Phosphatidylethanolamide derivatives of prostaglandins E1 and E2

Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) have been coupled with the amine group of phosphatidylethanolamine (PE) by means of dicyclohexylcarbodiimide. These complexes basically mimic the relaxant and contractile effects of the corresponding free prostaglandins (PGs) on various smooth muscle preparations, but exhibit a delayed onset of action and a lower affinity for the PG receptors. The complexes are comparable with the free, parent PGs, in their intrinsic activities. The same holds true for the effects on blood pressure and on the motility of the uterus . The PGE₂-PE complex is hydrolysed to release obviously free PGE₂ by cell-free homogenates prepared from various tissues, but not by blood plasma. The PGE₂-PE complex is immunologically indistinguishable from the free PGE₂.     

Effect of gestational age on pulmonary metabolism of prostaglandin E1 & E2

The fetus and prematurely delivered newborn lamb have high concentrations of circulating PGE₂ that may play a hormonal role, particularly in maintaining the patency of the ductus arteriosus. We studied the ability of the isolated, perfused lung from immature (100 ± 150 days) lamb fetuses to metabolize PGE₂ as a function of PGE₂ concentration in the perfusate. After an intra-arterial infusion of ³H-PGE₂ and ¹⁴C-inulin (to act as a marker of extracellular space), the bulk of the ¹⁴C-inulin was rapidly cleared through the isolated lung and the majority of the ³H activity appeared after the ¹⁴C activity had fallen to negligible values. The ³H activity that was retained longer in the lung was primarily associated with the 15-keto prostaglandin E₂ and 15-keto-13,14 dihydro prostaglandin E₂ metabolites. Lungs from immature fetal lambs metabolized 25% less PGE₂ than did lungs from animals near term. This is consistent with our prior observation that premature lambs have decreased plasma clearance rates (in vivo) and elevated circulating concentrations of PGE₂ when compared with term newborn lambs.     

Acute toxicity of prostaglandins E2,F2α and 15 (s) 15 methyl prostaglandin E2 methyl ester in the baboon

The cardiovascular, uterine stimulant and gastrointestinal effects of prostaglandins E₂, F_2α and 15 (S) 15 methyl PGE₂ methyl ester in the East African Baboon (P. Anubis) have been studied. In these three parameters the baboon responds both qualitatively and quantitatively in a similar manner to man. The lethal doses of the prostaglandins given by bolus intravenous injelctions have been determined and the human lethal doses estimated.     

Levuglandin E2 crosslinks proteins

Levuglandin E₂ (LGE₂), a γ-ketoaldehyde produced by rearrangement of the prostaglandin endoperoxide PGH₂ under the aqueous conditions of its biosynthesis, causes extensive intermolecular crosslinking of ovalbumin at pH 6 or pH 7 and 37°C. The time dependence of protein oligomerization is monitored by SDS-PAGE. Effects of pH and concentration on the extent of LGE₂-induced crosslinking are examined. The efficacy of LGE₂ for inducing crosslinking is compared with other oxidative metabolites of arachidonic acid (AA), including the prostaglandins PGE₂, PGD₂, PGA₂, PGB₂, and PGF_2α, as well as malondialdehyde and E-4-hydroxy-non-2-enal. LGE₂ is orders of magnitude more effective in crosslinking protein than any other cyclooxygenase or lipoxygenase metabolite of AA tested.     

