Prostaglandins have limited actions on abnormalities of beating induced in cultured heart cells

Prostaglandins are antiarrhythmic in a variety of situations including ischaemic arrhythmias, but the mechanisms involved are not known. In view of this, the protective actions of prostaglandins A₂, E₂, F_1α, F_2β, and I₂ against abnormalities of beating induced in cultured heart cells were investigated. Abnormalities of beating were induced in single cells by a variety of agents including ouabain, Ca⁺⁺, K⁺, dinitrophenol (DNP), and toxic material from the jellyfish . Abnormalities were assessed in terms of rate, rate range, subjective arrhythmic behaviour and percent cells beating. The prostaglandins (at 10⁻⁷-10⁻⁵ M) were added with the arrhythmogenic agent to test for their ability to modify agent-induced beating abnormalities and were compared with lidocaine and quinidine. Prostaglandins alone had minimal direct effects on the cells and only minimally reduced responses to arrhythmogenic agents. The most protective prostaglandins, PGE₂ and PGF_1α, tended to normalise beating behaviour most noticeably in DNP-treated cells, unlike lidocaine and quinidine which were effective against Ca⁺⁺-induced changes while worsening those of K⁺. Thus, a general ability to protect disturbed cardiac cells is not seen with high concentrations of prostaglandins.     

Prostaglandin responses in isolated perfused rat liver: Ca2+ and K+ fluxes, hemodynamic and metabolic effects

Addition of prostaglandin F2 alpha and prostaglandin E2 to isolated perfused rat liver led to a dose-dependent, transient net Ca2+ release, which was completed within 3 min. Withdrawal of the prostaglandins resulted in a Ca2+ re-uptake over a period of about 10 min. Simultaneously, these prostaglandins induced an increase of portal pressure, stimulated hepatic glucose output and 14CO2 production from [1-14C]glutamate and led to K+ movements across the hepatocyte plasma membrane similar to those observed with other Ca2+-mobilizing agents. With prostaglandin F2 alpha there was a close correlation between the net Ca2+ release and the maximal rate of initial net K+ uptake by the liver (linear regression coefficient r = 0.902; n = 20). Prostaglandin F2 alpha was more effective than prostaglandin E2 or D2. Because prostaglandins are known to be produced by hepatic non-parenchymal cells during stimulation by phagocytosis or by addition of extracellular ATP or UTP, these data suggest an interaction between non-parenchymal and parenchymal liver cells and point to a modulating role of prostaglandins in hepatic metabolism and microcirculation, which is mediated by Ca2+-mobilizing mechanisms.     

Prostaglandins E3 and F3 alpha are excreted in human urine after ingestion of n - 3 polyunsaturated fatty acids

Prostaglandins E3 and F3 alpha, presumably of renal origin, were characterized for the first time in urine of volunteers after ingestion of n - 3 polyunsaturated fatty acids by combined gas chromatography-mass spectrometry. Quantitation of prostaglandins E3, E2, F3 alpha and F2 alpha using deuterated internal standards showed low levels of the 3 series prostaglandins in the control period. Levels of prostaglandins E3 and F3 alpha rose about 10-fold by the 12th week of the dietary trial and were still elevated 4-fold after a wash-out period of 20 weeks. Excretion of prostaglandins E2 and F2 alpha tended to be depressed in the 12th week of the dietary trial and rose again to control values after the wash-out period. Our data indicate that n - 3 polyunsaturated fatty acids are incorporated into the human kidney and are retained there for a long time. Prostaglandins E3 and F3 alpha may contribute to the observed favorable effects of marine oils rich in n - 3 polyunsaturated fatty acids on certain renal diseases.     

Conversion of beating to bursting pacemaker activity: Action of quinidine

External quinidine converts the pacemaker neurone L-11, found in the Aplysia abdominal ganglion, from spontaneously "beating" to "bursting" discharge activity. Quinidine-induced bursting ceased when entry of Ca2+ ions into the cells was blocked in a Ca2+-free, Co2+-containing solution or if internal Ca2+ accumulation was prevented by the injection of EGTA. The analysis of membrane currents from voltage clamp experiments showed that quinidine blocks the Ca2+ inward current in a dose- and time-dependent manner. In addition, the currents were displaced to the left on the voltage axis, causing an increase of the inward current at negative membrane potentials. External quinidine suppresses the Ca2+-activated K+ current induced by intracellular Ca2+ injections and acts to prolong its decay phase. The slowing of the decay phase of the Ca2+-activated K+ current by quinidine was prevented after intracellular injection of EGTA, indicating that Ca2+ removal is impaired by the drug. It is suggested that the increase of Ca2+ inward current at negative potentials and the prolonged activation of the Ca2+-activated K+ current play a major role in causing the bursting discharge behavior in normally beating cells.     

