Arachidonic acid-induced inflammation: inhibition by dual inhibitor of arachidonic acid metabolism, SK&F 86002

The antiinflammatory activity of the structurally novel dual inhibitor of arachidonic acid metabolism, SK&F 86002 was evaluated using arachidonic acid-induced edema and inflammatory cell infiltration. Histological examination demonstrated extensive subcutaneous edema and neutrophil (PMN) accumulation in perivascular and interstitial locations one hour after application of arachidonic acid to the ear. SK&F 86002 and, to a lesser extent, phenidone demonstrated potent inhibition of this inflammatory response following oral and topical administration. Nordihydroguaiaretic acid (NDGA) displayed only topical activity. The selective cyclooxygenase inhibitors ibuprofen and naproxen were either inactive or stimulated ear swelling. Histological evaluation of the lesion in drug-treated animals revealed that SK&F 86002 impaired edema formation and caused a significant reduction in numbers of infiltrating neutrophils. Using arachidonic acid-induced peritoneal exudation, a reduction in the cellular infiltrate was observed after oral treatment with SK&F 86002 or phenidone, but not with naproxen. Taken together, these data illustrate the potent antiinflammatory effects of SK&F 86002 and support the suggestion that 5-lipoxygenase products play a significant role in both the edematous and cellular phases of arachidonic acid-induced inflammation.

N-ethylmaleimide inhibits Ca2+ influx induced by collagen or arachidonate on rabbit platelets

N-Ethylmaleimide dose dependently inhibited platelet aggregation induced by collagen or arachidonate but did not inhibit the aggregation by thrombin or ionophore A23187 within the concentrations tested. [3H]Arachidonate release from membrane phospholipids of the collagen-stimulated platelets was inhibited by N-ethylmaleimide in parallel with the inhibition of aggregation, but not in response to A23187. N-Ethylmaleimide prevented 45Ca2+ influx into platelet cells from outer medium induced by collagen, and also inhibited the increase in the concentration of cytoplasmic free Ca2+, which probably results from Ca2+ influx, as monitored by quin2 fluorescence, under stimulation with arachidonate. The concentration of N-ethylmaleimide giving a complete inhibition of Ca2+ influx was consistent with that required to inhibit collagen- or arachidonate-induced aggregation. Prostaglandin metabolism from arachidonate to thromboxane A2 was not disturbed by N-ethylmaleimide, while phosphatidate formation induced by arachidonate was slightly inhibited by it at concentrations at which aggregation was completely inhibited. These data suggest that N-ethylmaleimide preferentially suppresses increase in cytoplasmic free Ca2+ which is linked to thromboxane A2-receptor occupation in collagen- or arachidonate-stimulated platelets, probably due to blockage of Ca2+ influx through Ca2+-channel protein, thereby inhibiting aggregation induced by these agonists.

A novel synthetic vitamin A-like compound (a polyprenoic acid derivative, E-5166) inhibits the release of arachidonic acid stimulated by epidermal growth factor

Little is known about the mechanisms of anti-inflammatory activity of retinoids. A new synthetic vitamin A-like compound (polyprenoic acid derivative, E-5166) has a strong in vitro binding affinity to intracellular binding proteins for acidic retinoids. In order to elucidate the anti-inflammatory activity of E-5166, we studied the effect of E-5166 on the epidermal growth factor (EGF)-stimulated arachidonic acid (AA) release of pig epidermis. E-5166 significantly inhibited the EGF-stimulated AA release and this inhibitory effect of E-5166 required a longer incubation than hydrocortisone did. Furthermore, E-5166 inhibited the EGF-stimulated phosphatidylinositol (PI) turnover of pig epidermis. These results indicate that E-5166 inhibited the EGF-stimulated AA release through the inhibition of the EGF-stimulated PI turnover.

