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

We attempted to explore possible mechanism(s) subserving the influence of oxytocin on uterine motility by studying the action of the hormone on: 1) the contractile activity of isolated rat uteri in the presence or absence of indomethacin; 2) the synthesis and release of prostaglandins (PGs) into the solution incubating the uterine tissue as well as the metabolism of labelled arachidonic acid; 3) the uptake of 45Ca2+ by uterine strips. The experiments were bone with uterine preparations isolated from spayed rats treated or not with 17-beta-estradiol. The values of isometric developed tension (IDT) and of frequency of contractions (FC) induced by oxytocin in uterine strips isolated from spayed and spayed-estrogenized rats, were not modified by indomethacin at 10(-6) M. On the other hand, uterine strips from untreated spayed rats, release into the incubating medium approximately equal amounts of PGE1, PGE2 and PGF2 alpha. The in vitro presence of oxytocin (50 mU/ml) increased significantly (p 0.05) the output of PGF 2 alpha without changing the release of PGE1 or PGE2. Uteri from spayed rats injected prior to sacrifice with 17-beta-estradiol released significantly less PGE1 and PGE2 (p less than 0.005) than preparations from non-injected animals, whereas the output of PGF2 alpha in the suspending solution remained unchanged. Following estrogenization the addition of oxytocin to preparations obtained from spayed-estrogenized rats also increased the output of uterine PGF2 alpha (p less than 0.001) without changing that of PGs E1 or E2.(ABSTRACT TRUNCATED AT 250 WORDS)     

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)     

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     

In SHR aorta, calcium ionophore A-23187 releases prostacyclin and thromboxane A2 as endothelium-derived contracting factors

In mature spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY), acetylcholine and the calcium ionophore A-23187 release endothelium-derived contracting factors (EDCFs), cyclooxygenase derivatives that activate thromboxane-endoperoxide (TP) receptors on vascular smooth muscle. The EDCFs released by acetylcholine are most likely prostacyclin and prostaglandin (PG)H(2), whereas those released by A-23187 remain to be identified. Isometric tension and the release of PGs were measured in rings of isolated aortas of WKY and SHR. A-23187 evoked the endothelium-dependent release of prostacyclin, thromboxane A(2), PGF(2alpha), PGE(2), and possibly PGH(2) (PGI(2) > thromboxane A(2) = PGF(2alpha) = PGE(2)). In SHR aortas, the release of prostacyclin and thromboxane A(2) was significantly larger in response to A-23187 than to acetylcholine. In response to the calcium ionophore, the release of thromboxane A(2) was significantly larger in aortas of SHR than in those of WKY. In both strains of rat, the inhibition of cyclooxygenase-1 prevented the release of PGs and the occurrence of endothelium-dependent contractions. Dazoxiben, the thromboxane synthase inhibitor, abolished the A-23187-dependent production of thromboxane A(2) and inhibited by approximately one-half the endothelium-dependent contractions. U-51605, an inhibitor of PGI synthase, reduced the release of prostacyclin elicited by A-23187 but induced a parallel increase in the production of PGE(2) and PGF(2alpha), suggestive of a PGH(2) spillover, which was associated with the enhancement of the endothelium-dependent contractions. These results indicate that in the aorta of SHR and WKY, the endothelium-dependent contractions elicited by A-23187 involve the release of thromboxane A(2) and prostacyclin with a most likely concomitant contribution of PGH(2).     

Influences of estradiol and of catechol and non-catechol estrogens on the output of prostaglandins in uteri from spayed rats

