Inhibitory Effect Of Prostaglandins Research Articles

Stimulatory and inhibitory effects of prostaglandins on the gonadotropin-sensitive adenylate cyclase in the monkey corpus luteum

Detailed analysis of the action of prostaglandins (PGs) on the corpus luteum in primate species is very limited. In this study we examined the response of the adenylate cyclase system to PGs in homogenates prepared from the corpus luteum of rhesus monkeys at midluteal phase of the menstrual cycle. The conversion of [α32P] ATP to [32P] cyclic AMP (cAMP) was assessed in the absence (control activity; 50 μM GTP) and presence of various concentrations of seven PGs and arachiodonic acid, either alone or in combination with 250 nM hCG. Cyclic AMP production increased up to three-fold in the presence of PGD2, PGE2, PGI2 or PGF2α; however PGA2, PGB2, 13,14-dihydro-15-keto PGE2 and arachidonic acid alone did not alter cAMP levels. In dose-response studies, adenylate cyclase was 10 and 100-fold more sensitive to PGD2 (Vmax at 1 × 10−5M) than to PGE2 or to PGI2 and PGF2α, respectively. Activity in the presence of hCG plus either PGD2, PGE2, PGI2 or PGF2α did not differ from that for hCG (or the PG) alone. In contrast, addition of PGA2 or arachidonate inhibited (p‹0.05) hCG-stimulated cAMP production by 50 and 100 percent. We conclude that the gonadotropin-sensitive adenylate cyclase of the macaque corpus leteum is also modulated by several PGs. These factors may either mimic (e.g., PGD2, PGE2, PGI2) or suppress (PGA2)_ gonodotropin-stimulated cAMP production and possibly cAMP-mediated events in luteal cells.

Independent action of prostaglandins and kinins on vasopressin-stimulated water flow

The kallikrein-kinin and the prostaglandin systems are both important modifiers of vasopressin action. This study examines whether the systems are dependent on one another for their action. Four groups of toad hemibladders were examined. In groups 1 and 2 animals the endogenous prostaglandin system was inhibited. Inhibition of kallikrein by aprotinin caused vasopressin-stimulated water flow to increase further (24.8 +/- 4.9 to 34.5 +/- 4.8 microliters/min) while potentiation of kinins by captropril caused vasopressin-stimulated water flow to decrease (45 +/- 6.3 to 30.5 +/- 5.4 microliters/min). In groups 3 and 4 endogenous kallikrein was inhibited by aprotinin. The addition of prostaglandin E2 caused vasopressin-stimulated water flow to decrease (17.5 +/- 2.7 to 5.71 +/- 1.0 microliter/min) while the inhibition of endogenous prostaglandins caused vasopressin-stimulated water flow to increase (26.7 +/- 3.4 to 39.2 +/- 3.5 microliters/min). Thus, the inhibitory effects of prostaglandins and kinins on vasopressin-stimulated water flow are independent of one another.

Stimulatory and inhibitory effects of prostaglandin E 2 on prolactin release in the domestic fowl

In vivo prolactin secretion was increased in immature cockerels 20–30 min after the intravenous administration of prostaglandin (PG) E 2 at a dose of 200 μg/kg. The addition of PGE 2 to incubation medium had no direct effect on the release of pituitary prolactin during short-term (3-hr) culture, but augmented the stimulatory effect of hypothalamic tissue on prolactin secretion. The stimulatory effect of serotonin, noradrenaline, acetylcholine, and histamine on hypothalamus-induced prolactin release was also increased when pituitaries were coincubated with 10 −7 M PGE 2, as was the stimulatory effect of thyrotrophin-releasing hormone (TRH) and hypothalamic extract (HE). The long-term (24-hr) preincubation of pituitaries with 10 −7 M PGE 2 reduced the responsiveness of the prolactin-secreting cells to TRH or HE stimulation. PGE 2 treatment also reduced the stimulatory effect of hypothalamic tissue on prolactin release and diminished the stimulatory effect of serotonin on hypothalamus-induced prolactin secretion. A 24-hr preincubation of hypothalamic tissue with 10 −7 M PGE 2 also reduced its stimulatory effect on prolactin release when subsequently incubated with control pituitary glands. These results demonstrate that PGE 2 initially stimulates in vivo and in vitro prolactin secretion in the fowl, possibly by increasing the release of hypothalamic prolactin-releasing activity and/or by increasing pituitary sensitivity to provocative stimuli. Chronic PGE 2 stimulation appears to result in a reduction in pituitary responsiveness to stimulatory influences and in the release of hypothalamic-releasing activity.

