M. Chaud

Spontaneous motility and prostaglandin generation in rat uterine horns isolated during the estrous cycle

Measurements were made of spontaneous contractions and release of prostaglandin E-and F-like material into the bathing medium by uterine horns isolated from rats in different stages of the sex cycle. After 70 min of contractile activity the preparations from estrous rats released more PGF than those from proestrous or metestrous rats. On the other hand, similar amounts of PGF-like material is generated by estrous and diestrous horns. Less PGE-like material was found in the bathing solution during estrus than in metestrus or diestrus; the values obtained during proestrus were similar to those in estrus. PGI2 like material produced by chopped uterine tissue was greater during diestrus than in estrus. The initial isometric developed tension (IDI) and tension constancy varied depending of the stage of the sex cycle. Uteri from metestrous rats exhibited greater IDT and less % change with time than preparations from estrous or proestrous rats. The initial IDT, the tension change with time and contractile frequency correlate with the PGE-like material in the bathing solution during the 4 days of the sex cycle. There was no correlation with PGF-like material.

Norepinephrine alters PGE2/PGE1 output ratio in isolated uterus from ovariectomized rats.

The rat uterus generates and releases prostaglandins (PGs) of the series 2 as well as PGs of the series 1. The main purposes of the present study are to compare the effects of norepinephrine (NE) on the production and outputs of PGE1, PGE2 and PGF2 alpha by the uterus isolated from ovariectomized rats, treated or not with 17-beta-estradiol and to explore also, whether the effects of NE on PG synthesis are mediated through alpha, beta or both types of adrenoreceptors. Segments of control uterine horns obtained from ovariectomized rats generated and released into the incubating solution, equal amounts of PGE1, PGE2 and PGF2 alpha and propranolol (10(-6) M) or phentolamine (10(-6) M) failed to alter this basal production of PGs. Norepinephrine (3 X 10(-6) M) significantly depressed the outputs of PGE1 and PGF2 alpha but enhanced, also significantly, the release of PGE2. In the presence of the beta-adrenoreceptor blocker, propranolol, the reduction induced by NE on the output of PGE1 was not altered, but the stimulatory influence of NE on the release of PGE2 as well as the depression on the output of PGF2 alpha, were abolished. On the other hand the diminution evoked by NE on the release of PGF1 and PGF2 alpha as well as the increment induced on PGE2 output, were inhibited by the presence of phentolamine in the incubating solution. Uterine horns from ovariectomized rats treated with 17-beta-estradiol released into the incubating solution significantly more PGF2 alpha than PGE1 or PGE2. NE, either alone of in the presence of alpha 0 or beta-adrenoceptor blockers, did not modify this pattern of PG production. A possible mechanism(s) of action for NE on PG synthesis is discussed.

Effects of experimental diabetes on spontaneous contractions, on the output of prostaglandins and on the metabolism of labelled arachidonic acid, in uteri isolated from ovariectomized rats. Influences of estradiol

Spontaneous changes in isometric developed tension (IDT) as a function of time after isolation (contractile constancy) in uteri from control-castrated and castrated chronic streptozotocin-diabetic rats, were explored. The effects of injecting 17-beta estradiol (Eo) were also studied. No differences in the minor changes of contractile constancy, between control and diabetic preparations, during a period of 60 min, were detected, whereas uteri from non-diabetic Eo injected animals (0.5 + 1.0 ug, prior to sacrifice), exhibited a profound reduction of IDT, significantly greater than in tissues obtained from Eo injected-diabetic rats. Moreover, basal generation and outputs into the suspending solution of prostaglandins (PGs) E1, E2 and F2 alpha, were explored in the same groups, at 60 min following tissue isolation. The basal outputs of these three PGs were similar in castrated control rats, but preparations from castrated-diabetics released significantly more PGE1. The administration of Eo to castrated-diabetics, failed to alter the releases of the three PGs explored. In addition, the metabolism of labelled arachidonic acid (AA) into different prostanoids (6-keto-PGF1, PGF2, PGE2 and thromboxane B2-TXB2), was also investigated. The non-diabetic spayed rat uterus converted AA into these four prostanoids, the transformation into 6-keto-PGF1 alpha (as an index of PGI2 formation) being the most prominent. In preparations from diabetic rats the formation) being the most prominent. In preparations from diabetic rats the formation of 6-keto-PGF1 alpha, PGF2 alpha and PGE2, was significantly smaller than in controls, whereas a greater % of TXB2 formation (as an index of TXA2), was detected. On the other hand uterine preparations from non-diabetic spayed rats injected with Eo formed less 6-keto-PGF1 alpha and PGE2 and similar amounts of PGF2 alpha or of TXB2 from AA, than Eo injected controls, whereas uteri from castrated diabetic animals injected with Eo, formed a similar % of 6-keto-PGF1 alpha, PGF2 alpha and PGE2 from AA, than tissue preparations from non-estrogenized controls. However, the enhanced transformation of the labelled fatty acid precursor (AA) into TXB2 in the diabetic group, was significantly reduced by the steroid. The role of the augmented generation and release of PGE1 in uteri from diabetic rats is discussed in terms of precedents indicating the relevance of PGs type E supporting rat uterine motility. In addition the influence of Eo is attractive, because its reducing effect on TX production, in diabetes, a disease known to be accompanied by enhanced synthesis of vasoconstrictor and platelet aggregation TXA2, and by frequent obstructive circulat

