Effects of epidermal growth factor, interleukin 1 and nitric oxide on prostaglandin production by guinea-pig uterus.

Initial experiments in the present study investigated the effects of epidermal growth factor (EGF), interleukin 1beta (IL-1beta) and sodium nitroprusside (a nitric oxide donor) on the output of prostaglandins from guinea-pig uterus on day 7 of the oestrous cycle. Superfusion of day 7 guinea-pig uterus in vitro with either EGF or sodium nitroprusside increased the output of PGF(2alpha) and 6-keto-PGF(1alpha), but not of PGE(2). IL-1beta had no effect on the output of these three prostaglandins. EGF still increased the output of PGF(2alpha), but did not increase the output of 6-keto-PGF(1alpha) in a calcium-depleted superfusate. Subsequent experiments investigated the effect of sodium nitroprusside on contractile activity of day 7 guinea-pig uterus. Basal spontaneous activity of both the intact uterus and isolated myometrium superfused in vitro was low. Sodium nitroprusside increased the contractile activity of these tissues two- to fourfold. EGF did not affect the contractile activity of the uterus, indicating that sodium nitroprusside-induced contractions are not due to increased prostaglandin production. Overall, the findings indicate that EGF and nitric oxide may act as mediators in the mechanism by which oestradiol acting on a progesterone-primed uterus stimulates the increase in PGF(2alpha) production by the guinea-pig uterus necessary for luteolysis. Nitric oxide may increase the spontaneous activity of the uterus when this activity is low.

Investigations into the mechanisms controlling prostaglandin production by the guinea-pig placenta: roles of calcium and gonadotrophin-releasing hormone.

The outputs of PGF(2 alpha), PGE(2) and 6-keto-PGF(1 alpha) were higher from the day 29 guinea-pig placenta than from the sub-placenta in culture, with PGF(2 alpha)being the major prostaglandin produced by the placenta. Lack of extracellular calcium reduced the production of all three prostaglandins by the sub-placenta and 6-keto-PGF(1 alpha) production by the placenta, but had no effect on the production of PGF(2 alpha) and PGE(2) by the placenta. EGTA (a calcium chelator) and a low concentration (30 microM) of TMB-8 (an intracellular calcium antagonist) generally inhibited prostaglandin output from the placenta and sub-placenta at various time points during culture, although EGTA had no effect on PGE(2) output from the placenta. Trifluoperazine and W-7 (calmodulin inhibitors) had no inhibitory effect on the outputs of PGF(2 alpha) and PGE(2) from the placenta, nor on the outputs of any prostaglandin from the sub-placenta. However, these two compounds inhibited the output of 6-keto-PGF(1 alpha) from the placenta. Nifedipine and verapamil (calcium channel blocking drugs) generally reduced the outputs of prostaglandins from the placenta and sub-placenta, except verapamil had no inhibitory effect on PGF(2 alpha) output from the sub-placenta. Gonadotrophin-releasing hormone (GnRH) did not stimulate the output of prostaglandins from the placenta, and tended to have a weak inhibitory action on this tissue. On the sub-placenta, GnRH had an initial inhibitory action on the outputs of PGF(2alpha) and 6-keto-PGF(1 alpha), which was then followed by a stimulation of the outputs of PGF(2 alpha) and, to a lesser extent, of PGE(2).

Effects of indomethacin, NS-398 (a selective prostaglandin H synthase-2 inhibitor) and protein synthesis inhibitors on prostaglandin production by the guinea-pig placenta.

The outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)were similar from the day 22 guinea-pig placenta and sub-placenta in culture, except for PGE2 output from the sub-placenta which was lower. Between days 22 and 29 of pregnancy, the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)during the initial 2 h culture period increased 6.9-, 1.1- and 3.2-fold, respectively, from the placenta, and 2.1-, 1.4- and 2.2-fold, respectively, from the sub-placenta. Therefore, there was a relatively specific increase in PGF(2 alpha)production by the guinea-pig placenta between days 22 and 29 of pregnancy. The output of PGFM from the cultured placenta also increased between days 22 and 29, indicating that the increase in PGF(2 alpha)output was due to increased synthesis rather than to decreased metabolism. By comparing the amounts of prostaglandins produced by tissue homogenates during a 1 h incubation period, it appears that there is approximately a 2-fold increase in the amount of prostaglandin H synthase (PGHS) present in the guinea-pig placenta between days 22 and 29. NS-398 (a specific inhibitor of PGHS-2) and indomethacin (an inhibitor of both PGHS-1 and PGHS-2) both inhibited prostaglandin production by homogenates of day 22 and day 29 placenta. Indomethacin was more effective than NS-398, except for their actions on PGF(2 alpha)production by the day 29 placenta where indomethacin and NS-398 were equiactive. Indomethacin and NS-398 were both very effective at inhibiting the outputs of PGF(2 alpha), PGE2 and 6-keto-PGF(1 alpha)from the day 22 and day 29 placenta and sub-placenta in culture, indicating that prostaglandin production by the guinea-pig placenta and sub-placenta in culture is largely dependent upon the activity of PGHS-2. The high production of PGF(2 alpha)by the day 29 placenta is not dependent on the continual synthesis of fresh protein(s), as inhibitors of protein synthesis did not reduce PGF(2 alpha)output from the day 29 guinea-pig placenta in culture.

The effects of P2Y receptor agonists and adenosine on prostaglandin production by the guinea-pig uterus.

1. This study has investigated the effects adenosine 5'-triphosphate (ATP), analogues of ATP, uridine 5'-triphosphate (UTP) and adenosine on prostaglandin output from the guinea-pig uterus superfused in vitro, and from guinea-pig endometrium and myometrium cultured for 24 h. 2. ATP, 2-methylthio ATP and adenosine increased the outputs of prostaglandin F(2 alpha) (PGF(2 alpha)) and 6-keto-PGF(1 alpha) (reflecting PGI(2) production), and UTP increased the output of PGF(2 alpha) from the superfused guinea-pig uterus. These findings support the hypothesis that the contractile effects of ATP, 2-methylthio ATP, UTP and adenosine are mediated by prostaglandins. 3. Suramin (a P2 receptor antagonist) and 8-sulphophenyltheophylline (an A receptor antagonist) blocked the stimulatory actions of ATP and adenosine, respectively, on PGF(2 alpha) output, suggesting that ATP acts on P2 receptors (probably of the P2Y type) and adenosine acts on A receptors in the guinea-pig uterus to increase PGF(2 alpha) production. 4. ATP, 2-methylthio ATP, alpha,beta-methylene ATP, beta,gamma-methylene ATP, UTP and adenosine increased the output of PGF(2 alpha) from guinea-pig endometrium and myometrium after 24 h of culture, with a greater stimulatory effect being exerted on the endometrium than on the myometrium. Little or no stimulatory effect was seen after 2 and 8 h of culture. In addition the effects of ATP, ATP analogues, UTP and adenosine on the outputs of PGE(2) and 6-keto-PGF(1 alpha) from cultured endometrium and myometrium were more variable, with both stimulation and inhibition being observed. 5. The stimulatory effects of ATP and adenosine on PGF(2 alpha) output from the endometrium and myometrium were associated with an increase in the prostaglandin synthesizing capacity of both tissues, due probably to an increase in the amount of prostaglandin H synthase present.

Effects of inhibitors of arachidonic acid turnover on the production of prostaglandins by the guinea-pig uterus.