Prostaglandin modulation of N-formylmethionylleucylphenylalanine-induced transmembrane potential changes in rat neutrophils

Prostaglandins of the E-series (PGEs) and PGI 2 will inhibit formylmethionylleucylphenylalanine- (f-Met-Leu-Phe) induced lysosomal enzyme release and superoxide-anion (O − 2) production by neutrophils. The inhibitory effects of PGEs and PGI 2 on neutrophil functional responses have been correlated with their ability to increase intracellular cAMP. In this study we have examined the effects of PGEs and PGI 2 on f-Met-Leu-Phe- and phorbol-myristate-acetate-induced rat neutrophil membrane potential changes using an optical probe of membrane potential 3,3-dipropylthiodicarbocyanine iodide. 15-( S)-15-methyl-PGE 1 (15-methyl-PGE 1), a stable analogue of PGE 1 and PGI 2 inhibited f-Met-Leu-Phe-induced transmembrane potential changes in a dose-dependent manner. This inhibition was correlated with the ability of these agents to increase intracellular cAMP levels and inhibit O − 2 production and degranulation. In contrast, 15-methyl-PGE 1 and PGI 2, did not inhibit phorbol-myristate-acetate-induced transmembrane potential changes and O − 2 production. These results suggest independent mechanisms of activation of neutrophils by phorbol myristate acetate and f-Met-Leu-Phe, and they also suggest that the inhibitory effects of prostaglandins and cAMP on f-Met-Leu-Phe-stimulated cells is at a step or steps prior to activation of those processes involved in effecting changes in transmembrane potential, which are common to both stimuli.

微小血管内血小板血せん形成の新しい実験モデルとその応用に関する２，３の基礎的検討

The intravascular platelet aggregation and the subsequent thrombus formation were found to be induced in the microvasculature by the irradiation of filtered light in combination with the intravascular administration of fluorescein sodium. Effects of several factors such as light intensity, dye concentration and vessel diameter were examined in venules of rat mesenteries. It was confirmed that the platelet thrombus was induced with excellent reproducibility depending on the combined condition of the light intensity and the dye concentration. In venules within the range of 20 to 80μm in diameter, almost the same values of the initiation time of thrombus formation were obtaind. On the other hand, the time to totally occlude the vessel lumen by the thrombus prolonged significantly with the increase of vessel diameter, which phenomenon seemed to be induced by almost the same growth rate of thrombus in the radial direction in all venules with different diameters. Inhibitory effects of prostaglandins (PGD2, PGE1) for the thrombus formation were also examined by the proposed model. The platelet aggregation in venules was significantly inhibited by higher concentration of these doses. This result well corresponded to that of in vitro experiments reported by other researchers. The present model seems useful for various purposes in studying the kinetics of intravascular thrombus formation as well as evaluating the effects of anti-platelet aggregating drugs.

Sodium ions discriminate between stimulatory and inhibitory effects of prostaglandin E 2 on human fat cell adenylate cyclase

Prostaglandin E 2 ( PG E 2 ) has biphasic effects on human fat cell adenylate cyclase with inhibition occurring in the nanomolar concentration range and stimulation at PG E 2-concentrations above l μmol/l. Sodium ions stimulate the human fat cell adenylate cyclase in a hormone-like manner. The inhibitory component of PG E2-action is markedly augmented by sodium ions. In addition, the monovalent cation, by interfering with the stimulatory component of PG E 2 discriminates between the opposing effects of PG E 2 suggesting that the antagonistic effects of the E-type prostaglandins are mediated through distinct processes.

Inhibitory effect of prostaglandin A 2 on Na +-K + -ATPase activity in synaptic plasma membrane of rat brain in vitro

1. 1. The Na + -K + -ATPase activity in the synaptic plasma membrane of rat brain was inhibited by PGA 2 in vitro. 2. 2. PGA 2 concentration required for 50% inhibition was 8.91 × 10 −5 M. 3. 3. Inhibition mode of PGA 2 for both ATP and Mg 2+ was uncompetitive type. 4. 4. PGA 2 was competitive and noncompetitive with Na + and K +, respectively. 5. 5. The K i values for PGA 2 inhibition for ATP, Na +, K + and Mg 2+ were 6.0 × 10 −5, 2.7 × 10 −5. 10.8 × 10 −5 and 0.6 × 10 −5 M, respectively.