The effects of 17-beta estradiol and of some catechol and non-catechol-estrogens on the synthesis and output of prostaglandins (PGs) E and F by uteri from ovariectomized rats, were explored. Uteri from castrated animals released twice as much PGE than PGF. When uterine tissue was obtained from spayed rats injected prior to sacrifice with a low dose of 17-beta estradiol (0.5 + 1.0 microgram, on two consecutive days), the output of PGE diminished significantly. With a higher dose of the hormone (0.5 + 50.0 micrograms) the depressive influence on the synthesis and release of PGE was even more marked, whereas the output of PGF rose significantly. Low or high doses of estrone or of estriol failed to affect the release of either one of the PGs determined. On the other hand, 2-0H-estradiol at a low dose had no action but at a higher one inhibited the release of PGE without influencing PGF. Neither low nor high doses of 2-0H estriol or of 2-0H estrone affected the synthesis and release of uterine PGs. It was also observed that all the compounds tested evoked a significant uterotrophic action. It appears plausible that some catechol metabolites of 17-beta estradiol, but not other catechol-estrogens, could be involved in the mechanism of action of 17-beta estradiol modulating the production of PGs by the rat uterus.     

Gamma-linolenic acid improves the constancy of contractions in uteri from sprayed rats and is metabolized to prostaglandin E1 but not to bisenoic prostanoids

The effects of gamma-linolenic acid (GLA) on the time-dependent constancy of spontaneous contractions (isometric developed tension = IDT and frequency of contractions = FC) in uterine strips isolated from spayed rats, were explored. Moreover, the influence of the unsaturated fatty acid on the basal generation and release of tissue prostaglandins (PGs) as well as the conversion of labelled GLA into prostanoids by the uterine tissue and the effects of p-bromo-phenacyl-bromide (BPB), were also studied. GLA (10(-7)M), attenuated significantly the spontaneous decrement of contractile constancy exhibited by control preparations during a period of 180 min of activity in isolation, whereas BPB (10(5) M) resulted in an augmented and faster decrement of inotropic constancy. Spontaneous changes in the constancy of uterine motility as time progressed involved similarly both IDT and FC. After 180 min of activity in isolation a basal generation and release of PGs E and F of the series 1 and 2, were detected. The challenge with 10(-7) M GLA (delivered immediately after isolation) enhanced significantly the output of PGE1 but did not influence the generation and release of PGE2 or PGF2 alpha. BPB (10(-5) M) had no significant effect on the basal output of PGE1, PGE2 or PGF2 but completely prevented the enhancing action of GLA on the synthesis and release of PGE1. Labelled GLA was mainly converted to PGE1 by rat uterine segments and negligible counts in the 2-series of prostanoids, were observed. In presence of BPB (10(-5) M) the conversion of 1-14C-GLA, to PGE1 was almost completely abolished. The foregoing evidences suggest that exogenous GLA is metabolized by the spayed rat uterus via an elongase, forming di-homogamma-linolenic acid (DHLA), which in turn is substrate for cyclo-oxygenase peroxidase reactions yielding finally PGE1. No evidence of a delta 5-desaturase activity, converting DHLA into arachidonate and further derivatives, was detected. Coincidently, exogenous GLA was able to support a better contractile constancy as a function of time than that evidenced in untreated uterine strips isolated from castrated rats.     

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)     

Interactive roles of progesterone, prostaglandins, and collagenase in the ovulatory mechanism of the ewe

Interrelationships between production of progesterone (P4), prostaglandin (PG) E2 and PGF2 alpha, and collagenase by periovulatory ovine follicles and their possible involvements in the ovulatory process were investigated. Follicles were isolated from ovaries at intervals (0 to 24 h) after the initiation of the preovulatory surge of luteinizing hormone (LH). Progesterone and PGs within follicles were determined by radioimmunoassay. Digestion of radioactive collagen during coincubation with tissue homogenates was used to assess the production of a bioactive follicular collagenase(s). Follicular accumulation of PGs and P4 increased at 12 and 16 h, respectively, after the onset of the surge of LH; PGE2 then decreased at 20 h. Collagenolytic activity of follicular tissue increased at 20 h and was maximal at 24 h (during the time of follicular rupture). An inhibitor of synthesis of P4 (isoxazol) or PGs (indomethacin) was injected into the follicular antrum at 8 h. Isoxazol did not prevent the initial rise in PGs, but inhibited synthesis of PGF2 alpha at 16 h and therafter. Isoxazol negated the decline in PGE2 and increase in collagenolysis. Indomethacin did not influence synthesis of P4; however, it suppressed collagenolytic activity of follicular tissue. Ovaries with treated follicles were left in situ and observed for an ovulation point at 30 h. Isoxazol or indomethacin was a potent inhibitor of ovulation. The blockade of ovulation by isoxazol was reversed by systemic administration of P4 or PGF2 alpha, but not by PGE2. Reversal of the blockade by indomethacin was accomplished with PGE2 or PGF2 alpha. Collagenolytic activity of follicular tissue was likewise restored by such treatments.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of oestradiol 17 beta on prostaglandin biosynthesis by the uterus of ovariectomized rat and guinea pig

