Plasma concentration of 13,14-dihydro-15-keto-PGE2 (PGEM) after various ways of cervix ripening with PGE2

PGEM concentration was determined radioimmunologically in a non-pregnant woman, in whom PGE₂ was infused intravenously at increasing rates and in women, in whom labor was induced by various methods for local application of PGE₂. There was excellent correlation between the amount of PGE₂ infused intravenously and the levels of PGEM determined in the peripheral plasma. The following methods of local application of PGE₂ were included in the study: 0.4mg PGE₂ gel placed retroamnially by means of a balloon catheter, 0.4 and 0.5mg PGE₂ applied endocervically and 3mg PGE₂ placed intravaginally in form of a single vaginal tablet; also induced was a control-group, where only vaginal examination was performed. Bloods were drawn before, 30 minutes, 1, 2 and 3 hours after PGE₂ administration. Mean levels of PGEM in the maternal peripheral plasma did not change neither within nor between the various groups. It is concluded from the present study, that local application of doses currently used to soften the cervix and/or induce labor at term do not lead to the same PGEM-concentration in the maternal blood as after intravenous infusion of PGE₂ in doses normally used to induce labor.     

Acute effects of testosterone on serum PGE2 levels in male dogs

Serum prostaglandin levels are influenced by testosterone. To test the hypothesis that the effect of testosterone is mediated through the prostate gland, testosterone was given acutely to intact and to prostatectomized male dogs. Intact dogs responded to testosterone with an abrupt, transient rise in plasma PGE₂ levels; prostatectomized dogs did not respond. We conclude that testosterone has an acute effect on the prostate gland which results in release of PGE₂ into the blood stream.     

The concurrent in vitro and in vivo release of PGE2 from controlled-release hydrogel polymer pessary for cervical ripening

Twenty five patients booked for induction of labour, at 38 weeks or more gestation, were administered a controlled release vaginal polymer pressary containing 10mg prostaglandin E₂(PGE₂), designed to release 0.6mg per hour in vivo. The release profile from the polymer was linear throughout the eight hour observation period with a correlation coefficient of 0.81, and regression slope of 0.93 mg/hr. with 95% confidence intervals of 0.63mg/hr. to 1.23 mg/hr. This compared with a concomitatnt release profile in vitro which was uniform with time for the first five hours, but then continued at a decreasing rate with a correlation coefficient of 0.98. The relationship between PGE₂ release and cervical score change was linear, with a correlation coefficient of 0.65. The results show that PGE₂ release from the pessary in vivo is predictable, and suggest that the controlled release pessary offers the advantages of greater control of cervical ripening than alternative vehicles currently available.     

Further studies on prostaglandin E2 (PGE2)-induced gonadotropin release: Comparison with the effect of 15-methyl PGE2, PGAs, PGBs and prostaglandin endoperoxide analogs

