Corticosteroids inhibit prostaglandin release from perfused mesenteric blood vessels of rabbit and from perfused lungs of sensitized guinea pig

Infusion of norephinephrine (NE) (1 – 3 μg/ml/min) into the isolated mesenteric vascular preparation of rabbit resulted in a rise in perfusion pressure, which was associated with the release of a prostaglandin E-like substance (PGE) at a concentration of 2.81 ± 0.65 ng/ml in terms of PGE₂. Indomethacin (3 μg/ml) abolished the NE-induced release of PGE. Arachidonic acid (0.2 μg/ml) in the presence of indomethacin did not restore the NE-induced release of PGE. Hydrocortisone (10 – 30 μg/ml) and dexamethasone (2 – 5 μg/ml) also inhibited the NE-induced release of PGE. The inhibitory action of both corticosteroids was abolished by arachidonic acid (0.2 μg/ml). Antigen-induced release of a prostaglandin-like substance(PGs) (43.1 ± 3.8 ng/ml in terms of PGE₂ and a rabbit aorta contracting substance (RCS) from perfused lungs of sensitized guinea pigs was completely abolished by indomethacin (5 μg/ml) or by hydrocortisone (100 μg/ml). Indomethacin, however, increased histamine release up to 280% of the control level, which was 470 ± 54 ng/ml, while hydrocortisone diminished histamine release down to 30% of the control level. A superimposed infusion of arachidonic acid (1 μg/ml) into the pulmonary artery reversed the hydrocortisone-induced blockade of the release of RCS and PGs. It may be concluded that corticosteroids neither inhibit prostaglandin synthetase nor influence prostaglandin transport through the membranes but they do impair the availability of the substrate for the enzyme.     

Corticosteroids inhibit prostaglandin release from perfused mesenteric blood vessels of rabbit and from perfused lungs of sensitized guinea pig

Infusion of norephinephrine (NE) (1 – 3 μg/ml/min) into the isolated mesenteric vascular preparation of rabbit resulted in a rise in perfusion pressure, which was associated with the release of a prostaglandin E-like substance (PGE) at a concentration of 2.81 ± 0.65 ng/ml in terms of PGE₂. Indomethacin (3 μg/ml) abolished the NE-induced release of PGE. Arachidonic acid (0.2 μg/ml) in the presence of indomethacin did not restore the NE-induced release of PGE. Hydrocortisone (10 – 30 μg/ml) and dexamethasone (2 – 5 μg/ml) also inhibited the NE-induced release of PGE. The inhibitory action of both corticosteroids was abolished by arachidonic acid (0.2 μg/ml). Antigen-induced release of a prostaglandin-like substance (PGs) (43.1 ± 3.8 ng/ml in terms of PGE₂ and a rabbit aorta contracting substance (RCS) from perfused lungs of sensitized guinea pigs was completely abolished by indomethacin (5 μg/ml) or by hydrocortisone (100 μg/ml). Indomethacin, however, increased histamine release up to 280% of the control level, which was 470 ± 54 ng/ml, while hydrocortisone diminished histamine release down to 30% of the control level. A superimposed infusion of arachidonic acid (1 μg/ml) into the pulmonary artery reversed the hydrocortisone-induced blockade of the release of RCS and PGs. It may be concluded that corticosteroids neither inhibit prostaglandin synthetase nor influence prostaglandin transport through the membranes but they do impair the availability of the substrate for the enzyme.     

Corticosteroids inhibit prostaglandin release from perfused mesenteric blood vessels of rabbit and from perfused lungs of sensitized guinea pig.

Infusion of norephinephrine (NE) (1 - 3 mug/ml/min) into the isolated mesenteric vascular preparation of rabbit resulted in a rise in perfusion pressure, which was associated with the release of prostaglandin E-like substance (PGE) at a concentration of 2.81 +/- 0.65 ng/ml in terms of PGE2. Indomethacin (3 mug/ml) abolished the NE-induced release of PGE. Arachidonic acid (0.2 mug/ml) in the presence of indomethacin did not restore the NE-induced release of PGE. Hydrocortisone (10 - 30 mug/ml) and dexamethasone (2 - 5 mug/ml) also inhibited the NE-induced release of PGE. The inhibitory action of both corticosteroids was abolished by arachidonic acid (0.2 mug/ml). Antigen-induced release of a prostaglandin-like substance (PGs) (43.1 +/- 3.8 ng/ml in terms of PGE2 and a rabbit aorta contracting substance (RCS) from perfused lungs of sensitized guinea pigs was completely abolished by indomethacin (5 mug/ml) or by hydrocortisone (100 mug/ml). Indomethacin, however, increased histamine release up to 280% of the control level, which was 470 +/- 54 ng/ml, while hydrocortisone diminished histamine release down to 30% of the control level. A superimposed infusion of arachidonic acid (1 mug/ml) into the pulmonary artery reversed the hydrocortisone-induced blockade of the release of RCS and PGs. It may be concluded that corticosteroids neither inhibit prostaglandin synthetase nor influence prostaglandin transport through the membranes but they do impair the availability of the substrate for the enzyme.     