In vitro prostaglandin biosynthesis by uteri of ovariectomized rats and guinea pigs treated or untreated with oestradiol 17 beta, administered subcutaneously, was measured by R.I.A. of PGF2 alpha and PGE2. Incubations with [1-14C] arachidonic acid were also performed and labelled metabolites were analyzed by TLC. The main metabolite in rats was 6 keto PGF1 alpha and in decreasing order of magnitude, PGF2 alpha and PGE2. In guinea pig PGF2 alpha was the main product. Ovariectomy in rats completely changed the pattern of synthetized prostanoids : PGI2 production was doubled when compared to cycling rats and PGE2 increased 10 fold. PGF2 alpha values were similar to the mean value measured during the cycle. OE2 treatment almost completely inhibited PGI2 synthesis and reduced PGE2 by half. Total PG synthesis in OE2 treated animals was decreased by 5 fold when compared to spayed rats. Endogenous PGF2 alpha synthesis was slightly stimulated. In the guinea pig OE2 treatment of ovariectomized animals increased the total synthesis from 50 per cent. PGF2 alpha was always the main metabolite. In conclusion OE2 regulation of uterine PG synthesis is depending on the animal species and cannot be explained by a unique effect on the cyclooxygenase, but rather by an interplay on the various enzymes of the arachidonic acid cascade.     

Prostaglandin E and E2 alpha secretion by glandular and stromal cells of the pig endometrium in vitro: effects of estradiol-17 beta, progesterone, and day of pregnancy.

Prostaglandins (PGs) are believed to play important roles in the establishment of pregnancy. Glandular and stromal cells were isolated from pig endometrium on days 11 through 19 of pregnancy and cultured in the presence of estradiol-17 beta (E2) and progesterone (P4) to determine the effect of day of pregnancy and steroids on the secretion of PGE and PGF2 alpha. Estradiol at concentrations between .01 and 1 microM did not affect PGE and PGF2 alpha secretion into the medium by glandular and stromal cells. Progesterone (.1 microM) suppressed (P less than .001) PGE and PGF2 alpha production from both cell types. Glandular cells secreted more (P less than .01) PGF2 alpha than PGE, whereas stromal cells collected on days 11, 12, 13, and 19 secreted more (P less than .05) PGE than PGF2 alpha. Stromal cells isolated from tissues collected on day 13 of pregnancy produced PGs with higher (P less than .01) PGE:PGF2 alpha ratio than those from tissues harvested on other days of pregnancy. Glandular cells isolated from tissues collected on days 13 and 19 and stromal cells isolated from tissue collected on day 13 of pregnancy secreted more (P less than .05) PGE and PGF2 alpha than cells isolated on other days of pregnancy. We conclude that: 1) P4 has a suppressing effect on PG secretion; 2) endometrial glandular and stromal cells each produce a unique profile of PGs; and 3) endometrial cells harvested on different days of pregnancy secrete different amounts of PGE and PGF2 alpha.     

Inhibition of ovulation in the gonadotropin-primed immature rat by exogenous prostaglandin E2.