It is known that PGE₂ is a potent stimulus of LH release. To determine if the effect of PGE₂ could be enhanced and/or prolonged by retarding its metabolic degradation, a derivative, 15-methyl PGE₂ (15-E₂) which is more slowly degraded than the natural compound was injected intravenously (i.v.) at various dose levels or into the third ventricle (3rd V) of ether-anesthetized, ovariectomized, estrogen (OVX, Eb)-treated rats and its effect on gonadotropin release was compared with that of PGE₂. Both PGs injected i.v. were equally effective in increasing plasma LH and maintaining the elevated levels, although 15-E₂ induced a larger and more sustained increase in plasma FSH than PGE₂. By contrast, 3rd V PGE₂ was clearly more effective than 3rd V 15-E₂ in releasing LH and to a lesser extent, FSH. The effect of 15-E₂ on LH was similar to that produced by 3rd V PGE₁ injected at a similar dose. However, its effect on FSH was greater than that of PGE₁.To evaluate the effect(s) of prostaglandins of the A and B series on gonadotropin release, PGA₁, PGA₂, PGB₁ or PGB₂ were injected intraventricularly in OVX, Eb-treated rats. PGBs were injected into conscious, free-moving rats. PGA₂ or PGB₂ increased plasma LH concnetrations although much less effectively than PGE₂. Third V PGA₁ or PGB₁ were ineffective. The 3rd V injection of two cyclic esters (U-44069 and U-46619), stable analogs of the PG endoperoxide PGG₂ and PGH₂, induced a small, transient increase in LH levels and did not alter plasma FSH in conscious, free-moving animals. PGE₂ injected intraventricularly at a similar dose was demonstrated to be much more potent than the analogs in stimulating LH and FSH release. The results indicate that: 1) 15-E₂, in spite of its described long-lasting activity, does not appear to be more potent than the natural compound in releasing LH, although when injected i.v., it appeared to induce a more sustained increase in plasma FSH; 2) although PGA₂ and PGB₂ can also act centrally to stimulate LH release, their low potency suggests that this is a pharmacological effect; and 3) the two analogs of PG endoperoxides tested proved to be poor stimuli for gonadotropin release. The significance of these findings is discussed.     

Differential PGE2 and cAMP production by allogeneic and syngeneic pregnant mice uteri

Prostaglandin E₂ (PGE₂) and cAMP production in allogeneic and syngeneic pregnant mice uteri, were measured in relation to the ratio of plasma estrogen/progesterone levels. PGE₂ generation by allopregnant uteri varied with the days of pregnancy. The increment of the prostanoid coincided with the increase in plasma estrogen concentration, whereas the decrement of its production was in parallel with the increment of plasma progesterone. The syngeneic pregnant uterus was unable to increase the release of PGE₂ above basal values during the whole pregnancy. The rise of PGE₂ production by the allogeneic pregnant uterus was correlated with an increase in cAMP levels. It is proposed that the pregnant mouse uterus increases its ability to release PGE₂ in response to an ovarian steroids.     

Metabolism of N-acetyl PGE2 carboxamide in the rat

After intratracheal administration to rats, the bronchodilator N-acetyl PGE₂ carboxamide was converted rapidly to PGE₂ and 13,14-dihydro-15-keto-PGE₂, the major plasma metabolite. Oxidation of the N-acetyl carboxamide by prostaglandin dehydrogenase and hydrolysis of the imide bond were demonstrated in vitro.     

PGE2 secretion from organ cultured gastric mucosa: Correlation with cyclooxygenase activity and endogenous substrate release

In gastrointestinal research the in vitro release of prostaglandins from incubated or cultured biopsies is a widely used method to estimate prostaglandin synthesis. We therefore investigated the rate limiting mechanisms of PGE₂ release in organ cultured gastric mucosa of the rabbit, determining PGE₂ secretion from organ cultured mucosal biopsies by radioimmunoassay and prostaglandin synthesizing capacity by in vitro incubation of mucosal homogenate or microsomes with [¹⁴C]-arachidonic acid.Freshly taken biopsies secreted PGE₂ at an initial high rate, that decreased during the following 4 hrs of culture. This PGE₂ release was dose dependently reduced by inhibitors of the prostaglandin cyclooxygenase. 5mM acetylsalicylic acid (ASA) maximally suppressed PGE₂ secretion to 7% of controls, and the inhibition by ASA was quantitatively similar at every given culture period. PGE₂ release was markedly increased by carbenoxolone but was only slightly activated by extracellular calcium and the Ca⁺⁺-ionophore A23187. However, Ca⁺⁺/A23187 were unable to maintain PGE₂ secretion at the initial rate.PGE₂ secretion was undisturbed in calcium-free medium but was reduced to 50–60% of controls by excess EDTA. The intracellular calcium chelator 1,2-bis-(2-aminophenoxy)-ethane-N,N,N′,N′,-tetraacetic acid-acetoxymethyl ester (BAPTA-AM) similarly inhibited PGE₂ release to 72% of controls. In contrast, PGE₂ release was unaffected by the intracellular calcium antagonist 3,4,5-trimethylene-bis(4-formylpyridinium bromide) dioxime (TMB-8), the calmodulin antagonists N-(6-aminohexyl)-1-5-chloro-1-naphthalenesulfonamide (W-7) and calmidazolium (compound R24571) or various direct inhibitors of endogenous arachidonic acid release like tetracaine, bromophenacyl bromid, neomycine or low dose quinacrine, indicating that the reduction of PGE₂ release by EDTA or BAPTA may be mediated by mechanisms different from substrate release. In contrast, an inhibition of PGE₂ secretion by quinacrine at high concentrations (≥ 0.8mM) was attributed to a direct inhibition of the prostaglandin cyclooxygenase, similar to ASA. Finally, the reduction of the prostaglandin synthesizing capacity by ASA was strongly correlated with the inhibition of PGE₂ secretion, also at low concentrations and minor degrees of inhibition.From these data we conclude, that the activity of the prostaglandin cyclooxygenase is rate limiting for PGE₂ secretion from organ cultured mucosal biopsies rather than arachidonic acid release by a phospholipase A₂. This should be considered for interpretation of studies based on prostaglandin release from cultured mucosa.     