The supply of free arachidonic acid from phospholipids is generally regarded as the rate-limiting step for prostaglandin (PG) synthesis by tissues. Two enzymes involved in arachidonic acid uptake into, and release from, phospholipids are acyl-CoA:lysophospholipid acyltransferase (ACLAT) and phospholipase A2 (PLA2), respectively. PGF2 alpha produced by the endometrium induces luteolysis in several species including guinea-pigs. Thimerosal, an inhibitor of ACLAT, and aristolochic acid, an inhibitor of PLA2, both reduced, in a concentration-dependent manner, the output of PGF2 alpha from guinea-pig endometrium cultured for 24 h on days 7 and 15 of the oestrous cycle. This study showed that the continual production of PGF 2 alpha by guinea-pig endometrium is not only dependent upon the activity of PLA2 for releasing free arachidonic acid for PGF2 alpha synthesis, but also on the incorporation of arachidonic acid into the phospholipid pool by the activity of ACLAT. The inhibitory effects of thimerosal and aristolochic acid on the outputs of PGE2 and 6-keto-PGF1 alpha were less marked, particularly on day 7 when the low output of PGE2 was unaffected and the output of 6-keto-PGF1 alpha was increased at the lower concentrations of thimerosal. This finding indicates that there are different pools of arachidonic acid bound as phospholipid for the syntheses of PGF2 alpha and 6-keto-PGF1 alpha by guinea-pig endometrium.

Heterogeneity in the bioactivity of LH secreted by peripubertal rats.

Treatment of immature rats with 5 iu equine chorionic gonadotrophin (eCG) on day 25 typically stimulates a preovulatory surge of LH on day 27 and ovulation on day 28. In rats weighing > 60 g at the time of treatment, an LH surge and ovulation occurred in 75% of the animals but, in rats weighing < 60 g, only 13% ovulated even though 69% showed an LH surge. Previous findings have shown that exogenous LH can stimulate ovulation in the rats < 60 g, indicating that the anovulation was not due to ovarian immaturity, but rather to an abnormal form of LH. Thus, it was important to determine whether the bioactivity of LH released at the time of the surge differs in rats < 60 g compared with rats > 60 g. Experiments showed that LH from both groups of eCG-treated animals were equipotent in stimulating testosterone production from incubated Leydig cells and progesterone production from cultured granulosa cells. Similarly the surge of progesterone in vivo, which occurs co-incident with the LH surge, was of similar magnitude in both groups of animals. Since prostaglandin synthesis increases at the time of ovulation and is also stimulated by LH, it was investigated whether the activity of ovarian phospholipase A2, the rate limiting enzyme in prostaglandin synthesis, and ovarian prostaglandin E2 concentrations differed in the animals > 60 g and < 60 g. Phospholipase A2 activities were similar in both groups of animals at the time of the LH surge, as were the prostaglandin E2 concentrations. However, in all animals that ovulated (15/20 in rats > 60 g and 2/15 in rats < 60 g), there was a threefold increase in ovarian prostaglandin E2 concentrations. The results show that, in underweight animals, the bioactivity of LH, in terms of its ability to stimulate steroidogenesis and phospholipase A2 activity, is similar to that released by animals > 60 g; however, the LH produced by the underweight animals fails to induce ovulation by failing to increase, either directly or indirectly, prostaglandin E2 production. Comparison of the profiles of plasma LH collected at the time of the LH surge on an anionic ion exchange column indicates that the LH from rats < 60 g possesses significantly less of the neutral or basic glycoform of LH than that from rats > 60 g. This finding provides a further index that the biopotency of LH produced by underweight animals is different from that of rats > 60 g.

Endogenous prostaglandin formation in the field-stimulated guinea-pig vas deferens: comparison of the inhibitory effects of indomethacin and NS-398.

Prostaglandin (PG) E2 inhibited both phases of contraction produced by electrical field stimulation of the guinea-pig vas deferens. PGF2alpha and PGD2 were without effect on this preparation. Carbacyclin (a PGI2) analogue inhibited the first phase of contraction at higher concentrations, whereas U46619 (a thromboxane mimetic) potentiated both phases of contraction. As exogenous arachidonic acid inhibits both phases of contraction of the electrically field-stimulated guinea-pig vas deferens, it is likely that the arachidonic acid is converted to PGE2 in the vas deferens. Indomethacin, a non-specific inhibitor of prostaglandin H synthase (PGHS), attenuated the inhibitory actions of exogenous arachidonic acid when examined on the first phase of contraction. NS-398, a relatively specific inhibitor of PGHS-2, also prevented the inhibitory action of exogenous arachidonic acid. However, NS-398 was much less effective than indomethacin in this respect even though NS-398 and indomethacin inhibit PGHS-2 with similar potencies. Consequently, the findings suggest that exogenous arachidonic acid is converted to PGE2 in the guinea-pig vas deferens by the actions of PGHS-1 and, to a lesser extent, by PGHS-2.