In the past two decades there have been innumerable reports that prostaglandins (PGs) are essential for mammalian ovulation. However, we have recently found that a relatively low dose of 0.03 mg indomethacin (INDO) sc to PMSG/hCG-primed immature Wistar rats can significantly reduce ovarian PG levels without inhibiting the control ovulation rate of 60+ ova/rat (1-3). In view of this information, the present study was an effort to duplicate the earlier reports that PGs can reverse the "inhibitory" effect of INDO on ovulation. In control animals, which received PMSG and hCG only, the ovulation rate was 63.8 +/- 4.5 ova/rat. This rate was reduced to 4.1 +/- 1.1 ova/rat when the animals were injected with 1.0 mg INDO at 3 h after hCG. In no instance was this inhibition reversed when the animals were treated with 1.0 mg of PGE2 or PGF2 alpha, or a combination of both prostanoids in either a single dose at 3 h after hCG, or in 4x doses at 2-h intervals beginning at 3 h after hCG. Furthermore, in animals that did not receive INDO, the ovulation rate in PGE2-treated animals was reduced to 20.0 +/- 6.7 ova/rat, and in animals treated with PGE2 and PGF2 alpha (combined) it was reduced to 19.4 +/- 6.5 ova/rat. In summary, not only did the PGs fail to reverse the anti-ovulatory effect of INDO, PGE2 actually suppressed the ovulation rate.     

A novel anti-lipolytic action of norepinephrine in uteri isolated from spayed rats appears subserved by the activation of alpha 1-adrenoreceptors diminishing the generation and release of lipolytic prostaglandins

The effects of norepinephrine (NE: 3 x 10(-6) M) on the outputs of prostaglandins (PGs) E1, E2 and F2 alpha, from uterine horns isolated from ovariectomized rats and suspended in solutions with or without exogenous glucose, were explored. The releases of the different PGs into the external medium were determined after incubating for one hour uterine preparations, mounted within a tissue bath and receiving a constant preload tension. In glucose-containing solutions, NE enhanced the basal output of PGE2 and failed to alter the basal releases of PGE1 or of PGF2 alpha. In glucose-free media, the basal output of PGE2 was comparable to that detected in presence of exogenous glucose, and its augmentation following added NE was again evident. However, the basal outputs of PGE1 and of PGF2 alpha, greater in glucose-free solutions than in glucose-containing media, were significantly diminished by added NE. Uterine triglyceride (TG) levels were also explored, both immediately after sacrifice (0 min) or following suspending uterine segments during one hour (60 min) in solutions containing exogenous glucose or not. In glucose-containing media, tissue TGs did not differ at 0 min or at 60 min, neither in controls, nor in NE-challenged preparations, whereas in glucose-free solutions, TGs were significantly smaller at 60 min than at 0. interestingly, the addition of NE completely prevented the dimunition of uterine TGs, present at 60 min in glucose-free medium. Neither propranolol nor yohimbine (10(-6) M) altered this sparing action of added NE on tissue TGs, but phentolamine or prazocin (10(-6) M), effectively antagonized the preventive effect of the agonist.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of progesterone on the spontaneous motility and prostaglandin synthesis in uterine horns isolated from ovariectomized rats

The motility of isolated uterine horns as well as the generation of PGE and PGF-like material by uterus from spayed rats, treated or untreated with progesterone or progesterone plus estradiol-17-beta, were studied. The changes of Functional Activity (FA) with time (constancy) of control uterine horns and that preparations treated wtih 2 mg of progesterone (P) were not significantly different. However, the PGF-like material released into the bathing solution was significantly higher when the animals were treated with P. PGE-like material in the medium was similar in both groups. With higher doses to P (4 mg/day/2 days) the constancy of FA was similar to that observed in untreated animals, and the PGF-like material released into the medium was significantly higher than in the control group FA and PGs releases into the bathing medium by uterine horns from supra-renalectomized-ovariectomized animals (treated or not with P) were similar to those obtained in spayed rats with the intact suprarenal gland, but the absolute values of PGF-like material were always lower than in this group. Estradiol-17-beta injected prior or after P diminished the stimulation induced by P on the release of PGF-like material into the medium. The constancy of the contractile activity as well as the uterine release of PGE-like material was also diminished in rats treated with P plus estradiol-17-beta. The novel finding that progesterone stimulates the synthesis of PGF in uterine horns from ovariectomized rats without changing that of PGE is discussed.     

