Acute anti-inflammatory effects of aspirin and dexamethasone in rats deprived of endogenous prostaglandin precursors

Methanolic leaf exctract of Otostegia integrifolia Benth reduces blood glucose levels in diabetic, glucose loaded and normal rodents

Background

Although the leaves of Otostegia integrifolia traditionally claimed in Ethiopian folklore medicine for management of diabetes mellitus, it has not been validated. The aim of this study was therefore to investigate the antidiabetic activity of Otostegia integrifolia in rodents.

Methods

Male rats or mice were randomly divided into five groups for diabetic, hypoglycemic and glucose tolerance test (OGTT) studies. In all models, group I received Tween 80, 2% v/v, Group II (GL5) treated with 5 mg/kg of glibenclamide and the remaining group: III, IV and V were given the plant extract at doses of 100 mg/kg 200 mg/kg and 400 mg/kg respectively. Blood glucose levels (BGL) were measured by collecting blood samples at different time points. Data was analyzed using one way ANOVA followed by Dunnet’s post hoc test to carry out between and within group comparisons. P < 0.05 was considered as statistically significant.

Results

Inter-group analysis revealed that O. integrifolia at 100 mg/kg and 200 mg/kg reduced the 4^th hour fasting blood BGL significantly (p < 0.001) compared to the control group. The intra-group analysis result has shown O. integrifolia at 200 mg/kg produced a significant (p < 0.05) reduction in BGL at the 1^st, 2^nd, 3rd and 4th hours of post treatment compared to their respective initial levels. Moreover, in the hypoglycemic and OGTT models, O. integrifolia extract at 200 mg/kg, has shown a significant reduction in blood glucose levels compared to negative controls and across all time points.

Conclusion

The crude extract of O. integrifolia has shown significant antidiabetic, hypoglyceamic and oral glucose tolerating effects. The effective dose of the extract was found to be 200 mg/kg in time dependent manner.

Prostaglandin D2 mediates the stimulation of glycogenolysis in the liver by phorbol ester

The tumour-promoting phorbol ester, phorbol 12-myristate 13-acetate (PMA), when added to the perfused liver, stimulates glycogenolysis 2-fold. This stimulation is not seen when aspirin is present in the perfusion medium. In isolated parenchymal liver cells. PMA is not able to stimulate glycogenolysis, suggesting that its effect on glycogenolysis might be indirect and depends on the presence of the non-parenchymal liver cell types. To test the possible operation of an indirect mechanism, we measured the amount of prostaglandin (PG) D2 in liver perfusates. After addition of PMA, the amount of PGD2 is doubled, in parallel with the increase in glycogenolysis. Glycogenolysis in both isolated parenchymal liver cells and perfused liver could be stimulated by the addition of PGD2. Our data indicate that stimulation of glycogenolysis in the liver by PMA may be mediated by non-parenchymal liver cells, which produce PGD2 in response to PMA. Subsequently PGD2 activates glycogenolysis in the parenchymal liver cells. The intercellular communication inside the liver in response to PMA adds a new mechanism to the complex regulation of glucose homoeostasis by the liver.

The formalin test in mice: dissociation between inflammatory and non-inflammatory pain

The formalin test in mice is a valid and reliable model of nociception and is sensitive for various classes of analgesic drugs. The noxious stimulus is an injection of dilute formalin (1% in saline) under the skin of the dorsal surface of the right hindpaw. The response is the amount of time the animals spend licking the injected paw. Two distinct periods of high licking activity can be identified, an early phase lasting the first 5 min and a late phase lasting from 20 to 30 min after the injection of formalin. In order to elucidate the involvement of inflammatory processes in the two phases, we tested different classes of drugs in the two phases independently. Morphine, codeine, nefopam, and orphenadrine, as examples of centrally acting analgesics, were antinociceptive in both phases. In contrast, the non-steroid anti-inflammatory drugs indomethacin and naproxen and the steroids dexamethasone and hydrocortisone inhibited only the late phase, while acetylsalicylic acid (ASA) and paracetamol were antinociceptive in both phases. The results demonstrate that the two phases in the formalin test may have different nociceptive mechanisms. It is suggested that the early phase is due to a direct effect on nociceptors and that prostaglandins do not play an important role during this phase. The late phase seems to be an inflammatory response with inflammatory pain that can be inhibited by anti-inflammatory drugs. ASA and paracetamol seem to have actions independent of their inhibition of prostaglandin synthesis and they also have effects on non-inflammatory pain.

