Sodium transport by isolated bullfrog small intestine. Effect of prostaglandin E1.

Addition of 446 micron prostaglandin E1 (PGE1) to the serosal medium of isolated short-circuited bullfrog small intestine elicited small increases transmural potential difference and short-circuit current while addition of PGE1 to the mucosal medium caused no change in the electrical parameters. Addition of 100 micron indomethacin to the mucosal medium inhibited both potential difference and short-circuit current with a resultant increase in steady-state tissue resistance. In the presence of mucosal 100 micron indomethacin, serosal 60 micron PGE1 markedly stimulated transmural potential difference and short-circuit current with a resultant decrease in steady-state tissue resistance. Serosal arachidonic acid (330 micron) stimulated transmural potential difference and short-circuit current and this effect was abolished by the addition of 100 micron indomethacin to the mucosal medium. Serosal 60 micron PGE1 only stimulated the M (mucosa) leads to S (serosa) unidirectional flux of sodium. These results strongly suggest that the PGE1 action is mediated either via a series of metabolic reactions which possibly increase the permeability of the mucosal membrane to sodium or via direct stimulation of rheogenic sodium pump activity.     

Prostaglandin E1 metabolism by human plasma

An enzymic prostaglandin E₁ metabolising system in human plasma is described. Various properties of the system have been investigated. Metabolism of prostaglandin E₁ added to whole human blood or plasma, particularly in low concentrations such as those found physiologically, can be extremely rapid and extensive. The importance of these findings in relation to the extraction of prostaglandins from human blood or plasma is discussed.     

Prostaglandin E1: A review

Work on the structure of prostaglandin E1 (PGE1), isolated from natural sources, was completed 25 years ago (1). Shortly after, methods for the chemical synthesis of PG with their natural configuration were developed in the laboratories of the UpJohn Company (2) and of E. J. Corey (3) and, by the late sixties, PGE1 became widely available. The information since accumulated about its biological and clinical effects is more substantial than for any other PG. This review will draw together some of this information, focusing on recent studies of its mechanisms of action.     

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.     

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.     

Prostaglandin E1 decreases circulating endothelial cells

Prostaglandin E₁ (PGE₁) has been claimed to have cytoprotective effects and also to decrease thrombogenicity. The effect of intraarterial (i.a.) and intravenous (i.v.) administration of PGE₁ on the number of circulating endothelial cells (CEC) was investigated in patients with peripheral vascular disease (PVD). Patients with hyperlipoproteinemia and also smokers exhibited higher numbers of CEC. PGE₁ significantly (p < 0.01) decreased CEC. In parallel, plate let survival was prolonged (r = −0.82). This effect lasted for more than a month after stopping PGE₁-therapy. The observed decrease in CEC reflects the decreased thrombogenicity and improved haemostasis achieved after PGE₁.     

Prostaglandin E1 specific binding in rhesus myometrium

Myometrial low speed supernatant prepared from non-pregnant rhesus uteri was incubated with ³H-Prostaglandin (PG) E₁ with or without addition of unlabelled prostaglandins. The uptake of ³H-PGE₁ was inhibited in a dose dependent fashion by PGE₂>PGE₁>PGA₁>PGF₂=PGA₁>PGB₁=PGB₂≥PGD₂. PGE₁ metabolites inhibited ³H-PGE₁ binding in the following order: 13,14-dihydro-PGE₁>13,14-dihydro-15-keto-PGE₁=15-keto-PGE₁. The specific binding of ³H-PGE₁ and ³H-PGF₂ was similarly affected by the temperature and time of incubation. Equilibrium binding constants determined using rhesus uteri obtained during the luteal phase of the menstrual cycle indicate the presence of high affinity PGE₁ binding sites with an average (n=3) apparent dissociation constant of 2.2 × 10⁻⁹M and a lower affinity PGE₁ binding site with a K_d 1 × 10⁻⁸M. No high affinity — low capacity ³H-PGF₂ sites could be demonstrated.

Relative uterine stimulating potencies of some natural prostaglandins and prostaglandin analogs tested after acute intravenous administration in mid-pregnant rhesus monkeys corresponded with the PGE₁ binding inhibition of the respective compound. The uterine stimulating potencies of the prostaglandin analogs tested were: (15S)-15-methyl-PGE₂=16,16-dimethyl-PGE₂>17-phenyl-18,19,20-trinor-P GE₂>16 phenoxy-17,18,19,20-tetranor-PGE₂=PGE₂=PGE₁=(15S)-15-methyl-PGE₂>PGF₂.     

Active transport of D-xylose in the isolated small intestine of the bullfrog

Fluxes of D-xylose-1-C¹⁴ (xylose) across the wall of the isolated intestine of the bullfrog were studied. When sodium was the principal cation in the mucosal bathing fluid, the transport rate of xylose from the mucosa to the serosa was about 5 times greater than the transport rate from the serosa to the mucosa, indicating an active intestinal transport for this sugar. With potassium as the principal cation on the mucosal side, the transport rate of xylose from the mucosal to the serosal compartment is reduced about 5 to 6 times without appreciable change in the serosal to mucosal transport. The asymmetry was also considerably reduced when ouabain was added to the mucosal and serosal compartments. The data confirm the in vitro and in vivo observations indicating active transport of xylose and are also in accord with the earlier findings that active transport of sugars in the intestine is dependent upon the presence of sodium ions in the mucosal compartment and is inhibited by cardioactive steroids. Since the chemical constitution of xylose does not meet the requirements which were hitherto considered necessary for active transport of sugars in the intestine, this structural requirement has to be revised.     

