Prostaglandin E2 and gestational hypotension in rabbits

Effects of a COX-2 preferential agent nimesulide on TNBS-induced acute inflammation in the gut

In inflammatory bowel disease, increased production of prostaglandins by cyclooxygenase-2 (COX-2) contributes to bowel dysfunction, inflammatory edema, and hyperemia suggesting that inhibitors of COX-2 may have beneficial effect in gut inflammation. We compared the effects of nimesulide, a preferential COX-2 inhibitor, with those of indomethacin, acetylsalicylic acid (ASA), and dexamethasone in a 24-h model of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis in the rat. TNBS-induced colitis was associated with enhanced COX-2 expression in the gut and increased circulating concentrations of PGE2 metabolite (PGEM). Treatment with nimesulide (10 mg/kg), indomethacin (10 mg/kg), or dexamethasone (1 mg/kg) reduced plasma PGEM concentrations and edema in the inflamed bowel. In addition, nimesulide and dexamethasone treatments decreased neutrophil infiltration into the inflamed colon mucosa. ASA (10 mg/kg) did not have a significant effect on any of these measures of inflammation. None of the studied drugs reduced the size of inflammatory mucosal lesions in the colon. In TNBS-induced acute inflammation of the colon, nimesulide reduced the formation of inflammatory edema, probably by a mechanism related to inhibition of PGE2 production by COX-2 pathway. In addition, nimesulide inhibited neutrophil infiltration into inflamed mucosa mimicking the action of dexamethasone.

Effects of a COX-2 preferential agent nimesulide on TNBS-induced acute inflammation in the gut

In inflammatory bowel disease, increased production of prostaglandins by cyclooxygenase-2 (COX-2) contributes to bowel dysfunction, inflammatory edema, and hyperemia suggesting that inhibitors of COX-2 may have beneficial effect in gut inflammation. We compared the effects of nimesulide, a preferential COX-2 inhibitor, with those of indomethacin, acetylsalicylic acid (ASA), and dexamethasone in a 24-h model of 2,4,6-trinitrobenzenesulfonic acid (TNBS)-induced colitis in the rat. TNBS-induced colitis was associated with enhanced COX-2 expression in the gut and increased circulating concentrations of PGE2 metabolite (PGEM). Treatment with nimesulide (10 mg/kg), indomethacin (10 mg/kg), or dexamethasone (1 mg/kg) reduced plasma PGEM concentrations and edema in the inflamed bowel. In addition, nimesulide and dexamethasone treatments decreased neutrophil infiltration into the inflamed colon mucosa. ASA (10 mg/kg) did not have a significant effect on any of these measures of inflammation. None of the studied drugs reduced the size of inflammatory mucosal lesions in the colon. In TNBS-induced acute inflammation of the colon, nimesulide reduced the formation of inflammatory edema, probably by a mechanism related to inhibition of PGE2 production by COX-2 pathway. In addition, nimesulide inhibited neutrophil infiltration into inflamed mucosa mimicking the action of dexamethasone.

Induction of iNOS in a rat model of acute colitis

Induction of colitis by 2,4,6-Trinitrobenzenesulphonic acid (TNB) in the rat is a widely used experimental model of inflammatory bowel disease. Action of TNB as a hapten, induces colitis involving infiltration of colonic mucosa by neutrophils and macrophages and increased production of inflammatory mediators. The aim of the present study was to measure nitric oxide synthase (NOS) activity and characterize relations between inducible NOS (iNOS) activity and other signs of inflammation in TNB-induced colitis. A profound and sustained increase in the activity of iNOS was found in the colon. The activity of NOS in the spleen was also increased, but remained at low levels as compared to those in colon. No increases in plasma nitrite + nitrate concentrations were found suggesting local rather than systemic induction of iNOS. The increase in iNOS activity in the colon was preceded by macroscopic inflammatory lesions, like hyperemia, ulcerations and edema formation as well as neutrophil accumulation in the gastric mucosa and increased circulating concentrations of PGE2 metabolite (PGEM). Concentrations of PGEM in the plasma and myeloperoxidase activity (MPO; marker of neutrophil infiltration) in the gut declined in 48h whereas increased iNOS activity and the macroscopic inflammatory lesions remained over the 72h follow-up period. The results demonstrate increased local iNOS activity in TNB-Induced colitis mimicking the situation in human inflammatory bowel disease.

