A. W. Ford‐Hutchinson

LEUKOTRIENE B4: A MEDIATOR OF VASCULAR PERMEABILITY

1 Intradermal injection of leukotriene B4 (LTB4) or prostaglandin E2 (PGE2), 1 to 100 ng per skin site produced little or no change in plasma exudation in the rabbit, guinea‐pig and rat. 2 Intradermal injection of LTB4 together with PGE2 produced a significant increase in plasma exudation in the rabbit, guinea‐pig and rat. 3 Intradermal injection of LTB4 or PGE2 together with bradykinin (500 ng) resulted in a significant potentiation of the plasma exudation produced by bradykinin alone in the rabbit and guinea‐pig. 4 LTB4 (1 to 10 ng) had no effect on blood flow in the rabbit skin, in contrast to PGE2 which was a potent vasodilator in this species. 5 It is concluded that LTB4 is a mediator of vascular permeability and that this effect can only be observed in the presence of a vasodilator such as PGE2.

Leukotriene B4: an inflammatory mediator in vivo.

Leukotriene B4 (LTB4 isomer III), which promotes the movement and aggregation of leucocytes in vitro also stimulates the chemo-attraction of leucocytes and their adherence to vascular endothelium in vivo. These effects were observed directly in the hamster cheek pouch preparation and on histological examination of sections from the rabbit mesentery. Intravenous injection of LTB4 (isomer III) into the rabbit resulted in a profound but transient neutropenia. Intradermal injection of LTB4 (isomer III) in the rabbit produced a rapid accumulation of neutrophils and this effect was also observed in skin chambers applied over abrasions on the rabbit back or the human forearm.

Anti-inflammatory drugs, prostaglandins and leucocyte migration

The action of some non-steroidal acidic anti-inflammatory drugs, aspirin, phenylbutazone and indomethacin, in reducing leucocyte migration into the exudates of inert porous sponges implanted subdermally in the rat has been shown to be distinct from their effect in reducing the content of prostaglandins in the exudates. It is concluded that a component of the anti-inflammatory and antirheumatic actions of the drugs is concerned with a mechanism other than inhibition of prostaglandin biosynthesis.

Isomers of leukotriene B4 possess different biological potencies

Rat elicited polymorphonuclear leucocytes (PMNs), when exposed to the ionophore A23187, release three isomers of leukotriene B4. The three isomers have been purified and tested for their ability to induce the chemokinesis of human PMNs in vitro, the aggregation of rat PMNs in vitro and changes in vascular permeability in rabbit skin in vivo in the presence of PGE2. The results demonstrate that all three isomers are biologically active and that the enzymatically produced isomer, in which the conjugated triene contains one cis and two trans double bonds, is more potent than the two diastereoisomers of LTB4 which contain all trans double bonds in the conjugated triene and which are produced by non-enzymatic hydrolysis.

The production and characterisation of products of the lipoxygenase enzyme system released by rat peritoneal macrophages

Rat peritoneal monocytes and macrophages when exposed to the ionophore A23187 release products of the lipoxygenase pathway of arachidonic acid metabolism which cause the aggregation and chemokinesis of polymorphonuclear leucocytes suspensions. The major biologically active compound released was leukotriene B which accounted for greater than 80% of the activity. The remaining biological activity was due to the release of a more polar as yet unidentified compound. In addition rat macrophages release 5, 12 and 15-HETE but these mono-HETEs do not significantly contribute to the biological activity.

The binding of paracetamol to plasma proteins of man and pig

The binding of N‐acetyl‐4‐aminophenol (paracetamol) to human and porcine plasma at both toxic and therapeutic concentrations was investigated by ultrafiltration and equilibrium dialysis over the range 50–300 μg ml−1. Plasma protein binding occurred at paracetamol concentrations greater than 60 μg ml−1. The extent of protein binding at a plasma concentration of 280 μg ml−1 of the drug is between 15 and 21% for both pig and man. There is no appreciable binding to erythrocytes in either species over the whole concentration range studied.

Prostaglandins and the anti‐inflammatory activities of aspirin and sodium salicylate

Acetylsalicylic acid (aspirin) and sodium salicylate are equally effective in reducing the swelling in the carrageenan‐induced paw test and the accumulation of leucocytes into the inflammatory exudate produced by the subcutaneous implantation of polyvinyl sponges in the rat. Aspirin but not sodium salicylate caused a significant reduction in the potentiation of paw oedema found after the concurrent administration of carrageenan and arachidonic acid. Some implications of these findings are discussed.