Comparative studies on hemolysis in the erythrocytes from various animals: Inhibitory effect of prostaglandins and phospholipid content

1. 1. The differences in hemolysis rate in erythrocytes from various animals were observed. 2. 2. Prostaglandin E 1 at concentrations of more than 10 −9 M, sharply reduced hemolysis induced by the frequent shaking and Superoxide radicals generated by the xanthine oxidase system. 3. 3. The degree of hemolysis induced by the hemolytic factors and the susceptibility to prostaglandin E 1 were found to be different among animal species. 4. 4. These differences may be correlated to the content of phosphatidylcholine in these erythrocytes.

The hamster adipocyte adenylate cyclase system II. Regulation of enzyme stimulation and inhibition by monovalent cations

In hamster adipocyte ghosts, ACTH and β-adrenergic agonists stimulate adenylate cyclase by a GTP-dependent process; in contrast, inhibition of the enzyme by hormonal factors requires both GTP and sodium ions. The interaction of various monovalent cations and guanine nucleotides was studied on basal, stimulated and inhibited adenylate cyclase activities. In the presence of GTP (0.03–10 μM), which reduced basal activity by up to 90%, monovalent cations (10–500 mM, added as chloride salts) increased the enzyme activity by up to about 8-fold. The potency order obtained was Na +>Li +>K +>choline. The stable GTP analogue, guanylyl-5′-imidodiphosphate, which like GTP was capable of decreasing basal activity, diminished the cation-induced activation. The stimulatory effects of ACTH and isoproterenol on adipocyte adenylate cyclase activity were impaired by the cations in the potency order, Na +>Li +>K +>choline. Additionally, NaCl shifted the concentration-response for ACTH to the right and caused an increase in the maximal activation by the hormone. Similar to basal activity, fluoride-stimulated activity was increased by NaCl, when GTP was present. The inhibitory effect of prostaglandin E 1 on basal adipocyte adenylate cyclase activity was revealed by the cations in the above mentioned potency order by an apparent reversal of the cation-induced activation. In the presence of NaCl, the ACTH- or fluoride-stimulated activities were also reduced by prostaglandin E 1, but the inhibitory hormonal factor did not reverse the NaCl-induced shift in the concentration-response curve for ACTH. Guanylyl-5′-imidodiphosphate completely prevented hormonal inhibition. The data suggest that monovalent cations interact with the guanine nucleotide-binding regulatory component of the adipocyte adenylate cylase system and that this interaction somehow changes the properties of this component, now revealing hormone-induced inhibition partially impairing hormone-induced stimulation.

Inhibitory effect of prostaglandins on the stimulation by glucagon and adrenaline of formation of cyclic AMP in rat hepatocytes.

Several prostaglandins were found to inhibit hormone-induced cyclic AMP accumulation in suspensions of intact rat hepatocytes. Prostaglandin E1 in concentrations of 0.05--25 micrometers inhibited the cyclic AMP response to glucagon. Maximal inhibition was about 50%. The effect was rapid, being evident within 30 s. Prostaglandins E2, F1 alpha, F2 alpha, A1 and A2 also inhibited the glucagon effect on cyclic AMP in hepatocytes. In cells made highly responsive to adrenaline, by pretreatment of the animals with the carcinogen 2-acetylaminofluorene, and inhibitory effect of prostaglandin E1 was seen also on adrenaline-induced cyclic AMP accumulation. The mechanism of the inhibitory effect of prostaglandins on hormone-stimulated cyclic AMP accumulation was not clarified. Prostaglandin E1 did not inhibit glucagon binding to intact hepatocytes, and so far we have not been able to demonstrate any effect of the prostaglandins on the adenylate cyclase or phosphodiesterase in broken cell preparations. It is concluded that while several previous studies have shown that stimulatory effects of prostaglandins on cyclic AMP are only marginal or lacking in parenchymal liver cells the present data indicate that several prostaglandins exert strong inhibitory interference with hormone-induced cyclic AMP accumulation.

Synergic effect of insulin and prostaglandin E 1 on stimulated lipolysis

1. 1. The inhibitory effect of prostaglandin E 1 on free fatty acid release from adipose tissue is significantly greater when the lipolysis is stimulated by 1-methyl-3-isobutyl xanthine than when stimulated by adrenaline. 2. 2. The antilipolytic effect of insulin on adrenaline and 1-methyl-3-isobutyl xanthine stimulated lipolysis, is suppressed in the presence of inhibitors of prostaglandin synthetase i.e. indomethacin or phenelzine. 3. 3. In the presence of phenelzine, the lack of effect of insulin on adrenaline and 1-methyl-3-isobutyl xanthine lipolysis is overcome by a small amount of prostaglandin El (10-10M) but not of prostaglandin F 1α. 4. 4. The addition of prostaglandin El (10-10M) restores the inhibitory effect of insulin on cyclic AMP accumulation.