Prostaglandin E1 effects on ethanol metabolism in the rat

Previous studies in our labaratory have shown that PGE₁ prevents alcohol induced fatty livers in the rat. Since PGE₁ could primarily affect alcohol metabolism, we studied the effect of this compound on the metabolism of a single intragastric dose of alcohol given to rats that had been previously maintained on a normal diet or on an alcohol supplemented diet. Neither the acute nor the chronic administration of PGE₁ affected the disappearance of alcohol from blood whether the animals had been previously fed the control or the alcohol diet. PGE₁ did not affect alcohol dehydrogenase activity of either group of animals. These studies suggest that the protective effect of PGE₁ on alcohol induced fatty liver in rats is not related to a direct action on alcohol metabolism.     

Triphasic effect of prostaglandins E1, E2 and F2α on the fluid transport of isolated gall-bladder of guinea-pigs

Prostaglandins (PGs) F_2α, E₁ and E₂ exerted a triphasic influence on the fluid transport of isolated guinea-pig gall-bladders, when applied to the serosal side. PGE₁ and PGE₂ produced these effects in lower concentrations than F_2α. Directly after PG addition to the serosal side a short stimulation of fluid transport to between 200 and 400% was observed. The stimulatory effect of PGs was most distinct in gall-bladders from female guinea-pigs, less pronounced in male and nearly absent in pregnant animals. Since PGs increased intraluminal hydrostatic pressure in gall-bladders by contraction of the smooth muscle, experiments were performed in which hydrostatic pressure was increased by different procedures. These included the addition of imidazole (10⁻² M), raising of K⁺ in the bathing solution and an increase in intraluminal pressure by addition of Ringer's solution into the lumen. All three procedures stimulated fluid reabsorption temporarily in the same way as PGs, hence increase of intraluminal pressure is thought to be the reason for the observed temporary stimulation of fluid transport. Direct evidence for this thesis was obtained when the gall-bladder was mounted as a flat sheet over a chamber; in this preparation no stimulation of fluid transport was obtained. The second phase of the PG influence was characterized by a concentration-related inhibition of fluid reabsorption followed by a significant but small reverse of fluid transport (secretion of fluid). When PGs were applied to the mucosal side, only an inhibition of fluid transport was observed, which was much weaker compared to the addition to the serosal side.     

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).     

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.     

Prostaglandin E2 effects on oxygen affinity by sickle erythrocytes

Prostaglandin E₂ slightly increases the oxygen affinity of normal and sickle cell trait erythrocytes. Sickle cell erythrocytes display decreased oxygen affinity in the presence of PGE₂, and more complex dissociation behavior, which is interpreted in terms of membrane mediated effects on hemoglobin oxygen carriage.     

Prostaglandin E2 levels and human periodontal disease

PGE₂ levels in human gingiva from healthy patients and patients with periodontal disease was measured by radioimmunoassay. There was a tenfold elevation of PGE₂ levels in diseased as compared with healthy tissue. PGE₂ levels of 10⁻⁶M or greater were found in purulent exudates from periodontal infections. The results suggest that local PGE₂ production may contribute to the inflammatory changes and bone resorption seen in periodontal disease.     

Prostaglandin E antagonist activity of 11,15-bisdeoxy prostaglandin E1 and congeners

$\text{d,?}$-11,15-bisdeoxy PGE₁ and certain of its congeners were shown to inhibit gerbil colon contractions induced by $\text{?}$-PGE₁. While some of these compounds were selectively antagonistic of PGE₁-induced contractions, others additionally inhibited the gerbil colon agonist activities of $\text{?}$-PGE_2α and acetylcholine. The PGE₁ inhibitory activity was apparently competitive in nature. With relatively weak potencies, the bisdeoxy PGE congeners displaced ³H-PGE₁ from a fat cell binding site, suggesting competition for a common, putative receptor. Structure-activity relationships and potential utility of these analogs are discussed.     

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.     

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.     

Prostaglandin E1 reversibly induces morphological changes in macrophages and inhibits phagocytosis

Light microscopy and scanning electron microscopy (SEM) show that PGE₁ induces a strong morphological change of cultured macrophages which are accompanied by a loss in membrane activity, cell locomotion and phagocytosis. All effects induced by PGE₁ are fully reversible and seem specific, since they are not induced by PGF_2α. Characterization of the cytoskeleton by immunofluorescence microscopy reveals that neither microfibrils nor microtubuli are drastically changed. All prostaglandin E₁ induced morphological and functional change are fully reversible: after repeated washings the cells restore their normal appearance, membrane movements and phagocytic capacity.     

Prostaglandin E2 in a diaphragm a further note

In a previous study we reported that the administration of Prostaglandin E₂ suppositories in a vaginal contraceptive diaphragm enhanced the effectiveness of the drug and reduced the incidence of side effects by 50%.1 Since that study there have been two reports which could not verify our experiences. 2, 3 Therefore we attempted to look at the problem again.