The influence of metyrapone on the synthesis and release of prostaglandins from the pregnant rat uterus in vitro

Comparison of the effects of inhibitors of cytochrome P-450-mediated reactions on human platelet aggregation and arachidonic acid metabolism

Metyrapone and SKF-525A, together with amphenone B, a structural analogue of metyrapone, which are all inhibitors of cytochrome P-450-mediated reactions, were shown to inhibit the arachidonic acid-induced aggregation of human platelets. Amphenone B, like metyrapone, exhibited a type II (ligand) binding spectrum with rat liver microsomal cytochrome P-450, in contrast to SKF 525A which is a type I (substrate) binding agent. Independently of their type of binding spectra and of their maximum spectral change, however, the affinity of the three compounds for rat liver cytochrome P-450 showed a close proportional correlation with their platelet aggregation inhibitory potency. All three compounds inhibited the formation of [1-14C]thromboxane B2 from [1-14C]arachidonic acid by human platelets aggregated with collagen. The effect of metyrapone on the remaining labelled products suggested that it is a selective thromboxane synthesis inhibitor, while amphenone B exhibited activity reminiscent of cyclo-oxygenase inhibitors. SKF 525A produced complex effects possibly attributable to cyclo-oxygenase inhibition and enhanced lipid peroxidation, since it also enhanced platelet malonaldehyde formation, which the other two compounds inhibited. These data provide further support for a role of cytochrome P-450 in thromboxane synthesis and platelet aggregation.

Cyclic AMP and prostaglandin E in perfusates of rat hind paws during the development of adjuvant arthritis

The contralateral uninjected hind paws of rats which had been injected with Freund's complete (FCA) or incomplete (FIA) adjuvant 10,14, 18, or 22 days previously were perfused under urethane anaesthesia using a stainless steel coaxial catheter. In one series of experiments cyclic AMP (cAMP) levels were determined after a 2-hour perfusion. cAMP levels were also determined in rats treated on days 16-22 with either prostaglandin E(1) (PGE(1)) (500 mug/kg per day subcutaneously) or saline. When compared with control rats injected with FIA, after 22 days, cAMP levels in FCA-injected rats fell between days 10 and 18 and then rose between days 18 and 22. After PGE(1) treatment, paw volume on day 22 increased in rats injected with FCA, but cAMP levels were not significantly altered when compared with day 22 FCA-injected controls treated with saline. In a second series of experiments, using a slightly modified perfusion method, PG levels in extracts of 30-minute perfusates were determined after chromatography and bioassay. Protein levels and paw volume were also measured. No PGF was detectable in any perfusate. Changes in PGE levels in FCA-injected animals paralleled changes in paw volume, increasing from day 14 and reaching a maximum on day 22. Both parameters remained unchanged in FIA-injected rats. Protein levels in perfusates from FCA-injected animals were significantly greater than FIA-injected controls only on day 22. We suggest that the early changes in cAMP reflect the infiltration of activated leucocytes into the inflamed joint and that the increase in PGE is attributable to lysosomal enzyme activity. Later increases in cAMP are attributable both to the increasing PGE levels and to other changes in cellular activation. We suggest that high levels of PGE contribute to tissue damage which is reflected in raised protein levels.

The effect of metyrapone on granuloma induced by carrageenan-impregnated sponges in normal and essential fatty acid deficient rats

Treatment of normal rats with metyrapone (20 mg kg-1 day-1, s.c.) for 5 days, starting on the day before implantation, inhibited the production of granuloma, induced by carrageenan-impregnated sponges, determined 8 days after implantation. Exudate volume and prostaglandin (PG) production were unaffected. In essential fatty acid deficient (EFAD) rats, metyrapone did not alter the already existing adrenal hyperplasia due to EFAD and did not affect either granuloma formation or exudate production. The results are discussed in relation to earlier work using adrenalectomy and with regard to the effect of EFA deficiency on adrenal corticosteroid production. It is suggested that metyrapone is a more useful tool than adrenalectomy in studying the role of endogenous corticosteroids.

Metyrapone: a possible tool in investigating the role of endogenous corticosteroids in inflammation

Despite much early work on corticosteroid levels in the blood and urine of patients with rheumatic diseases, little strong evidence is available concerning the role of endogenous corticosteroids in inflammation. Nevertheless, the modulating role of adrenal corticosteroids in inflammation seems to be taken for granted even though the small amount of evidence in laboratory animals is, in some cases, contradictory. In the light of the immunological aetiology of some chronic inflammatory diseases and the immunosuppressive properties of corticosteroids, investigations into the role of endogenous corticosteroids in these conditions seem particularly worthwhile. Adrenalectomy has been used widely in studies on the physiological roles of adrenal corticosteroids but the operation requires care to avoid mortality. The adrenal corticosteroid synthesis inhibitor, metyrapone, could be used quite profitably in such investigations. However, it has been shown to exert differential effects on prostaglandin (PG) production in uterine tissue and may produce non-selective antagonism of the actions of PGs. Because PGs are probably involved in inflammation, care should be exercised in the doses of metyrapone used in any studies on inflammatory models to avoid interactions with the PG system.

The effect of metyrapone on uterine prostaglandin output and smooth muscle activity

Metyrapone, at low doses (0.5-1.0 mM), stimulated the output of both PGE and PGF from the isolated uterus of the pregnant rat determined following extraction of bath fluid, chromatographic separation and bioassay of the prostaglandin. At higher doses (2-4 mM), metyrapone inhibited PGF output, but had no effect on PGE output. Uterine activity was rapidly inhibited by metyrapone in a dose-related manner. This inhibition was not related to PG output as, at 1 mM metyrapone, activity was inhibited and PG output stimulated. Both metyrapone and papaverine produced dose-dependent inhibition of the activity of the isolated rabbit ileum, papaverine being 10 times more potent than metyrapone. Propranolol antagonised the response of the ileum to isoprenaline, but had no effect on the response to metyrapone. These observations confirm earlier data, suggsting that metyrapone exerts a differential effect on uterine PGE and PGF production and indicate that metyrapone has a direct inhibitory effect on smooth muscle activity.