Oxytocin enhances the basal release of uterine prostaglandin F2 alpha, but not that of PGE1, or of PGE2, and changes the metabolism of exogenous arachidonate, favouring the formation of prostaglandin F2 alpha and 5-HETE. Relationships with its uterotonic action and modulation by estradiol

Genistein and daidzein modulate in vitro rat uterine contractile activity

The present study investigated the effect of genistein, daidzein and estradiol on in vitro rat uterine responsiveness to oxytocin (OT) and PGF(2)alpha or luprostiol (L). In a first experiment, animals were either sham-operated (SH; n=5), or ovariectomized (OVX; n=20) and orally treated for three months with either genistein (G; n=5; 10 microg/g BW/d) or daidzein (D; n=5; 10 microg/g BW/d) or 17 alpha-ethinylestradiol (E; n=5; 23 microg/kg BW/d) or untreated (OVX; n=5). At necropsy, the basal uterine tension was lower in OVX, G and D than in SH, the highest value being measured in E. Oxytocin (10(-12); 10(-11) M) or PGF(2)alpha (10(-12); 10(-9) M) induced an increase in SH, but not in OVX, E and G. In D, only the highest doses were efficient. In a second experiment, 20 intact animals were s.c. injected with either genistein (G; n=5; 10 microg/g BW) or daidzein (D; n=5; 10 microg/g BW) or estradiol benzoate (E; n=5; 23 microg/kg BW) or vehicle (C: controls; n=5), and killed 24 h later. In C and E, OT (10(-15) to 10(-10) M) or L (10(-12) to 10(-7) M) stimulated uterine contractile activity in a dose-dependent manner until a maximal level. On the opposite, in G and D, contractile agents (except the highest luprostiol doses) did not stimulate myometrium contractions. Moreover, radioligand binding assays showed that genistein or daidzein inhibited the specific binding of [(3)H] estradiol to the calf uterus estrogen receptor (ER). Therefore, it could be postulated that both genistein and daidzein might bind to the rat uterus ER, inducing either anti-estrogenic or very weak estrogenic effects (depending on the experimental conditions) on in vitro uterine responsiveness to OT and PGF(2)alpha or luprostiol.

Effect of an oxytocin receptor antagonist on ovarian and uterine synthesis and release of prostaglandin F2 alpha in pseudopregnant rats

There is substantial experimental evidence suggesting that oxytocin has a role in luteolysis in ruminates. Endogenous pulses of uterine prostaglandin (PG) F2 alpha occur synchronously with pulses of oxytocin during luteolysis; leading us to propose a possible feedback loop between uterine PGF2 alpha and luteal oxytocin. In rates, the mechanism whereby oxytocin acts has not been well elucidated. In the present report, the effects of an oxytocin receptor antagonist in pseudopregnant rats were investigated. Pseudopregnancy was induced in immature female rats by gonadotrophin treatment; this resulted in the formation of corpus luteum that remained functional for 9 +/- 1 days. The pseudopregnant rats were assigned to one of the following four groups. In the first group the relationship between the release of ovarian and uterine PGF2 alpha was tested. We also studied the serum progesterone during the pseudopregnancy. We found that PGF2 alpha released into the incubation medium from ovaries of pseudopregnant rats increased (p < 0.05) and was maximal on day 9 of pseudopregnancy. This concentration remained high until day 10 of pseudopregnancy and then decreased. The PGF2 alpha released from the uterus to the incubation medium rose (p < 0.05) on day 8 of pseudopregnancy and reached the peak value on day 10. the serum progesterone was increased (p < 0.001) on day 2 pseudopregnancy and was greater on day 5 (p < 0.001). The second and third group received a specific oxytocin receptor antagonist (1-deamino-2-O-methyltyrosine) in two different concentrations (0.05 or 0.2 mumol/l before the peak of PG release. Both doses employed decreased (p < 0.001) the release into the incubating medium of PGF2 alpha from ovaries and uterus. Indeed, after the treatment, the progesterone levels were higher (p < 0.001) than control on day 10 of pseudopregnancy. In the fourth group, a potent inhibitor of cyclooxygenase activity was administered on day 8 of pseudopregnancy into the ovarian bursa. The serum progesterone levels increased (p < 0.01) compared to control suggesting a possible role of ovarian PG in the luteolytic phase of the corpus luteum regression. Thus, our findings show that oxytocin is luteolytic in pseudopregnant rats and this action is mediated by oxytocin receptors, as it was blocked by a specific oxytocin receptor antagonist.