A comparison of the effects of indomethacin and NS-398 (a selective prostaglandin H synthase-2 inhibitor) on implantation in the rat.

Indomethacin (25 microM) inhibited the amount of prostaglandin (PG) E2, PGF2alpha and 6-keto-PGF1alpha synthesized by homogenates of day 5 pregnant rat uterus by 80-92%. In contrast, 25 microM NS-398, a selective inhibitor of prostaglandin H synthase-2 (PGHS-2), inhibited the synthesis of these three prostaglandins by homogenates of the same tissue by only 37-60%. Since it has been reported that idomethacin and NS-398 inhibit PGHS-2 with similar potencies and that indomethacin (unlike NS-398) is a potent inhibitor of PGHS-1, it may be concluded that prostaglandin production by homogenates of the rat uterus on day 5 of pregnancy is due to the activities of both PGHS-1 and PGHS-2. The administration of indomethacin (3 mg/kg) twice daily on days 3 and 4 of pregnancy reduced the implantation rate by 77%, whereas the similar administration of NS-398 (6 mg/kg) had no significant effect on implantation. It may be concluded that either the dose of NS-398 used was too low to affect uterine PGHS-2 activity in vivo sufficiently to prevent implantation, or that inhibiting uterine PGHS-2 activity in vivo has no effect on the implantation mechanisms or is compensated for by increased PGHS-1 activity such that the implantation process is not impaired.

Prostaglandin production by guinea-pig placenta and other uterine tissues during mid-pregnancy.

Prostaglandin (PG) output from cultured placenta, sub-placenta, endometrium and fetal membranes of guinea-pigs was measured on days 22, 29 and 36 of pregnancy to establish the source of increased PGF2alpha production during mid-pregnancy. PGF2alpha and 6-keto-PGF1alpha were produced in larger quantities than PGE2 by the placenta, sub-placenta and endometrium; 6-keto-PGF1alpha was in the major prostaglandin produced by the fetal membranes. The initial outputs of PGF2alpha, PGE2 and 6-keto-PGF1alpha from the sub-placenta, fetal membranes and endometrium either decreased or remained fairly constant between days 22 and 36. In contrast, the initial outputs of PGF2alpha, PGE2 and 6-keto-PGF1alpha from the placenta increased 14.7-, 2.5- and 2.0-fold, respectively, between days 22 and 36, indicating that the placenta is the tissue responsible for the increase in PGF2alpha output from the mid-pregnant guinea-pig uterus. Aristolochic acid (a phospholipase A2 inhibitor) inhibited prostaglandin output from the endometrium, but had a more variable effect in prostaglandin output from the other tissues. Thimerosal (an arachidonic acid uptake inhibitor) inhibited PGF2alpha and PGE2 outputs from the endometrium, but generally potentiated 6-keto-PGF1alpha output and prostaglandin output from the other tissues. Arachidonic acid release for prostaglandin synthesis in the endometrium, but not the placenta, sub-placental or fetal membranes, is apparently dependent upon a constant level of phospholipase A2 activity.

Detection of acyl-CoA synthetase, acyl-CoA:lysophospholipid acyltransferase and phospholipase A2 activities in non-pregnant and pregnant guinea-pig uterine tissues.

Acyl-CoA synthetase (ACS), acyl-CoA:lysophospholipid acyltransferase (ACLAT) and phospholipase (PL) A2 activities were detected in guinea-pig endometrium on days 7 and 15 of the cycle, and on days 15, 29 and 36 of pregnancy. Ovariectomy of non-pregnant animals resulted in an increase in the apparent activities of these three enzymes which was reversed by treatment with oestradiol and/or progesterone. ACS, ACLAT and PLA2 activities were detected in day 15 conceptuses, and in the placenta, sub-placenta, chorion and amnion on days 29 and 36 of pregnancy. Apparent activities of the enzymes were generally higher in the fetal membranes than in the placental tissue. This study has established that the enzymes involved in turnover of arachidonic acid in phospholipids are present in tissues in the non-pregnant and pregnant guinea-pig uterus. The higher apparent activities of enzymes (ACS and ACLAT) involved in arachidonic acid uptake compared to the enzyme (PLA2) involved in arachidonic acid release is in agreement with there being very low concentrations of free arachidonic acid in tissues.