Dissociation between renal medullary PGE2-synthesis and urine PGE2-excretion. Antagonism by bumetanide of chlorazanil induced urine PGE2-excretion in rats

Normal conscious female Sprague-Dawley rats were treated with chlorazanil (3 mg/kg i.p.), and urine was collected for 3 hours. Urine prostaglandin E₂-excretion increased from 25±3 to 271±32 ng/kg/3 h. The enhancement of urine PGE₂-excretion was inhibited by pretreatment with bumetanide (75 mg/kg p.o.). In separate experiments the papillary quantity of PGE₂ was determined in freshly homogenized tissue. The basal level (14±2 ng PGE₂/papilla) was increased by chlorazanil to 51±11 ng PGE₂/papilla and 24±7 ng PGE₂/papilla at one and two hours respectively after drug administration. The capacity of chlorazanil to increase medullary PGE₂ accumulation was unaffected by bumetanide dissociated the medullary PGE₂ level from the excretion of PGE₂ in urine, when the former was elevated by chlorazanil.     

Prostaglandin E1 or E2 (PGE1, PGE2) prevents premature luteolysis induced by progesterone given early in the estrous cycle in ewes

The objective of this study was to determine whether prostaglandin E₁ (PGE₁) or prostaglandin E₂ (PGE₂) prevents premature luteolysis in ewes when progesterone is given during the first 6 days of the estrous cycle. Progesterone (3 mg in oil, im) given twice daily from Days 1 to 6 (estrus = Day 0) in ewes decreased (P < 0.05) luteal weights on Day 10 postestrus. Plasma progesterone concentrations differed (P < 0.05) among the treatment groups; toward the end of the experimental period, concentrations in jugular venous blood decreased (P < 0.05) compared with the other treatment groups. Plasma progesterone concentrations in ewes receiving PGE₁ or PGE₁ + progesterone were greater (P < 0.05) than in vehicle controls or in ewes receiving PGE₂ or PGE₂ or PGE₂ + progesterone. Chronic intrauterine treatment with PGE₁ or PGE₂ prevented (P < 0.05) decreases in plasma progesterone concentrations, luteal weights, and the proportion of luteal unoccupied and occupied LH receptors on Day 10 postestrus in ewes given exogenous progesterone, but did not affect (P > 0.05) concentrations of PGF_2α in inferior vena cava blood. Progesterone given on Days 1 to 6 in ewes advanced (P < 0.05) increases in PGF_2α in inferior vena cava blood. We concluded that PGE₁ or PGE₂ prevented progesterone-induced premature luteolysis by suppressing loss of luteal LH receptors (both unoccupied and occupied).     