Suppressor cell regulation of cell-mediated immune responses in renal infection in vitro modulation of suppressor cell activity.

Infection-induced anergy is a frequent complication of bacterial, viral, and parsitic infection. A marked suppression of the thymus-derived (T) lymphocyte response to concanavalin A has been demonstrated in vitro during renal infection and the mechanisms by which suppression occurs have been investigated. In particular we have considered the possibility that suppression might result from the inhibitory effect of prostaglandins, secreted by activated macrophages with immunoregulatory potential. The experiments have shown that the T-lymphocyte effector status in experimentally-induced renal infection is determined by two suppressor cells, one infection-induced and the other naturally occurring. The inability to respond to mitogenic stimulation was reversible and restoration of immune responsiveness to splenic lymphocytes from infected animals could be achieved in two stepwise manipulations; differential centrifugation removed the infection-induced suppressor cells, and the suppressor activity of the naturally occurring suppressor cells could then be inhibited by indomethacin. Thus the two suppressor cells were distinguishable on the basis of their physical characteristics and their response to indomethacin. The dominant factor determining the immune responsiveness of splenic lymphocytes from the pyelonephritic animals was, however, the infection-induced suppressor cell. This cell has been characterized as a sedimentable cell (30 g) with suppressor activity demonstrable in co-culture experiments. Plastic-adherent cells from the sedimentable fraction of pyelonephritic animals' splenic cells were shown to have suppressor activity that was not inhibited by indomethacin. The infection-induced and naturally occurring suppressor cells can be viewed as prototypes for the equivalent cells in man and may be useful models for studying the role of these cells as determinants in the pathogenesis of infectious disease.

Interaction of prostaglandins and histamine with enzymes of cyclic AMP metabolism from guinea pig gastric mucosa.

Prostaglandins (PGE1, PGE2, PGA1) and histamine have opposing effects on gastric HCl secretion, but we found that both stimulate adenylate cyclase activity in cell-free membrane preparations of guinea pig gastric fundic mucosa. The stimulatory effect of prostaglandins was found in this study to be specific and dose-dependent over a concentration range from 10(-7) to 10(-4) M. In similar preparations from antral regions of guinea pig gastric mucosa, the adenylate cyclase was stimulated only by PGE1, PGE2, and PGA1 and not by histamine. Maximum stimulating doses of PGE1, PGE2, or PGA1, and of histamine had an additive effect on the adenylate cyclase activity from fundic gastric mucosa. Metiamide, a histamine H2-receptor antagonist, inhibited the stimulation of fundic mucosa adenylate cyclase by histamine but did not interfere with the stimulation by prostaglandins. Cyclic AMP phosphodiesterase activity of guinea pig gastric mucosa was unaffected by PGE1 and PGE2 or by histamine, and was slightly depressed by PGA1. These results indicate that histamine and prostaglandins stimulate two different adenylate cyclase systems both present in guinea pig gastric mucosa tissue. Therefore, the known inhibitory effect of prostaglandins on gastric acid secretion is not related to the interference with the stimulation of the histamine H2-receptor-sensitive adenylate cyclase complex by histamine nor do prostaglandins accelerate cyclic AMP breakdown by cyclic AMP phosphodiesterase to reduce cyclic AMP levels.

Inhibitory effect of prostaglandins on isosmotic fluid transport by rabbit gall-bladder in vitro, and its modification by blocade of endogenous PGE-Biosynthesis with indomethacin.

AbstractIn the presence of indomethacin serosal application of PGEi and PGE2 caused significant inhibition of net isosmotic fluid transport by the gall‐bladder with maximum effect (50 % inhibition) at 0.5 ftg PGE/ml. Mucosal application was much less effective. PGF2a was about 100 times less potent than PGE. In the absence of indomethacin the sensitivity to low concentrations of PGEi was about 10 times less than in the presence of this drug (p < 0.001). Maximum effective doses of PGEi depressed the unidirectional Na+‐efflux about 35 % and the Na+‐influx about 20 %. Transepithelial potential difference and ohmic resistance remained unchanged. It is concluded that PGE inhibits isosmotic fluid transport by an effect mainly on the active component of the transfer process. In the absence of indomethacin endogenous PGE2 (but not PGEi) was released to both serosal and mucosal medium. Net release to mucosal medium was 35–600 pg.h‐1.mg dry weight‐1; release was higher to the serosal medium. Mucosal concentrations of 0.2–4.5 ng PGEa/ml were independent of the serosal concentration, which did not exceed 0.8 ng/ml under the present conditions. The data suggest that mucosal PGEs‐release originates, in part at least, from the epithelial cells. Indomethacin (10 μg/ml) blocked almost completely the in vitro PGE‐biosynthesis.