Effects of zomepirac and indomethacin on renal blood flow and electrolyte excretion in anesthetized monkeys

Zomepirac sodium is a new inhibitor of prostaglandin cyclooxygenase with an $\text{in vitro}$ potency equivalent to indomethacin. Since inhibitors of prostaglandin synthesis have marked effects on renal hemodynamics, zomepirac may be expected to reduce renal blood flow (RBF) in a manner similar to indomethacin. This study compares the effects of zomepirac and indomethacin on RBF and electrolyte excretion in anesthetized Rhesus monkeys. Each experiment consisted of a control period followed by 3 or 4 drug treatment periods in which increasing doses of zomepirac (0.5 to 20 mg/kg) or indomethacin (0.5 to 10 mg/kg were given. Indomethacin (5 mg/kg) reduced RBF by 22% and the higher dose (10 mg/kg) reduced RBF by an additional 13%. Zomepirac had little effect on RBF in doses as high as 20 mg/kg. At any given dose the mean plasma concentration of zomepirac was equal to or greater than indomethacin. Peak indomethacin concentration was 48 μg/ml after the 10 mg/kg dose while the peak zomepirac, after 20 mg/kg, was 158 μg/ml. Neither drug had a significant effect on either glomerular filtration rate or excretion rate of sodium or potassium. Thus, zomepirac had only minimal effects on RBF while indomethacin decreased RBF of anesthetized monkeys in a manner qualitatively similar to its effect in other species. The minimal renal effects caused by zomepirac relative to indomethacin in this primate may indicate a therapeutic advantage for zomepirac in man.     

Comparison of the effect of nonsteroidal and steroidal antiinflammatory agents on prostaglandin production during ovulation in the rabbit

The antiinflammatory agents diclofenac, fenoprofen and aspirin were tested to determine how well they inhibit the pre-ovulatory elevation in prostaglandin (PG) production in rabbit follicles in comparison to indomethacin. In addition, the antiinflammatory agent dexamethasone and the antipyretic agent acetaminophen were tested. The agents were administered 8 h after the ovulatory process was stimulated by hCG (50 I.U./kg). At 10 h after hCG (i.e., at the expected time of ovulation) control follicles had PGF and PGE levels of 370.0 and 582.6 pg/mg of follicle, respectively. Diclofenac inhibited PG production the most-reducing PGF and PGE to 22.8 and 53.6 pg/mg, respectively. Indomethacin reduced the PGF and PGE levels to 27.4 and 76.6 pg/mg, respectively. Fenoprofen was less effective, reducing the PGF and PGE to 77.8 and 222.4 pg/mg, respectively. Aspirin reduced the PGF and PGE to 123.4 and 174.6 pg/mg, respectively. Dexamethasone and acetaminophen did not inhibit PG production. Ovulation was completely inhibited by diclofenac and indomethacin, partially inhibited by fenoprofen, and unaffected by aspirin, acetaminophen, or dexamethasone. The results suggest that any potent antiinflammatory agent can inhibit ovulation provided it adequately reduces PG production; whereas antiinflammatory agents are ineffective. The anti-inflammatory agent must completely abolish the preovulatory elevation in PGs in mature follicles in order to totally inhibit ovultion.     

An Ex Vivo Method for Evaluating Prostaglandin Synthetase Activity in Cortical Slices of Mouse Brain

The release of prostaglandin E2 (PGE2) from cortical slices of mice into incubation medium is followed for 3 h and compared to PGE2 levels in the corresponding slice. Immediately after decapitation, the rate of PGE2 released into the incubation medium is elevated and a steady low rate of spontaneous release is gained within 1-2 h of incubation. PGE2 synthesis and release is blocked in a dose-dependent manner by either indomethacin (3 X 10(-6) -3 X 10(-4) M) or flufenamic acid (2.6 X 10(-6) M) either when added in vitro or administered in vivo. Full recovery of PGE2 synthesis is reached after 3 h incubation of slices following in vivo administration of indomethacin. In vivo administration of flufenamic acid results in prolonged inhibition of PGE2 released in vitro. The inhibition of PGE2 released by indomethacin is also correlated with the slice PGE2 content. Administration of lipopolysaccharide (LPS), a known activator of phospholipase A2, results in a fivefold increase in PGE2 and a twofold increase in 6-keto-PGF1 alpha released into the medium. The release of thromboxane B2 is not affected by LPS.     