Beneficial effects of ibuprofen in oleic acid induced lung injury

Metabolites of arachidonic acid, particularly thromboxanes, have been implicated as mediators of lung injury. The formation of thromboxane A2 can be decreased by glucocorticoid steroids by inhibiting the enzyme phospholipase A2 or by ibuprofen which inhibits fatty acid cyclooxygenase. This study was performed to determine if ibuprofen, methylprednisolone, or a combination of both could improve the pulmonary injury induced by oleic acid. Five groups of dogs were instrumented with pulmonary artery and extravascular lung water (EVLW) catheters and ventilated with 100% O2. Serial determinations of hemodynamic and pulmonary parameters were performed before and after oleic acid infusion. Plasma immunoreactive thromboxane B2 (iTxB2) and ibuprofen levels were also determined. Oleic acid rapidly induced a significant pulmonary injury as evidenced by hypoxemia and increases in extravascular lung water. Plasma iTxB2 rose significantly in the control group receiving only oleic acid. Pulmonary function and hemodynamic parameters were not changed by ibuprofen infusion alone. Ibuprofen attenuated the oleic acid induced hypoxemia and increased EVLW but did not significantly reduce plasma iTxB2. Methylprednisolone did not prevent the increase in plasma iTxB2 and was less effective than ibuprofen in preventing hypoxemia and increases in EVLW. The combination of ibuprofen and methylprednisolone did significantly inhibit the production of iTxB2, however in combination they protected less against the hypoxemia and increased EVLW than either agent alone. These results indicate that ibuprofen may have a protective effect in oleic acid induced lung injury that is not mediated through the inhibition of fatty acid cyclooxygenase. The results are also further evidence that thromboxane is probably not a pathogenetic factor in oleic acid induced lung injury.

Effect of inhibitors of arachidonic acid metabolism on efflux of intracellular enzymes from skeletal muscle following experimental damage

The role of arachidonic acid metabolism in the efflux of intracellular enzymes from damaged skeletal muscle has been examined in vitro using inhibitors of cyclo-oxygenase and lipoxygenase enzymes. Damage to skeletal muscle induced by either calcium ionophore A23187 (25 microM) or dinitrophenol (1 mM) caused an increase in the efflux of prostaglandins E2 and F2 alpha together with a large efflux of intracellular creatine kinase. Use of a cyclo-oxygenase inhibitor completely prevented the efflux of prostaglandins, but had no effect on creatine kinase efflux. However, several agents having the ability to inhibit lipoxygenase enzymes dramatically reduced creatine kinase efflux following damage. These data suggest that a product or products of lipoxygenase enzymes may be mediators of the changes in plasma membrane integrity which permit efflux of intracellular enzymes as a consequence of skeletal muscle damage.

Present status and new perspectives in non-steroidal anti-inflammatory drugs therapy

The mere mechanism of inhibition of synthesis of prostaglandins (PGs) is unable to account for the whole anti-inflammatory activity of non-steroidal anti-inflammatory drugs (NSAIDs). In fact most of them have been found to inhibit, to a varying degree from drug to drug, some polymorphonuclear (PMN) functions, namely their aggregation, superoxide anion generation, lysosomal enzyme release and, in addition the production of leukotriene B4, which induces an intense inflammatory response. The observation that some patients with chronic inflammatory arthropathies on treatment with NSAIDs undergo an impressive clinical remission together with the reduction of inflammation indices in plasma is sustained by many in vitro and in vivo experiences, where different NSAIDs have been found able to influence the behaviour of the immune system cells and of the para-immune one (PMNs and macrophages). A support mechanism might be through an inhibition of IL-1 synthesis. Furthermore the aspect of the "responders" and "non-responders" subjects is reviewed in the light of new knowledge of the problem of the rate of racemate of the administered NSAID, of the unbound plasma fraction of a given NSAID, of the relevance of the entero-hepatic recirculation etc. Anyway, the unpredictable range of inter-disease variability of response to NSAIDs from the clinical standpoint remains to be explained; it could be due to different pathogenic mechanisms acting in the relative diseases. Finally possible perspectives of development of new NSAIDs are put forward.

Antitumor effects of inhibitors of arachidonic acid cascade on experimentally induced intestinal tumors

The antitumor action of inhibitors of cyclooxygenase (indomethacin) and lipoxygenase activity (nordihydroguaiaretic acid) of arachidonic acid cascade was investigated in the chemically induced large bowel tumors in Sprague-Dawley rats. Indomethacin treatment completely prevented the carcinogenic effect of methylazoxymethanol. Thus, no tumors were found in the 14 rat test group, compared with 13 of 14 tumor-bearing rats in the untreated control group. Although nordihydroguaiaretic acid treatment does not abolish prostaglandin synthesis, it does reduce the effect of the carcinogen and tumors were found in only five of 14 treated rats. From this study it can be postulated that not only is reduction in prostaglandin formation responsible for the inhibition of tumor growth, but also leukotrienes may play some role.