Modulating effects of prostaglandins on parasympathetic-mediated secretory activities of rat salivary glands

Exogenously administered PGE1 or PGE2, like atropine, markedly decreased both the flow and calcium concentration of parasympathetically evoked rat parotid saliva; PGF2 alpha was less effective. Despite the fact that prostaglandins greatly reduced the Ca concentration of nerve-evoked saliva, they did not change the glandular Ca concentration of either control or parasympathetically stimulated parotid glands. Prostaglandins (20 micrograms/kg, i.a.) decreased the Na or K concentration of nerve-evoked parotid saliva, but at lower doses had no significant effect. PGE1, PGE2, PGF2 alpha or atropine markedly decreased flow rates of similarly evoked rat submandibular saliva. Prostaglandins and atropine, however, decreased the Na concentration and increased the K concentration of parasympathetically evoked submandibular saliva. PGF2 alpha, like atropine, increased the Ca concentration of such saliva. Drug vehicle, ethanol, slightly decreased the flow of both parotid and submandibular saliva but not the ion secretion, Endogenous prostaglandins themselves may not play a role in secretory activities during parasympathetic nerve stimulation of rat salivary glands, since administration of indomethacin, and inhibitor of prostaglandin biosynthesis, prior to or during nerve stimulation did not significantly alter nerve-evoked salivary secretion, The mechanisms by which prostaglandins modulate secretory responses of salivary glands during parasympathetic stimulation are not understood.     

Metabolism of prostaglandins, prostaglandin analogs and thromboxane B2 by lung and liver microsomes from pregnant rabbits

Liver microsomes from pregnant rabbits converted prostaglandins F2 alpha, E1, and E2 to their 20-hydroxy metabolites along with smaller amounts of the corresponding 19-hydroxy compounds. Prostaglandins E1 and E2 were also reduced to prostaglandins F1 alpha and F2 alpha, respectively, and prostaglandin E1 was isomerized to 8-isoprostaglandin E1. The above products were also identified after incubation of prostaglandins with liver microsomes from non-pregnant rabbits. In this case, the yield of 20-hydroxy metabolites was much lower. Thromboxane B2 and a number of prostaglandin F2 alpha analogs were also hydroxylated by lung and liver microsomes from pregnant rabbits. The relative rates of hydroxylation by lung microsomes were: prostaglandin E2 approximately prostaglandin F2 alpha approximately 16,16-dimethylprostaglandin F2 alpha approximately 13,14-didehydroprostaglandin F2 alpha greater than thromboxane B2 greater than 15-methylprostaglandin F2 alpha approximately 17-phenyl-18,19,-20-trinorprostaglandin F2 alpha approximately ent-13,14-didehydro-15-epiprostaglandin F2 alpha. Similar results were obtained with liver microsomes except that thromboxane B2 was a relatively poorer substrate for hydroxylation.     

Effect of prostaglandins on cell function and multiplication of parainfluenza 3 viruses in WISH cells.

Cytotoxic effect of prostaglandins E2 and F2alpha on cells grown in vitro and the influence of these compounds on multiplication of myxovirus parainfluenza 3 were investigated. The prostaglandins were added to culture medium (0-01-10 mug/ml) 24 hr before virus infection, or for 2 and 48 hr after inoculation with viruses. WISH cells and monkey kidney cell cultures were used. No direct cytotoxic effect of prostaglandins at concentrations 0-01-1 mug/ml was found (viability, supravital staining, phase-contrast system, Nitro-BT reduction and succinic dehydrogenase tests), whereas the concentration of 10 mug/ml within 48 hr led to reduction and succinic dehydrogenase tests), whereas the concentration of 10 mug/ml within 48 hr led to partial injury of the cell population with symptoms of damage to mitochondria. Prostaglandins E2 and F2alpha inhibited multiplication of parainfluenza 3 virus at concentrations 0-1-10 mug/ml. The inhibitory effect was most pronounced if prostaglandins were added to medium for the whole period of virus multiplication i.e. for 48 hr but little or no effect was found if they were added prior to inoculation or for 2 hr after it. Inhibitory effect of prostaglandins on replication phase of viruses is suggested.     

