Nanoclusters and nanolines: the effect of molybdenum oxide substrate stoichiometry on iron self-assembly.

The growth of Fe nanostructures on the stoichiometric MoO2/Mo(110) and oxygen-rich MoO2+x /Mo(110) surfaces has been studied using low-temperature scanning tunnelling microscopy (STM) and density functional theory calculations. STM results indicate that at low coverage Fe nucleates on the MoO2/Mo(110) surface, forming small, well-ordered nanoclusters of uniform size, each consisting of five Fe atoms. These five-atom clusters can agglomerate into larger nanostructures reflecting the substrate geometry, but they retain their individual character within the structure. Linear Fe nanocluster arrays are formed on the MoO2/Mo(110) surface at room temperature when the surface coverage is greater than 0.6 monolayers. These nanocluster arrays follow the direction of the oxide rows of the strained MoO2/Mo(110) surface. Slightly altering the preparation procedure of MoO2/Mo(110) leads to the presence of oxygen adatoms on this surface. Fe deposition onto the oxygen-rich MoO2+x /Mo(110) surface results in elongated nanostructures that reach up to 24 nm in length. These nanolines have a zigzag shape and are likely composed of partially oxidised Fe formed upon reaction with the oxygen-rich surface.

Atomically resolved STM imaging with a diamond tip: simulation and experiment.

The spatial resolution of a scanning tunneling microscope (STM) can be enhanced using light element-terminated probes with spatially localized electron orbitals at the apex atom. Conductive diamond probes can provide carbon atomic orbitals suitable for STM imaging with sub-Ångström lateral resolution and high apex stability crucial for the small tunneling gaps necessary for high-resolution experiments. Here we demonstrate that high spatial resolution can be achieved in STM experiments with single-crystal diamond tips, which are generally only considered for use as probes for atomic force microscopy. The results of STM experiments with a heavily boron-doped, diamond probe on a graphite surface; density functional theory calculations of the tip and surface electronic structure; and first-principles tunneling current calculations demonstrate that the highest spatial resolution can be achieved with diamond tips at tip-sample distances of 3-5 Å when frontier p-orbitals of the tip provide their maximum contribution to the tunneling current. At the same time, atomic resolution is feasible even at extremely small gaps with very high noise in the tunneling current.

Human fetal serum cortisol levels at delivery: a review.

A review of the data for fetal cortisol levels at delivery suggests that many of the values published over the past decade are too high owing to the use of methods insufficiently specific for cortisol in cord blood. Pitfalls in the assay of cortisol have been discussed elsewhere (40). The recent use of nonspecific methods is surprising since apparently correct values were established using DIDD in the early 1960s. The high values have mainly been associated with RIA and fluorometry, which have been shown to lack specificity in human urine as well (41). The nature of the interfering material in cord serum and urine is still not entirely clear. At least part of it probably represents cortisol metabolites. The mode of delivery and anesthetic used are also important since values obtained at elective cesarean section are lower than those after vaginal delivery. The lower values at cesarean section may be due to the decreased stress to the infant, the common use of general anesthesia, and/or lower gestational age. Gestational age is very important since values in premature infants are only about half those of mature infants, and are lower in those who go on to develop the respiratory distress syndrome.

Conversion of cortisol to cortisone by the human uterus and its reversal in pregnancy.

Inter-conversion of cortisol (F) and cortisone (E) was investigated by incubating minced tissue with tritiated cortisol or cortisone and then separating the products by Sephadex LH-20 column chromatography. In non-pregnant subjects conversion of F to E predominated (43.4+/-3.4% vs 0.1+/-0.4% for E to F). In early pregnancy F leads to E decreased and E leads to F rose while at term E leads to F (46.3+/-9.1%) exceeded F leads to E (15.1+/-6.8%). These results were in accord with those obtained by assaying the endogenous concentrations. In non-pregnant subjects the F/E ratio (1.1+/-0.6) was lower than that found in serum (6.3+/-2.2) while at term the uterine F/E (9.0+/-1.8) was similar to that of serum (8.8+/-2.0). These changes resulted in an 8-fold increase in uterine F compared with a 3-fold increase in serum F, while uterine E fell to 1/2 and serum E doubled. Thus, during pregnancy there is a dramatic reversal of the reaction in the uterus in favour of the active hormone. It seems possible that the increase in cortisol thus brought about may play an anti-immune role in uterine wall, the single tissue apart from blood in direct contact with fetal tissue.