The metabolism of prostaglandin E2 in perinatal rabbit lungs

The inactivation of prostaglandin E₂ (PGE₂) was studied in isolated perfused lungs of fetal and neonatal rabbits. 200 nmol of ¹⁴C-PGE₂ was infused into the pulmonary circulation and the metabolites of PGE₂ were analysed from the nonrecirculating perfusion effluent. The amount of the main metabolite, 13,14-dihydro-15-keto-PGE₂, increased significantly between the 28th and 30th day of fetal life, remained relatively constant at the time of birth and increased again between 1st and 7th postnatal day. In contrast the amount of 15-keto-PGE₂ remained relatively stable during the studied period. The activity of NAD⁺-dependent 15-hydroxyprostaglandin dehydrogenase (15-OH-PGDH) was determined from the 100.000 g supernatant fraction of fetal, neonatal and maternal rabbit lungs using ¹⁴C-PGE₂ (20 μM) as the substrate. In the lungs of late fetal rabbits the activity of 15-OH-PGDH was significantly higher compared to the early postnatal period. Maternal rabbit lungs possessed, however, very high activities compared to the studied perinatal lungs. The results show, that the activity of the pulmonary 15-OH-PGDH is high already during the late fetal period. The inactivation of PGE₂ in isolated perfused lungs seems, however, to increase during the last prenatal days. Thus it seems possible that the uptake mechanism could be the rate limiting step in the metabolism of PGE₂ in rabbit lungs during the perinatal period.     

Presence of prostaglandins E2 and A2 in canine gastric secretions

The presence of prostaglandins (PGs) was determined in gastric juice obtained from 3 conscious dogs, provided with a chronic gastric fistula. Outputs of acid (mequiv min^?1) and PGs (pg min^?1) were measured in gastric secretions stimulated by pentagastrin (100 or 200 ng kg^?1min^?1). Prostaglandin activity was estimated, after extraction and thin layer chromatography, by radioimmuno-assay of the PGB formed by treatment with alkali. Tritiated PGs were added to gastric juice for the purpose of correcting for PGs recovery. Using this method, the minimum mass of PGB which could be satisfactorily distinguished from zero was 25 pg. Prostaglandins A₂ and E₂ were present in pentagastrin-activated gastric secretions and averaged (mean ± SE, n = 8) 200.7 ± 18.1 and 260.1 ± 18.0 pg min^?1 respectively. The identity of PGA₂ and PGE₂ was confirmed by gas liquid chromatography combined with mass spectrometry. The amount of PGE₂ converted to PGA₂ during extraction, separation and conversion procedures was estimated from the amount of [³H] PGA₂ found when only [³H] PGE₂ had been added to a sample of gastric juice and averaged 14.5% ± 2.0. Our preliminary results support the possibility that PGE₂ and PGA₂ may be of physiological importance in the regulation of canine gastric secretions.     

Prostaglandins E1 and E2 stimulate the proliferation of pulmonary artery smooth muscle cells

Prostaglandins E₁ and E₂ are thought to be inhibitors of the growth of systemic vascular smooth muscle cells (SMC). However, their effect on the proliferation of SMC from the pulmonary artery (PA) has not been described and was the subject of this investigation. Cultures of bovine PA SMC were exposed to PGE₁ and PGE₂ under various conditions and their growth was assessed. PGE₁ and PGE₂ did not inhibit the growth of PA SMC in 10% fetal calf serum (FCS), but instead caused a dose dependent (10 ng - 1 μg/ml) increase in [³H]-thymidine incorporation when added to cultures containing 0.5% FCS; the highest doses resulted in 95% and 75% increases in [³H]-thymidine uptake at 24 hours with PGE₁ and PGE₂ respectively. This was accompanied by a modest increase in actual cell numbers (e.g., 20% with 1 μg/ml PGE₁). Furthermore, PGE₁ could mimic insulin-like growth factor (IGF-1) by potentiating the stimulation of SMC growth by fibroblast growth factor, suggesting that PGE₁ may act as a progression factor in the growth cycle of these cells. There was, however, no effect of PGE₁ on the proliferation of bovine aortic SMC. We conclude that, contrary to most reported effects on systemic SMC, PGE₁ and PGE₂ do not inhibit the proliferation of PA SMC but rather stimulate it.     

Effect of prostaglandins E1, E2 and F2α on neutrophil aggregation

Recently we have found that chemotactic factors stimulate neutrophils in suspension to aggregate. Because of an obvious analogy to platelet aggregation, we examined the influence of three prostaglandins on this process. Prostaglandins E₁, E₂ and F_2α alone did not cause aggregation of the neutrophils but were able to partially inhibit the aggregation response induced by the synthetic chemotactic tripeptide, formly-methionyl-leucyl-phenylalanine. The minimal inhibitory concentrations for prostaglandins E₁, E₂ and F_2α were 10⁻⁷, 10⁻⁶ and 10⁻⁵M, respectively. These results are similar to those found for the prostaglandin-induced inhibition of platelet aggregation. It may be, therefore, that neutrophil aggregation, like platelet aggregation, is modulated by intracellular prostaglandins and other products of arachidonic acid metabolism.     