Functional disturbances in brain following injury

It was shown previously that local cerebral glucose utilization is less than 50% of normal in all cortical areas of rat brain 3 days following a focal freeze-lesion and that this effect of trauma is significantly diminished by dexamethasone (0.25 mg/Kg/day), and by indomethacin (7.5 mg/Kg single dose). To elucidate the mechanism of action of steroids and non-steroidal antiinflammatory drugs in traumatized brain, the effects of dexamethasone and indomethacin on arachidonic acid release, malondialdehyde production and prostaglandin synthesis in the lesion area were investigated. Five seconds after a freezing lesion arachidonic acid was significantly increased in the lesion area of untreated animals. Neither dexamethasone nor indomethacin had any effect on this release. The thiobarbituric acid reaction, as an estimate of malondialdehyde and non-enzymatic free radical lipoperoxide formation from unsaturated free fatty acids showed no change in the control and lesion areas of untreated and both dexamethasone and indomethacin treated groups. There was a marked increase in PGF2 alpha, PGE2, PGD2 in the lesion area of untreated animals. Indomethacin prevented the formation of prostaglandins by more than 90% while dexamethasone had no effect. These results suggest that some components of the arachidonic acid metabolism must be involved in functional disturbances resulting from trauma while steroid action is mediated in injured brain independently from the prostaglandin cascade.     

Estradiol effect on indomethacin and prostaglandin E2-modulation of adrenergic transmission in rabbit oviduct.

The effect of prostaglandin E2 /PGE2/ and indomethacin on 3H-noradrenaline (3H-NA) release- and on contractions-evoked by field electrical stimulation (FES) was studied in vitro in oviductal isthmus of mature rabbits (untreated and treated with estradiol). FES evoked guanethidine-sensitive contractions and calcium-dependent tritium overflow, which reflected 3H-NA overflow. Marked and concentration-dependent decrease of FES-evoked contractions by PGE2 (0.1-100 nM) was observed in both groups of animals. The inhibitory effect of PGE2 was more pronounced in estradiol treated animals (IC50 1.5 nM, n = 9) than in untreated animals (IC50 18 nM, n = 6). Indomethacin, 1 microM, induced a remarkably pronounced increase of FES-evoked contractions in estradiol treated (by 57.3 +/- 6.3%, n = 8) in comparison with untreated rabbits (21.4 +/- 3.8%, n = 7). The amount of FES-evoked release of tritium was significantly higher in untreated than in estradiol treated rabbits. PGE2 decreased and indomethacin increased tritium-evoked release. The effects of PGE2 and indomethacin on tritium-evoked release showed no estradiol dependence. The competitive results of PGE2 and indomethacin on both evoked contraction and 3H-NA release suggest that endogenous prostaglandin E2 takes part in modulation of adrenergic mediated contraction and that estradiol enhanced the prostaglandin effect.     

Action of luteinizing hormone-releasing hormone and synthesis of prostaglandin in the pituitary gland.

The possibility that prostaglandin E2 (PGE2) may play a role in luteinizing hormone (LH) release was examined using an in vitro model. Addition of luteinizing hormone-releasing hormone (LH-RH) to the culture medium stimulated cyclic AMP accumulation and LH-release by incubated hemipituitaries, but did not affect the level of PGE2 or prostaglandin synthetase activity in the gland. Aspirin and indomethacin reduced both prostaglandin synthetase activity and PGE2 or prostaglandin synthetase activity in the gland. Aspirin and indomethacin reduced both prostaglandin synthetase activity and PGE2 content in the pituitary, but did not impair the stimulatory action of LH-RH on either cyclic AMP accumulation or LH-release. Flufenamic acid on its own caused LH-release, but the drug abolished the effect of LH-RH on cyclic AMP accumulation. The mechanism of this action of flufenamic acid is not understood. It is concluded that the stimulatory action of LH-RH on pituitary cyclic AMP production and LH release is not mediated by prostaglandins.     

Detection of regional ischemia in perfused beating hearts by phosphorus nuclear magnetic resonance.