Prostaglandin E2 (PGE2)-induced growth hormone (GH) release: Effect of intrahypothalamic and intrapituitary implants

Overiectomized rats were unilaterally implanted with a 23-gauge stainless steel cannula in different hypothalamic areas or in the pituitary gland and subsequently were treated with estrogen (sc, 10 μg estradiol benzoate, Eb). Two days after the estrogen injection, an inner cannula containing PGE₂ or PHF_2α at its tip was inserted into the cannula. Other animals were implanted with empty inner cannula. Plasma GH concentrations were measured by RIA in blood samples drawn from the jugular vein while the animals were lightly etherized before (−2) and at 20, 40, 60 and 120 min following the implantation. Plasma GH levels in control animals bearing an empty cannula in the body of the arcuate nucleus-median eminence region (BARH-ME) were signifantly depressed by the ether stress. The implantation of PGF_2α in this area was completely ineffective in preventing ether stress-induced decline in plasma GH. By contrast, PGE₂ implanted in BARH-ME or the post-chiasmatic region of the hypothalamus (HARH-ME) elevated plasma GH 20 min following its implantation and partially prevented the subsequent decrease in GH levels induced by ether stress. PGE₂ implants located in several other hypothalamic areas failed to induce GH release or to prevent the decline in GH levels induced by ether stress. However, PGE₂ implanted in the pituitary gland elicited a marked increase in plasma GH at 20 min and completely prevented the subsequent ether stress-induced decline in GH levels.The results suggest that PGE₂ can act at both hypothalamic (ARH-ME) and pituitary levels to stimulate GH release. At the hypothalamus, PGE₂ may inhibit GH-inhibiting factor (GIF) release or induce release of GH releasing factor (GHRF).     

Oral PGE2 inhibits gastric acid secretion in man

The effect of oral prostaglandin E₂ (PGE₂) on gastric acid secretion was examined in healthy subjects. The gastic secretion was stimulated by a modified shamfeeding procedure. Each subject underwent one control test and three tests with intragastrically administered graded doses of PGE₂: 0.5, 1.0 and 2.0 mg.Oral PGE₂ significantly suppressed the peak and total acid response to vagal stimulation. The total acid output in controls was 27.5 ± 3.2 mol/90 min and 20.8 ± 2.8, 15.8 ± 2.2 (p<0.01) and 15.9±3.8 (p<0.005)mol/90 min in test series with 0.5, 1.0 and 2.0 mg PGE₂ respectively. The two higher doses were equally inhibitory to an average 40%. Gastric outputs on sodium and potassium in response to modified shamfeeding were reduced by PGE₂.In controls there was a significant release of plasma-gastrin in response to shamfeeding. Plasma-gastrin was apparently suppressed after the two lower doses of PGE₂ but 2.0 mg PGE₂ gave an elevation similar to controls.Thus the study demonstrates that the oral natural PGE₂ suppresses the gastric acid secretion in man. The absence of such an effect in prior studies has been one of the objections against an acid regulatory action of endogenously formed prostaglandins. The present results do not support this argument.     

Prostaglandins and renin release: III. Effects of PGE1, E2 F2α and D2 on renin release from rabbit renal cortical slices

We have investigated the direct effects of prostaglandins E₁, E₂, F_2α and D₂ on renin release from rabbit renal cortical slices. Prostaglandin E₁ (PGE₁) was the most potent stimulant of renin release, while PGE₂ was 20–30 fold less active. PGF_2α was found not to be an inhibitor of renin release as reported by others, but rather a weak agonist. PGD₂ up to a concentration of 10 μg/ml had no activity in this system. That the stimulation of renin release by PGE₁ is a direct effect is supported by the finding that PGE₁-induced release is not blocked by L-propranolol or by Δ^5,8,11,14-eicosatetraynoic acid (ETYA), a prostaglandin synthesis is inhibitor. The fatty acid precursor of PGE₁, Δ^8,11,14-eicosatrienoic acid, also stimulated renin release, an effect which was blocked by ETYA. In addition to the above findings, ethanol, a compound frequently used to dissolve prostaglandins, was shown to inhibit renin release.     