Molecular conformation of prostaglandin E2

The crystal and molecular structure of prostaglandin E₂ (PGE₂) has been determined by X-ray diffraction. The compound crystallizes in the triclinic space group P1 with Z = 1 and , , , α = 87.347°, β = 94.042°, and γ = 91.010°. Gauche-gauche interactions appear in both side chains. The efficient molecular packing and hydrogen bonding network appears to stabilize the observed molecular conformation.     

Bronchodilatory properties of 2-decarboxy-2-hydroxymethyl prostaglandin E1

We evaluated in a double-blind study the bronchodilatory properties of 2-decarboxy-2-hydroxymethyl prostaglandin E₁ (PGE₁-carbinol), described recently as a nonirritant bronchodilator in animals. Fifteen asthmatic patients received by inhalation single doses of 1, 10, and 30 μg PGE₁-carbinol, 55 μg PGE₂, and placebo (10% ethanol in normal saline, which was also used as diluent for the PGs). Such pulmonary function tests as forced expiratory volume in 1 second, forced vital capacity, and maximal expiratory flow were monitored during 2 hours following inhalation of each compound. 10 and 30 μg PGE₁-carbinol produced significant but short-acting bronchodilation, similar to that caused by 55 μg PGE₂. One-third of the patients reported mild cough and throat irritation during and shortly after inhalation of 30 μg PGE₁-carbinol or 55 μg PGE₂. Placebo and 1 μg PGE₁-carbinol produced minimal side effects, but neither agent caused bronchodilation. In an adjunctive, unblinded trial, the same patients received 400 μg fenoterol. Fenoterol caused greater bronchodilation 15 and 30 minutes after inhalation than did the PGs in the double-blind study.     

Failure of prostaglandins E1 and E2 to alter canine gastric mucosal cyclic nucleotides

The action of prostaglandins and indomethacin on gastric mucosal cyclic nucleotide concentrations was evaluated in 18 anesthetized mongrel dogs. Prostaglandins E₁ (PGE₁) and E₂ (PGE₂) (25 μg/kg bolus, then 2 μg/kg/min) were administered both intravenously (4 experiments; femoral vein) and directly into the gastric mucosal circulation (10 experiments; superior mesenteric artery). The possible synergistic effect of pre-treatment and continuous arterial infusion of indomethacin (5 mg/kg bolus for 5 min, then 5 mg/min), a prostaglandin synthetase inhibitor, with PGE₂ was studied in 4 experiments. Antral and fundic mucosa were biopsied and measured by radioimmunoassay for cyclic nucleotides. Doses of PGE₁ and PGE₂ which inhibited histamine-stimulated canine gastric acid secretion did not significantly alter antral or fundic mucosal cyclic nucleotide concentrations. Concomitant infusion of PGE₂ with indomethacin did not potentiate the mucosal nucleotide response compared to PGE₂ alone. These studies fail to implicate cyclic nucleotides as mediators of the inhibitory acid response induced by PGE₁ or PGE₂ in intact dog stomach.     

Gastric antisecretory actions of (15S)-15-methyl prostaglandin E2 methyl ester and natural prostaglandin E2 in rhesus monkeys