Effect of prostaglandins E1, E2 and F2alpha 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 F2alpha alone did not cause aggregation of the neutrophils but were able to partially inhibit the aggregation response induced by the synthetic chemotactic tripeptide, formyl-methionyl-leucyl-phenylalanine. The minimal inhibitory concentrations for prostaglandins E1, E2 and F2alpha were 10(-7), 10(-6) and 10(-5)M, 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.     

Action of quinidine on ionic currents of molluscan pacemaker neurons

The effects of quinidine on the fast, the delayed, and the Ca2+- activated K+ outward currents, as well as on Na+ and Ca2+ inward currents, were studied at the soma membrane from neurons of the marine mollusk Aplysia californica. External quinidine blocks these current components but to different degrees. Its main effect is on the voltage- dependent, delayed K+ current, and it resembles the block produced by quaternary ammonium ions (Armstrong, C. M., 1975, Membranes, Lipid Bilayers and Biological Membranes: Dynamic Properties, 3:325-358). The apparent dissociation constant is 28 microM at V = +20 mV. The blocking action is voltage and time dependent and increases during maintained depolarization. The data are consistent with the block occurring approximately 70-80% through the membrane electric field. Internal injection of quinidine has an effect similar to that obtained after external application, but its time course of action is faster. External quinidine may therefore have to pass into or through the membrane to reach a blocking site. The Ca2+-activated K+ current is blocked by external quinidine at concentrations 20-50-fold higher compared with the delayed outward K+ current. In addition, it prolongs the time course of decay of the Ca2+-activated K+ current. Na+ and Ca2+ inward currents are also blocked by external quinidine, but again at higher concentrations. The effects of quinidine on membrane currents can be seen from its effect on action potentials and the conversion of repetitive "beating" discharge activity to "bursting" pacemaker activity.     

The stimulation of the initiation of DNA synthesis and cell division in Swiss mouse 3T3 cells by prostaglandin F2 alpha requires specific functional groups in the molecule

Among a number of prostaglandins, PGF2 alpha had the highest specific activity for stimulating the initiation of DNA synthesis in confluent resting Swiss 3T3 cells. At a saturating concentration of 8.5 X 10(-7) M, PGF2 alpha stimulated 21% of the cells to incorporate [ methyl-3H ]thymidine within 28 h. To elicit similar effects, prostaglandins F1 alpha, E1, E2, and D2 were required in 10-fold higher concentrations. Prostaglandins A1, A2, B1, and prostacyclin had no mitogenic activity. Insulin at 10(-8) M enhanced the stimulatory effect of PGF2 alpha and also of prostaglandins F1 alpha, E1, E2, and D2 by increasing the fraction of labeled nuclei. Methyl derivatives of PGF2 alpha were as effective as PGF2 alpha. Epimerization of the hydroxyl group at C-9 abolished the activity of the molecule. In contrast, upon epimerization at C-11 and C-15, some mitogenic activity was retained. In the presence of insulin, the latter molecules were as active as PGF2 alpha. Oxidation of the hydroxyl group at C-15 to a ketone abolished the mitogenic effect, while methyl ether formation led to only a slight loss of activity. Reduction of the delta 13 double bond also led only to a small reduction of activity. Similar differences in the activity of the various prostaglandins and analogues of PGF2 alpha were observed for 2-deoxyglucose uptake and increases in cell number. The relationships between structure and activity of prostaglandins suggest the existence of some specific receptor for PGF2 alpha to confer mitogenic response.     

Subcellular and functional effects of quinidine, procaine amide, and lidocaine on rat myocardium.

Different antiarrhythmic agents such as quinidine, procaine amide, and lodocaine at 1 mM concentrations were found to depress the ability of an isolated perfused rat heart to generate contractile force. Quinidine, but not procaine amide or lidocaine, decreased calcium uptake by both mitochondrial and microsomal fractions at different concentrations of calcium. The mitochondrial phosphorylation rate, respiratory control index, and state 3 oxygen consumption, but not ADP:O ratio and state 4 oxygen consumption, were depressed by only quinidine. None of these agents had any effect on myofibrillar Mg2+-ATPase or Ca2+-stimulated ATPase activities. On the other hand, sarcolemmal Mg2+-ATPase and Ca2+-ATPase activities, but not Na+-K+-ATPase activity, were increased by all these drugs. The sarcolemmal adenylate cyclase (EC 4.6.1.1) activity was decreased by quinidine only. These results suggest some similarities and differences in the sites of action of quinidine, procaine amide, and lidocaine within the myocardium.     