Conjugated glucocorticoids in amniotic fluid and fetal lung maturation.

While recent studies suggest that cortisol plays a role in lung maturation, conflicting reports have recently appeared relating cortisol in amniotic fluid to indices of lung maturation. the variation in the levels and differences in correlation appear to be due to differences in methodology, principally with respect to cross-reactivity in the radioimmunoassays with the conjugates of cortisol and corticosterone. We have found that the glucocorticoid conjugates correlate better with lung maturation (rs = 0.79) than does cortisol itself (rs = 0.58). This is probably because the conjugates are derived exclusively from the fetal compartment whereas cortisol is also produced by the chorionic membrane. In anencephaly, conjugate levels were very low while cortisol levels were relatively normal. Conjugate levels (mainly sulfates) appear promising as an adjunct to tests of fetal maturation.

Cortisol production and inactivation by the human lung during gestation and infancy.

The enzyme which interconverts the active hormone cortisol (F) and its biologically inactive analog cortisone (E), viz. 11 beta-hydroxysteroid dehydrogenase, is known to be present in many tissues. In this study, its possible role as a regulator of cortisol concentration in the human lung was investigated. Small amounts of minced tissue were incubated for 2 h at 37 C in the presence of tracer F or E. After extraction, the steroids were chromatographed using Sephadex LH-20 column chromatography. From 11-21 weeks of gestation, inactivation of F to E occurred (54.7 +/- 8.0%), while in 11 premature infants there was no conversion in either direction and in 9 infants (4 months to 2 yr of age) there was slight conversion of E to F (7.0 +/- 3.4%). Activity in children was negligible. Lung tissue from 4 anencephalics (35-40 + weeks) retained the ability to inactivate F to E (21.3 +/- 4.3%), though to a lesser extent (P less than 0.01) than fetuses up to 21 weeks. The validity of these in vitro studies was borne out by assays of the endogenous steroids in lung tissue and serum. These results suggest that there is an alteration from rapid inactivation of F to E in early fetal life to slight F production in infancy and that this change is advanced by pituitary or other factors which are decreased in anencephaly. This decreasing inactivation by the lung during late gestation results in higher intracellular F levels which probably act to promote lung maturation in preparation for birth.

Non-chromatographic radiotransinassay for cortisol: application to human adult serum, umbilical cord serum, and amniotic fluid.

Rapid (1-2 hour) non-chromatographic radiotransinassay using horse transcortin can be used to measure cortisol in umbilical cord serum (after hexane-carbon tetrachloride prewash and methylene chloride extraction), in amniotic fluid (after methylene chloride extraction only), and in adult serum (after dilution and boiling without extraction). Since horse transcortin has high affinity (2.4 x 10(9) l/mol) for cortisol, only a few microlitres of sample is required. The assay appears to be highly specific for cortisol clinically except in congenital adrenal hyperplasia.

In vitro stimulation of placental progesterone production by 19-nortestosterone and C19 steroids in early human pregnancy.

To explore the regulatory mechanism at the critical period of the luteal-placental shift, the effects of various steroids and peptides on the production of progesterone by placental explants at 7-10 weeks were studied. Androstenedione increased progesterone production 3-fold at a concentration of 1 mumol and more than 20-fold at 18 mumol. 19-Nortestosterone (1-18 mumol) stimulated progesterone production 10- to 100-fold. 5 alpha-Androstane-3 beta,17 beta diol (1-18 mumol) stimulated progesterone production about 2- to 5-fold while its 3 alpha isomer (1-6 mumol) increased it 2-fold. Estrone, estradiol, and estriol up to a concentration of 30 mumol had no effect. Dehydroepiandrosterone sulfate (to 36 mumol), androst-5-ene-3 beta,17 beta diol (1-6 mumol), 5 beta-androstane-3 alpha,17 beta diol (1-6 mumol), and dihydrotestosterone (1-12 mumol) had no effect. Cortisol and dexamethasone (up to 12 mumol), hCG (20,000 IU/L), GnRH (4 mumol), and ACTH 1-24 (20 mumol) also had no effect. Thus, of all the compounds tested, only 19-nortestosterone and, to a lesser extent, androstenedione, 5 alpha-androstane-3 beta,17 beta diol, and 5 alpha-androstane-3 alpha,17 beta diol stimulated progesterone production in early pregnancy; at term, only 5 alpha-androstane-3 beta,17 beta diol was stimulatory. 19-Nortestosterone was found to be less efficiently aromatized compared to other androgens; since it is also known to be present in blood from pregnant women and thought to be made in the placenta, the stimulation observed may be a paracrine effect. These observations suggest that C18 and C19 steroids may be important in the regulation of progesterone synthesis by the human placenta in early pregnancy.