The gastric antisecretory actions of (15S)-15-methyl prostaglandin E₂ methyl ester (Me-PGE₂) and Prostaglandin E₂ (PGE₂) were evaluated in the unanesthetized gastric fistula rhesus monkey. Secretion was submaximally stimulated by multiple subcutaneous injections of histamine acid phosphate given every hour for four consecutive hours. When a steady-state plateau of gastric secretion was reached, the PG's were administered as a single bolus dose either intravenously (i.v.) or intragastrically (i.g.). Both PG's inhibited histamine-stimulated gastric secretion. The PG's showed greater sensitivity in inhibiting acid concentration while not affecting volume output. Active i.v. and i.g. antisecretory doses of Me-PGE₂ ranged from 3 to 10 μg/kg, while PGE₂ showed significant antisecretory activity at i.v. bolus doses of 30–100 μg/kg and i.g. bolus dose of 1.0 mg/kg. Thus, Me-PGE₂ is estimated to be at least 10 and 300 times more potent than PGE₂ by the i.v. and i.g. administration routes, respectively. These findings indicate that the rhesus monkey shows some similarities to man in responsiveness to gastric secretory inhibition by E-prostaglandins.     

Isolation and biosynthesis of 18-hydroxyprostaglandins E1 and E2 in human seminal fluid

18-Hydroxy-PGE₁ and 18-hydroxy-PGE₂ were identified in human seminal fluid by capillary gas-liquid chromatography-mass spectrometry. The levels of these prostaglandins was 1–2% of the corresponding 19-hydroxy-PGE compounds in human semen. 18Hydroxy-PGE₁ and 18-hydroxy-PGE₂ are likely formed by cytochrome P-450 in seminal vesicles in analogy with the 19-hydroxy-PGE compounds. This was supported by the finding that microsome of seminal vesicles of the cynomolgus monkey, Macaca fascicularis, supplemented with 1 nM NADPH, metabolized PGE₁ to both 19-hydroxy-PGE₁ (92%) and 18-hydroxy-PGE₁ (8%). The hydroxylation of prostaglandins in seminal vesicles of primates may thus show a high but not absolute specificity for the penultimate carbon of prostaglandins.     

Endocervical prostaglandin E2 gel for preinduction cervical softening

A single, endocervical application of a new commercial preparation of prostaglandin E₂ (PGE₂) gel, 0.5 mg of PGE₂ in 2.5 ml (3g), was evaluated for preinduction cervical softening. Safety and efficacy were assessed in a comparison with a 2.0 mg PGE₂ vaginal tablet and placebo in normal nulliparous women at term, with low Bishop scores. Treatment was administered in randomized, double blind fashion. Overall success, defined as a progression in Bishop score of at least 3 points within 12 hours, was achieved in 22/40 (55 %) of the gel group, 15/41 (37 %) in the tablet treated women, and 8/40 (20 %) in those receiving placebo. Od interest was the observation that of women with very unfavorable induction features (Bishop score 0–2), the cervical gel treatment resulted in a 6/8 (75 %) success rate compared with 2/13 (15 %) success for the vaginal tablet and 0/7 (0 %) for placebo. In as much as a very low incidence of side effects accompanied this treatment scheme, expanded multi-center testing is recommended.     

Radioimmunoassay of prostaglandins E1, E2, and F2α in unextracted plasma, serum and myocardium

A radioimmunoassay procedure for the determination of PGE₁, PGE₂, and PGF₂α is presented. The procedure involves the pre-precipitation of each prostaglandin specific antiserum with the precipitating antisera (ARGG), and the use of these antisera mixtures in assaying for PGE₁, PGE₂, and PGF₂α. Applicability of the methods to unextracted plasma, serum and myocardial homogenate has been demonstrated through tests of specificity, recovery, reproducability and parallelism. A mathematical correction for cross-reactivity between PGE₁ and PGE₂, and their opposing antisera is given. To demonstrate the utility of the methodology in differentiation of experimental variables, prostaglandin concentrations in unincubated serum, incubated serum, and the rate of prostaglandin production in serum of dogs are given.     

Prostaglandin E1 and E2 in bovine semen: Quantification by gas chromatography

Prostaglandins PGE₁ and PGE₂ extracted from bovine semen, purified via silicic column chromatography were quantified by gas chromatography as their methoxime methyl ester trimethylsilyl ether derivatives. The PGE₁ and PGE₂ concentrations of 19 bovine semen samples ranged from 395 ± 225 and 487 ± 407 ng/ml, respectively. A constant 1:1 ratio between PGE₁ and PGE₂ was observed. There was no relationship between PGE and sperm motility, but high sperm counts were apparently associated with decreased PGE levels. The direct precursors of PGE₁ and PGE₂, i.e. 20:3n6 and 20:4n6, occurred in low concentrations compared to other related unsaturated fatty acids, i.e. 18:2n6 and 22:5n6 of the n-6 family.     