A comparison of the contractile activity of PGD2 and PGF2 alpha on human isolated bronchus

Prostaglandins may be implicated in the bronchoconstriction which occurs in asthma. Prostaglandins F2 alpha (PGF2 alpha) and D2 (PGD2) have been reported to produce bronchoconstriction in asthmatic subjects in vivo and PGF2 alpha contracts human isolated airway smooth muscle. We examined the relative efficacy and potency of PGF2 alpha and PGD2 on human bronchial spiral strips taken from 6 patients at thoracotomy. PGF2 alpha had greater efficacy than PGD2. The mean % Tmax (percentage of maximal contractile response) +/- s.e. mean were 84 +/- 7 and 54 +/- 7 respectively (P less than 0.05). PGF2 alpha (mean pD2 +/- s.e. mean = 6.39 +/- 0.6) tended to be more potent than PGD2 (5.68 +/- 0.2). Since, in vivo, PGD2 has greater efficacy and potency than PGF2 alpha, our results suggest that the in vivo effect of these prostaglandins does not result solely from an action on airway muscle.     

What regulates placental steroidogenesis in 90-day pregnant ewes?

By day-90, the placenta secretes half of the circulating progesterone and 85% of the circulating estradiol-17beta [Weems YS, Vincent D, Tanaka Y, et al. Effects of prostaglandin F(2alpha) on sources of progesterone and pregnancy in intact, ovariectomized, and hysterectomized 90-100 day pregnant ewes. Prostaglandins 1992;43:203-22; Weems YS, Vincent DL, Nusser K, et al. Effects of prostaglandin F(2alpha) (PGF(2alpha)) on secretion of estradiol-17beta and cortisol in 90-100 day hysterectomized, intact, or ovariectomized pregnant ewes. Prostaglandins 1994;48:139-57]. Ovariectomy (OVX) or prostaglandin (PG) F(2alpha) (PGF(2alpha)) does not abort intact or OVX 90-day pregnant ewes and PGF(2alpha) regresses the corpus luteum, but does not affect placental progesterone secretion in vivo [Weems YS, Vincent D, Tanaka Y, et al. Effects of prostaglandin F(2alpha) on sources of progesterone and pregnancy in intact, ovariectomized, and hysterectomized 90-100 day pregnant ewes. Prostaglandins 1992;43:203-22]. Luteal progesterone secretion in vitro at day-90 of pregnancy in ewes is regulated by PGE(1)and/or PGE(2), not by ovine luteinizing hormone (LH; 3). Concentrations of PGE in uterine or ovarian venous plasma averaged 6 ng/ml at 90-100 days of pregnancy in ewes [Weems YS, Vincent DL, Tanaka Y, Nusser K, Ledgerwood KS, Weems CW. Effect of prostaglandin F(2alpha) on uterine or ovarian secretion of prostaglandins E and F(2alpha) (PGE; PGF(2alpha)) in vivo in 90-100 day hysterectomized, intact or ovariectomized pregnant ewes. Prostaglandins. 1993;46:277-96]. Ovine placental PGE secretion is regulated by LH up to day-50 and by pregnancy specific protein B (PSPB) after day-50 of pregnancy [Weems YS, Kim L, Humphreys V, Tsuda V, Weems CW. Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E(2) (PGE(2)) and F(2alpha) (PGF(2alpha)), and progesterone in vitro. Prostaglandins Other Lipid Mediators 2003;71:55-73]. Indomethacin (INDO), a prostaglandin synthesis inhibitor [Lands WEM. The biosynthesis and metabolism of prostaglandins. Annu Rev Physiol 1979;41:633-46], lowers jugular venous progesterone [Bridges PJ, Weems YS, Kim L, et al. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on pregnancy, progesterone and pregnancy specific protein B (PSPB) secretion in 88-90 day pregnant ewes. Prostaglandins Other Lipid Mediators 1999;58:113-24] and inferior vena cava PGE of pregnant ewes with ovaries by half at day-90 [Bridges PJ, Weems YS, Kim L, LeaMaster BR, Vincent DL, Weems CW. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on prostaglandin E (PGE), PGF(2alpha) and estradiol-17beta secretion in 88-90 day pregnant sheep. Prostaglandins Other Lipid Mediators 1999;58:167-78]. In addition, treatment of 90 day ovine diced placental slices with androstenedione in vitro increased placental estradiol-17beta, but treatment with PGF(2alpha)in vitro did not decrease placental progesterone secretion, which indicates that ovine placenta progesterone secretion is resistant to the luteolytic action of PGF(2alpha) [Weems YS, Bridges PJ, LeaMaster BR, Sasser RG, Vincent DL, Weems CW. Secretion of progesterone, estradiol-17beta, prostaglandins (PG) E (PGE), F(2alpha) (PGF(2alpha)), and pregnancy specific protein B (PSPB) by day 90 intact or ovariectomized pregnant ewes. Prostaglandins Other Lipid Mediators 