of neural prostanoid receptors on adrenergic nerves in the porcine uterine longitudinal muscle. In [3H]-noradrenaline-loaded longitudinal muscle strips of porcine uterus, electrical field stimulation (EFS) evoked [3H]-noradrenaline release in a stimulation frequency-dependent manner. The EFS-evoked release was completely abolished in Ca2+-free (EGTA, 1 mM) incubation medium and by tetrodotoxin or ω-conotoxin GVIA, suggesting that [3H]-noradrenaline was released from neural components. The EFS-evoked [3H]-noradrenaline release was significantly enhanced by treatment with indomethacin. In the presence of indomethacin, PGE2 and PGF2α, but not PGD2, inhibited the EFS-evoked [3H]-noradrenaline release. Of synthetic prostanoid receptor agonists examined, both U46619 (TP) and sulprostone (EP1/EP3) decreased the EFS-evoked [3H]-noradrenaline release in a concentration-dependent manner, while fluprostenol (FP), BW245C (DP) and butaprost (EP2) were almost ineffective. SQ29548 (TP receptor antagonist) blocked the effect of U46619, but SC19220 (EP1 receptor antagonist) did not change the inhibition by sulprostone or PGE2. Double immunofluorescence staining using protein gene product 9.5, tyrosine hydroxylase, EP3 receptor and TP receptor antibodies suggested the localization of EP3 or TP receptors on adrenergic nerves in the porcine uterus. These results indicated that neural EP3 and TP receptors are present on adrenergic nerves of the porcine uterine longitudinal muscle. Endogenous prostanoid produced by cyclooxygenase can regulate noradrenaline release in an inhibitory manner through activation of these neural prostanoid receptors.