Sex hormones and the motility of and prostaglandin output from, uterine horns of immature rats

The effects of injecting estradiol, progesterone or both hormones to immature rats, on the spontaneous contractions of isolated uterine horns and on prostaglandin (PG) E and F-like materials released into the bathing medium, were studied. The in vitro contractile decrement detected both in controls as well as in the group receiving progesterone (P4) alone, was only minor. On the other hand, preparations from rats treated with 17-beta-estradiol (E2) exhibited a significant and progressive reduction of spontaneous motility. Coincident with these smaller contractions a significant diminution of PGE-output accompanied by an enhancement of the release of PGF-like material into the suspending solution, were found. The initial (postisolation) isometric developed tension (IDT) of uterine preparations from immature rats injected with sex hormones was significantly higher than that of tissues from untreated control animals. Neither the initial contractile frequency (CF) nor its constancy changed following hormonal treatment (E2 or P4), except in the case of uteri from animals treatment (E2 or P4), except in the case of uteri from animals administered with P4, which showed a smaller decrement of CF than controls. Furthermore, tissue preparations obtained from animals injected with P4 released into the bathing media similar amounts of PGE-like material as controls, but significantly more PGF. It is interesting that the injection of E2 plus P4 increased the output of PGE-like material but did not modify that of PGE i. e., the depressive effect of estradiol on the release of PGE into the bathing media was abolished by the administration of P4. On the other hand, the addition of indomethacin or acetylsalicylic acid to the bath solution reduced significantly contractions of uterine horns isolated from immature animals. The foregoing results, supporting our previous findings on the effect of P4 on PGF release from the rat uterus, are in keeping with the hypothesis holding that better spontaneous motility correlates well with a greater release of PGE and that E2 injection coincides with a depression of both PGE output and myometrial contractions.

Role of nitric oxide on oxytocin-evoked contractions and prostaglandin synthesis in isolated pregnant rat uterus.

Uterine contractions elicited by oxytocin (OT), possibly linked with uterus prostaglandin (PG) release, are involved in the final pathway of labor. It is known that nitric oxide (NO) may contribute to the maintenance of uterine contractile quiescence during gestation. Therefore in this study the effect of the inhibition of NO synthase (NOS), with N-monomethyl L-arginine (L-NMMA), on the ability of OT to stimulate uterine contractions and PG synthesis was investigated in isolated rat uterus at days 13 and 21 of pregnancy. L-NMMA did not modify the frequency and the force of contractions elicited by OT at day 13. On day 21 the frequency of contractions evoked by OT were better sustained in the presence of L-NMMA. PGs were not affected by OT on day 13. OT stimulated PGF2alpha on day 21 when NOS had been inhibited with L-NMMA, but not in the absence of L-NMMA. NOS activity was stimulated by OT at day 21 of gestation. In summary these findings indicate that near term NO can regulate OT PGF2alpha induced contractions and PG synthesis in isolated pregnant rat uterus.

Prostaglandin F2α modifies the action of norepinephrine on α- and β-adrenoceptors of isolated rat uterus

Abstract Cumulative dose-response curves were constructed for the effect of norepinephrine (NE) and isoproterenol (ISO) on the contractions of uterine strips from proestrous, estrous and metestrous rats. Both adrenergic agonists inhibited uterine spontaneous contractions in all three stages of the cycle. However strips isolated from estrous rats were more sensitive to the inhibitory action of NE or ISO than preparations obtained from proestrous or metestrous animals. It was also observed that PGF-like material released by uterine horns was significantly higher during estrus than during proestrus or metestrus, whereas PGE-like material was significantly higher in metestrus than in estrus or proestrus. The EC50 of NE and ISO and the amount of PGF-like material generated by uterine horns correlated significantly during the three stages of the sex cycle. No correlation was found between the β-adrenergic inhibitory action of catecholamines and the PGE-like material released in the medium. A sub-threshold dose of PGF2α (10−10 M) shifted to the left the dose-response curves to NE of strips isolated from metestrous rats. When the tissue was pretreated with indomethacin and propranolol the dose-response curve to NE showed a clear shift to the left. On the other hand, the combination of indomethacin and propranolol shifted the NE dose-response curve to the right in the presence of sub-threshold doses of PGF2α. Dose-response curves to methoxamine were constructed in the presence or absence of several PGs using uterine strips isolated from estrous rats. With indomethacin, a threshold dose of PGE1 (10−8 M) and PGE2 (10−8 M) shifted to the left the control curve of methoxamine, whereas PGF2α (10−8 M) shifted the curve to the right. The interaction between sex hormones, PGs and catecholamines acting on α- and β-adrenoceptors in the isolated rat uterus is discussed.