Rat Graafian follicles isolated intact responded to 8-Br-cyclic GMP (0.3 and 1.0 mM) with increased prostaglandin E (PGE) production (4-fold and 8-fold, respectively) during a 6 h incubation. The effect of 8-Br-cyclic GMP was noted after a lag period of 2–4 h. 8-Br-cyclic AMP (1.0 mM) also stimulated PGE production (4-fold increase), while 8-Br-cyclic IMP, 8-Br-5′GMP and 8-Br-5′AMP were inactive in this respect. Actinomycin D (10 μg/ml) and cycloheximide (10 μg/ml) given simultaneously with 8-Br-cyclic GMP prevented the stimulatory effect of the cyclic nucleotide. The results suggest that cyclic GMP induces de novo synthesis of a macromolecular component of the ovarian prostaglandin synthetase system, and that this cyclic nucleotide, along with cyclic AMP, may play a role in the known stimulatory action of luteinizing hormone on follicular prostaglandin production.     

Dissociation of hyperreninemia and renal prostaglandin synthesis in the adrenalectomized rat

The aim of this study was to determine whether hyperreninemia in the adrenalectomized (ADX) rat is dependent on renal prostaglandin synthesis, as has been suggested for two other hyperreninemic conditions, Bartter's syndrome and chronic liver disease. Plasma renin concentration (PRC) in anesthetized, ADX rats was significantly increased (delta +480%; p less than 0.001) compared to sham-operated controls. In vivo, indomethacin (10 mg/kg i.v.) significantly reduced PRC of anesthetized, ADX rats after both 45 min (delta -34%; p less than 0.05) and 90 min (delta -47%; p less than 0.05). In vitro renin release from renal cortical slices of ADX rats was also significantly greater (delta +130%; p less than 0.05) than from sham-operated control cortical slices. Renin release from cortical slices of ADX rats given dexamethasone (10 micrograms/kg/day) for 4 days prior to sacrifice did not differ from sham-operated control values. Prostaglandin E2 (PGE2) release from cortical slices of ADX rats did not differ significantly from controls. However, PGE2 synthesis in glomeruli microdissected from ADX rats was significantly increased (delta +110%; p less than 0.001) compared to controls. PGE2 synthesis in glomeruli of dexamethasone-treated ADX rats remained significantly elevated compared to controls. Ibuprofen (10(-6) M) decreased PGE2 synthesis in cortical slices by 80%. However, prostaglandin synthesis inhibition had no effect on renin release from either ADX or control renal cortical slices. These results suggest that despite increased glomerular synthesis, prostaglandins do not directly influence renin release in the ADX rat.     

Regulation of leptin release and lipolysis by PGE2 in rat adipose tissue

The role of eicosanoids formed by adipose tissue from rats was examined in the presence of the specific cyclooxygenase-2 inhibitor NS-398. This agent totally blocked the release of prostaglandin E2 (PGE2) by rat adipose tissue over a 24-h incubation in primary culture. The final concentration of PGE2 after 24 h was 12 nM, and half-maximal inhibition of PGE2 formation required 35 nM NS-398. While inhibition of PGE2 formation by NS-398 had no effect on basal leptin release or lipolysis, it enhanced the lipolytic action of 10 nM isoproterenol by 36%. The in vivo administration of PGE2 doubled serum leptin. PGE2 also directly stimulated leptin release by rat adipose tissue incubated in the presence of 25 nM dexamethasone, which inhibited endogenous PGE2 formation by 94%. The inhibition of lipolysis as well as the stimulation of leptin release by PGE2 were mimicked by N6-cyclopentyladenosine (CPA). These data indicate that exogenous PGE2 can stimulate leptin release by adipose tissue when the basal formation of PGE2 is blocked by dexamethasone. However, while the endogenous formation of PGE2 does not appear to regulate basal lipolysis or leptin release, it may play a role in the activation of lipolysis by catecholamines.     

Effects of prostaglandins on adrenal steroidogenesis in the rat

To elucidate the role of prostaglandins in adrenal steroidogenesis, we studied aldosterone and corticosterone responses to 3 x 10(-8) M--3 x 10(-4) M of prostaglandin E2 (PGE2), prostaglandin F2 alpha (PGF2 alpha), prostacyclin (PGI2), and arachidonic acid (AA) in collagenase dispersed rat adrenal capsular and decapsular cells. Whereas adrenocorticotrophic hormone (ACTH) and angiotensin II (AII) stimulated aldosterone production in capsular cells and ACTH stimulated corticosterone production in decapsular cells in a dose dependent fashion, aldosterone and corticosterone production were not stimulated significantly by PGE2, PGF2 alpha, PGI2, and AA. Although preincubation of dispersed adrenal cells with indomethacin (3 x 10(-5) M) markedly inhibited PGE2 synthesis, ACTH- and AII-stimulated aldosterone production and ACTH-stimulated corticosterone production were not attenuated despite prostaglandin blockade. These results indicate that prostaglandins are unlikely to play an important role in adrenal steroidogenesis.     

