Arachidonic acid stimulates short-circuit current in the isolated toad urinary bladder

The effects of the prostaglandin (PG) precursors 5,8,11,14-eicosatetraenoic acid (arachidonic acid) and 8,11,14-eicosatrienoic acid (dihomo-gamma-linolenic acid) on short-circuit current (SCC) were assessed in the isolated toad urinary bladder. Arachidonic acid added to the serosal bathing media increased SCC and immunoreactive PGE2 (iPGE2) synthesis in a dose-related manner. Pretreatment with eicosatetraynoic acid (50 micrometer), a prostaglandin synthetase inhibitor, completely blocked the arachidonic acid-induced increase in SCC and significantly reduced iPGE2 synthesis (P less than .025, n = 9). Eicosatrienoic acid (100 micrometer) was equieffective with arachidonic acid in increasing SCC and iPGE1 synthesis. Addition of arachidonic acid (100 micrometer) to the mucosal bathing media produced no significant increase in SCC and only increased iPGE2 synthesis from 0.03 +/- 0.01 pmol/min (n = 5) to 0.31 +/- 0.03 pmol/min, a level not different from the serosal basal rate of iPGE synthesis (0.21 +/- 0.16 pmol/min, n = 5). PGE1 (1 micrometer) added to the serosal media significantly increased SCC reaching a maximum increase of 157 +/- 43% (P less than .025, n = 6) by 30 min whereas addition to the mucosal media resulted in a delayed (60 min) and lesser maximum increase (59 +/- 19%, P less than .02, n = 6). It is concluded that prostaglandin precursors increase SCC and PGE synthesis in the isolated toad urinary bladder. However, the present data do not support PGE as the metabolite responsible for the increase in SCC.

Dihomogammalinolenic acid (20:3 omega 6) is more anti-aggregatory than eicosapentaenoic (20:5 omega 3) in a platelet-endothelial cell mixture

The effect of 20:3 omega 6, the precursor of 1 series prostaglandins was to inhibit platelet aggregation more strongly than either 20:5 omega 3, the precursor of 3 series prostaglandins or 20:3 omega 3 which is not a substrate of prostaglandin synthetase. When platelets and dissociated endothelial cells were pretreated with 20:3 omega 6, platelet aggregation in the presence of endothelial cells was much more inhibited than after 20:5 omega 3 pretreatment.

Endogenous synthesis of prostaglandins E1 and I2 in 3T3 fibroblasts transformed by polyoma virus. Effects on adenosine 3':5'-monophosphate production

Prostaglandins (PG)E1, E2 and I2 were produced by polyoma virus transformed (py) 3T3 fibroblasts. The levels of PGE1, PGE2 and 6-keto-PGF1 alpha (degradation product of PGI2) were 22.7, 225 and 33.2 ng/ml medium, respectively, 72 h after medium change. The stimulatory potencies of exogenous PGE1, PGE2 and PGI2 on adenosine 3':5'-monophosphate (cyclic AMP) formation were similar. Therefore, the prostaglandin mediated increase in cyclic AMP levels observed during growth of these cells (Claesson, H.-E., Lindgren, J.A. and Hammarström, S. (1977) Eur. J. Biochem. 74, 13) is largely (greater than 80%) mediated by PGE2 and to lesser extents by PGE1 and PGI2.

Manipulation of platelet aggregation by prostaglandins and their fatty acid precursors: pharmacological basis for a therapeutic approach

