Sites of metyrapone inhibition of steroid biosynthesis by rat adrenal mitochondria

Immunolocalization of Glutathione-Peroxidase (GPx1) in the Rat Adrenal Cortex: Correlation between Steroidogenesis and Lipid Peroxidation

In order to confirm the relationship between glutathione-peroxidase (GPx1) and biological significance on steroidogenesis, we have studied the immunocytochemical localization of GPx1 in the rat adrenal cortical cells. GPx1 was observed not only in cytoplasm (cytosol GPx1) but in mitochondria (mitochondrial GPx1). The staining intensity was altered by the functional state of the adrenal cortical cells. Furthermore, cytosol- and mitochondrial-GPx1 was modified by lipoperoxidative damage in the adrenal cortical cells. Therefore, we proposed that the pattern of GPx1 staining should be a more sensitive and specific indicator of oxidative damage in cells. Thus, the staining pattern of GPx1 is thought to be a useful marker for lipid peroxidation in the adrenal cortical cells.

Pharmacodynamic and pharmacokinetic characterization of the aldosterone synthase inhibitor FAD286 in two rodent models of hyperaldosteronism: comparison with the 11beta-hydroxylase inhibitor metyrapone

Aldosterone synthase (CYP11B2) inhibitors (ASIs) represent an attractive therapeutic approach for mitigating the untoward effects of aldosterone. We characterized the pharmacokinetic/pharmacodynamic relationships of a prototypical ASI, (+)-(5R)-4-(5,6,7,8-tetrahydroimidazo[1,5-a]pyridin-5-yl]benzonitrile hydrochloride (CGS020286A, FAD286, FAD) and compared these profiles to those of the 11beta-hydroxylase inhibitor metyrapone (MET) in two rodent models of secondary hyperaldosteronism and corticosteronism. In chronically cannulated Sprague-Dawley rats, angiotensin II (ANG II) (300 ng/kg bolus + 100 ng/kg/min infusion) or adrenocorticotropin (100 ng/kg + 30 ng/kg/min) acutely elevated plasma aldosterone concentration (PAC) from approximately 0.26 nM to a sustained level of approximately 2.5 nM for 9 h. Adrenocorticotropin but not ANG II elicited a sustained increase in plasma corticosterone concentration (PCC) from approximately 300 to approximately 1340 nM. After 1 h of Ang II or adrenocorticotropin infusion, FAD (0.01-100 mg/kg p.o.) or MET (0.1-300 mg/kg p.o.) dose- and drug plasma concentration-dependently reduced the elevated PACs over the ensuing 8 h. FAD was approximately 12 times more dose-potent than MET in reducing PAC but of similar or slightly greater potency on a plasma drug concentration basis. Both agents also decreased PCC in the adrenocorticotropin model at relatively higher doses and with similar dose potencies, whereas FAD was 6-fold weaker based on drug exposures. FAD was approximately 50-fold selective for reducing PAC versus PCC, whereas MET was only approximately 3-fold selective. We conclude that FAD is a potent, orally active, and relatively selective ASI in two rat models of hyperaldosteronism. MET is an order of magnitude less selective than FAD but is, nevertheless, more potent as an ASI than as an 11beta-hydroxylase inhibitor.

Biosynthesis and metabolism of steroid hormones by human adrenal carcinomas

Over a 15-year period, our university-based laboratory obtained 125 adrenal tumors, of which 15 (12%) were adrenal cortical carcinomas. Of these, 6 (40% of the carcinomas) occurred in patients with clear clinical manifestations of steroid hormone excess. Adrenal cortical carcinoma cells derived from the surgically resected tumors in 4 of these patients were isolated and established in primary culture. Radiotracer steroid interconversion studies were carried out with these cultures and also on mitochondria isolated from homogenized tissues. Large tumors had the lowest steroidogenic activities per weight, whereas small tumors had more moderately depressed enzyme activities relative to cells from normal glands. In incubations with pregnenolone as substrate, 1 mM metyrapone blocked the synthesis of corticosterone and cortisol and also the formation of aldosterone. Metyrapone inhibition was associated with a concomitant increase in the formation of androgens (androstenedione and testosterone) from pregnenolone. Administration of metyrapone in vivo before surgery in one patient resulted in a similar increase in plasma androstenedione, though plasma testosterone levels were not significantly affected. In cultures of two of four tumors examined, dibutyryl cAMP stimulated 11ss-hydroxylase activity modestly; ACTH also had a significant stimulatory effect in one of these tumors. Unlike results obtained with normal or adenomatous adrenal cortical tissues, mitochondria from carcinomatous cells showed a lack of support of either cholesterol side-chain cleavage enzyme complex or steroid 11ss-hydroxylase activity by Krebs cycle intermediates (10 mM isocitrate, succinate or malate). This finding is consistent with the concept that these carcinomas may tend to function predominantly in an anaerobic manner, rather than through the oxidation of Krebs cycle intermediates.