Prostaglandin production by guinea-pig endometrial cells: effects of caffeine and other modulators of intracellular calcium.

The glandular epithelial cells were found to be the main source of PGF2 alpha (the uterine luteolytic hormone) in guinea-pig endometrium. There was a selective increase in PGF2 alpha production by these cells in culture at the time of the cycle (i.e. day 15) at which there is increased PGF2 alpha release from the guinea-pig uterus in vivo. TMB-8 (an intracellular calcium antagonist), W-7, trifluoperazine (both calmodulin antagonists), thapsigargin (an inhibitor of intracellular calcium uptake) and berberine (an inhibitor of calcium release) reduced the output of PGF2 alpha from day 7 glandular epithelial cells indicating that intracellular calcium is necessary for PGF2 alpha production by these cells. In contrast to its stimulatory effect on PGF2 alpha output from the guinea-pig uterus superfused in vitro and guinea-pig endometrium in culture, caffeine inhibited the output of PGF2 alpha from guinea-pig glandular epithelial cells in culture. Its effect was not fully shared by theophylline, nor mimicked by forskolin showing that cyclic AMP is not involved. The inhibitory actions of caffeine and those of the compounds which interfere with the action of intracellular calcium were not additive, suggesting that caffeine modulates the action of intracellular calcium in some way. Caffeine reduced the intracellular free calcium concentration in endometrial cells, but it was not particularly effective in this respect on day 7 glandular epithelial cells. Caffeine may therefore modulate the action of intracellular calcium in some other way.

Effects of caffeine and theophylline on prostaglandin production by guinea-pig endometrium.

Caffeine and theophylline increased prostaglandin output from day 7 and day 15 guinea-pig endometrium in culture. Ryanodine and forskolin had no effect on endometrial prostaglandin output. These results show that methylxanthines stimulate endometrial prostaglandin synthesis. However, the intracellular mechanisms involved apparently do not entail an increase in the intracellular free concentration by activation of a ryanodine-sensitive receptor or an increase in the cyclic AMP concentration.

Factors controlling prostaglandin production by guinea-pig endometrial cells.

The main cell type in the guinea-pig endometrium responsible for prostaglandin (PG) F2 alpha production and some of the intracellular mechanisms responsible for PGF 2 alpha synthesis in this cell type have been investigated. The glandular epithelial cells and not the stromal cells were found to be the main prostaglandin forming cells in the endometrium. A23187 (a calcium ionophore), phospholipase A2 and melittin (an activator of endogenous phospholipase A2) increased PGF 2 alpha output from the glandular epithelial cells, although only the action of melittin was specific to this cell type. Phospholipase A2 also increased the intracellular free calcium concentration in both cell types by an action largely dependent upon the presence of extracellular calcium. Protein synthesis inhibitors (actinomycin D, cycloheximide and puromycin), oestradiol, progesterone and aristolochic acid (an inhibitor of phospholipase A2) reduced PGF 2 alpha output from the glandular epithelial cells, although only the inhibitory action of aristolochic acid was specific. Protein synthesis inhibitors also reduced PGF 2 alpha output from stromal cells, and the outputs of PGE2 and 6 keto-PGF 1 alpha from both cell types. The steroid hormones also reduced PGE2 output from stromal cells. The findings indicate that PGF 2 alpha production by the glandular epithelial cells is dependent upon fresh protein synthesis and the activity of endogenous phospholipase A (which is a calcium-requiring enzyme).

Effect of a selective prostaglandin H synthase-2 inhibitor (NS-398) on prostaglandin production by the guinea-pig uterus.