Modulation of arachidonic acid metabolism by phenols: relation to their structure and antioxidant/prooxidant properties

The effects of substituted catechols (3-methylcatechol, 4-methylcatechol, 4-nitrocatechol, and guaiacol) and trihydroxybenzenes (pyrogallol, propyl gallate, 1,2,4-trihydroxybenzene, and 1,3,5-trihydroxybenzene) on the synthesis of prostaglandin (PG)E2 and leukotriene (LT)B4 were tested in human A23187-stimulated polymorphonuclear leukocytes. The effects were related to their peroxyl-radical-scavenging (antioxidant), superoxide-scavenging (antioxidant), and superoxide-generating (prooxidant) properties. In general, compounds with hydroxyl groups in the ortho position increased PGE2/LTB4 ratio, and compounds with hydroxyl groups in the meta position decreased PGE2/LTB4 ratio. Catechols, which have hydroxyl groups in the ortho position, were the most potent peroxyl radical and superoxide anion scavengers. Trihydroxybenzenes (pyrogallol, 1,2,4-trihydroxybenzene, and 1,3,5-trihydroxybenzene) generated superoxide, whereas dihydroxybenzenes did not. Thus, the positions and number of hydroxyl groups seem to be the most important properties determining the action of phenolic compounds on PGE2/LTB4 ratio and their antioxidant/prooxidant activities.

Peripheral blood neutrophil leukotriene B4 release and migration in rheumatoid arthritis

The present study was designed to compare peripheral blood neutrophil migration and leukotriene (LT) release between patients with rheumatoid arthritis (RA) and healthy controls and to correlate the neutrophil functions with clinical disease activity. Nineteen patients with moderately active RA and 19 age and sex matched healthy volunteers participated in this study. Isolated peripheral blood neutrophils from RA patients released equal amounts of LTB4 but their random migration was enhanced as compared with neutrophils from healthy controls. LTB4 release in whole blood was significantly lower in samples from RA patients than in those from the healthy volunteers (13.5 +/- 1.4 and 19.1 +/- 1.4 ng/10(6) neutrophils respectively; P < 0.001). LTB4 release from isolated RA neutrophils correlated with the levels of C-reactive protein, duration of morning stiffness and Ritchie articular swelling index. Concentrations of hyaluronate, cyclic AMP and 13, 14-dihydro-15-keto prostaglandin were not different between patients with RA and healthy volunteers. Neither was there any difference in TXB2 production by platelets during blood clotting. In conclusion, peripheral blood neutrophils of RA patients seem to be primed and/or activated as their random migration is enhanced as compared with those of healthy volunteers. In RA, LTB4 release from peripheral blood neutrophils seems to reflect the clinical activity of the disease. However, RA neutrophils released smaller (in whole blood) or equal (isolated cells) amount of LTB4 as compared with the respective controls. These contradictory findings suggest that LTB4 release from peripheral blood neutrophils has no major role in the regulation of disease activity in rheumatoid arthritis.

Prostaglandin-metabolizing enzymes during pregnancy: characterization of NAD(+)-dependent prostaglandin dehydrogenase, carbonyl reductase, and cytochrome P450-dependent prostaglandin omega-hydroxylase

Prostaglandins E2 and F2 alpha regulate a number of physiological functions in reproductive tissues, and concentrations of these bioactive modulators increase during pregnancy. Corresponding to the increase in circulating levels of prostaglandins during pregnancy is an increase in enzymes that metabolize these agents. Three prostaglandin-metabolizing enzymes induced during pregnancy are NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH), NADPH-dependent carbonyl reductase, and cytochrome P450-dependent prostaglandin omega- or 20-hydroxylase. This review discusses the biochemical properties, regulation, and possible functions of these three enzymes.