Leukotrienes as common intermediates in the cyclic AMP dependent and independent pathways in adrenal steroidogenesis

Aldosterone secretion from adrenal glomerulosa cells can be stimulated by angiotensin II (AII), extracellular potassium and adrenocorticotropin (ACTH). Since the mitochondria can recognize factors generated by AII (cyclic-AMP-independent) and ACTH (cyclic AMP dependent), it is reasonable to postulate the existence of a common intermediate in spite of a different signal transduction mechanism. We have evaluated this hypothesis by stimulation of mitochondria from glomerulosa gland with fractions isolated from glomerulosa gland stimulated with AII or from fasciculata gland stimulated with ACTH; the same fractions were tested using mitochondria from fasciculata cells. Postmitochondrial fractions (PMTS) obtained after incubation of adrenal zona glomerulosa with or without AII (10(-7) M) or ACTH (10(-10) M), were able to increase net progesterone synthesis 5-fold in mitochondria isolated from non-stimulated rat zona glomerulosa. In addition, AII in zona glomerulosa produced in vitro steroidogenic fractions that were able to stimulate mitochondria from zona fasciculata cells. Inhibitors of arachidonic acid release and metabolism blocked corticosterone production in fasciculata cells stimulated with ACTH. This concept is supported by the experiment in which bromophenacylbromide and nordihydroguaiaretic acid also blocked the formation of an activated PMTS. In fact, non-activated PMTS, in the presence of exogenous arachidonic acid AA, behaved as an activated PMTS from ACTH stimulated cells. We suggest that the mechanisms of action of ACTH and AII involve an increase in the release of AA and an activation of the enzyme system which converts AA in leukotriene products.

[Influence of nonsteroidal anti-inflammatory preparations on the in vitro and in vivo effects of sodium arachidonate]

It has been demonstrated on isolated guinea-pig ileum and rats that nonsteroid antiinflammatory drugs (acetylsalicylic acid, ibuprofen, diclofenac sodium, butadione, and indomethacin) antagonized spasmogenic and inflammatory effects of sodium arachidonate, but not of other mediators of inflammation such as histamine, serotonin, bradykinin and PGE2. "Antiarachidonic" potency of nonsteroid antiinflammatory drugs correlated well with their antiinflammatory activity and their ability to inhibit endogenous PG biosynthesis. This method determining the antagonism to arachidonic acid effects in simple in vitro and in vivo models can be useful for screening nonsteroid antiinflammatory drug potential.

Pharmacological investigations of the new antiinflammatory agent 2-(10,11-dihydro-10-oxodibenzo[b,f]thiepin-2-yl)propionic acid. 2nd communication: inhibitory effects on acute inflammation and prostaglandin-related reactions

Since a newly synthesized nonsteroidal antiinflammatory drug (NSAID) having weaker effects on gastrointestinal tract, 2-(10,11-dihydro-10-oxodibenzo[b,f]thiepin-2-yl)propionic acid (CN-100), was found to markedly inhibit rat paw edema induced by carrageenin and other phlogists, the effects of the drug on other acute inflammatory reactions and prostaglandins (PGs)-related reactions were compared with those of known NSAID in this study. At even a large dose of CN-100, 20 mg/kg, the drug did not significantly inhibit the increased vascular permeability induced by histamine in rat skin, but CN-100 could dose-dependently inhibit the increased vascular permeability induced by acetic acid in mouse peritoneum. The inhibitory activity of CN-100 in the latter was equivalent to that of pranoprofen and indometacin. CN-100 exerted a potent inhibitory action on erythema induced by UV irradiation, which was equal to and 3 times stronger than pranoprofen and indometacin in activity, respectively. Since PGs participate in these acute inflammatory reactions, the effects of CN-100 on reactions relevant to PGs were examined. The drug at dose levels lower than antiinflammatory doses could prevent acute death and diarrhea induced by i.v. injection of arachidonic acid in rabbits and endotoxin in mice, respectively, suggesting that the drug had a potent inhibitory action on biosynthesis of PGs. The adverse effects of CN-100 on gastric and small intestinal mucosa was very weak, the activity being about one-tenth of that of pranoprofen and indometacin.