Inhibition of testosterone metabolism in the human prostate.

PIP: The conversion of carbon-14-testosterone (T) to 5alpha-dihydrotestosterone (DHT) and androstanediol (A-diol) was studied in vitro using a crude homogenate of prostate from patients with benign prostatic hypertrophy. Under standard conditions, the mean conversion to DHT was 70 + or -1 (standare error, SE)% and to A-diol 14 + or -1 (SE)%. Addition of various antiandrogens and other substances decreased the T to DHT conversion to 0-55% and the T to A-diol to 0-10%. The most potent inhibitors were desoxycorticosterone and progesterone. Estradiol-17beta, cyproterone acetate, medrogestone, medroxyprogesterone acetate, estriol and 4'-nitro-3'trifluoromethylisobutyramilide were also effective inhibotors. To determine whether this effect might be significant in vivo, similar conversion studies were carried out on prostatic tissue obtained from 3 patients who had received oral medrogestone for 1-2 weeks. T to DHT was reduced to 12.2 + or -2.8 (SE)% and T to A-diol to 6.5 + or -1.0 (SE)%. The ability of such compounds to inhibit DHT formation represents 1 mode of action which may account at least in part for their efficacy in the treatment of benign prostatic hypertrophy.^ieng

Cortisol-cortisone interconversion in human fetal lung: contrasting results using explant and monolayer cultures suggest that 11 beta-hydroxysteroid dehydrogenase (EC 1.1.1.146) comprises two enzymes.

Since cortisol (F) can influence fetal lung maturation, alterations in its intracellular metabolism may be important. In fetal lung at midgestation, both the in vivo studies of Pasqualini et al. and the in vitro studies of Murphy showed the activity of the enzyme 11 beta-hydroxysteroid dehydrogenase (EC 1.1.1.146) to be strongly oxidative, converting F to its inactive analog cortisone (E). By contrast, Smith et al. observed only reductive activity (E to F) in monolayer cultures. The object of this study was to resolve this discrepancy. Human fetal lung (HFL) of gestational age 9-13 weeks was grown in monolayer cultures or as explants on grids in Ham's F-10 medium plus 10% fetal calf serum and [3H]F and [14C]E (12-20 ng/ml of each). Extracts of media were chromatographed to separate the steroids, and the percent conversion was calculated. Explants converted F to E 20-40% and maintained day 1 levels for at least 7 days of culture. E to F conversion was initially low (1-5%) and rose to 14-20% by the end of culture, corresponding to fibroblast-like outgrowth. In monolayer cultures, which appeared to consist almost entirely of fibroblast-like cells, F to E conversion was less than 10% by 5 days, while E to F conversion steadily increased to 20-85% and plateaued at confluence. Homogenates of fresh tissue demonstrated F to E but no E to F conversion, even in the presence of cofactors. Thus, it appears that when tissue structure is maintained as in the explants, HFL cells oxidize F to E by a unidirectional enzyme; activation of E to F is only expressed by HFL fibroblast-like cells in culture and does not reflect the in vivo situation.

Metabolism of progesterone by human lymphocytes: production of neuroactive steroids.