Dietary fish oil reduces progression of established renal disease in (NZB x NZW)F1 mice and delays renal disease in BXSB and MRL/1 strains

Previous studies have shown that dietary marine lipids containing large quantities of n-3 polyunsaturated fatty acids, administered to (New Zealand black X New Zealand white)F1 and MRL-lpr/lpr mice before the development of renal disease, reduce the severity of glomerulonephritis in mice of these strains. The present study demonstrated that delayed administration of a marine lipid diet, 25% menhaden oil (MO) by weight, until after the onset of overt renal disease, also resulted in significant improvement in rates of mortality, proteinuria, and histologic evidence of glomerular injury, compared with control animals fed a diet that contained mostly saturated fatty acids, 25% beef tallow. The MO diet also reduced the histologic severity of renal disease in male BXSB/MpJ and male MRL-lpr/lpr mice. In contrast, necrotizing vasculitis was more frequent in small and medium-sized renal arteries of the MRL-lpr/lpr mice fed MO than in those fed beef tallow (33.4% versus 7.6%, respectively).

Dissociation between antinociceptive and anti-inflammatory effects of acetylsalicylic acid and indomethacin in the formalin test

It is assumed that the mild analgesia produced by acetylsalicylic acid (ASA) and indomethacin is due to a common mode of action, namely inhibition of the cyclo-oxygenase reaction in the synthesis of prostaglandins. It has, however, been difficult to separate the influence of the anti-inflammatory activity from pure analgesia in standard animal tests using a fully developed inflammatory state. In the present experiments a modification of the formalin test in mice is used. Licking of the injected paw is recorded after the injection of a small nociceptive amount of formalin (20 microliters, 1%). The results show that the response to formalin is biphasic with an early (0-5 min) and a late (20-30 min) phase of high licking activity. ASA had a dose-dependent antinociceptive effect during both the early and the late phases. In contrast, antinociceptive effect of indomethacin was found only during the late phase. On the basis of these results it may be suggested that inhibition of the cyclo-oxygenase reaction has no major effect on the early phase in the formalin test. This also suggests that ASA and indomethacin are antinociceptive through partially different modes of action. In addition to an anti-inflammatory effect common to both drugs, ASA may have a direct antinociceptive action.

Prostaglandin biosynthesis is not affected by the anti-inflammatory effect of turpentine

In turpentine-pretreated rats, the development of carrageenan induced oedema is reduced, while dextran and PGE2-induced oedemas are not influenced. In these pretreated rats, carrageenan oedema is potentiated by arachidonic acid, the hypotensive effect of arachidonic acid is not decreased and the production of malonaldehyde by platelets is not inhibited. Thus, the reduction of carrageenan oedema in turpentine treated-rats does not appear to depend on an endogenous PG synthesis inhibition, while plasma level of acute phase reactants is greatly increased.

Effects of dietary enrichment with eicosapentaenoic acid upon autoimmune nephritis in female NZB X NZW/F1 mice

A menhaden oil diet, rich in eicosapentaenoic acid, protected female NZB X NZW/F1 mice from autoimmune nephritis. Only 15% of mice treated with the diet from weaning had died with severe renal disease at 19 months, versus 98% of controls on a beef tallow diet. The menhaden oil also protected these mice from renal disease when instituted at 4 and 5 months of age and, under these conditions, levels of anti-native DNA antibodies were similar in both dietary groups. Our data suggest that the menhaden oil diet may act primarily to reduce inflammation via the ability of eicosapentaenoic acid to alter the production of prostaglandins and leukotrienes.