Anti-inflammatory effects of Houttuynia cordata supercritical extract in carrageenan-air pouch inflammation model

Anti-inflammatory effects of Houttuynia cordata supercritical extract (HSE) were investigated in rat carrageenan-air pouch model. Oral administration of HSE (50-200 mg/kg) suppressed carrageenan-induced exudation and albumin leakage, as well as inflammatory cell infiltration at a high dose (200 mg/kg). Intraperitoneal injection of dexamethasone (2 mg/kg) only decreased exudation and cell infiltration, while indomethacin (2 mg/kg, i.p.) reduced exudate volume and albumin content without influence on the cell number. HSE lowered tumor-necrosis factor-α (TNF-α) and nitric oxide (NO), as well as prostaglandin E(2) (PGE(2)). Dexamethasone only reduced TNF-α and NO, while indomethacin decreased PGE(2). The results indicate that HSE exhibits anti-inflammatory effects by inhibiting both TNF-α-NO and cyclooxygenase-2-PGE(2) pathways.     

The unfolding and attempted refolding of mitochondrial aspartate aminotransferase from pig heart.

The role of prostaglandins in the regulation of muscle protein breakdown is controversial. We examined the influence of arachidonic acid (5 microM), prostaglandin E2 (PGE2) (2.8 microM) and the prostaglandin-synthesis inhibitor indomethacin (3 microM) on total and myofibrillar protein breakdown in rat extensor digitorum longus and soleus muscles incubated under different conditions in vitro. In other experiments, the effects of indomethacin, administered in vivo to septic rats (3 mg/kg, injected subcutaneously twice after induction of sepsis by caecal ligation and puncture) on plasma levels and muscle release of PGE2 and on total and myofibrillar protein breakdown rates were determined. Total and myofibrillar proteolysis was assessed by measuring production by incubated muscles of tyrosine and 3-methylhistidine respectively. Arachidonic acid or PGE2 added during incubation of muscles from normal rats did not affect total or myofibrillar protein degradation under a variety of different conditions in vitro. Indomethacin inhibited muscle PGE2 production by incubated muscles from septic rats, but did not lower proteolytic rates. Administration in vivo of indomethacin did not affect total or myofibrillar muscle protein breakdown, despite effective plasma levels of indomethacin with decreased plasma PGE2 levels and inhibition of muscle PGE2 release. The present results suggest that protein breakdown in skeletal muscle of normal or septic rats is not regulated by PGE2 or other prostaglandins.     

Adenosine as a natural prostaglandin antagonist in vascular smooth muscle

Adenosine has actions on smooth muscle similar to those of prostaglandin (PG) antagonists. Like some PG antagonists it is a phosphodiesterase inhibitor and seems to interfere with calcium effects. It has agonist/antagonist interactions with theophylline, a PG antagonist. In rat mesenteric vascular smooth muscle adenosine blocked responses to noradrenaline which depend on release of intracellular calcium but not those to potassium ions which depend on calcium entry from extracellular fluid. Partial inhibition of endogenous PG synthesis by indomethacin enhanced the adenosine effect. In preparations in which vascular reactivity had been abolished by indomethacin and then partly restored by 1 or 5 ng/ml PGE2, adenosine also inhibited responses to noradrenaline: the curve for the 5 ng/ml PGE2 concentration was to the right of and parallel to the 1 ng/ml curve consistent with a competitive interaction between adenosine and PGE2. Similar interactions between adenosine and PGE2 were shown in human lymphocytes in which activation also depends on calcium release. These findings suggest how calcium-dependent metabolic responses may be controlled and indicate further reasons for caution in the interpretation of cyclic AMP experiments.     

Studies on the cyclic AMP response to prostaglandin in human lymphocytes

It is generally thought that cyclic AMP acts as the second messenger for prostaglandin E in human lymphocytes. We have recently found that the mitogen-induced proliferation of human lymphocytes is no longer inhibited by PGE₂ if the lymphocytes are preincubated overnight prior to the addition of mitogens and PGE₂. In this paper we report that lymphocytes also lose their cyclic AMP response to mitogens after preincubation. The loss of sensitivity to PGE with preincubation can be blocked by cyclohexamide (25 μg/ml). Indomethacin (1 μg/ml) partially blocked the loss of sensitivity, but removal of the glass-adherent cells did not. Since either manipulation effectively stops prostaglandin production in the preincubation cultures, it would appear that indomethacin prevented the loss of sensitivity to PGE₂ by a mechanism other than inhibition of PG synthetase. The addition of phytohemagglutinin to the preincubation cultures also blocked the loss of sensitivity to PGE₂.