A dose-response comparison of PGA2, PGE1 and PGE2 using the phenylephrine-stimulated perfused oviduct of the rabbit

The phenylephrine-stimulated perfused oviduct of the rabbit was evaluated as a model for studying the activity of prostaglandins that produce inhibition of the oviducal smooth muscle. Elevation of the normal “tone” of the oviduct by perfusing phenylephrine through the lumen permitted quantitation of the responses to PGA₂, PGE₁ and PGE₂ by measuring the magnitude of the inhibitory response produced by the agents. PGE₂ was relatively more potent, efficacious and specific for the oviduct than PGA₂ or PGE₁. It was concluded that the model was suitable for comparative dose-response studies of PGA₂, PGE₁ and PGE₂ and their analogs.     

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.     

Effects of PGE1 or PGE2 on luteal function in pseudopregnant rats

Effects of PGE₁ or PGE₂ on luteal function were studied in 163 pseudopregnant rats. PGE₁ (10, 100, or 300μg) given intrauterine every 6 hr did not shorten pseudopregnancy (P < 0.05), however, the same doses of PGE₂ given intrauterine every 6 hr advanced luteolysis (P < 0.05). PGE₁ (100 or 300μg) given every 4 hr intramuscular maintained levels of progesterone in peripheral blood above controls (P < 0.05) while 100 or 300μg of PGE₂ hastened the decline in progesterone (P < 0.05). The antiluteolytic effect of PGE₁ was not via an inhibition of PGF secretion (P < 0.05) by the uterus or by induction of ovulation in treated animals. Moreover, PGE₁ (100, 200, or 500μg) given intramuscular every 4 hr from day 4 of pseudopregnancy until the next proestrus delayed luteal regression around 3 days (P < 0.05). PGE₂ at doses of 100, 200, or 500μg every 4 hr given intramuscular consistently shortened pseudopregnancy (P < 0.05). Lower doses were without effect (P < 0.05). Based on the above data it is concluded that PGE₂ is consistently luteolytic whereas PGE₁ is not luteolytic in pseudopregnant rats and that PGE₁ may be an antiluteolysin.     

Basal level of human platelet prostaglandins: PGE1 is more elevated than PGE2

Radioimmunoassays of platelet prostaglandins E₁ and F_1α in platelet rich plasma or platelet suspension, demonstrate that both PGE₁ and PGF_1α are present at higher concentrations than prostaglandins E₂ and F_2α. Gas chromatography — mass spectrometry determinations of prostaglandins E₁ and E₂ in resting washed platelets confirm this difference. Lastly, there is a greater incorporation of [1-¹⁴C] acetate into prostaglandins E₁ and F_1α compared to that into prostaglandins E₂ and F_2α.     

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.     

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).     

Circulating and urinary metabolites of PGE2 and PGF2a

Fig. 1 summarizes the structures of primary PGE₂ and PGF_2a (upper line), their initially formed 15-ketodihydro-metabolites which appera early in blood after release (middle), and their β- and ω-oxidized metabolites, which appear later and remain longer in the circulation and also dominate the urinary profile (lower line). No single compound can be put forward as the ideal assay parameter: depending on aim and design of the study, either of these compounds may be monitored. The chemical instability of PGE compounds should however be kept in mind: generally it is safer to induce degradation by alkali treatment into a stable product prior to assay.     

Plasma levels of 13,14-dihydro-15-keto PGE2 after vaginal application of a new PGE2 film

To determine the release and absorption profile of prostaglandin E₂ from a new vaginal film formulation containing 850 μg PGE₂, serial plasma levels of 13,14-dihydro-15-keto PGE₂ were measured by radioimmunoassay in pregnant women between 16 and 18 weeks gestation. A control group, using placebo vaginal film was included in the study. There was a somewhat uniform increase in the plasma levels of the PGE₂ metabolite, reaching peak levels between 4 and 6 hours after application of the film. The findings suggest that this drug formulation could be used clinically when slow constant release of the prostaglandin is required over a period of hours such as in pre-induction cervical ripening of term pregnancy.     

Synthesis of two PGE2 human urinary metabolites

A synthesis (+) and (−) 7-α-hydroxy-5,11-diketo-tetranor prostanoic acid (Ia) and 7-α-hydroxy-5,11-diketotetranor prostan-1,16-dioic acid (Ib) is described. The biological activities of these C₁₆ metabolites are also discussed.     