Addition of the one-, two- or three- series endoperoxide to human platelet-rich plasma tend to suppress aggregation, through the action of their respective non-enzymatic breakdown products PGE1, PGD2, or PGD3 all of which elevate cyclic AMP levels. On the other hand, these stable primary products do not arise in appreciable amounts from intrinsic endoperoxides generated from either endogenous or exogenous free fatty acids. 5,8,11,14,17-Eicosapentaenoic acid (EPA) suppresses arachidonic acid (5,8,11,14-eicosatetraenoic acid) conversion by cyclooxygenase (as well as lipoxygenase) to aggregatory metabolites in platelets. Exogenously added EPA was capable of inhibiting PRP aggregation induced either by exogenous or endogenous (released by ADP or collagen) arachidonate. The hypothetical combination of an EPA-rich diet and a thromboxane synthetase inhibitor might abolish production of the pro-aggregatory species, thromboxane A2, and enhance formation of the anti-aggregatory metabolite, prostacyclin. Whereas EPA is not detectably metabolized by platelets, dihomo-gamma-linolenic acid (8,11,14-eicosatrienoic acid) is primarily converted by cyclooxygenase and thromboxane synthetase into the inactive metabolite, 12-hydroxyheptadecadienoic (HHD) acid. Pretreatment of human platelet suspensions with the thromboxane synthetase inhibitor imidazole unmasks the aggregatory property of PGH1 and DLL which was partially compromised by the PGE1 formed. The combination of the thromboxane synthetase inhibitor and an adenylate cyclase inhibitor unmasks a complete irreversible aggregation by DLL or PGH1. The basis of a dietary strategy that replaces AA with DLL must rely on the production by the platelet of an inactive metabolite (HHD) rather than thromboxane A2.

Prolactin and zinc effects on rat vascular reactivity: possible relationship to dihomo-gamma-linolenic acid and to prostaglandin synthesis

Ovine PRL at low concentrations potentiated pressor responses to norepinephrine and angiotensin in an isolated perfused rat mesenteric vascular preparation. Higher concentrations inhibited these pressor responses. Pressor responses to potassium which depend on extracellular calcium entry into the muscle were unaffected by PRL at any concentration. Either cortisol or lithium could completely block the PRL effect. Dihomo-gamma-linolenic acid (DHGL) and prostaglandin E1 had effects similar to those of PRL in that they potentiated norepinephrine responses at low concentrations, inhibited at high ones, and had no effect on potassium responses. Arachidonic acid and prostaglandin E2 potentiated both norepinephrine and potassium responses and had no inhibitory effects at high concentrations. Neither lithium nor cortisol blocked the effects of DHGL or arachidonic acid. Zinc had actions similar to those of PRL and DHGL, but which could be blocked only by lithium and not by cortisol. These results are consistent with the concept that PRL increases synthesis of the 1 series of prostaglandins by mobilizing DHGL. They provide further evidence that zinc may play a role in some actions of PRL.

Metabolism of arachidonic acid by platelets: utilization of arachidonic acid by human platelets in presence of linoleic and dihomo-gamma-linolenic acids

In vitro human platelet prostaglandin synthesis has been studied from added radioactive arachidonic acid (i) as function of substrate concentration, (ii) as function of platelet concentration and (iii) as function of pH. Platelets, as in platelet rich plasma when labelled with arachidonic acid, washed and treated with thrombin, released radioactivity mainly from phosphatidylcholine and phosphatidylinositol. The released radioactivity was mostly accounted for by the formation of the previously identified oxygenation products of arachidonic acid. Platelet utilization or arachidonic acid was also studied in presence of linoleic and dihomo-gamma-linolenic acids, the two essential fatty acids known for antithrombotic effect. At its high concentrations linoleic acid decreased platelet cyclo-oxygenase activity as seen by a decreased formation of endoperoxides from arachidonic acid. Dihomo-gamma-linolenic acid was found to be a mutually competitive substrate with arachidonic acid for the platelet prostaglandin synthetase thus causing reduced utilization of arachidonic acid as shown by measuring the various oxygenation products of arachidonic acid. These two acids were utilized differently by platelet prostaglandin synthetase.

Mechanism of luteinizing hormone regulation of prostaglandin synthesis in rat granulosa cells