Influence of dietary restriction and protein deficiency on plasma half-life and tissue distribution of tetracycline in rats

1. The effects of dietary restriction and protein deficiency on plasma half-life and tissue distribution of tetracycline were studied in rats by feeding either a 20% protein diet in restricted quantity or a 9% protein diet ad lib and compared with rats given a 20% protein diet ad lib (control group). 2. It was observed that half-life of tetracycline was shortened and that plasma and tissue Cmin levels at steady-state were lower in undernourished rats. Tissue concentrations in liver, kidney, muscle and bone correlated well with plasma levels. A high degree of correlation was also observed between plasma and tonsillar concentrations of tetracycline in human subjects. 3. These studies indicate that undernourished subjects may require an altered dosage regimen of tetracycline to maintain effective steady-state concentrations of the drug.

Dietary enrichment with the polyunsaturated fatty acid eicosapentaenoic acid prevents proteinuria and prolongs survival in NZB x NZW F1 mice

Prostaglandins and related compounds are active mediators of inflammation, but data concerning their role in the pathogenesis of the glomerulonephritis of New Zealand Black x New Zealand White (NZB x NZW) F1 mice are conflicting. Dietary eicosapentaenoic acid (EPA, C20:5), a fatty acid analogue of arachidonic acid (C20:4), has been shown to impair platelet aggregation in humans, apparently through inhibition of the synthesis of prostaglandins and thromboxanes from arachidonic acid. We report here the effects of a diet high in EPA on the development of renal disease and survival in female NZB x NZW F1 mice. Animals from 4--5 wk of age were fed diets containing 25% lipid, supplied either as beef tallow or menhaden oil, with fatty acid analysis of less than 0.05 and 14.4% EPA, respectively. In the first experiment, by 13.5 mo of age, mice on the beef tallow diet had all (9/9) developed proteinuria and the majority (6/9) had died, with renal histologic examination revealing severe glomerulonephritis. In contrast, none of 10 menhaden oil-fed animals had developed proteinuria, and all were alive at this time (P less than 0.005 for both proteinuria and survival). In a second experiment using 50 mice in each dietary group, 56% of the beef tallow group vs. none of the menhaden oil group had developed proteinuria at 9 mo of age (P less than 0.005). Native DNA binding at 6 mo of age was 23.9 +/- 14.7 vs. 10.1 +/- 9.7% in the beef and menhaden oil groups, respectively (P less than 0.01). Weights were similar in all groups, and there was no evidence of essential fatty acid deficiency in any group. These results demonstrate that a diet high in EPA protects NZB x NZW F1 mice from the development of glomerulonephritis.

Insulin and glucagon secretion in essential fatty acid deficient rats

Insulin and glucagon secretion in response to common secretagogues were ascertained in the perfused pancreas isolated from essential fatty acid deficient rats. The pattern of insulin secretory response to glucose (16.7 mmol/L) by isolated rat pancreas perfused for 30 min was biphasic in EFA-deficient and control rat pancreas. The amplitude of glucose-stimulated acute secretion (phase I) was significantly greater (p less than 0.01) in magnitude and amplitude in EFA-deficient rats than in the control rats. There was no significant difference in the second phase of glucose-stimulated insulin secretion in the two groups. Glucagon secretion in EFA-deficient and control rats was inhibited by glucose (16.7 mmol/l). Glucagon secretion induced by L-arginine (10 mmol/l) was not significantly different in EFA-deficient and in control rat pancreata (p greater than 0.05). However, arginine (10 mmol/l)-stimulated insulin release was significantly higher in EFA-deficient than in control rats. Growth hormone (100 mumol/l)-induced glucagon and insulin secretion was variable in the two groups but significantly higher than basal secretion. The level of L-leucine (10 mmol/l)-stimulated glucagon and insulin secretion in EFA-deficient rats was minimal but significant. Our results show that isolated pancreata of rats devoid of precursors for endogenous prostaglandin synthesis secreted insulin and glucagon in response to common secretagogues. On the basis of our data, it is concluded that endogenous prostaglandins are probably not obligatory for normal secretory functions of islets of Langerhans.