1999;58:139-48]. This also explains why ovine uterine secretion of decreased around day-50 [Weems YS, Kim L, Humphreys V, Tsuda V, Weems CW. Effect of luteinizing hormone (LH), pregnancy specific protein B (PSPB), or arachidonic acid (AA) on ovine endometrium of the estrous cycle or placental secretion of prostaglandins E(2) (PGE(2)) and F(2alpha) (PGF(2alpha)), and progesterone in vitro. Prostaglandins Other Lipid Mediators 2003;71:55-73], when placental estradiol-17beta secretion is increasing [Weems C, Weems Y, Vincent D. Maternal recognition of pregnancy and maintenance of gestation in sheep. In: Reproduction and animal breeding: advances and strategies. Enne G, Greppi G, Lauria A, editors, Elsevier Pub., Amsterdam 1995. p. 277-93]. Treatment of 90 day pregnant ewes with estradiol-17beta+ PGF(2alpha), but not either treatment alone, caused a linear increase in both estradiol-17beta and PGF(2alpha) and ewes were aborting [Bridges PJ, Weems YS, Kim L, Sasser RG, LeaMaster BR, Vincent DL, Weems CW. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on pregnancy, progesterone and pregnancy specific protein B (PSPB) secretion in 88-90 day pregnant ewes. Prostaglandins Other Lipid Mediators 1999;58:113-24; Bridges PJ, Weems YS, Kim L, LeaMaster BR, Vincent DL, Weems CW. Effect of prostaglandin F(2alpha) (PGF(2alpha)), indomethacin, tamoxifen or estradiol-17beta on prostaglandin E (PGE), PGF(2alpha) and estradiol-17beta secretion in 88-90 day pregnant sheep. Prostaglandins Other Lipid Mediators 1999;58:167-78]. Pregnant ewes OVX on day 83 of pregnancy and placental slices cultured in vitro secretes 2-3-fold more estradiol-17beta, PSPB, PGE, and progesterone than placental slices from 90 day intact pregnant ewes, but placental PGF(2alpha) secretion by placental slices from intact or OVX ewes did not change [Denamur R, Kann G, Short R V. How does the corpus luteum of the sheep know that there is an embryo in the uterus? In: Pierrepont G, editor. Endocrinology of pregnancy and parturition, vol. 2. Cardiff, Wales, UK: Alpha Omega Pub Co.; 1973. p. 4-38]. The objective of these experiments was to determine what regulates ovine placental progesterone and estradiol-17beta secretion at day-90 of pregnancy, since the hypophysis [Casida LE, Warwick J. The necessity of the corpus luteum for maintenance of pregnancy in the ewe. J Anim Sci 1945;4:34-9] or ovaries [Weems CW, Weems YS, Randel RD. Prostaglandins and reproduction in female farm animals. Vet J 2006;171:206-28] are not necessary after day-55 to maintain pregnancy. In Experiment 1, diced placental slices from day-90 intact or OVX pregnant ewes that were ovariectomized or laparotomized and ovaries were not removed on day 83 were collected on day-90 and incubated in vitro in M-199 with Vehicle, ovine luteinizing hormone (oLH), ovine follicle stimulating hormone (oFSH), ovine placental lactogen (oPL), PGE(l), PGE(2), PGD(2), PGI(2), insulin-like growth factor (IGF) 1 or 2 (IGF(l); IGF(2)), leukotriene C(4) (LTC(4)), platelet activating factor (PAF) 16 or 18 (PAF-16; PAF-18) at doses of 0, 1, 10, or 100ng/ml for 4h. In Experiment 2, placental slices from day-90 intact and OVX (intact or OVX laporotomized 7 days earlier) pregnant ewes were incubated in vitro with vehicle, INDO, Meclofenamate (MECLO), PGE(l), PGE(2), INDO+PGE(1), MECLO+PGE(l), INDO+PGE(2), or MECLO+PGE(2) for 4h. Media were analyzed for progesterone, estradiol-17beta, PGE, or PGF(2alpha) by RIA. Hormone data in media were analyzed in Experiment 1 by a 2x3x13 and in Experiment 2 by a 2x9 Factorial Design for ANOVA. In Experiment 1, placental progesterone, PGE, or estradiol-17beta secretion were increased (P< or =0.05) two-fold by OVX. Progesterone was not increased (P> or =0.05) by any treatment other than OVX and only FSH increased (P< or =0.05) estradiol-17beta secretion by placental slices in both OVX and intact ewes 90-day pregnant ewes. In Experiment 2, INDO or MECLO decreased (P< or =0.05) placental progesterone secretion by 88% but did not decrease (P> or =0.05) placental estradiol-17beta secretion from intact or OVX ewes. PGE(l) or PGE(2) increased (P< or =0.05) progesterone secretion only in ewes treated with INDO or MECLO. It is concluded that FSH probably regulates day-90 ovine placental estradiol-17beta secretion, while PGE(l) or PGE(2) regulates day-90 placental progesterone secretion.     