The present study was undertaken to examine the mechanism by which luteinizing hormone (LH) stimulates prostaglandin (PG) synthesis in rat granulosa cells. Immature rats were injected with 20 IU of pregnant mare's serum gonadotropin and granulosa cells isolated 48 h later. LH (5 microgram/ml) stimulated PGE synthesis markedly over the control with no additions in 6-h incubations (1.98 +/- 0.24 and 0.24 +/- 0.05 ng/2 X 10(6) cells, respectively, n = 6). When arachidonic acid (100 microgram/ml) was included during the last hour of incubation, further increases to 15.4 +/- 2.9 and 2.48 +/- 0.48 ng of PGE/2 X 10(6) cells in LH and control incubations were observed. The cause of the increased response to a 1-h incubation with arachidonic acid in the LH-treated cells did not appear to be a stimulation of fatty acid uptake. In addition, when cellular lipids were labeled by a 2-h incubation with radioactive arachidonic acid, LH did not stimulate intra- or extracellular release of arachidonic acid. A 5-fold stimulation of prostaglandin synthetase activity, however, was observed in cells incubated with LH for 5 h. Our results, therefore, indicate that LH acts at a step in the prostaglandin pathway after hydrolysis of arachidonic acid esters and produces an increase in prostaglandin synthetase activity.

Effect of dihomo-gamma-linolenic acid on the canine pulmonary vascular bed

The effect of dihomo-gamma-linolenic acid (DGLA), the precursor of the monoenoic prostaglandins (PG), F1alpha and E1, on the pulmonary vascular bed of the intact dog was studied under conditions of controlled pulmonary blood flow. DGLA increased pulmonary vascular resistance in a dose-related manner by constricting intrapulmonary veins and upstream segments, presumably pulmonary arteries. Intrapulmonary injection of DGLA also increased transpulmonary injection of DGLA also increased transpulmonary airway pressure, presumably by increasing airway resistance and decreasing lung compliance or both. The vasoconstrictor response, however, was independent of changes in transpulmonary pressure since similar pressor responses were obtained in ventilated and nonventilated lungs. Further, the response was not dependent on factors or elements in whole blood, since the increase in pulmonary vascular resistance occurred during perfusion with saline or dextran and was enhanced in these media. Conversion of DGLA to PGs by a lung cyclo-oxygenase appears to mediate the response, since it was blocked by indomethacin and dose not occur with injection of nonprecursor long-chain fatty acids. These data suggest that the response to DGLA is due to formation of vasoactive products in the monoenoic PG pathway.

Fatty acids and their prostaglandin derivatives: inhibitors of proliferation in aortic smooth muscle cells

Prostaglandins are synthesized from eicosa-8,11,14-trienoic acid and eicosa-5,8,11-14-tetraenoic acid by smooth muscle cell cultures from guinea pig aorta. Production is inhibited by indomethacin. The precursor fatty acids and their prostaglandin derivatives inhibit proliferation of the cell cultures. The relative availability of fatty acids for prostaglandin biosynthesis may represent a control mechanism for cell proliferation.

Vascular responses to the monoenoic prostaglandin precursor dihomo-gamma-linolenic acid in the perfused canine lung

Dihomo-gamma-linolenic acid (DGLA; 2 mg/kg i.v.), the monoenoic prostaglandin (PG) precursor was reported earlier to produce systemic hypotension in the intact dog. It is shown here to produce pulmonary vasoconstriction when given (50-500 microng/kg) in the pulmonary artery of the isolated perfused canine lung lobe. This effect is similar to that of arachidonic acid (AA), the bisenoic PG precursor. PGF1alpha was vasopressor in both preparations. The DGLA response at 100 microng/kg in the lung was nearly identical with that of AA25 microng/kg; DGLA 200 microng/kg=AA50 microng/kg;DGLA 300microng/kg=AA 100 microng/kg. The DGLA 100 microng/kg response was nearly equal to that with PGF1alpha 1 microng/kg. The equipressor dose ratio, DGLA/AA, varied 2.5 to f1 and DGLA/PGF1alpha was 100:1. DGLA and AA vascular responses were blocked by indomethacin. Linoleic acid, used as a control fatty acid, had no pulmonary pressor action. When a dextran-based artificial perfusate was used, the vasopressor response to DGLA was essentially unchanged from that in the blood-perfused lobe. The effects of DGLA appear to be due to conversion to vasoactive products in the PG biosynthetic pathway. These products are less potent than those formed in the metabolism of AA.