Lack of platelet effect with the aspirin analog, salsalate

Platelet function as determined by platelet aggregation and the release reaction was found to be normal in 8 patients receiving a nonacetylated analog of aspirin, salsalate, while all 5 aspirin controls had abnormal platelet function. Mean bleeding time in patients taking salsalate was less than that in aspirin controls. This study demonstrates that salsalate, which has anti-inflammatory activity and reduces prostaglandin synthesis, does not interfere with normal platelet function.

Evidence that histamine does not participate in carrageenan-induced pleurisy in rat

The injection of carrageenan into the rat pleural cavity provoked an intense inflammatory reaction with the formation of an exudate which contained mainly neutrophils but which was also rich in mast cells and histamine. There was, however, no evidence that histamine participated in the reaction. The mast cells remained intact, and no increase in extracellular histamine levels was observed. Prior treatment with bot H1 and H2 histimine receptor antagonists or depletion of the histamine stores by pretreatment with compound 48/80 did not alter the reaction. In contrast, the exudate formed in response to the intrapleural injection of small doses (0.05 mg/kg) of compound 48/80 was reduced by pretreatment with the antihistamine compounds and, unlike the exudate formed after carrageenan injection, was devoid of neutrophils. Since saline washes of the pleural cavity of untreated rats had histamine and mast cell contents similar to those of the exudates of the carrageenan-treated rats, the source of histamine appeared to be mast cells from the pleural cavity.

Potential therapeutic applications of aspirin and other cyclo-oxygenase inhibitors

1 The ubiquitous actions of the cyclo-oxygenase inhibitors are described. 2 These include the inhibitory effect on prostaglandin synthesis and the direct effect of aspirin on lymphocytes and their ability to produce lymphokines. 3 Aspirin reduces some types of platelet aggregation possibly involving inhibition of the precursors of thromboxane A2 and prostacyclin. 4 The therapeutic implications in relation to transient ischaemic attacks, coronary artery disease and reno-allograft rejection are discussed. 5 The beneficial and adverse effects on the gastro-intestinal tract are described. 6 The effects of aspirin-like drugs on the genito-urinary tract are described with particular reference to their adverse effects on labour and their therapeutic effect on dysmenorrhoea.

Anti-inflammatory and platelet anti-aggregant activity of phospholipase-A2 inhibitors

Mepacrine, papaverine, p-bromophenacyl bromide and 2,3-dibromo(4'-cyclohexyl-3'-chloro)-phenyl-4-oxo-butyric acid (CB 874) inhibit the hydrolysis of phospholipids induced by thrombin in dog platelets. They also exhibit anti-inflammatory and anti-aggregant properties. These biological activities may be explained by a direct or indirect inhibitory action on phospholipase A2. Phospholipase A2 inhibitors may block not only the release of arachidonic acid and its subsequent conversion into prostaglandins but also the formation of lysophospholipids involved in inflammation and/or platelet aggregation.

A comparison of the carrageenan edema test and ultraviolet light-induced erythema test as predictors of the clinical dose in rheumatoid arthritis

Twelve non-steroidal anti-inflammatory agents (NSAI's) and one steroidal anti-inflammatory agent, dexamethasone, were examined in the carrageenan edema test (CET) in the rat and in the ultraviolet light-induced erythema test (UVE) in the guinea pig to evaluate the correlation between those models of inflammation and the clinical dose of the NSAI's in the treatment of rheumatoid arthritis. The regression of the logarithm of the clinical dose with the logarithm of the ED50 for UVE gave a slope of 0.54 implying a non-parallelism of assays and a difference in mechanism. Dexamethasone failed to inhibit the UVE thereby corroborating this point. The parallelism of the logarithm of the clinical dose with the logarithm of the ED50 for the CET was substantially better (slope = 0.86). Dexamethasone was active in CET and its dose would be predicted by the CET regression. When only one variable was used for a prediction, log(CET) was a better predictor of log (clinical dose) than log(UVE). Standard methods for best regression selection indicated that even when both predictor variables were considered, log(CET) alone gave the best regression equation for predicting clinical dose. The view that inhibition of prostaglandin biosynthesis is the primary anti-inflammatory mechanism of NSAI's in rheumatoid arthritis is discussed in terms of these findings.