Noradrenaline and dopamine infusions modulate arachidonic acid cyclooxygenase and 5-lipoxygenase pathways ex vivo in man

We have previously demonstrated that adrenaline infusion increases the thromboxane/leukotriene (TX/LT) ratio in whole blood in healthy volunteers. The aim of the present study was to see whether other catecholamines--noradrenaline and dopamine--are also capable of modulating arachidonic acid (AA) metabolism in man. Low doses of noradrenaline (0.025 microgram/kg/min) and dopamine (3.0 micrograms/kg/min), which did not change hemodynamics, were infused for 60 min into healthy male volunteers. Both dopamine and noradrenaline decreased TX synthesis stimulated by spontaneous clotting, but no remarkable effect was seen when calcium ionophore A23187 was used as a stimulus. Dopamine but not noradrenaline increased prostaglandin E2 (PGE2) synthesis in A23187-stimulated whole blood. They both marginally decreased LTB4 formation in A23187-stimulated whole blood. The findings indicate that not only adrenaline but also noradrenaline and dopamine modulate AA metabolism in man.

Effects of Trolox C and SIN-1 on arachidonic acid metabolism and on cyclic GMP formation in leukocytes

The effects of Trolox C (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid), a vitamin E analogue, (60-900 microM) and SIN-1 (3-morpholino sydnonimine), a nitric oxide donor, (30-3000 microM) on arachidonic acid metabolism and on cyclic GMP formation in calcium ionophore A23187 (calcimycin)-stimulated human polymorphonuclear leukocytes were investigated. Trolox C elicited a dose dependent decrease in leukotriene B4 levels and increase in prostaglandin E2 levels but did not affect cyclic GMP levels. SIN-1 dose dependently inhibited leukotriene B4 and stimulated prostaglandin E2 and cyclic GMP formation. Dibutyryl cyclic GMP did not affect the formation of leukotriene B4 and prostaglandin E2. Trolox C (180 microM), which itself had no effect on cyclic GMP levels, enhanced the effect of SIN-1 (100 microM) on cyclic GMP levels more than 5-fold. The effects of SIN-1 on arachidonic acid metabolism seem to be independent of cyclic GMP and are probably due to nitric oxide. In this experimental model both Trolox C and SIN-1 have similar actions on the prostaglandin/leukotriene ratio, and Trolox C potentiates the SIN-1-induced increase in cyclic GMP levels.

Effects of prostaglandin inhibition on the renal function curve during ovine pregnancy

OBJECTIVE

This study was designed to assess the influence of prostaglandins on the steady-state relationship of mean arterial pressure and urinary sodium excretion.

STUDY DESIGN

Ten nonpregnant and nine pregnant ewes were chronically prepared with indwelling catheters and maintained in metabolism cages. All the ewes received a continuous intravenous infusion of indomethacin (5 mg/kg/day) for 24 days. Step increases in sodium intake (20, 100, 400, and 1200 mmol per day), each maintained for 6 days, were administered as a fixed dietary (20 mmol) component with the balance infused intravenously. Mean arterial pressure was continuously monitored. The renal function curves were constructed from the steady-state mean arterial pressure-urinary sodium excretion relationships after sodium balance was attained.

RESULTS

Indomethacin inhibited urinary excretion of prostaglandin E2 by 62% +/- 4% in nonpregnant and 47% +/- 6% in pregnant ewes, and 6 keto-prostaglandin F1 alpha, the stable metabolite of prostaglandin I2, by 55% +/- 4% and 65% +/- 6% in nonpregnant and pregnant ewes, respectively. Blood volume was not affected by indomethacin or salt in either group. Plasma angiotensin II was suppressed less in pregnant ewes (60% vs 80%) by increases in salt intake. Chronic treatment with indomethacin did not alter the renal function curves of either nonpregnant or pregnant ewes.