Utility of d4-PGE2 as an internal standard to quantify endogenous levels of PGE1, PGE2, 190H PGE1 and 190H PGE2 in human seminal fluid by GC-MS-SIM

Four prostaglandins-PGE₁, PGE₂, 190H PGE₁ and 190H PGE₂-were quantified in human seminal fluid by GC-MS-SIM using only the internal standard, d₄-PGE₂. Methods and calculations were developed to minize errors inherent in using only one internal standard for quantifying four closely related prostaglandins. Preliminary data concerning the statistical significance of the differences found between PGE and 190H PGE levels in fertile, azospermic and oligospermic men are reported.     

The effect of PGE2 on the activation of quiescent lung fibroblasts

The effect of prostaglandin E₂ (PGE₂) on fibroblast proliferation was examined. The presence of PGE₂ for 24 h inhibited the growth of quiescent cells stimulated with serum, platelet-derived growth factor and macrophage-derived factors. Maximal inhibition of nuclear labeling with [³H]thymidine occurred at concentrations greater than 10⁻⁷ M. The inhibitory effect of PGE₂ was less potent in exponentially growing cells and was not the result of conversion of PGE₂ to PGA₂ during incubation in growth medium. The G₁ phase was determined to be 12–14 h in untreated cultures. The extent of growth inhibition by PGE₂ was similar with addition of PGE₂ at 0, 3, 6, or 9 h following restimulation of quiescent cell cultures. Approximately 25% of the cells that enter S phase are refractory to PGE₂-induced growth inhibition. Short-term exposure to PGE₂ (5 min and 30 min) caused substantial growth inhibition. The serum-induced proliferation was also inhibited by the cAMP analogue, dibutyrl cAMP. Our results suggest that PGE₂ affects a distinct subpopulation of cells. Restimulation of quiescent cells treated with PGE₂ for 24 h, indicated that release from PGE₂ exposure is associated with prolongation of the G₁ phase of the cell cycle.     

Inotropic effect of PGE1 and PGE2 on isolated rat atria. Influence of adrenergic mechanisms

The effects of a wide range of PGE₁ and PGE₂ concentrations on the isometric developed tension of isolated rat atria beating spontaneously or paced at a fixed rate, were explored. PGE₁ only produced a negative inotropic effect (NIE), whereas PGE₂ elicited a biphasic inotropic action; negative at low concentrations and positive (PIE) at higher ones. Phenoxybenzamine and phentolamine failed to modify either the NIE or the PIE, but subthreshold exogenous norepinephrine abolished the NIE, suggesting a presynaptic inhibitory effect of PGEs on the adrenergic neurotransmitter release. Auricles pretreated with subthreshold norepinephrine react with a PIE to PGE₁, but not to PGE₂. On the contrary in the presence of subthreshold methoxamine the PIE of PGE₂ was increased whereas the action of PGE₁ was not modified.     

Regulations of macrophage-mediated tumor cell killing by prostaglandins: Comparison of the effects of PGE2 and PGI2

Mouse resident peritoneal macrophages stimulated by purified bacterial lipopolysaccharide (LPS) produced both prostaglandin E₂ (PGE₂) and prostaglandin I₂ (PGI₂), the latter detected as its stable metabolite, 6-keto PGF_1α. Maximum production, induced in each case by 1 ng/ml purified LPS, was in the range of 10⁻⁷M for PGI₂ and 3 × 10⁻⁸M for PGE₂. A quantitatively similar increase in intracellular levels of macrophage cyclic AMP (measured on a whole cell basis), with a similar duration of effect, was stimulated by PGE₂ and PGI₂; however, only PGE₂ had a negative regulatory effect on macrophage activation for tumor cell killing. These data confirm that more than a whole cell increase in the concentration of cyclic AMP is needed to shut off nonspecific tumor cell killing mediated by LPS-activated resident peritoneal macrophages.     