Effects of prostaglandins F alpha on dog thyroid cyclic AMP level and function

Prostaglandins F1 alpha and F2 alpha, at high concentrations (greater than or equal to 28 microM) enhanced cyclic AMP accumulation in dog thyroid slices. At lower concentrations, they inhibited the cyclic AMP accumulation induced by thyrotropin (TSH), prostaglandin E1, and cholera toxin. This effect was rapid in onset and of short duration, calcium-dependent and suppressed by methylxanthines. Prostaglandin F alpha also inhibited TSH-induced secretion and activated iodide binding to proteins. These characteristics are similar to those of carbamylcholine action, except that prostaglandins F did not enhance cyclic GMP accumulation. The effect of prostaglandin F alpha was not inhibited by atropine, phentolamine and adenosine deaminase and can therefore not be ascribed to an induced secretion of acetylcholine, norepinephrine or adenosine. It is suggested that prostaglandins F act by increasing influx of extracellular Ca2+. Arachidonic acid also inhibited the TSH-induced cyclic AMP accumulation. However this effect was specific for TSH, it was enhanced in the absence of calcium and was not inhibited by methylxanthines or by indomethacin at concentrations which completely block its conversion to prostaglandin F alpha. Arachidonic acid action is sustained. This suggests that arachidonic acid inhibits thyroid adenylate cyclase at the level of its TSH receptor and that this effect is not mediated by prostaglandin F alpha or any other cyclooxygenase product.     

Effect of prostaglandins on 3H-thymidine uptake into human epidermal cells in vitro.

Prostaglandins A2, B1, E1, E2, F1alpha and F2alpha were added to cultures of human epidermal cells (keratinocytes) for 24 hours at 37 degrees C, and the effects on 3H-thymidine uptake into DNA was measured. At 70 mu/ml all prostaglandins tested except PGF2alpha inhibited the uptake of 3-thymidine greater than 50%. However, at 35 mug/ml, PGA2 and PGB1 were the only two prostaglandins to show significant inhibition, 96% and 51% respectively. At 17.5 mug/ml only PGA2 caused substantial inhibition, 68%. In order to determine if the PGA2 action was mediated by membrane receptors propranolol, phentolamine, metiamide and prostynoic acid were added in conjunction with PGA2. None of the above receptor antagonists were able to reduce the PGA2-induced inhibition of 3H-thymidine uptake. These results indicate that the pre-incubation of human keratinocytes with prostaglandins for 24 hours results in a decrease of 3H-thymidine incorporation in DNA. The precise mechanism of action is unknown at this time.     

Fasciola hepatica: increase of glycogen phosphorylase activity due to prostaglandins

Both prostaglandin E1 (PGE1) and prostaglandin F2 alpha (PGF2 alpha) stimulate the glycogen phosphorylase (EC 2.4.1.1.) activity of Fasciola hepatica. Whole or sliced parasites were incubated with PGE1 (2.8 X 10(-7) and 2.8 X 10(-5) M) and PGF2 alpha (2.1 X 10(-7) and 2.1 X 10(-5) M) and enzyme activity was measured in homogenates prepared immediately following the incubation. No substantially different effect was noted between the two assayed doses of prostaglandins. Prostaglandins appeared to be less effective in sliced parasites.     