Effects of prostaglandin E1 on acid secretion, mucosal histamine content and histidine decarboxylase activity in rat stomach.

1. Prostaglandin E(1) inhibits basal and pentagastrin-stimulated gastric acid secretion. The mechanism of this action is not clear. One possible explanation might be that prostaglandin E(1) interferes with the local release or synthesis of histamine which has been proposed as the mediator of the effects of gastrin on the parietal cell.2. A single injection of prostaglandin E(1) did not affect mucosal histamine content or histidine decarboxylase activity in the rat stomach. Pentagastrin lowered the histamine content and activated the histidine decarboxylase to the same extent in prostaglandin E(1)-pretreated and in control rats. We conclude therefore that the inhibitory effect of prostaglandin E(1) on basal and pentagastrin-stimulated acid secretion is not caused by inhibition of histamine release or histamine synthesis.3. Repeated injections of prostaglandin E(1) resulted in a significant elevation of the gastric histidine decarboxylase activity in normal but not in antrectomized rats. Conceivably, this increase in enzyme activity is secondary to prostaglandin E(1)-induced inhibition of acid secretion, which will stimulate release of gastrin due to the rise in intragastric pH.

Inhibitory effect of prostaglandin E 2 on noradrenaline secretion from sympathetic nerves as a function of external calcium

The calcium dependence of the inhibitory effect of prostaglandin E 2 on sympathetic neurotransmitter secretion was studied in isolated superfused field stimulated guinea-pig vas deferens, by determination of the nerve stimulation induced rise in efflux of total tritium after preincubation of the tissue with tritium-labelled 1-noradrenaline. Reuptake of noradrenaline was blocked by desipramine and normetanephrine, added to the medium. Reduction of the calcium in the superfusion medium strongly depressed the nerve stimulation induced rise in efflux of tritium. Addition of the alpha-adrenoceptor blocking drug phentolamine markedly raised the efflux of tritium on nerve stimulation, even at low calcium. The inhibitory effect of prostaglandin E 2 on nerve stimulation induced rise in efflux of tritium was inversely related to the calcium concentration. The results are consistent with the possibility that prostaglandin E 2 depresses neural secretion by facilitating efflux of intraaxonal calcium.

Effect of prostaglandins E 1 , E 2 and A 2 on vascular resistance and responses to noradrenaline, nerve stimulation and angiotensin in the dog hindlimb.

1. The relationship between the vasodilator and inhibitory effects of prostaglandin E(1) (PGE(1)), E(2) and A(2) on responses to nerve stimulation, noradrenaline and angiotensin was evaluated in the dog hindlimb preparation.2. PGE(1) and PGE(2) were equipotent as vasodilators in the hindlimb; however, PGE(1) was much more potent as an inhibitor of vasoconstrictor responses to nerve stimulation, noradrenaline and angiotensin.3. PGA(2) and PGE(2) were approximately equal as inhibitors of vasoconstrictor responses to noradrenaline, nerve stimulation and angiotensin; however, PGE(2) was far more potent as a vasodilator.4. Since there is no relationship between the vasodilator and inhibitory effects of PGE(1), E(2) and A(2), and since the inhibitory effect of PGA(2) was present at a time when hindlimb perfusion pressure had returned to control value, it is concluded that the inhibitory action is probably not the result of a physiological antagonism.5. Since each prostaglandin inhibited responses to nerve stimulation and noradrenaline to approximately the same extent and responses to angiotensin were also inhibited, it is suggested that these agents antagonize vasoconstrictor responses by a nonspecific depressant effect on smooth muscle cells.

The effect of prostaglandins on junction potentials in the mouse vas deferens

Low concentrations of prostaglandins E 1 and E 2 (10 −11 g/ml) inhibited contractions of the mouse vas deferens in response to transmural stimulation. Excitatory junction potentials were reduced by low concentrations of prostaglandins E 1 and E 2 without change in the resting membrane potential. Higher concentrations of prostaglandin E 1 and E 2 (10 −5 g/ml) abolished contractions and decreased the resting membrane potential. Prostaglandin F 2α had similar effects but caused depolarisation at 10 −11 g/ml. The inhibitory effects of prostaglandin E 1 and E 2 on nerve induced contractions were antagonized by elevated external calcium concentrations and potentiated by low calcium containing solutions. These results support the view that prostaglandins reduce transmitter output at sympathetic nerve terminals.