Role of interferon-alpha in arachidonic acid metabolism by the rat uteri from spayed animals: effect of 17 beta-estradiol

Interferon-like trophoblastic proteins modulate prostaglandin (PG) synthesis from endometrium in early ovine and bovine pregnancy. We attempted to explore the effect of interferon (IFN)-alpha in the isolated rat uterus from ovariectomized animals on the metabolism of labelled arachidonic acid (AA). The experiments were performed with uterine preparations isolated from spayed rats treated or untreated with 17 beta-estradiol prior to sacrifice. The pre-incubation of uterine tissue isolated from ovariectomized rats with three different doses (4, 150 and 300 IU/ml) of IFN-alpha decreased the radioconversion of [14C]AA into 6-keto PGF1 alpha, PGF2 alpha and PGE2, whereas the formation of thromboxane B2 (TXB2) decreased after treatment with 4 IU/ml of INF-alpha but was augmented with 150 and 300 IU/ml. The three doses used diminished the synthesis of 5-hydroxyeicosatetraenoic acid (5-HETE) and increased the production of 12-HETE. We also studied the synthesis of uterine products of cyclooxygenase and lipoxygenase in uterine tissue from ovariectomized rats injected with 17 beta-estradiol and preincubated with IFN-alpha. We found that the three doses of IFN-alpha diminished the production of 6-keto-PGF1 alpha, PGE2, PGF2 alpha and TXB2 as well as 5-HETE and 12-HETE. These findings show that IFN-alpha modifies the basal synthesis of PGs from uterine tissue. Ovine and bovine trophoblastic protein prevents luteolysis by inhibiting the synthesis of PGF2 alpha. On the other hand, IFN-alpha shows 70% homology with ovine trophoblastic protein and binds to the same receptor. The results of the present study suggest that IFN-alpha may also act in the rat as a luteotrophic agent.

The control of prostaglandin production by the endometrium in relation to luteolysis and menstruation

Oestradiol acting on a progesterone-primed uterus stimulates prostaglandin (PG) F2 alpha synthesis by the endometrium. In some species (notably the sheep, cow and goat) oxytocin released from the ovary also forms part of the physiological stimulus for increased endometrial PGF2 alpha production. The corpus luteum contains high concentrations (> 1 microgram/g tissue) of this peptide in these species. The intracellular mechanisms by which these three hormones control endometrial PGF2 alpha synthesis and release are far from clear. Oxytocin stimulates the synthesis of inositol phosphates and diacylglycerol in the endometrium of some species, but whether this pathway is involved in endometrial PGF2 alpha synthesis is still open to question. There is evidence that increased endometrial PGF2 alpha synthesis is dependent upon increased endometrial protein synthesis but, apart from the recorded effects of steroid hormones on the concentrations of phospholipase A2, prostaglandin H synthase and oxytocin receptors, it is not known what other endometrial proteins are involved. Some disorders of menstruation are associated with abnormal PG production by the endometrium, but the reasons for this abnormality are not clear. During early pregnancy an increase in PGF2 alpha synthesis by the endometrium is prevented, except in the pig where the PGF2 alpha produced is directed from the venous drainage to the uterine lumen. In those species in which endometrial PGF2 alpha synthesis is dependent upon oxytocin secreted by the ovary, the conceptus secretes an interferon-tau (previously named trophoblast protein-1) which prevents oestradiol and oxytocin acting on a progesterone-primed uterus from stimulating endometrial PGF2 alpha synthesis. The identities of the factors produced by the conceptus which prevent endometrial PGF2 alpha synthesis during early pregnancy in other species are not known, although it is clear that they are not interferons.