Cervical ripening and plasma prostaglandin levels. Comparison of endocervical and extra-amniotic PGE2

Two modes of cervical application of a gel containing PGE₂ have been compared in a total of 30 patients with indication for induction of labor and unripe cervix. Fifteen patients had gel injected endocervically; in 10 patients the gel contained 400μg PGE₂, in 5 controls the gel was inactive. Fifteen subjects had a 15 ml Foley catheter passed through the cervix and placed extra-amniotically; in 10 of them 3 ml gel with 400 or 800μg PGE₂ was injected, while 5 controls received inactive gel. Plasma levels of 13,14-dihydro-15-keto-PGF_2α (PGFM) were measured in blood samples drawn before and , 1, 2, 4, 6, and 8 hours after gel application. Neither the Foley catheter nor the application of inactive gel caused significant changes in the cervical scores or the PGFM levels. PGE₂ in the endocervix increased cervical scores without altering plasma PGFM levels. Extra-amniotic PGE₂ caused a more rapid increase of the cervical scores and a progressive rise in PGFM levels. The plasma (PGFM) levels were found to be related to the degree and to the rate of cervical dilatation. The correlation with cervical dilatation was highly significant. Labor began spontaneously or after artificial rupture of the membranes in 80% of the extra-amniotic, and 50% of the endocervical PGE₂-group, but in none of the controls. These data indicate that the increased uterine PGF_2α production is not necessary for the early stages of cervical ripening, whereas dilatation beyond 4 cm does not proceed without such increase.     

The effect of locally administered PGE2 on the contractility of the nonpregnant human uterus

The effect of locally administered prostaglandin E₂ on the sensitivity and reactivity of the nonpregnant human uterus during the menstrual cycle was studied in seven women. An increase in uterine contractility in response to as little as 0.25 μg PGE₂ could be observed during both the mid-proliferative and mid-secretory phases of the menstrual cycle, but around ovulation a marked decrease in sensitivity to PGE₂ was noted. An inhibition of uterine motility was observed during menstruation in response to 30–40 μg PGE₂. Endogenous E prostaglandin normally occurs in the secretory endometrium in levels comparable to the amount of exogenous PGE₂ which elicited increased or decreased uterine activity in this study. These findings suggest that PGE₂ may play an important role in the cyclical regulation of uterine motility during the menstrual cycle.     

PGE2 involvement in experimental infection with Trypanosoma cruzi subpopulations

PGE₂ involvement in experimental Trypanosoma cruzi infection depends on the lethal capacity of the parasite subpopulation used. Mice acutely infected with non-lethal K98 displayed an enhancement in PGE₂ serum levels during the acute period, while those infected with lethal T. cruzi subpopulations (RA or K98-2) showed levels not different from normal mice. The enhancement detected in K98 group could be related both to an increased number of CD8+ T cell number and to enhanced PGE₂ release per cell by CD8+; values of PGE₂ release by adherent cells were not altered in this group. Treatment with cyclooxygenase inhibitors enhanced mortality rates of mice infected with K98, and administration of 16,16-dimethyl PGE₂ (dPGE) reversed this effect. However, mice infected with RA did not reduce their mortality rates by administration of diverse doses of dPGE. These findings suggest that PGE₂ could play a role in resistance in mice infected with K98.     

Inhibitory effects of aspirin and indomethacin on the biosynthesis of PGE2 and PGF2α

A gas-liquid chromatography system has been used to study the effects of indomethacin and aspirin on the biosynthesis of PGE₂ and PGF_2α by the prostaglandin synthetase system of bovine seminal vesicle. Both compounds were found to inhibit the production of PGE₂ and PGF_2α. However, based on statistical analyses, the inhibitory effect of indomethacin was found to be non-selective while aspirin produced statistically significant preferential inhibition of PGE₂ over PGF_2α.