PGE2 and PGF2α release by human peritoneal macrophages in endometriosis

Objective: To test for differences in the amount and activity of peritoneal macrophages present in the peritoneal fluid of women with, and without endometriosis using prostaglandin release by macrophages in culture as a marker.Patients: Women of reproductive age undergoing laparoscopy for infertility or chronic pelvic pain with postoperative diagnosis of endometriosis and women undergoing laparoscopy for sterilization.Methods: Peritoneal fluid was aspirated during laparoscopy, volume was recorded, macrophages were isolated via a Ficoll Paque gradient and kept in primary culture. PGE₂ and PGF_2α release of the cells were measured before and after stimulation with zymosan.Results: Women with endometriosis had significantly more peritoneal macrophages than controls. Peritoneal macrophages of women with endometriosis released significantly more PGE₂ than those of the control group: 8.4 ± 2.0 versus 1.4 ± 0.4 ng/ml/10⁶cells (mean ± SEM, p=0.0005) and PGF_2α : 10 ± 4.3 (endometriosis) versus 1.8 ± 0.4 (control) ng/ml/10⁶cells (mean ± SEM, p = 0.045).Conclusion: There is a significant increase in the amount of prostaglandins released by peritoneal macrophages from women with endometriosis. These prostaglandins might alter uterine and tubal contractility, thereby affecting fertility.     

PGE1 metabolism by the perfused rat liver

The hepatic and biliary metabolites of PGE₁ have been isolated and identified after infusions of PGE₁ into isolated rat liver preparations. The results demonstrate that in general PGE₁ undergoes metabolism similar to that of PGE₂ in the rat and reveals the possibility of a selective PG metabolite transport system across the biliary canalicular membrane.     

Synthesis and PGE2 inhibitory activity of novel diarylheptanoids

Prostaglandin E₂ (PGE₂) is a lipid mediator of inflammation and its inhibition has become a popular drug target due to its harmful physiological roles. Diarylheptanoids are one class of compounds that have shown successful inhibition of PGE₂. This paper reports the synthesis and PGE₂ inhibitory activity of a series of analogues of a naturally occurring diarylheptanoid. The most efficacious compounds were examined for dose-dependent PGE₂ inhibition. Among several promising compounds, the lead candidate exhibited an IC₅₀ value of 0.56?ng/µL or 1.7?µM with no detectable toxicity at the highest dose of 10?ng/µL.     

Interactions of prostaglandin E1 (PGE1) and LRH on anterior pituitary function

Numerous biochemical pathways influence the synthesis and release of anterior pituitary hormones. Releasing factors extracted from the hypothalamus and prostaglandins (PGs) appear to alter a common biochemical activity, adenyl cyclase, in pituitary cells. Luteinizing hormone releasing hormone (LRH), prostaglandin (PGE₁), 7 oxa-13-prostynoic acid and cycloheximide were tested for individual and interacting effects on the in vitro release of FSH, LH and prolactin from hemipituitaries of 15 day old female rats. LRH (10 ng/ml) consistently released both LH and FSH in all in vitro experiments and inhibited prolactin release in 1 of 2 experiments. Lower concentrations (5 and 1 ng/ml) also stimulated LH and FSH release but did not influence prolactin release. Concurrent depletion of stored LH and FSH in the gland was observed. PGE₁ in a 6.5 hour incubation increased the storage of LH within the gland in the absence of LRH. In a 1.5 hour incubation in the presence of LRH, storage of LH was also increased. PGE₁ had no effect on LH and FSH release; however, in 1 of 2 experiments it stimulated prolactin release in the absence of LRH. Prostynoic acid stimulated LH and FSH release but did not synergize with LRH action in the same tissue. Cycloheximide did not affect LH release during the first 30 minutes of incubation; however, the release during the subsequent 1 hour was significantly inhibited. Similar tissue also exposed to cycloheximide was still responsive to LRH during the latter 1 hour incubation period. Cycloheximide had no effect on prolactin storage and release from the same tissue.     