Release of prostaglandins and leukotrienes from the rat uterus is an early estrogenic response

The early estrogenic responses are considered to be involved in inducing embryo implantation in a progesterone (P4)-primed uterus. Because of their involvement in the process of implantation and decidualization, prostaglandins (PGs) and leukotrienes (LTs) could be the mediators of early estrogenic responses in a P4-primed uterus. Therefore, temporal effects of estrogen on the production and/or release of PGF2, PGF2 alpha, LTB4 and LTC4 by the P4-primed uterus of hypophysectomized rats were examined. Hypophysectomized mature female rats were injected for 4 days with P4 (2 mg/rat, s.c.) or with P4 plus a single injection of estradiol-17 beta (E2) (100 ng or 200 ng/rat, i.v.) on the last day of P4 treatment. In one set of experiments, animals were killed at 0.5, 2, 4, 8, 12 and 30th after the last steroid treatment. The production of PGs and Lts by uterine homogenates was measured by radioimmunoassays (RIAs). The production of PGE2 and PGF2 alpha in P4-treated animals showed peaks at 2, 6 and 12h. The superimposition of E2 on P4 treatment induced a higher production rate of PGE2 and PGF2 alpha at 0.5h and abolished the peaks induced by P4 at 2h, but not the peaks at 6 or 12h. Irrespective of the kind of steroid hormonal treatments, uterine production of LTs showed a rapid decline between 6 and 8h followed by a sharp rise at 12h. The superimposition of E2 on P4-treatment again increased the production rates of LTB4 and LTC4 at early hours, i.e. at 0.5 and 2h, respectively, as compared to P4 treatment only.     

Interrelationship between nitric oxide and prostaglandins in bovine granulosa cells

It is well recognized that prostaglandins of the E (PGE) and F (PGF) series play an important role in ovarian physiology; in addition, nitric oxide (NO) has been recently demonstrated to be an important mediator of granulosa cell function. There is now evidence for a biologic relationship between PGs and the NO biosynthetic pathway. The aim of this study was to investigate the relationship between NO and PGE2 and PGF2alpha in bovine granulosa cells. Granulosa cells collected from small (<5mm) and large (>8mm) follicles were treated with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) or with indomethacin, an inhibitor of PGs synthesis, and PGE2 and PGF2alpha were quantified; in addition, the effects of PGE2 PGF2alpha and indomethacin on steroidogenesis and NO production were determined. The highest concentration of SNAP inhibited (P < 0.001) PGE2 production in cells from both kinds of follicles, while the lowest dose was effective only in cells from small follicles. The highest concentration of SNAP inhibited and stimulated (P < 0.001) PGF2alpha production in cells from small and large follicles, respectively. Progesterone (P4) production was stimulated by PGE2 and inhibited by PGF2alpha (P < 0.001) in cells from both types of follicles. Estradiol 17beta (E2) secretion was inhibited in cells from small and stimulated in those from large follicles by PGE2 (P < 0.05), while PGF2alpha was stimulatory in cells from both kinds of follicles (P < 0.001). P4 production by cells from small follicles was inhibited and stimulated by those from large follicles by indomethacin (P < 0.001), which also increased E2 output in cells from small follicles (P < 0.001). NO production was inhibited by both PGE2 and PGF2alpha except at the lowest concentration, which was stimulatory (P < 0.001). Indomethacin stimulated (P < 0.001) NO production. Taken together, the present data suggest a cross-talk between NO and PGs biosynthetic pathways, which needs to be further clarified.     

Effects of prostaglandins and of leukotriene C4 on the metabolism of labelled glucose in uteri isolated from ovariectomized-diabetic rats. Influences of 17-beta-estradiol and of insulin.

