Epidermal strips, free of sebaceous gland and hair follicle contamination, were prepared from mouse tail skin. Epidermal homogenates synthesized prostaglandins and 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) from exogenously added [1-14C]arachidonic acid. The effects of pH, assay time, substrate concentration, and several selective inhibitors upon the lipoxygenase and cyclooxygenase pathways were determined. Ultracentrifugation of the crude homogenate at 105,000 g sedimented both activities, and pellet 12-HETE synthesis increased 2-fold relative to the crude homogenate. Recombination of the 105,000 g pellet and supernatant gave yields of prostaglandins and 12-HETE essentially equivalent to that of crude homogenate. When tested in homogenate with 4.5 microM arachidonic acid, anthralin specifically inhibited 12-HETE production with IC50 of 50.0 microM; no significant effect against cyclooxygenase was observed over the dose range of 2-200 microM. 1,8-Dihydroxy-9,10-anthraquinone (DHAQ) also specifically inhibited 12-HETE synthesis, but the dose response curve was flatter and maximum inhibition was only 55% at 200 microM. 6-Chloro-2,3-dihydroxy-1,4-naphthoquinone (CDNQ), an agent with topical antipsoriatic activity, also inhibited 12-HETE synthesis with an IC50 of 25 microM, but simultaneously stimulated prostaglandin production, up to 2.5-fold at 200 microM. When tested with washed human platelets, anthralin again specifically inhibited 12-HETE production with an IC50 of 10 microM, while DHAQ inhibited lipoxygenase activity by only 40% at 25 microM. When tested in platelets, CDNQ gave 33% inhibition of 12-HETE production at 200 microM, although prostaglandin synthesis was stimulated over the range of 25-200 microM. It is proposed that certain antipsoriatic agents may exert their action through modulation of arachidonic acid metabolism.

Animals↗

PubMed1983

Tachyphylaxis in 12-0-tetradecanoylphorbol acetate- and arachidonic acid-induced ear edema.

12-0-Tetradecanoylphorbol acetate (TPA) applied to mouse ears rapidly induces an edema which is maximal by 6 hr but has substantially waned by 24 hr. (This is in contrast to many inflammatory agents that cause a prolonged edema lasting many days.) Reapplication of TPA at 16-24 hr will not provoke a second edematous response although increased erythema is evident. Arachidonic acid (AA) applied to mouse ears (4 mg) provokes an even more rapid edema which is maximal at 1 hr and has substantially waned by 6 hr. Reapplication of AA at 3-24 hr also will not provoke a second edematous response although, again, increased erythema does result. Pretreatment of ears with AA results in inhibition of the edema response to subsequent application of TPA, and TPA pretreatment moderately inhibits a subsequent response to AA. TPA-induced edema can be delayed by agents such as naproxen, an inhibitor of AA cyclooxygenase. In contrast, AA-induced edema is inhibited only by agents, such as phenidone, that inhibit both cyclooxygenase and lipoxygenase. The data suggest that the edemas result from interaction of the products of the cyclooxygenase and lipoxygenase pathways of AA metabolism. The lack of secondary edema response appears to be related to the inability of TPA or AA to reinduce vascular permeability. The effect is specific to AA and TPA; responses to xylene or anthralin are unaffected by TPA or AA pretreatment. It is postulated that the tachyphylactic effects observed involve lipoxygenase metabolites of AA.

Animals↗

PubMed1983

Connective tissue disease--historical perspective.

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Collagen Diseases↗