Serum stimulates the production of prostaglandins by transformed mouse fibroblasts. Hydrocortisone (cortisol) inhibits this stimulation. The half-maximal inhibition occurs at 6 X 10-9 M. Studies with cells labeled with [3Hlara-chidonic acid in their lipids show that the stimulation by serum results in the release of arachidonic acid from the cellular lipids, mostly phospholipids. Hydrocortisone inhibits this release but does not inhibit the production of prostaglandins from exogenously supplied arachidonic acid. This inhibition of arachidonic acid release from phospholipids may be the mechanism for the anti-inflammatory action of corticosteroids. Prostaglandins E2 and F2a (PGE2 and PGF2a) are present in the culture medium of a methylcholanthrene-transformed mouse fibroblast, MC5-5 (1, 2). This cell line proves to be a useful model for the study of the effect of vasoactive substances on the production of prostaglandins. We have shown that mechanical manipulation and vasoactive substances such as bradykinin, arachidonic acid, serum, and thrombin stimulate the production of prostaglandins. Cofactors for in vitro microsomal prostaglandin synthetase systems, such as hydroquinone and glutathione, also stimulate prostaglandin synthesis by the cells. Indomethacin, a nonsteroid anti-inflammatory drug, inhibited all of the above-mentioned stimulations of prostaglandin formation.Prostaglandins have been implicated in inflammation (3). Nonsteroid, aspirin-like anti-inflammatory drugs such as aspirin and indomethacin inhibit in vitro microsomal prostaglandin biosynthesis, and this inhibition has been postulated to be the basis of their therapeutic effects (4). On the other hand, hydrocortisone (cortisol), an anti-inflammatory steroid, did not inhibit in vitro prostaglandin synthetase systems in some studies (4, 5); but in another study fluocinolone, at high concentrations, did inhibit (6). Corticosteroids do inhibit prostaglandin formation by mouse fibrosarcoma cells (7) and by rheumatoid synovia (8). Lewis and Piper, based on their study on the infusion of adrenocorticotropic hormone into rabbit adipose depots, concluded that inhibition of release of prostaglandins from the tissue was the mechanism of some actions of corticosteroids in inflammation, in gastric mucosa, and in the central nervous system (9). Gryglewski et al. (10), working with perfused guinea pig lungs, suggested that corticosteroids act by reducing the availability of the substrate for the prostaglandin synthetase.The mechanism involving inhibition of release would be less likely if tissue storage of prostaglandins were low, as has been suggested by Ramwell and Shaw (11). In this paper, we report studies on the effect of hydrocortisone on prostaglandin synthesis in MC5-5 cells and provide evidence for the mechanism of the action of corticosteroids in inhibiting prostaglandin synthesis.Abbreviations: PGE2, prostaglandin E2; PGF2a, prostaglandin F2a.
MATERIALS AND METHODSCell and Cell Culture. MC5-5, a methylcholanthrenetransformed mouse BALB/3T3 cell...