Influence of some inhibitors of arachidonic acid metabolism on oxytocin contractions in the isolated testicular capsule of the rat

Oxytocin (50-750 nM) contracted the isolated testicular capsule of the rat. Mepacrine, a phospholipase A2 inhibitor (3 X 10(-5) M) and the lipoxygenase inhibitor nordihydroguaiaretic acid (10(-5) M) inhibited this response whereas the cyclooxygenase inhibitor, diclofenac sodium (10(-5) M), and the thromboxane synthetase inhibitor imidazole (10(-5) M) did not. It appears that metabolites of arachidonic acid dependent on lipoxygenase are involved in the contractile response of the rat testicular capsule to oxytocin.

LG 30435, a new bronchodilator/antiallergic agent, inhibits PAF-acether induced platelet aggregation and bronchoconstriction

LG 30435 is a quaternary phenothiazinic antihistamine, endowed with bronchodilator and antiallergic activity. Since PAF-acether (PAF) is a potential mediator of asthma, LG 30435 was assayed for its ability to counteract PAF-induced platelet aggregation (PA) in rabbit platelet rich plasma and bronchoconstriction (BC) in anaesthetized guinea-pigs, in comparison with other antihistamines. LG 30435 was the most potent and selective inhibitor of PAF-induced PA (IC50: 66 microM), concentrations three and more than fifteen fold higher being needed to inhibit PA induced by collagen and arachidonic acid respectively. The other antihistamines, namely mepyramine, promethazine, mequitazine, thiazinamium methyl sulfate and ketotifen were less potent inhibitors of PAF-induced PA, while interfered at lower concentrations with collagen-induced PA. LG 30435 and thiazinamium, administered intravenously, inhibited dose-dependently PAF-induced BC, starting from the dose of 0.1 mumol/kg. The ED50 of LG 30435 was 0.28 mumol/kg, while the inhibition obtained with thiazinamium did not reach 50% even at 3 mumol/kg. Ketotifen and promethazine were partially active only at 3 mumol/kg, while mequitazine and mepyramine were inactive up to this dose. These results show that LG 30435 is endowed with a peculiar anti-PAF action, which may be advantageous in the treatment of asthma.

Hyperalgesic action in mice of intracerebroventricularly administered arachidonic acid, PG E2, PG F2 alpha and PG D2: effects of analgesic drugs on hyperalgesia

Hyperalgesic actions in mice of intracerebroventricularly (i.c.v.) administered arachidonic acid, prostaglandin (PG) E2, PG F2 alpha and PG D2 were studied. For the analgesic assay, the mouse tail pressure method was employed. The i.c.v. administration of arachidonic acid (0.01-100 micrograms/mouse), PG E2 (0.01-100 ng/mouse), PG F2 alpha (0.1-1000 ng/mouse) and PG D2 (0.1-1000 ng/mouse) decreased the pain threshold in a dose dependent manner. The doses that produced the maximal decrease in pain threshold for arachidonic acid, PG E2, PG F2 alpha and PG D2 were 10 micrograms/mouse, 10 ng/mouse, 100 ng/mouse and 100 ng/mouse, respectively. Acidic nonsteroidal antiinflammatory drugs (NSAIDs) produced much more potent analgesic effects in arachidonic acid-induced hyperalgesic mice than in normal mice and in PG E2-, PG F2 alpha- and PG D2-induced hyperalgesic mice, but nonacidic NSAIDs and morphine produced the same analgesic effect in both hyperalgesic and normal mice. Linoleic acid, linolenic acid and gamma-linolenic acid induced weak hyperalgesia, but this unsaturated fatty acids-induced hyperalgesia was not affected by indomethacin (2 mg/kg, p.o.). These findings indicate that the arachidonic acid and its metabolites were related to mediation or modulation of central pain pathways and that the central nervous system may be partially involved in the action of acidic NSAIDs.

Antioxidants and blockers of arachidonate metabolism inhibit the mitogenic effects of TPA in hepatocytes: differences in the operative mechanisms according to the cell cycle setting

A single exposure to a low concentration (10(-10) mol/l) of TPA doubled the size of the fraction of neonatal rat hepatocytes flowing into DNA synthesis within 24 hours in 4-day-old primary cultures kept in low-calcium (0.01 mmol/l) HiWoBa2000 synthetic medium, thereby evoking a phenotypically neoplastic feature in normal, i.e. non-initiated cells. Inhibition kinetics studies, in which several antioxidants and blockers of the arachidonate cascade were given, each by itself, simultaneously with or at various time intervals after TPA, showed that the early mitogenic effects of TPA, i.e. the commitment of GO hepatocytes to grow and the reactivation of hepatocytes poised at the G1/S boundary required oxygen radicals and all the main metabolites of arachidonate. Instead, the subsequent flow into S phase of TPA-committed hepatocytes was not controlled by oxygen radicals and prostaglandins but by retinoid-modulable activities and by products of the lipoxygenase and thromboxane synthase pathways of arachidonate metabolism.