Using guinea-pig uterine tissues, indomethacin (a non-selective inhibitor of prostaglandin H synthase) inhibited prostaglandin (PG) synthesis by homogenates of the endometrium, by cultured endometrium and myometrium, and by cultured epithelial glandular cells and stromal cells derived from the endometrium. NS-398, a selective inhibitor of prostaglandin H synthase-2 (PGHS-2), also inhibited PG synthesis by endometrial homogenates, by cultured endometrium and myometrium, and by cultured epithelial glandular cells and stromal cells. Indomethacin and NS-398 inhibited PG production to similar extents, except for 6-keto-PGF1 alpha production by the myometrium where indomethacin was more effective. In particular, indomethacin and NS-398 produced over 90% inhibition of PGF2 alpha output from the epithelial glandular cells, the main source of PGF2 alpha in the endometrium. These functional studies indicate that prostaglandin H synthase-2 is the predominant PG-forming enzyme in the guinea-pig uterus.

Prostaglandin F2 alpha and E2 production into uterine lymph of pregnant and non-pregnant ewes.

Uterine lymphatic cannulation was performed in pregnant and non-pregnant ewes so that serial lymph samples could be analysed for prostaglandins (PGs) on day 12 to 18 after oestrus. The production of PGF2 alpha into uterine lymph showed peaks of > 1000 pg/h between days 14 and 18 of the oestrous cycle. Such peaks were either absent or much reduced (< 900 pg/h) over the same period in four pregnant animals. PGE2 production into uterine lymph remained low (< 510 pg/h) both in the four non-pregnant animals in the later part of the oestrous cycle and in three of four pregnant animals between days 14 to 18 post mating.

A comparison of the effects of exogenous and endogenous prostaglandins on fast and slow contractions of field-stimulated guinea-pig vas deferens.

1. This study has compared the effects of exogenous and endogenous prostaglandins on the two phases of contraction of the guinea-pig vas deferens produced by electrical field stimulation. Prostaglandin E2 (PGE2), sulprostone and arachidonic acid dose-dependently and completely inhibited the first (fast) phase of contraction, with IC50s of 2.6 nM, 0.65 nM and 2.2 microM, respectively. 2. Following desensitization of the receptor for adenosine triphosphate (ATP) with alpha, beta-methylene ATP, PGE2, sulprostone and arachidonic acid dose-dependently inhibited the second (slow) phase of contraction of the guinea-pig vas deferens produced by electrical field stimulation, but the inhibition was incomplete (up to only 30%). Indomethacin (2.8 microM) reduced the effect of arachidonic acid. On its own, indomethacin (0.3 to 6.0 microM) had no consistent effect although, on some tissues, a slight potentiation of the contractions was seen. 3. Cicaprost (a PGI2 analogue) at low concentrations (0.5 to 30 nM) potentiated the first phase of contraction but even at high concentrations, had no consistent effect on the second phase of contraction of the guinea-pig vas deferens produced by electrical field stimulation. 4. PGE2, sulprostone and cicaprost potentiated contractions of the guinea-pig vas deferens produced by exogenous ATP. PGE2 and sulprostone also potentiated contractions produced by exogenous noradrenaline, whereas cicaprost had no consistent effect on the response to noradrenaline. 5. These findings indicate that prostaglandins of the E-series inhibit the second phase of contraction as well as the first phase of contraction of the guinea-pig vas deferens produced by electrical field stimulation. However, the extent of the inhibition is much less for the second phase than for the first phase. The reasons for this differential action of PGE are not clear. 6. Cicaprost potentiates the first phase but not the second phase of contraction. Since cicaprost potentiates the contractions produced by exogenous ATP, but not by exogenous noradrenaline, by an action presumably on post-junctional IP receptors, the potentiating action of cicaprost on the first phase of contraction produced by electrical field stimulation would appear to be satisfactorily explained through the action of cicaprost on these post-junctional IP receptors. 7. Exogenous arachidonic acid is apparently converted predominantly to PGE2 by the vas deferens, since the action of arachidonic acid mimicked that of PGE2 and was reduced by indomethacin. However, there was little evidence that sufficient PGE2 is generated during a short period (15 s) of sympathetic nerve stimulation for it to have any significant inhibitory effect on the size of the contractions produced.