The influences of exogenous PGE1, PGE2, PGF2 alpha, LTC4 and insulin (INS) on glucose oxidation in uterine strips isolated from ovariectomized-diabetic (OVD) and ovariectomized-estrogenized-diabetic (OVED) rats, were studied. The spayed animals were made diabetic by a single injection of streptozotocin (65 mg.kg-1 body weight). The effects of prostaglandins were studied in the presence of indomethacin (INDO) in the incubation medium and the effects of LTC4 in the presence of INDO and nordihydroguaretic acid (NDGA). These procedures were followed in order to avoid the possible influences of endogenous derivatives of arachidonic acid formed by the activity of cyclooxygenase and of lipoxygenases. INDO and NDGA did not modify significantly the formation of 14CO2 from U-14C-glucose in uteri from OVD and from OVED rats. INS (0.5 U.ml-1) augmented significantly labelled glucose metabolism, both in OVD as well as in OVED rats. On the other hand, added PGE1, PGE2, PGF2 alpha or LTC4 failed to alter glucose metabolism in uteri from OVD rats. Only PGE1 was able to increase significantly (p less than 0.05) 14CO2 production from labelled glucose in uterine strips from OVED rats. In OVD rats the stimulatory action of INS on uterine glucose metabolism was significantly enhanced by exogenous PGE1, but not modified by PGE2, by PGF2 alpha or by LTC4. PGE1, PGE2 and LTC4 sensitized uterine strips obtained from OVED rats to the effects of INS. The possible importance of PGE1 in improving uterine glucose metabolism in diabetic animals is discussed.     

Changes in prostaglandin secretion by the regressing bovine corpus luteum

Secretion of prostaglandins (PGs) by the regressing corpus luteum (CL) was investigated in the cow. Six cows were implanted with microcapillary dialysis membranes of a microdialysis system (MDS) into the CL during Days 8-9 (Day 0 = estrus), and a prostaglandin (PG) F2alpha analogue (Estrumate) was injected intramuscularly (i.m.) to induce luteolysis. Acute increases in intraluteal release of PGF2alpha and PGE2 were observed during the first 4 h, followed by decreases over the next 8 h. Intraluteal release of both PGs gradually increased again during the period 48-72 h. Concentrations of PGF2alpha in ovarian venous plasma (OVP) were 4-13 times higher than those of jugular venous plasma (JVP) (P < 0.001) during the period of the experiment, and increased from 24 h after treatment with Estrumate (P < 0.05). Cyclooxygenase (COX)-2 mRNA expression increased (P < 0.05) at 2 and 24 h after treatment with Estrumate. The results indicated that local release of PGF2alpha and PGE2, and COX-2 mRNA expression were increased by Estrumate in the regressing CL at the later stages of luteolysis. Thus, luteal secretion of PGs may be involved in the local mechanism for structural rather than functional luteolysis.     

Structural specificity for prostaglandin effects on hepatocyte glycogenolysis.

Prostaglandins (PGs) are known to have effects on hepatic glucose metabolism. Some actions of PGs in intact liver systems may not involve PG effects directly at the level of the hepatocyte. To define the ability of structurally distinct prostaglandins to affect hepatocyte metabolism directly, the regulation of glycogenolysis was studied in hepatocytes isolated from male Sprague-Dawley rats. PGF and PGB2 inhibited glucagon-stimulated glycogenolysis in the hepatocyte system. Pinane thromboxane A2 (PTA2) and PGD2 had no effect on glucagon-stimulated glycogenolysis. Consistent with their inhibition of glucagon-stimulated glycogenolysis, PGF2 and PGF2 alpha inhibited glucagon-stimulated hepatocyte cyclic AMP accumulation. These actions of PGB2 and PGF2 alpha are identical with those previously reported for PGE2. Additionally, PGE2, PGF2 alpha and PGB2 inhibited glucagon-stimulated adenylate cyclase activity in purified hepatic plasma membranes. In contrast, PGF2 alpha, PGD2 and PTA2 were all without affect on basal rates of hepatocyte glycogenolysis or hepatocyte cyclic AMP content. PGE2 also inhibited glycogenolysis stimulated by the alpha-adrenergic agonist phenylephrine. Exogenous arachidonic acid was not able to reproduce the affects of PGE2 or PGF2 alpha on hepatocyte glycogenolysis, consistent with an extra-hepatocyte source of the prostaglandins in the intact liver. Thus PGE2 and PGF2 alpha act specifically to inhibit glucagon-stimulated adenylate cyclase activity. No prostaglandin tested was found to stimulate glycogenolysis. PGE2 and PGF2 alpha may represent intra-hepatic modulators of hepatocyte glucose metabolism.     