The adrenal gland of stranded whales (Kogia breviceps and Mesoplodon europaeus): in vitro modulation of mitochondrial steroid enzyme activities

The effects of adrenocorticotropic hormone (ACTH), cyclic AMP (cAMP), NADPH, Krebs cycle intermediates (KCl), and metyrapone on the two key mitochondrial reactions in the biosynthesis of glucocorticoids--11 beta-hydroxylation and cholesterol cleavage--were studied in preparations from the adrenal glands of stranded whales (Kogia breviceps and Mesoplodon europaeus) and some terrestrial mammals. ACTH (30 pM) and cAMP (1.0 mM) enhanced the 11 beta-hydroxylation of [11-3H]deoxycorticosterone ([3H]DOC) in monolayer cultures of whale adrenal cells during a 4-hr incubation period. Mitochondria from whale and beef adrenals responded in a similar dose-related fashion to NADPH generated by the addition of increasing amounts of NADP (0-0.6 mM) to the in vitro system: at each level of NADPH, 11 beta-hydroxylation of [14C]DOC was several-fold greater than the cleavage of [14C]cholesterol. Metyrapone interfered in a dose-related manner with both the 11 beta-hydroxylation of [14C]DOC and the cleavage of [14C]cholesterol by mitochondria from whale and beef adrenals; inhibition of 11 beta-hydroxylation exceeded 60% at 0.1 mM metyrapone and was virtually complete at 1.0 mM in both species, while inhibition of [14C]cholesterol cleavage averaged 25% at 0.1 mM metyrapone and 50% at 1.0 mM. The effect of exogenous NADPH in supporting the 11 beta-hydroxylation of [14C]DOC could be maintained in beef and rat adrenal mitochondria to the extent of 70-100% by substitution with any of the KCl. This phenomenon was not found in similar whale studies where the KCl were all ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Short-term kinetics of serum adrenal steroids and plasma ACTH after a single dose of metyrapone in man

The in vivo influence of metyrapone (M) on different adrenal enzymes has been studied by simultaneous measurement of serum progesterone (P), 17-hydroxyprogesterone (17-OHP), deoxycorticosterone (DOC), corticosterone (B), deoxycortisol (S), 18-hydroxydeoxycorticosterone (18-OHDOC), aldosterone and cortisol (F) as well as by the measurement of plasma ACTH before and after oral administration of 40 mg of M/kg at 08:15 in four healthy male subjects. The well known inhibitory effect of M on adrenal 11-hydroxylase is demonstrated by a decrease of serum F and B and synchronous increase of serum S and DOC after administration of M. The additional inhibition of 18-hydroxylase by M is documented by a decrease of serum 18-OHDOC in spite of a marked increase of serum DOC after M. The moderate increase of serum P and 17-OHP soon after drug administration, although plasma ACTH is highly elevated at this time, as well as the marked increase of these steroids in the afternoon synchronously to a rise of serum F and B suggest a further inhibitory effect of M on the enzyme prior to the total corticosteroid biosynthesis. This effect of M should be taken into account if ACTH activity is monitored in terms of adrenal steroid output in the metyrapone test.

Effect of the adrenocorticostatic agent, metopirone, on thermoregulatory heat production in the European hedgehog*

1. Non-shivering thermogenesis (NST) was studied in 8 hedgehogs before and after a single injection of metopirone ditartrate (150-450 mg/kg, i.p.) at a thermoneutral chamber temperature (Ta) of 28C and during cold exposure (Ta = 8 degrees C for 20 min). 2. An average metabolic increase of 149% of the standard metabolic rate (SMR) was observed 12-26 min after an injection of metopirone ditartrate at thermoneutral chamber temperature. Average temperatures simultaneously increased by 2.1C in the brown adipose tissue (BAT) and 2.0C in the deep colon. This initial effect lasted for 40 plus or minus 8 min. 3. In a period of 3-48 h after injection of metopirone ditartrate, cold-induced NST was reduced by 89% of SMR (av.). Concomitant exposure to cold caused average temperatures to decrease by 1.0C in the BAT and 1.1 C in the colon relative to control experiments. 4. Our results suggest the participation of corticosteroids in the control of NST in the hedgehog. As metopirone blocks enzymatic 11 beta-hydroxylation in the steroid ring, there is a pronounced increase of endogenous 11-deoxycorticosteroids, such as deoxycorticoterone (DOC). An injection of DOC (3 mg/kg, i.m.) increases NST at hermoneutrality similar to the initial metabolic effect elicited by metopirone ditartrate. The reduced response to cold exposure after several hours may be explained by competitive inhibition of glucocorticoid receptors since there is also an increased production of other 11-deoxycorticosteroids.

Kinetics of plasma corticosteroids during metyrapone infusion in man

The effect of metyrapone on plasma kinetics of cortisol (F), 11-deoxycortisol (S), corticosterone (B), 11-deoxycorticosterone (DOC), aldosterone (Aldo) and 17 hydroxyprogesterone (17 OHP) was studied in ten normal prepubertal children intravenously infused with the drug (1 gm/1.73 m2 body surface area in 4 h). Similar falls in F, B and Aldo were observed during the first hour expressing similar sensitivity of the 11 hydroxylases to the drug. The effect of the compensatory increase of endogenous ACTH could be detected after 1 hour by the rise in 17 OHP. However the concentrations of the 11-hydroxy compounds, F, B and Aldo, remained low throughout the infusion period. From the second hour onwards, facilitation of the synthesis of DOC was noticed. After the end of infusion, the levels of the precursors decreased and F and B were restored to initial values. Aldo remained low probably due to the inhibitory effect of the elevated DOC on the renin-angiotensin system.

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.