Synthesis of thromboxane B2 and 6-keto-prostaglandin F1 alpha by bovine gastric mucosal and muscle microsomes

Bovine gastric mucosal and muscle microsomes synthesize prostaglandins and thromboxane b/ (TXB2) from aratchidonic acid (AA). TXB2 and 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) were the majro products synthesized by pylorus, body, and cardiac region of the gastric mucosa. Gastric muscle mainly synthesized 6-keto-PGF1 alpha. TXB2 and 6-keto-PGF1 alpha synthesis occurs at an appreciable rate from endogenous precursors but more rapidly with added arachidonate. Prostaglandins E2, F2 alpha and D2 were synthesized in smaller amounts under the conditions studied.     

Prostaglandins and renin release: I. Stimulation of renin release from rabbit renal cortical slices by PGI2.

Prostaglandins have been shown to be involved in the mechanism of renin secretion in a variety of situations. Both arachidonic acid and prostaglandin endoperoxide have been shown to release renin from cortical slices and to be converted to PGI2 by cortical microsomes. In the present studies PGI2 was found to cause a time dependent increase in renin release from rabbit renal cortical slices, a system isolated from any indirect effects that result from the administration of prostaglandins in vivo. The stimulation was linear up to 30 minutes and effective over a range of concentrations from 10(7 M to 10(-5) M. At similar concentrations 6-keto-prostaglandin F1alpha was not active on these slices. Thus, it is proposed that PGI2 exerts a direct effect on the release of renin from cortical cells and may be the mediator of arachidonate or prostaglandin endoperoxide stimulated renin secretion.     

Immunohistochemical localization of prostaglandins E and F2 alpha in the developing murine palate

Prostaglandins E2 and F2 alpha (PGE2 and PGF2 alpha) have been shown to cause changes in adenosine 3',5'-cyclic monophosphate (cAMP) levels in a wide variety of tissues. In particular, murine palatal mesenchyme responds to PGE2 stimulation with dose-dependent increases in intracellular cAMP levels. These same mesenchymal cells also synthesize PGE2 and PGF2 alpha. The purpose of this study is to localize PGE and PGF2 alpha in the developing murine palate by using immunohistochemical techniques. Fresh frozen cryostat sections of murine C57BL/6J embryo palates (days 12-14 of gestation) were incubated with anti-PGE or PGF2 alpha monoclonal antibodies. On day 12 of gestation, PGE and PGF2 alpha, identified as 3',3-diaminobenzidine (DAB) reaction products, were localized throughout palatal mesenchyme and epithelium; on day 13 of gestation, reaction product indicative of both PGE and PGF2 alpha was detectable primarily in mesenchyme subjacent to palatal epithelium. Extracellular spaces of the adjacent mesenchyme in the central region of the day 13 palate exhibited less reaction product. Palatal epithelium, particularly the medial edge epithelium, exhibited a diminished amount of reaction product for both prostaglandins on day 13 as compared to the underlying mesenchyme. After formation of a midline epithelial seam between homologous palatal processes on day 14 of gestation, medial edge, oral, and nasal epithelium exhibited light staining for PGE or PGF2 alpha. Palate mesenchymal cells subjacent to the midline seam exhibited a diminished amount of reaction product for both PGE and PGF2 alpha as compared to day 13 of gestation. Overall, the results show local and temporal changes in the distribution of prostaglandins in the developing murine palate.     

E and F alpha series prostaglandins in developing muscles

Prostaglandins are known to affect myoblast proliferation and fusion in vitro and are putative regulators of in vivo myogenesis. The levels of E and F alpha series prostaglandins in the thigh muscles of chicken embryos were measured by radioimmunoassays and correlated with indicators of muscle development. Just prior to the onset of secondary myogenesis, the amounts of PGE1, PGE2 and PGF1 alpha plus PGF2 alpha per mg of protein were high. In temporal association with myotube formation, the amount of PGE1 and PGE2 per mg of protein decreased. PGF alpha levels also fell, but at a slower rate than observed with the E series prostaglandins. The decreases in the amounts of prostaglandins per mg protein appeared to be due to a decline in the total amount of prostaglandin within each muscle. These observations are consistent with prostaglandins being one of the factors that controls in vivo muscle formation.