Vitamin E and vitamin C inhibit arachidonate-induced aggregation of human peripheral blood leukocytes in vitro

Arachidonate induces aggregation of human polymorphonuclear (PMN) and mononuclear (MNL) blood leukocytes. This is mediated by the lipoxygenase pathway, as it is prevented by lipoxygenase inhibitors and can also be induced by leukotriene B4 (LTB4). Vitamin E and vitamin C have profound effects on the functional state of leukocytes, some of which may involve the lipoxygenase pathway. This study shows that both vitamins inhibit arachidonate-induced aggregation of PMN and MNL, in a concentration-dependent way. BW-755, previously shown to inhibit arachidonate-induced PMN and NML aggregation, was found to potentiate the inhibitory activity of both vitamins. When LTB4 was used as an aggregating agent, vitamin E markedly inhibited PMN and MNL aggregation, whereas vitamin C was ineffective. The prevention of PMN and MNL aggregation by vitamin E might account, at least partially, for the reported beneficial effects of vitamin E supplementation in some experimental syndromes characterized by leukocyte activation.

Effects of inhibitors of arachidonic acid metabolism on Paf-induced gastric mucosal necrosis and haemoconcentration

The effects of several inhibitors of arachidonic acid metabolism on gastric necrosis, hypotension, haemoconcentration, leukopenia and plasma exudation induced by platelet-activating factor (Paf) were studied in the rat. A 10 min intravenous infusion of Paf (100 ng kg-1 min-1) caused extensive gastric damage and a marked fall in systemic blood pressure which had not recovered to basal levels 30 min after the infusion had been terminated. Paf also caused significant haemoconcentration, plasma exudation and transient leukopenia. Pretreatment with dexamethasone (0.2 or 2 mg kg-1 s.c.) or prednisolone (20 mg kg-1 s.c.) two hours before Paf significantly reduced the gastric damage and accelerated the recovery of blood pressure after the Paf infusion. Likewise, BW755C (50 mg kg-1 p.o.) significantly reduced the gastric damage. Acute pretreatment with dexamethasone (2 mg kg-1 i.v.) 15 min before Paf, or with indomethacin (5 mg kg-1 s.c.), acetylsalicylic acid (10 mg kg-1 i.v.) or 1-benzylimidazole (50 mg kg-1 s.c.) did not significantly affect the gastric damage induced by Paf. The Paf-induced haemoconcentration and plasma exudation were significantly reduced by pretreatment with prednisolone (20 mg kg-1 s.c.) or BW755C (50 mg kg-1 p.o.), while Paf-induced leukopenia was unaffected by either drug. These studies indicate that cyclo-oxygenase products of arachidonic acid are unlikely to contribute significantly to the gastric damage or the prolonged hypotension induced by Paf. The ability of corticosteroids and BW755C to reduce the gastric damage, haemoconcentration and plasma exudation suggests that lipoxygenase products of arachidonic acid may contribute to these actions of Paf.

[Pharmacological studies on proglumetacin maleate, a new non-steroidal anti-inflammatory drug. (3) Damaging effects on the gastrointestinal tract]

Damaging effects on the gastrointestinal tract of proglumetacin maleate (PGM), a new indomethacin (IND) derivative, were examined in comparison with those of IND. Gastric and small intestinal lesions were maximum 4 and 24 hr after a single oral administration of PGM, respectively. Ulcerogenic effects of PGM on the gastric mucosa were approximately 1/7 and 1/10 times as potent as those of IND on a molar ratio 4 hr after single oral dosing to fasting and feeding rats, respectively. PGM was also less active on the small intestinal mucosa 24 hr after single oral dosing. After repeated dosing for 7 days, ulcerogenic effects of PGM were about 1/3 and 1/2 times more potent than those of IND on the gastric and the small intestinal mucosa, respectively. The weak ulcerogenicity of PGM appears to be due to the fact that it has little direct action on the gastrointestinal mucosa. On the other hand, protective effects of PGM on diarrhea induced by arachidonic acid in mice were about 1/2 times as potent as those of IND in both 1 and 4 hr pretreatments. So PGM must have less inhibitory effects on prostaglandin biosynthesis in the intestine than IND. PGM is a safer drug than IND because it has less damaging effect on the gastrointestinal mucosa. Therefore, it may be much more useful for the treatment of chronic inflammatory disorders like rheumatoid arthritis.