Effects of prostaglandin E2 (PGE2) on estradiol-17β-induced luteolysis in the nonpregnant ewe

Fifteen ewes were assigned as they came into estrus to the following randomized treatment groups: 1) Vehicle (1 ml corn oil + vehicle Na₂CO₃ buffer), 2) Estradiol-17β + vehicle and 3) Estradiol-17β + PGE₂ (500 μg) in Na₂CO₃ buffer (5 ewes/treatment group). Prostaglandin E₂ was given through an intrauterine cannula every four hours from days 8 through 15 postestrus. PGE₂ prevented a luteolytic dose of estradiol-17β given on days 9 and 10 from causing a precious luteolysis. PGE₂ maintained concentrations of progesterone in peripheral blood (days 8 through 15) and weights and concentrations of progesterone in corpora lutea on day 15 postestrus of ewes receiving estradiol-17β. It is concluded that chronic intrauterine infusions of PGE₂ can prevent an estradiol-17β-induced premature luteolysis.     

Prostaglandin E1 and E2 in bovine semen: Quantification by gas chromatography

Prostaglandins PGE₁ and PGE₂ extracted from bovine semen, purified via silicic column chromatography were quantified by gas chromatography as their methoxime methyl ester trimethylsilyl ether derivatives. The PGE₁ and PGE₂ concentrations of 19 bovine semen samples ranged from 395 ± 225 and 487 ± 407 ng/ml, respectively. A constant 1:1 ratio between PGE₁ and PGE₂ was observed. There was no relationship between PGE and sperm motility, but high sperm counts were generally associated with decreased PGE levels. The direct precursors of PGE₁ and PGE₂, i.e. 20:3n6 and 20:4n6, occurred in low concentrations compared to other related unsaturated fatty acids, i.e. 18:2n6 and 22:5n6 of the n-6 family.     

Enterohepatic circulation of N-acetyl-leukotriene E4

N-Acetyl-leukotriene E₄, the end product of leukotriene C₄ metabolism in the mercapturic acid pathway, was rapidly eliminated from the blood circulation into the bile of rats. Part of the N-acethyl-leukotriene E₄ secreted from bile into the intestine undewent enterohepatic circulation. Leukotriene absorption occurred from the small intestine and from the colon. Biliary and urinary excretion within 5.5 h amounted to 15 and 2%, respectively, of the intraduodenally administered N-acetyl- H leukotriene E₄ in animals anesthetized with ketamine. HPLC analyses indicated that 35% of the biliary radioactivity corresponded to unchanged N-acetyl- H leukotriene E₄, while 65% in bile and 100% in urine were polar metabolites. Enterohepatic circulation extends the biological half-life of N-acetyl-leukotriene E₄.     

The effect of zinc defficiency and food restriction on prostaglandin E2 and thromboxane B2 in saliva and plasma of rats

Zinc has been implicated in the regulation of prostaglandins and other arachidonic acid derivatives. Studies of zinc-deficient animals, however, are compromised by concomitant reduction in food intake that may also alter eicosanoid levels in body tissues and fluids. In this study, three groups of rats, designated as zinc-deficient, pair-fed and control, were fed diets containing 1 ppm, 15 ppm (in amounts paired to deficient rats) and 15 ppm Zn adlibitum, respectively, for 6 weeks. Saliva and blood were analyzed for PGE₂ adn TXB₂ by radioimmunoassay. Saliva concentrations of both eicosanoids were lower (p<0.05) in the pair-fed animals, but not significantly altered by zinc deficiency. Plasma levels of PGE₂ and TXB₂ were unchanged by either zinc deficiency or food restriction. The results of this study support the contention that the effect of zinc on these prostaglandins is not mediated by altered rates of synthesis or degradation but rather by effects on eicosanoid function.