Involvement of inducible isoforms of COX and NOS in streptozotocin-pancreatic damage in the rat: interactions between nitridergic and prostanoid pathway

Streptozotocin-induced pancreatic damage involves nitric oxide (NO) and prostaglandins (PGs) overproduction. In this work we aim to evaluate a putative relationship between the elevated NO levels and the altered prostanoid production in pancreatic tissue from streptozotocin-diabetic rats. Total NOS activity and nitrate/nitrite pancreatic levels in tissues from diabetic rats are decreased when the cyclooxygenase (COX) inhibitor indomethacin (INDO) is added to the incubating medium, while the addition of PGE(2)increases nitrate/nitrite production and NOS levels. INDO and PGE(2)selectively affect Ca(2+)-dependent NOS (iNOS) activity in diabetic tissues, and they have not been able to modify nitrate/nitrite levels, iNOS or Ca(2+)-dependent (cNOS) in control tissues. When the NOS inhibitor L-NMMA was present in the incubating medium, control pancreatic [(14)C]-Arachidonic Acid ([(14)C]-AA) conversion to 6-keto PGF(1 alpha)and to TXB(2)was lower, and PGF(2 alpha), PGE(2)and TXB(2)production from diabetic tissues diminished. The NO donors, spermine nonoate (SN) and SIN-1, enhanced TXB(2)levels in control tissues, while PGF(2 alpha), PGE(2)and TXB(2)levels from diabetic tissues were increased. PGE(2)production from control and diabetic tissues was assessed in the presence of the NO donor SN plus INDO or NS398, a specific PG synthase 2 inhibitor. When SN combined with INDO or NS398 was added, the increment of PGE(2)production was abolished by both inhibitors in equal amounts, indicating that the activating effect of nitric oxide is exerted on the inducible isoform of cyclooxygenase. In the diabetic rat, prostaglandins and NO seem to stimulate the generation of each other, suggesting a lack of regulatory mechanisms that control the levels of vasoactive substances in acute phase of beta-cell destruction.     

Evolution of Streptozotocin–Pancreatic Damage in the Rat: Modulatory Effect of Endothelins on the Nitridergic and Prostanoid Pathway

Many lines of evidence indicate that an increased pancreatic production of nitric oxide (NO) and prostaglandins (PGs) is found in the pancreas of streptozotocin-diabetic rats and that endothelins (ETs) are closely related to the nitridergic and prostanoid pathway in several tissues. In the present study the relationship between NO, ETs, and PGs has been explored in isolated pancreatic tissue from streptozotocin-diabetic rats. Pancreatic ET levels are higher in pancreatic tissues from diabetic (D) rats compared to control (C) animals. The addition of nitric oxide synthase (NOS) inhibitors (1 mM N(G)-nitro-l-arginine methyl ester, 600 microM N(G)-monomethyl-l-arginine) in the incubating medium reduces and NO donors (SIN-1, 300 microM spermine suppress, NONOate 100 microM) increases ET levels in pancreatic slices from C and D animals. PGE(2) (10(-7) M) increases and indomethacin (10(-6) M) decreases ET pancreatic production only in D but not in C tissues when added into the incubating bath. When tissues are incubated in the presence of endothelin 1 (ET-1) (10(-7) M), NOS activity is higher in C pancreas, while the ET-receptor antagonist bosentan (B) decreases NOS levels in D but not in C tissues. When pancreatic arachidonic acid (AA) conversion to prostaglandins was explored, ET-1 increased PGF(2alpha), PGE(2), and TXB(2) levels in C but not in D tissues. B abolishes TXB(2) increment due to the diabetic state, but failed in modulating AA conversion to 6-keto PGF(1alpha), PGF2(alpha) and PGE(2) in D pancreas. Our results show an alteration in AA metabolism, ET production, and NO increment associated with pancreatic damage due to streptozotocin.