Although it has long been recognized that lymphocytes have the capacity to reduce cortisol at the C3, C5, and C20 positions, the specificity and the physiological variation of these reactions have received little attention. We have shown that such reactions also occur with progesterone. Lymphocytes were isolated from whole blood using Percoll density gradient centrifugation. The cells were incubated for 20 h with tritiated progesterone as radioactive tracer. After extractions into ethyl acetate, the residue was subjected to high performance liquid chromatography, and the radioactivities of the separated compounds were determined. Without cells, 95-97% of the tracer added was recovered in the progesterone peak, while in the presence of 4 x 10(6) lymphocytes, this was reduced to 45-90%. The metabolites obtained included at least 10 different compounds, including those corresponding in their retention times to the neuroactive 5 alpha and 5 beta dihydroprogesterones and their 3 alpha- and 3 beta- tetrahydroprogesterone derivatives. The conversion decreased with the addition of other steroids such as testosterone, cortisol, and corticosterone, suggesting that these steroids are metabolized by the same enzymes. When the cells from two pregnant patients were combined and incubated with tracer, and with and without nonradioactive progesterone, no peaks were detected by two progesterone radioimmunoassays in the absence of added nonradioactive progesterone, while in its presence three peaks corresponding to 5 alpha-dihydroprogesterone, 3 alpha-hydroxy-5 alpha-pregnane-20-dione and 3 beta-hydroxy-5 alpha-pregnane-20-dione eluted before the P peak. Their identities were confirmed using the two different progesterone radioassays that cross-reacted with these metabolites. The highest mean conversion (44.7% +/- 3.2 SE) was found with the lymphocytes of pregnant women and with that of one lactating woman (50%). Conversions by lymphocytes of women in the follicular phase (29.3% +/- 1.3 SE) were significantly lower than those in pregnancy (P = 0.014) but did not differ significantly (P > or = 0.05) from those of women in the luteal phase (22.2% +/- 3.4 SE), those of postmenopausal women (23.5% +/- 4.9 SE), or of men (22.5% +/- 2.4 SE). Lymphocytes appear to provide a hitherto unrecognized but possibly important source of neuroactive steroids.

Neuroactive ring A-reduced metabolites of progesterone in human plasma during pregnancy: elevated levels of 5 alpha-dihydroprogesterone in depressed patients during the latter half of pregnancy.

Progesterone and its 5 alpha reduced metabolite, 5 alpha-dihydroprogesterone, rise greatly in pregnancy. Both are known to have anesthetic properties, as do a number of other ring A-reduced progesterone metabolites. The possible significance of these steroids with respect to the mood changes that are common in pregnancy and in the puerperium has not been explored. In this study, pregnenolone, progesterone, and five neuroactive progesterone metabolites: the 5 alpha and 5 beta dihydroprogesterones (DHP), and three tetrahydroprogesterones (THP)-3 alpha,5 alpha-THP, 3 beta,5 beta-THP, and 3 beta,5 alpha-THP-were studied at various stages of pregnancy and in the early postpartum period. Levels of all of the steroids rose greatly during pregnancy (P < 0.001), being highest for progesterone (562-fold the follicular level), 5 alpha-DHP (161-fold), 3 beta,5 alpha-THP (56-fold), 3 alpha,5 alpha-THP (37-fold), pregnenolone (30-fold), 5 beta-DHP (16-fold) and 3 beta,5 beta-THP (16-fold) at 37 wk of gestation. During the period 2-7 d postpartum, the level of progesterone fell precipitously, whereas those of pregnenolone and the metabolites fell more slowly and mean levels were still elevated compared with follicular levels 2 wk after delivery. By 7 wk postpartum, only 3 alpha,5 alpha-tetrahydroprogesterone and 3 beta,5 beta-tetrahydroprogesterone remained slightly elevated (P < or = 0.012 and 0.007, respectively). Mean levels of the progesterone metabolites tended to be higher in depressed patients compared with controls, and this difference reached significance for 5 alpha-dihydroprogesterone both at 27 wk (P = 0.04) and at 37 wk (P = 0.02) of gestation (combined, P = 0.003). These results show that all five of these metabolites rise markedly during pregnancy and suggest that alterations in progesterone metabolites may be involved in the mood changes of pregnancy and the puerperium.

Lack of specificity of cortisol determinations in human urine.

The specificity of 7 different binding proteins (4 antibodies and 3 transins) was investigated in human urine. Pregnant and nonpregnant urine samples were extracted and chromatographed, and values were compared before and after chromatography. Without chromatography, all methods grossly overestimated the amount of cortisol present. Four methods gave higher values than the other 3 even after chromatography, possibly due to cross-reactivity with 20-dihydrocortisone which coelutes in part with cortisol. Interference also occurred in both the less polar and the more polar regions of the chromatograms with all assay systems. Values for a series of 20 urines were closely similar for the RTAs but widely divergent for the RIAs. Close correlations were found for all of the RTAs with each other and with the RIAs if simple methylene chloride extraction was used. A high degree of correlation was also found between extracted and unextracted urine values in the 4 systems studied. Cortisol values by RTA (dog transcortin) after chromatography on Sephadex LH-20 gave mean values of 20.5 +/- 9.7 microgram/day in men, 14.0 +/- 5.7 micrograms/day in cycling women, and 38.0 +/- 24.5 micrograms/day in women in late pregnancy (n = 6 in each group). It is concluded that there is no simple practical method currently available for true cortisol in urine, but that the measurement of adrenal corticoids in urine can afford an accurate reflection of adrenocortical function provided there is no gross metabolic abnormality present and that the normal range is carefully established for each particular method used.