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.

The effect of caffeine on prostaglandin output from the perfused mesenteric vascular bed of the rat.

Caffeine significantly (p < 0.05) increased the output of prostacyclin (PGI2) from the perfused rat mesenteric vascular bed. The outputs of PGE2 and PGF2 alpha were also increased by caffeine. This stimulatory response to caffeine did not show rapid desensitization. Ryanodine also increased PG output, suggesting that caffeine may be acting via the stimulation of a ryanodine receptor. The increased production of a vasodilator such as PGI2 from blood vessels following exposure to caffeine may explain why caffeine has a beneficial effect in angina.

The effect of caffeine on prostaglandin output from the guinea-pig uterus.

1. Caffeine increased the outputs of prostaglandin F2 alpha (PGF2 alpha), PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus on days 7 and 15 of the oestrous cycle. The effect on PGE2 output depended on the age of the animals and was absent in younger guinea-pigs (< 4 months). Theophylline also stimulated the outputs of PGF2 alpha and 6-keto-PGF1 alpha, but not the output of PGE2, from the day 7 guinea-pig uterus. 2. The stimulatory effects of caffeine on the outputs of PGF2 alpha, PGE2 and 6-keto-PGF1 alpha from the guinea-pig uterus were not prevented by lack of extracellular calcium, ryanodine or ruthenium red (both inhibitors of calcium release via the ryanodine receptor), although the increase in PGF2 alpha output tended to be slower when extracellular calcium was absent. Also, ryanodine flattened and broadened the peak of increased PGF2 alpha release. 3. The calmodulin antagonists, W-7 and trifluoperazine, had no inhibitory effect on the caffeine-stimulated increases in uterine prostaglandin output. In fact, W-7 (but not trifluoperazine) greatly potentiated the action of caffeine on uterine PGF2 alpha output, but had little or no potentiating effect on the action of caffeine on uterine PGE2 and 6-keto-PGF1 alpha outputs. 4. TMB-8, an intracellular calcium antagonist, inhibited the increase in PGF2 alpha output produced by caffeine without preventing the increases in outputs of PGE2 and 6-keto-PGF1 alpha. 5. These studies suggest that caffeine stimulates uterine PGF2 alpha synthesis and release by a mechanism dependent upon intracellular calcium, but this mechanism is not mediated by activation of any of the three well-characterized ryanodine receptors or by calmodulin. Furthermore, the increases in the synthesis and release of PGE2 and 6-keto-PGFI alpha. in the guinea-pig uterus induced by caffeine appear to involve mechanism(s) different from that which stimulates PGF2 alpha production.

Effects of exogenous and endogenous prostaglandins on the fast phase of contraction of the guinea-pig vas deferens produced by electrical field stimulation.

The initial, fast phase of contraction of the guinea-pig vas deferens produced by electrical field stimulation (10 pulses) was dose-dependently and completely inhibited by prostaglandin (PG) E2, sulprostone and, at high concentrations, by cicaprost. Sulprostone was more potent than PGE2 indicating that the EP3 receptor was involved. Cicaprost (a PGI2 analogue) apparently had weak EP3 receptor against activity. At low concentrations, cicaprost potentiated the contractions of the vas deferens, presumably by acting on an IP receptor. Exogenous arachidonic acid also dose-dependently and completely inhibited contractions of the guinea-pig vas deferens. The action of arachidonic acid was delayed when compared to PGE2 and was inhibited by indomethacin, suggesting that the arachidonic acid was converted to PGE2 by the vas deferens. Indomethacin (1.4 to 6.0 microM) had no significant, potentiating effect on the contractions of the guinea-pig vas deferens which suggests that endogenous PGs do not normally inhibit this fast phase of contraction. In higher concentrations, the contractions were reduced by indomethacin. The fast phase of concentration of the guinea-pig vas deferens consisted of 3 components. PGE2, sulprostone and arachidonic acid inhibited all components. The order of inhibition of the components was component 2, then component 3, followed by component 1.