Effects of β-endorphin on spontaneous uterine contractions. Prostaglandins production and 45Ca 2+ uptake in uterine strips from ovariectomized rats

Abstract

The effects of β-endorphin, Met-enkephalin, dynorphin and SKF 10047 on the constancy of the isometric developed tension (IDT) of the spontaneous contractions of uterine strips isolated from ovariectomized rats were explored. β-endorphin (10 −6 M) was the only opioid that depressed significantly uterine constancy of IDT in a concentration dependent fashion. Naloxone, neither at 10 −8 M nor at 10 −6 M, altered the negative inotropic influence of β-endorphin. Moreover, the basal synthesis and outputs of some prostaglandins (PGE 1, PGE 2 and PGF 2α) from rat uteri and the effect of β-endorphin (10 −6 M), were determined. It was found that the basal synthesis and release of PGs in uteri were significantly inhibited by this endogenous opioid. The effects of β-endorphin (10 −8, 10 −6 and 10 −5 M) on the basal; and oxytocin or A23187, induced 45Ca 2+ uptake, as well as the influence of naloxone were also studied. β-endorphin at three of the concentrations tested decreased basal uterine 45Ca 2+ uptake and this action was not prevented by naloxone (10 −8 M). The presence of oxytocin and of A23187 augmented significantly 45Ca 2+ uptake, an effect that was antagonized by β-endorphin (10 −6 M). The possible role of β-endorphin in uterine functioning via the modulation of uterine PG synthesis and Ca 2+ uptake is discussed.