The effect of steroidal and non-steroidal antiinflammatory drugs on chronic muscle inflammation

Direct inhibition of cyclooxygenase pathway in platelets by tixocortol 21-pivalate: comparison with related structures, steroidal and non steroidal anti-inflammatory drugs

Direct activity of the local anti-inflammatory steroid, tixocortol 21-pivalate (21 thioester derivative of cortisol) on metabolism of exogenous arachidonate by rabbit platelets was investigated in vitro. Tixocortol 21-pivalate inhibited generation of prostanoids from cyclooxygenase with an IC50 value of 19.6 microM without affecting the 12-lipoxygenase pathway. In this model, reference anti-inflammatory glucosteroids were ineffective, whereas indomethacin and aspirin inhibited the cyclooxygenase activity. Among tixocortol 21-pivalate related structures, tixocortol and its disulfide dimere or several other tixocortol esters exhibited a quite similar efficacy while S-methylation and subsequent S-oxydations of tixocortol abolished inhibitory activity. These results indicate that tixocortol 21-pivalate in contrast to other glucosteroids is able to act directly on cyclooxygenase pathway and that some specific chemical environment of the 21 thiol side chain are required for this inhibition.

Effects of short- and long-term protriptyline treatment on phospholipid metabolism in rat brain

Wistar rats were injected intraperitoneally with 10 mg/kg of protriptyline according to one of the following schedules: a single dose or daily for 4 days (short-term), or daily for 2 or 13 weeks (long-term). Total lipid, total phospholipid, and individual phospholipid contents in the brain were determined. Further, the incorporation of 32P into individual phospholipids in vivo and the fatty acid composition of phosphatidylethanolamine in the brains of rats treated with protriptyline for 13 weeks were studied. Three alternative phases of changes of total and individual phospholipid contents in the brain during 13 weeks of experimentation were distinguished. An increase of phospholipid contents after 4 days, a decrease after 2 weeks, and a further increase after 13 weeks of protriptyline administration were found. However, phosphatidylinositol and phosphatidic acid levels after 13 weeks of protriptyline administration were diminished. The decrease of specific radioactivity of phosphatidylethanolamine, phosphatidylcholine, and phosphatidylserine and the increase of phosphatidylinositol, phosphatidic acid, and sphingomyelin in rats treated with the drug for a longer period of time were noted. No greater differences in fatty acid composition of phosphatidylethanolamine in the brains of the same group of rats were observed as compared to control. These results indicate that during long-term treatment with protriptyline the contents of lipids and phospholipids in rat brain are altered. The modification of the biological function of phospholipids in brain cell membranes is suggested.

Induction of zymosan-air-pouch inflammation in rats and its characterization with reference to the effects of anticomplementary and anti-inflammatory agents

Induction of an experimental inflammation of the air-pouch type with the aid of zymosan (known to activate the alternative pathway of the complement system) was carried out in an attempt to induce a reproducible inflammatory model suitable for quantitative studies. Rats were injected subcutaneously with 8 ml of air on the dorsal surface to make an air-pouch, followed 24h later by 4 ml of 1.6% (w/v) zymosan suspension. This induced inflammatory responses. Treatment with zymosan suspension provoked exudation of fluid, accumulation of polymorphnuclear leukocytes (PMN) in the pouch and the development of granulation tissue as a wall of the pouch. Approximately half of the PMN in the pouch formed a characteristic layer of aggregated cells sticking onto the inner surface of the pouch wall. They were counted after being completely disaggregated by means of incubation with trypsin. In preliminary experiments with potential anti-inflammatory drugs, local application of a novel anti-complementary agent, K-76COONa, inhibited leukocyte accumulation in the pouch, whereas the potent anti-inflammatory agent, dexamethasone, was ineffective. By contrast, exudation of the pouch fluid was effectively inhibited by dexamethasone but not by K-76COONa.