Prostacyclin is an autocrine regulator in the contraction of oviductal smooth muscle

Background: It was recently discovered that prostacyclin constituted 40-50% of prostaglandins (PG) produced by minced human oviduct. It is well established that prostacyclin relaxes vascular smooth muscle, but whether oviductal smooth muscle synthesizes prostacyclin and whether its contraction is affected by prostacyclin remain unclear. Methods: Smooth muscle microdissected from human oviducts was used for the study. The expression of prostacyclin synthase (PGIS) and prostacyclin receptor (IP) was confirmed by Western blot analysis. Metabolites of [H-3]PGH(2) were analysed for prostacyclin. Functional coupling of IP to adenyl cyclase was assessed by the accumulation of intracellular cAMP upon prostacyclin challenge. The presence of saturable, specific binding sites for prostacyclin was confirmed by binding assay. The identity of IP was further confirmed by RT-PCR and nucleotide sequence analysis. Finally, the effects of prostacyclin on muscle contraction were studied. Results: Human oviductal smooth muscle expresses functionally active PGIS and IP. The IP expressed is the same as that cloned from human lung tissue. The ED50 of prostacyclin to increase intracellular cAMP was 16 nmol/l. Prostacyclin dose-dependently decreased the amplitude of muscle contraction. Conclusions: Human oviductal smooth muscle produces prostacyclin, which, in turn, decreases its contractility. Prostacyclin may regulate embryo transport.