The use of essential fatty acid deficient rats to study pathophysiological roles of prostaglandins. Comparison of prostaglandin production with some parameters of deficiency

In a retrospective study on essential fatty acid deficient (EFAD) rats used to study pathophysiological roles of prostaglandins (PGs), slight increases in the linoleic acid content of the diet were found to gradually restore the depressed growth rate and to increase the reduced endogenous PG production. These apparently poorly deficient animals had a serum triene tetraene (omega9:omega6) ratio much higher than the value of 0.4 used as a criterion for EFA deficiency by nutritionists. Changes in body weight, serum omega9:omega6 and platelet PG production were not correlated with each other. Feeding rats on a diet containing less than 0.1 mg/g/linoleic acid led to decreasing platelet PG production as the degree of EFA deficiency increased. At this high level of deficiency, a serum omega9:omega6 ratio of 6 or over was achieved. This high ratio may be taken as an indicator of the degree of EFA deficiency required for studies on PG deprivation, but PG production by the tissue investigated or by platelets should preferentially be measured.

The effect of 5,8,11,14-eicosatetraynoic acid on lipid metabolism

The purpose of this presentation is to review the current state of knowledge regarding 5,8,11,14-eicosatetraynoic acid (ETYA, Ro 3-1428) and its effects on lipid metabolism. Accordingly, the topics discussed include hypocholesterolemic and dermatological studies involving ETYA in both animals and man, as well as the effects of ETYA on desaturase enzymes. Metabolic studies involving ETYA are also noted. Primary interest is focused on the effects of ETYA on selected processes of arachidonate metabolism, and the effect of ETYA on inflammation, platelet aggregation and tumor growth are discussed, keeping in mind the relevance of arachidonate metabolism to these processes.

Carrageenan oedema in copper-deficient rats

Carrageenan-induced hind paw oedema has been studied in rats deprived of copper for different lengths of time. A common feature observed in normally fed and copper-deficient rats was the rise of serum copper levels occurring between 10 and 24 h after the injection of the irritant. After 1 month of copper-deficient diet no differences are seen in the oedema developed by controls and copper-deprived animals, while after 3 months the oedema developed by copper-deficient rats was significantly greater compared with the controls.

Aspirin and prostaglandins: some recent developments

The results of experiments designed to test the validity of the hypothesis that the anti-inflammatory and anti-rheumatic actions of aspirin are due to the inhibition of prostaglandin synthetase activity are reviewed.

Effect of fenclofenac on prostaglandin production in carageenin air bleb exudates in rats

Employing a modified carrageenin air bleb technique in rats, the effect was studied of fenclofenac and standard drugs (acetylsalicylic acid, indomethacin and phenylbutazone) on prostaglandin production in inflammatory exudate. In common with the standard drugs, fenclofenac reduced exudate prostaglandin levels, being approximately equipotent with phenylbutazone in this respect. Also, an attempt was made to relate the effect of fenclofenac and standard drugs on prostaglandins to their acute anti-inflammatory activity as determined in a modified carrageenin paw oedema test in rats. Whilst acetylsalicylic acid and phenybutazone significantly inhibited oedema at doses producing 80% inhibition of prostaglandin production in air bleb exudate, fenclofenac and indomethacin did not. The overall results were considered to support the view expressed by other workers that the acute anti-inflammatory activity of acidic anti-inflammatory agents does not result solely, if at all, from inhibition of prostaglandin synthesis.