Effects of inhibitors of arachidonic acid metabolism on intercellular adhesion of SV40-3T3 cells

Mepacrine, an inhibitor of arachidonic acid mobilisation, and NDGA, a lipoxygenase inhibitor, were found to impair the aggregation of SV40-3T3 cells but the effects could not be unequivocally dissociated from non-specific actions of the drugs. No effect on aggregation was observed even after prolonged exposure of the cells to the cyclooxygenase inhibitors aspirin and indomethacin. These results argue against a possible regulatory role for endogenous AA metabolites in intercellular adhesion of SV40-3T3 cells.

Glucocorticoid-induced vasoconstriction in human skin. An inhibitory role on phospholipase A2 activity

The ability of topically applied betamethasone valerate to reduce erythema produced by a variety of vasodilators was assessed. The steroid significantly reduced the erythema induced by topical arachidonic acid, intradermal histamine, and compound 48/80. We postulated that the steroid reduced endogenous phospholipase activity either before or after application of the vasodilators, or both. This action may explain the mechanism of glucocorticoid-induced vasoconstriction in the skin and part of the steroids' action in acute inflammatory skin disease.

Blockade of N1E-115 murine neuroblastoma muscarinic receptor function by agents that affect the metabolism of arachidonic acid

Inhibitors of arachidonate metabolism and perturbants of the oxidation-reduction state of the cell were employed to develop a pharmacologic profile for muscarinic receptor-mediated cyclic GMP formation in murine neuroblastoma cells (clone N1E-115). Several lipoxygenase inhibitors [eicosatetraynoic acid (ETYA), nordihydroguaiaretic acid (NDGA), FPL 57231, FPL 55712, BW755c, propylgallate, and AA861] blocked the elevation of [3H]cyclic GMP induced by muscarinic receptor activation. The cyclooxygenase inhibitors indomethacin and ibuprofen were two orders of magnitude less potent in blocking the muscarinic receptor-mediated [3H]cyclic GMP response than in blocking cyclooxygenase in other systems. ETYA and NDGA did not affect the muscarinic inhibition of the prostaglandin E1-mediated increases in [3H]cyclic AMP levels in N1E-115 cells. ETYA did not have a reproducible effect on the muscarinic receptor-induced release of inositol phosphates. Thus, these lipoxygenase inhibitors appeared to be selective for the effector system coupled to the low-affinity muscarinic agonist-receptor conformation, i.e. that which induces cyclic GMP formation. Other effective inhibitors of the cyclic GMP response were methylene blue, catalase, bromphenacyl bromide, retinal, dithiothreitol, quinacrine, and oxidized glutathione. The antioxidant alpha-tocopherol in the concentration range of 100 microM to 1 mM potentiated the receptor response. Arachidonic acid itself was an inhibitor of the muscarinic receptor-mediated cyclic GMP response (IC50 = 45 microM). Linoleic acid and oleic acid were less potent (IC50 = 130 and 190 microM, respectively), and stearic acid was ineffective. When arachidonic acid was air-oxidized, its inhibitory potency was increased 10-fold. Most but not all of the spontaneously-produced oxidative metabolites, separable by reverse-phase high pressure liquid chromatography, were inhibitory to the receptor response. Enzymatically synthesized 12-hydroxyeicosatetraenoic acid and 15-hydroxyeicosatetraenoic acid inhibited the muscarinic receptor [3H]cyclic GMP response, with IC50 values of 17 and 8 microM respectively. Catalase was effective in blocking the muscarinic cyclic GMP response (IC50 = 5 microM) while having no effect on either the muscarinic receptor-induced inositol phosphate release or the reduction of cyclic AMP levels. Thus, the effector system for increasing cyclic GMP in these cells displays may of the expected characteristics for the involvement of a lipoxygenase or a related enzyme that oxidatively metabolizes arachidonate in order to activate the guanylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)