Prostaglandin H synthase activity in the sheep placenta during cortisol-induced labor at 128-131 days of gestation and during spontaneous delivery at term

This study investigated whether the prostaglandin H synthase (PGHS) enzyme activity of sheep fetal placental cotyledon can be induced by cortisol at 128-131 days of gestation (dga) as compared to gestational age matched controls, before PGHS's normal gestational increase would occur (experiment 1). This study also investigated whether active PGHS is diminished following prostanoid synthesis in the labor process (experiment 2). A PGHS activity assay was employed in which PGE2 product was measured under initial velocity conditions. Labor was induced before term by continuous infusion of 10 mg of cortisol succinate per day (day 1) followed by 15 mg per day (days 2-4, or until delivery) of cortisol succinate administered through the fetal saphenous vein. Cotyledonary tissue was collected from sheep at term (142-145 dga), as judged by the absence of labor-type myometrial electromyogram (EMG) activity, and during cortisol induction at 128-131 dga. Tissue was also collected from term laboring animals immediately after fetal delivery while the fetus was still attached to the umbilicus and before placental delivery. At 128-131 dga, cortisol had no significant effect on PGHS activity as compared to gestational age matched saline-infused controls; thus, it is unlikely that cortisol directly induces PGHS. In experiment 2, normal progression of active spontaneous labor led to a significant diminution of PGHS activity (p < 0.05) that may be partially explained, based on thin-layer chromatography (TLC) results, as a significant decrease in PGE2 (p < 0.05) production coincident with a lesser compensatory increase in PGD2 (p = 0.06) output.

On the role of 'in vivo' injected progesterone and of the 'in vitro' presence of oxytocin, modulating Ca2+ uptake by the rat uteri from spayed animals and as controllers of the production of arachidonic acid metabolism

We attempted to explore possible mechanism(s) subserving the influence of oxytocin (O) and of progesterone (P) in the isolated rat uterus studying the action of these hormones on: the synthesis and release of prostaglandins (PGs), the metabolism of labelled arachidonic acid and the uptake of Ca2+ 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 PGF2 alpha, and PGE2, the 'in vitro' addition of O (50 mU/ml) increased significantly (p < 0.05) the output of PGF2 alpha without changing the release of PGE2. In tissue from rats injected with P prior to sacrifice the output of PGF2 alpha 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 PGF2 alpha (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-PGF1 alpha from uteri, but increased that of PGF2 alpha (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of exogenous phospholipase A2 and triacylglycerol lipase on the synthesis and release of monoenoic and bisenoic prostaglandins from isolated rat uterus

The possible existence of a selective and independent mechanism subserving the formation of prostaglandin E1 (PGE1) and of prostaglandin E2 (PGE2) has been reported in previous studies from our group. In the present experiments we have demonstrated that neutral lipid lipases play an important role yielding dihomo-gamma-linolenic acid for the formation of PGE1. Indeed, exogenous triglyceride lipase added to the incubation bathing solution at a concentration of 150 U/ml increased several fold the production of PGE1 by isolated uterine strips obtained from spayed rats. Nevertheless the presence of the enzyme did not modify significantly the synthesis and release of bisenoic PGs (PGE2 and PGF2 alpha). When triarachidonin was added, as an artificial substrate into the incubating medium in order to detect the presence of endogenous triacylglycerol lipase, we observed a significant increment in the generation of PGE2 (p less than 0.005) and of PGF2 alpha (p less than 0.001) without evident changes in the basal release of PGE1. On the other hand, the addition of phospholipase A2 (PLA2) at 0.2 U/ml, increased significantly the production of PGE2 (p less than 0.001) but failed to alter the concentration of PGE1 in the incubating solution. Surprisingly, PLA2 did not enhance the synthesis of PGF2 alpha in the present experiments, a situation for which we do not have a clear explanation. Exogenous bradykinin (10(-6) M), a well known stimulant of PLA2 activity in several tissues, also increased significantly (p less than 0.001) the production of PGE2 without altering that of PGE1.(ABSTRACT TRUNCATED AT 250 WORDS)