CONCLUSIONS

These results suggest that prostaglandins do not influence the steady-state relationship between mean arterial pressure and urinary sodium excretion in either nonpregnant or pregnant sheep.

Modulation of arachidonic acid metabolism by phenols: relation to positions of hydroxyl groups and peroxyl radical scavenging properties

We have shown earlier that catecholamines have opposite regulative effects on prostaglandin (PG)E2 and leukotriene (LT)B4 formation with a receptor-independent mechanism in human polymorphonuclear leukocytes (PMNs) and whole blood. To shed further light on the mechanisms involved and structure-action relationship, we tested the effects of phenols (catechol, hydroquinone, phenol, and resorcinol) on the synthesis of PGE2 and LTB4 in human A23187-stimulated PMNs. To study the mechanism of how phenols influence PGE2 and LTB4 synthesis, their peroxyl radical-scavenging properties were analyzed. In general, low concentrations of phenols stimulated (catechol > hydroquinone >> phenol) and high concentrations inhibited (resorcinol > catechol > hydroquinone > phenol) PGE2 formation. Resorcinol was different from the other phenols: It did not stimulate PGE2 synthesis at all, but it was effective inhibitor at high concentrations. Phenols had only an inhibitory effect on LTB4 formation (catechol = hydroquinone >> phenol > resorcinol). The order of both stochiometric factors and reactivities of phenols for scavenging peroxyl radicals was catechol > hydroquinone > resorcinol >> phenol. According to these results, phenols having hydroxyl groups in ortho- or paraposition have the greatest stimulative effect on PGE2 synthesis, the highest inhibitory action on LTB4 synthesis, and are good antioxidants. Resorcinol, having hydroxyl groups in the metaposition, behaves differently. It neither stimulates PGE2 nor inhibits LTB4 formation, but it is the most potent inhibitor of PGE2 formation. In spite of resorcinol's two hydroxyl groups, it mimics as an antioxidant phenol more than catechol and hydroquinone.

Increased peripheral resistance during reduced uterine perfusion pressure hypertension in pregnant rabbits

The role of an increase in total peripheral resistance (TPR) and the contribution of angiotensin II (ANG II) to the hypertension induced by reduced uterine perfusion pressure (RUPP) was explored in pregnant rabbits. On the 22nd day of gestation, a catheter and a microthermocouple were placed in the aorta to measure mean arterial pressure (MAP) and cardiac output (CO), respectively. Three days later, RUPP was induced by a clip on the aorta proximal to the ovarian and distal to the renal arteries. Mean arterial pressure distal to the clip (uterine perfusion pressure) was reduced to 56 +/- 8% (mean +/- SD) of the initial level. Twenty-four hours later, MAP rose from 65 +/- 3 to 84 +/- 11 mm Hg; CO index decreased from 207 +/- 18 to 169 +/- 27 ml/min/kg; and TPR index increased from 0.32 +/- 0.03 to 0.51 +/- 0.08 mm Hg kg/ml/min, respectively (n = 7, all p less than 0.01). Sham-operated pregnant rabbits (n = 7) and non-P rabbits (n = 5) with a comparable distal aortic pressure reduction experienced no change in MAP or CO. Infusion of a receptor antagonist of angiotensin II (Sar1,Ile8-Ang II, 1 microgram/kg/min for 20 min) decreased MAP in sham-operated pregnant rabbits from 64 +/- 6 to 54 +/- 6 mm Hg (p less than 0.01) but did not change MAP in RUPP hypertensive rabbits (86 +/- 9 mm Hg before and 87 +/- 8 at the end of infusion, n = 6). These data indicate that RUPP in pregnant rabbits leads to a high resistance form of hypertension in which the formation of Ang II is not increased.