PGI2: a potential mediator of inflammation.

PGI2, but not its metabolite 6oxoPGF1alpha, is equivalent in potency to PGE1 as a potentiator of carrageenan, histamine and bradykinin-induced rat paw oedemas. PGI2 must, therefore, be considered as a potential mediator of inflammatory processes.

Separate anti-inflammatory effects of indomethacin, flurbiprofen and benoxaprofen

An important query about non-steroidal anti-inflammatory drugs is whether they have either a common single mode of action or different multiple interactions with various aspects of inflammatory responses. An inhibitory action on prostaglandin biosynthesis has been advanced as a mechanism for the first possibility (Vane, 1973). More recently evidence has accumulated that the drugs possess anti-inflammatory effects which appear to be independent of prostaglandin systems (Bonta, Bult & others, 1977; Crook, Collins &others, 1976). One of the most relevant is an interference with the emigration of leucocytes into inflammatory sites (Walker, Smith & Ford-Hutchinson, 1976a). In the present work the effects of three acidic non-steroidal drugs, indomethacin, flurbiprofen and benoxaprofen, on the production of prostaglandins and the migration of leucocytes into an inflammatory exudate in vivo, have been studied. All three drugs possess a similar spectrum of experimental anti-inflammatory activity (Glenn, Rohloff & others, 1973 ; Adams, McCullough & Nicholson, 1975; Cashin, Dawson & Kitchen, 1977) but differ in that the first two are potent inhibitors of prostaglandin synthetase activity in vitro (Crook & Collins, 1975) whereas benoxaprofen is only a weak inhibitor of the enzyme system (Cashin & others, 1977). Indomethacin was obtained from Merck Sharp and Dohme. Benoxaprofen (2-[4-chlorophenyl]-cc-methyl-5benzoxazone acetic acid) was obtained from Dr W. Dawson, Lilly Research Centre, Ltd, Windlesham, Surrey, England, and flurbiprofen (2-[fluoro-4-biphenylyl] propionic acid) was obtained from Dr S. Adams, Boots Drug Co. Ltd, Nottingham, England. The 9 h sponge implantation technique, the estimation of leucocyte migration and prostaglandin-like activity in the sponges were as described previously (Walker & others, 1976a). Drugs were administered orally as a suspension in Tween 80 to groups, each of 5 rats, 1 h before sponge implantation. The effects of the three drugs on prostaglandin accumulation and leucocyte migration into the 9 h sponge exudates are shown in Table 1 . Indometha& and flurbiprofen, which are potent inhibitors of prosta. glandin synthetase in vitro, strongly inhibited the accumulation of prostaglandin activity in vivo in the sponges. This inhibition occurred at lower dosages than those required to inhibit white cell migration in the system and well below those required to inhibit other experimental models of inflammation (Glenn & others, 1973; Adams & others, 1975). Benoxaprofen only showed inhibition of prostaglandin production in vivo at doses equivalent to those required to inhibit white cell migration in the model and similar to those needed to affect other experimental models (Cashin & others, 1977). These findings demonstrate a lack of correlation

CALCIUM IONOPHORE A23187 INDUCES RELEASE OF CHEMOKINETIC AND AGGREGATING FACTORS FROM POLYMORPHO-NUCLEAR LEUCOCYTES

1 Rat and human polymorphonuclear leucocytes (PMNs) when exposed to calcium ionophore A23187 10 μm release products which cause aggregation of rat PMNs and chemokinesis of human PMNs. 2 Aggregating and chemokinetic activities are rapidly generated; maximal release occurs after 4 min, and can be detected in dilutions of the supernatant of up to 1:1000. 3 Generation of aggregating and chemokinetic activities is inhibited by nordihydroguaiaretic acid 10−4 to 10−7 m, 5,8,11,14‐eicosatetraynoic acid 10−4 and 10−5 m, BW 755C 10−4 m and benoxaprofen 10−4 m, all compounds known to inhibit lipoxygenase pathways of arachidonic acid (AA) metabolism. 4 Conventional non‐steroidal anti‐inflammatory agents, such as aspirin and indomethacin, inhibited little or not at all the generation of these activities. 5 We conclude that the aggregating and chemokinetic activities induced by A23187 represent generation of biologically active products of lipoxygenase pathways of AA metabolism.