Inhibition of prostaglandin biosynthesis by triynoic acids

Prostaglandin biosynthesis from eicosa-8,11,14-trienoic acid in microsomes from bovine seminal vesicles is inhibited by acetylenic acids. Octadeca-6,9,12-triynoic acid and eicosa-8,11,14-triynoic acid are the most potent inhibitors. These acids both contain an omega-8 methylene group. Within the 20-carbon acetylenic acid series, inhibition decreases in the sequence eicosa-8,11,14-triynoic acid greater than eicosa-7,10,13-triynoic acid greater than eicosa-5,8,11-triynoic acid. Furthermore, eicosa-8,11,14-triynoic acid is a more potent inhibitor of arachidonic acid induced platelet aggregation than either eicosa-7,10,13-triynoic acid or eicosa-5,8,11-triynoic acid. The omega-8 methylene group is not the only determinent of inhibitory potency since docosa-10,13,16-triynoic acid is less potent than its 18 and 20 carbon analogs and all of these acids have an omega-8 methylene group.

Further characterization of bovine thyroid prostaglandin synthase

1. Prostaglandin synthase activity (EC 1.14.99.1) was demonstrated in bovine thyroid homogenates. 2. The synthase was characterized and shares many characteristics of the well-studied seminal vesicle enzyme and can be inhibited by indomethacin and eicosa-5,8,11,14-tetraynoic acid. 3. The enzyme is localized in the microsomal fraction and is probably associated with the plasma membranes. 4. Thyrotropin, but no other hormone tested, increased the activity of the enzyme when added to a microsomal fraction obtained from bovine thyroid. This effect is tissue-specific since thyrotropin has no effect on bovine seminal esicle or lung prostaglandin synthase. 5. Thyrotropin, cyclic AMP and the phosphodiesterase inhibitors, theophylline and quazodine increase enzyme activity when preincubated with bovine thyroid slices. 6. EDTA, when included in the pre-incubation mixture, enhances the thyrotropin effect on the enzyme but not the cyclic AMP, theophylline, or quazodine augmentation of enzyme activity in bovine thyroid slices. This suggests that phospholipase A is involved in the thyrotropin stimulation of prostaglandin formation.

Cardiovascular and platelet responses in the dog to the monoenoic prostaglandin precursor dihomo-gamma-linolenic acid

The monoenoic prostaglandin precursor, dihomo-gamma-linolenic acid (DGLA), in a single dose intravenously (2.0 mg/kg) in dogs, produced a biphasic alteration in systemic arterial pressure (SAP) with a predominant and marked depressor effect. This SAP response is approximately equidepre-sor to the effect of PGE1 5 mug/kg. DGLA had a positive inotropic effect, causing a greater increase in myocardial contractility than PGE1 in an equidepressor dose. The effect of DGLA on MC was not altered by ganglion blockade or beta-adrenergic blockade. Aspirin blocked the sustained depressor response to DGLA but not an initial drop in SAP and increase of MC of very short duration. Aspirin had no effect on PGE1 or PGF1 alpha responses. DGLA caused no thrombocytopenia, but caused a decrease in sensitivity to platelet aggregation. Control fatty acid injections produced variable effects with no resemblances to DGLA responses. It is concluded that DGLA produces direct depressor and positive inotropic responses as well as responses which may be due to conversion to an endoperoxide formed in the biosynthesis of prostaglandins. In contrast, in equidepressor doses, arachidonic acid (AA), the bisenoic prostaglandin precursor, produces a delayed, single-phase depressor effect which may be due to endoperoxide formation alone. Further, the effect of AA on MC is reflex and is blocked by hexamethonium.

Prostaglandins, antipyretic analgesics and adrenergic stimuli on the isolated artery

In untreated, and cocaine- and DOCA-treated rabbit ear arteries, PGE2 and arachidonic depressed to responses to intramural sympathetic nerve stimulation. Constrictor responses to extraluminal NA in the treated arteries were also depressed. A comparison of its inhibitory potency on the two types of responses suggest that the effects of arachidonic acid, but not PGE2 on adrenergic nerve stimuli, were selectively blocked by aspirin 200 mug/ml and by indomethacin 3 mu/ml. In these concentrations, aspirin, but not indomethacin, enhanced the magnitude of the resoonses to the stimuli. Aspirin also selectively reduced the inhibition by arachidonic acid of the response to extraluminal NA (tested in cocaine0 and DOCA-treated arteries).