On the role of ‘in vivo’ injected progesterone and of the ‘in vitro’ presence of oxytocin, modulating Ca 2+ uptake by the rat uteri from spayed animals and as controllers of the production of arachidonic acid metabolism

Abstract

We attempted to explore possible mechanism(s) subserving the influence of oxytocin (O) and of progesterone (P) in the isolated rat uterus studyng the action of these hormones on: the synthesis and release of prostaglandins (PGs), the metabolism of labelled arachidonic acid and the uptake of Ca 2+ by the tissue from ovariectomized animals. The experiments were done with uterine preparations isolated from spayed rats treated or not with P prior to sacrifice and afterward incubated or not with O ‘in vitro’. While uterine strips from untreated spayed rat uterus exhibited a basal release into the incubating medium of approximately the same amounts of PGF 2α, and PGE 2, the ‘in vitro’ addition of O (50 mU/ml) increased significantly (p<0.05) the output of PGF 2α without changing the release of PGE 2. In tissue from rats injected with P prior to sacrifice the output of PGF 2α rose significantly (p<0.01) as it did after the addition of O to preparations obtained from spayed rats treated with P in comparison to findings in uteri from spayed rats but not in comparison to uteri from spayed rats treated with P alone. Moreover, the ‘in vitro’ addition of O (50 mU/ml) only increased the formation of PGF 2α (p<0.05) and of 5-HETE (p<0.05); nevertheless the administration of P to spayed rats diminished significantly (p<0.05) the formation of 6-keto-PGF 1α from uteri, but increased that of PGF 2α (p<0.05). The formation of PGF 2α in uteri from spayed rats treated with P and then exposed after isolation to the ‘in vitro’ presence of O in the incubating medium, was not modified. Neither P nor the ‘in vitro’ addition of O were able to alter the formation of thromboxane (TX)B 2. On the other hand the addition of O (50 mU/ml) enhanced 45Ca 2+ uptake by uterine tissue (p<0.05) as much as the treatment with P did (p<0.001). However, the addition of O into the incubating medium failed to influence the effect of P and the uptake of Ca 2+ did not differ from that observed in uteri from spayed animals treated with P. The present findings suggest that P and O augmented PGF 2α synthesis by the same mechanism, i.e. enhancing the influx of Ca 2+ towards uterine cells.