Interactions of prostaglandin E1 (PGE1) and LRH on anterior pituitary function

Numerous biochemical pathways influence the synthesis and release of anterior pituitary hormones. Releasing factors extracted from the hypothalamus and prostaglandins (PGs) appear to alter a common biochemical activity, adenyl cyclase, in pituitary cells. Luteinizing hormone releasing hormone (LRH), prostaglandin (PGE₁), 7 oxa-13-prostynoic acid and cycloheximide were tested for individual and interacting effects on the $\text{in vitro}$ release of FSH, LH and prolactin from hemipituitaries of 15 day old female rats. LRH (10 ng/ml) consistently released both LH and FSH in all $\text{in vitro}$ experiments and inhibited prolactin release in 1 of 2 experiments. Lower concentrations (5 and 1 ng/ml) also stimulated LH and FSH release but did not influence prolactin release. Concurrent depletion of stored LH and FSH in the gland was observed. PGE₁ in a 6.5 hour incubation increased the storage of LH within the gland in the absence of LRH. In a 1.5 hour incubation in the presence of LRH, storage of LH was also increased. PGE₁ had no effect on LH and FSH release; however, in 1 of 2 experiments it stimulated prolactin release in the absence of LRH. Prostynoic acid stimulated LH and FSH release but did not synergize with LRH action in the same tissue. Cycloheximide did not affect LH release during the first 30 minutes of incubation; however, the release during the subsequent 1 hour was significantly inhibited. Similar tissue also exposed to cycloheximide was still responsive to LRH during the latter 1 hour incubation period. Cycloheximide had no effect on prolactin storage and release from the same tissue.     

Selective antagonism of the systemic vasodepressor response to PGE1 by d,1–11, 15-bisdeoxy PGE1

Several bisdeoxy PGE₁ analogs are potent, competitive antagonists of PGE₁-induced colonic contractions in the gerbil. The efficacy of these analogs in antagonizing PGE₁-mediated systemic vasodepression has not been previously demonstrated. In this study, serial doses of PGs were administered before, during and after infusion of d,1–11, 15-bisdeoxy PGE₁. Bolus injections of PGE₁ (3.0 μk/kg), PGE₂ (3.0 μg/kg) and PGI₂ (0.3 μg/kg) were administered via the right external jugular vein to male Wistar rats. PGE₁, PGE₂ and PGI₂ decreased systemic arterial pressure 41%, 38% and 38%, respectively. The PGE₁ analog was infused (200 μg/kg/min) through the right common carotid artery. The analog itself had no effect on mean systemic arterial pressure, but maximum reversible inhibition (51%) of PGE₁-mediated vasodepression occurred following a 50 minute infusion. No significant effect of the PGE₁ analog was observed on PGE₂ or PGI₂-mediated vasodepression. These data demonstrate the ability to antagonize PGE₁-mediated vasodepression, and to differentiate the vascular responses to PGE₁ and PGE₂ or PGI₂.     

Desensitization of PGE1 receptors in neuroblastoma-glioma hybrid cells

Prostaglandin E₁ receptor sites were measured in homogenates of NG108-15 neuroblastoma-glioma hybrid cells after exposure of intact cells to PGE₁. Scatchard analysis of competitive binding studies showed that incubation of NG108-15 cells in the presence of 2.5 μM PGE₁ for 16 h resulted in a loss of PGE₁ receptors and an increase in the dissociation constant of the remaining receptors. Thus, cells challenged with PGE₁ not only lose adenylate cyclase activity, but also lose PGE₁ receptors and decreased the affinity of the remaining receptors for PGE₁.     

Inhibition of PGE1-stimulated cAMP accumulation in human platelets by thromboxane A2

The prostaglandin endoperoxide PGH₂, HHT, HETE, thromboxane A₂, and thromboxane B₂, which are all products of arachidonic acid metabolites of human platelets, were tested for their ability to modulate platelet cyclic nucleotide levels. None of the compounds tested altered the basal level of cAMP or cGMP, and only PGH₂ and thromboxane A₂ inhibited PGE₁-stimulated cAMP accumulation. Thromboxane A₂ was found to be a more potent inhibitor of PGE₁-stimulated cAMP accumulation and inducer of platelet aggregation thatn PHG₂.     

Antihypertensive activity of 16,16-dimethyl-oxa-alkyl-prostaglandins of the PGA2, PGE2 and trans-Δ 2-11-deoxy-PGE1 series: Structure-activity relationships

Utilizing Corey's synthesis, a variety of prostaglandins (PGs) with a modified ω-side chain were prepared. The 16,16-dimethyl-oxa-alkyl analogues of PGA₂ had potent antihypertensive activity. HR 466 (16,16-dimethyl-18-oxa-PGA₂), the best compound out of this series was active for 5–6 hours after oral administration of 0,1 mg/kg to conscious renal hypertensive dogs. The corresponding analogues of PGE₂ were also potent antihypertensive compounds, but were much more spasmogenic. Structural variations within the trans-Δ2-11-deoxy-PGE₁-series, in both side chains, gave HR 601 (trans-Δ2-15α-acetoxy-16,16-dimethyl-18-oxa-11-deoxy-PGE₁-methylester) which was orally active in the hypertensive dog with similar activity to HR 466.