Inflammatory models in rats depleted of endogenous precursors of prostaglandins

Inflammatory models in rats, depleted of prostaglandin precursors, are discussed as a novel approach to investigate anti-inflammatory drug mechanisms independent of interaction with the production of prostaglandins and to study the ambivalent (pro- or anti-inflammatory) role of endogenous prostaglandins.

The effect of metyrapone on granuloma induced by carrageenan-impregnated sponges in normal and essential fatty acid deficient rats

Treatment of normal rats with metyrapone (20 mg kg-1 day-1, s.c.) for 5 days, starting on the day before implantation, inhibited the production of granuloma, induced by carrageenan-impregnated sponges, determined 8 days after implantation. Exudate volume and prostaglandin (PG) production were unaffected. In essential fatty acid deficient (EFAD) rats, metyrapone did not alter the already existing adrenal hyperplasia due to EFAD and did not affect either granuloma formation or exudate production. The results are discussed in relation to earlier work using adrenalectomy and with regard to the effect of EFA deficiency on adrenal corticosteroid production. It is suggested that metyrapone is a more useful tool than adrenalectomy in studying the role of endogenous corticosteroids.

Prostaglandins and leucocyte migration in inflammatory reactions

The effects of a variety of particulate irritants on the prostaglandin content, protein concentration and the leucocyte counts in the exudate of implanted inert sponges and on the development of paw oedema in the rat have been studied. Variations in prostaglandin accumulation and leucocyte migration were not related but irritants causing a long-standing paw oedema increased both parameters.

Reduced exudation and increased tissue proliferation during chronic inflammation in rats deprived of endogenous prostaglandin precursors

Two models of chronic inflammation were studied in rats deprived of endogenous precursors of prostaglandins by feeding the animals on essential fatty acid deficient (EFAD) food. During kaolin-induced pouch-granuloma, exudate production was markedly reduced in EFAD rats, when compared with normal animals. The exudates from normal rats contained large amounts of PGE, but in the exudates from EFAD rats the amount of PGE was very markedly reduced. Similarly, with carrageenan-impregnated polyether sponges, the exudative component of inflammation was reduced in EFAD rats. However, the proliferative component was significantly increased, particularly in relation to the stunted growth of EFAD rats. Sponge exudates from EFAD rats contained fewer leucocytes than those from normal animals but the fall in leucocyte count was much smaller than the very marked reduction in PGE activity. EFAD rats also exhibited a significant increase in adrenal weights. The results are discussed in the light of the ambivalent (pro- or anti-inflammatory) role of endogenous PGS. It appears that, in the proliferative phase of inflammation, the anti-inflammatory role of PGs is more dominant.

Comparison of the mediator release from platelets and the development of acute inflammation in rats which lack prostaglandin precursors

Rat platelet rich plasma (PRP) generates prostaglandin endoperoxide-like activity, thromboxane A2 (TXA2) and stable prostaglandins (PGs) after collagen addition. Of the stable PGs, PGE is the main product and its formation is related to the dose of collagen. Indomethacin and eicosatetraynoic acid (TYA), both cyclo-oxygenase inhibitors, inhibit TXA2 and PGE formation simultaneously. PRP of essential fatty acid deficient (EFAD) rats, however, generates far less PG-endoperoxide like activity, TXA2 and PGE, though the release of serotonin (5-HT) is unaltered. In normal rats a marked inhibition of the cyclo-oxygenase by TYA also has no effect on 5-HT release. For these 2 reasons the role of PG endoperoxides and TXA2 seems to be unimportant for the 5-HT release reaction. The diminished biosynthesis of PGs and TXA2 in EFAD PRP is not due to an impaired cyclo-oxygenase activity since addition of AA causes an equal formation of PGE in both types of PRP. The use of platelets as in-vitro model for testing anti-inflammatory activity of drugs is discussed. The results, obtained with platelets support the hypothesis that the main reason for the decreased acute inflammatory reaction in EFAD rats is a diminished supply of endogenous PG precursors.