Synthesis and release of prostaglandins D2 and E2 by rat uterine tissue throughout the sex cycle. Effects of 17-β-estradiol and progesterone

Abstract The synthesis and release of prostaglandins (PGs) D2 and E2 by rat uterine tissue was studied during the whole sex cycle. The PGs released into the bathing solution after 60 min of incubation were measured by specific radioimmunoassays. It was found that PGD2 released at diestrous was significantly higher than at proestrous and estrous. We also observed that PGE2 produced at diestrous was significantly higher than at proestrous and estrous, i.e. both PGs follow the same pattern of production throughout the sex cycle, but in all the cases the uterine strips released higher amounts of PGE2 than of PGD2. The influence of the sex hormones on PGD2 and PGE2 synthesis, was also studied. We observed that the treatment of ovariectomized rats with 17-β-estradiol decreased significantly the synthesis and release of PGD2 and PGE2. On the other hand, progesterone treatment did not modify the production of PGE2 but decreased significantly the synthesis of PGD2. In conclusion, in the present study we have found that PGD2 and PGE2 production varied similarly during the sex cycle and that 17-β-estradiol negatively regulates their synthesis. In addition, we have found that progesterone depressed only PGD2 synthesis without affecting PGE2 production.

On the inotropic effects of leukotrienes in the isolated urinary bladder of guinea pigs and rats

Leukotrienes (LTs) B4, C4 and D4 were tested on the motility of rings isolated from the urinary bladder of guinea pigs and rats. LTB4 did not evoke inotropic influences in any of the preparations, whereas LTC4 and LTD4 augmented the magnitudes of tonic and phasic contractions in the guinea pig but not in the rat detrusor muscle, LTC4 evoking a greater enhancement than LTD4. On molar bases, acetylcholine induced smaller positive inotropic effects. In the presence of 10(-4) acetylsalicylic acid (ASA), cumulative dose-response curves of phasic and tonic contractions for LTC4 were shifted to the right of controls, whereas curves of the phasic motility for LTD4 remained unaltered. However, ASA shifted to the left the dose-response curve of tonic contractions for LTD4 and in addition evoked an augmentation of the absolute developed tension. The initial (postequilibrium) contractile levels of basal phasic contractions did not differ between controls and preparations incubated with ASA (10(-4) M), nordihydroguaiaretic acid (10(-7) M) or FPL-55712 (3 X 10(-6) M). The findings suggest that some musculo-active prostanoid(s) could be modulating, in opposite directions, the smooth muscle contractile reactivity of the guinea pig urinary bladder when challenged in vitro with LTC4 and LTD4. Our data reported hereing also suggest that the role, if any, of endogenous prostanoids and leukotrienes for the normal basal contractile functioning of the guinea pig urinary bladder, remains obscure.

Is there a role for dopamine in the regulation of motility of sow oviducts

Dose-response curves for norepinephrine (NE), dopamine (DA) and 2-bromo-alpha-ergocryptine (BEC) in the isthmic and ampullary regions isolated from proestrous sow oviducts, were drawn. NE, DA and BEC depressed the contractile activity of ampullary segments in dose-dependent fashion. In the isthmic region, NE induced a dose-related stimulation whereas DA and BEC evoked relaxation. Propranolol (10(-6)M) did not modify significantly the effect of DA on the ampulla, whereas spiperone, chlorpromazine and haloperidol, shifted to the right DA dose-response curves. Haloperidol and spiperone were able to partially antagonize responses to DA of the isthmus. The catecholamine contents of the ampullary (a) and isthmic (i) regions of sow oviducts during proestrus (P), estrus (E) and metestrus (M) proved to be quite different and differently affected by the variations of the sex cycle: NE, DA and epinephrine (EPI) in (i) higher than in (a); NE in (i) and (a) during M higher than during E; NE in (i) lower during E than during P. The probable presence of specific dopamine receptors in sow oviducts as well as their eventual role in modulating tubal motility are discussed in this paper.

Nitric oxide mediates plateletactivating factor stimulatory action on uterine prostaglandin production

Accumulated evidence suggests that platelet-activating factor (PAF) may have a role in implantation by stimulating prostaglandin (PG) production. Since we had demonstrated that nitric oxide (NO) can increase uterine PGs, the aim of this study was to explore whether or not NO could mediate rat uterus responses to PAF on day 5 of gestation, when implantation takes place. Uterine motility was enhanced by PAF as compared to controls. This action was abolished by either the arginine analogue, N-monomethyl L-arginine (L-NMMA) or the cyclooxygenase inhibitor, indomethacin. On the other hand, NOS activity was detected in uterine strips and could be stimulated by PAF. The cyclooxygenase product PGE2 was also significantly stimulated by PAF. Inhibition of endogenous NO formation abolished the PAF effect on PG synthesis. Our results suggest that NO is an important intermediate in the interaction between PAF and PGs.