The psychotropic effects of inhibitors of steroid biosynthesis in depressed patients refractory to treatment.

Twenty patients, diagnosed as suffering from treatment-resistant major depression, were treated with one or more drugs that decrease corticosteroid biosynthesis. Nine were psychotic, 11 nonpsychotic. Seventeen completed the treatment (8 psychotic, 9 nonpsychotic); 13 responded (5 psychotic, 8 nonpsychotic; 11 responded completely (i.e., a drop in the Hamilton Depression Scale of at least 50%, to < or = 15), and 2 responded partially. The mean age of the responders (45.2 +/- 12.6 years) did not differ significantly from that of the nonresponders (48.7 +/- 12/3). Data were analyzed in the following categories; (1) the presence or absence of psychosis, (2) response or nonresponse to treatment, and (3) the drug(s) used (aminoglutethimide, ketoconazole, or a combination of either of these with metyrapone). The patients improved over time on the Hamilton Depression Scale independent of the medication used. Responders demonstrated improvement in mood, insomnia, anxiety, diurnal variation, paranoia and obsessive compulsiveness. Nonpsychotics responded better than psychotics.

Antiglucocorticoid therapies in major depression: a review.

In major depression there are two well-documented biochemical abnormalities: hypercortisolism, and its resistance to dexamethasone suppression. It therefore seems reasonable to see if giving drugs which interfere with cortisol biosynthesis might bring about a remission. An open trial was begun in our institution of 20 refractory patients with major depression. Aminoglutethimide, metyrapone, ketoconazole or combinations of these drugs along with a maintenance dose of cortisol were used for eight weeks. Of the 17 completers, eleven patients were considered to have good responses and two partial responses. Four had complete remissions lasting several years. A similar study of four patients who received oral RU 486 also gave encouraging results. Two patients with obsessive compulsive disorder associated with depression showed striking improvement on aminoglutethimide combined with a serotonin re-uptake inhibitor. In addition to a case report in 1988 by Ravaris et al. of a patient hypophysectomized for previous Cushing's syndrome whose depression responded to ketoconazole, several other studies over the past five years have had similar favorable results. Wolkowitz et al. (1993) gave oral ketoconazole to 10 depressed patients for three weeks which resulted in a significant drop in their Hamilton Depression Scale ratings. O'Dwyer et al. (1995) conducted a placebo-controlled single-blind crossover study using lifetyrapone and maintenance cortisol in eight inpatients for two weeks; six responded. Thakore and Dinan (1995) studied eight inpatients using ketoconazole for four weeks; there were five responders and three partial responders. Anand et al. (1995) conducted a four-week double-blind trial of ketoconazole in a single treatment-refractory patient with good results. Arana et al. (1995) used a different approach but one which also leads to suppression of endogenous corticosteroids-i.e. short-term dexamethasone suppression (4 mg/day for four days). When tested at 14 days, 7/19 of the dexamethasone group had responded well while only 1/18 of the placebo group had responded. While these studies have shortcomings, antiglucocorticoid therapy appears to be an effective tool in the treatment of major depression. Possible mechanisms are discussed, and a unifying hypothesis is attempted.

Double-blind randomized crossover trial of luteal phase estrogens (Premarin) in the premenstrual syndrome (PMS).

Eleven patients with moderate to severe premenstrual syndrome were given Premarin during the latter half of the menstrual cycle for at least two cycles, and a placebo for at least two cycles. Mental and physical symptoms were monitored daily with a self-rating scale. Premarin was significantly less effective than placebo in relieving the severity of both mental (p less than 0.02) and physical (p less than 0.02) symptoms of PMS (combined data p less than 0.01). It is concluded that luteal phase Premarin is ineffective as a treatment for PMS, and may actually aggravate the symptoms.

Elevated levels of some neuroactive progesterone metabolites, particularly isopregnanolone, in women with chronic fatigue syndrome.

Chronic fatigue syndrome (CFS) is a controversial entity whose cause is unknown. In this study we have explored the possibility that progesterone metabolites may be involved. Plasma levels of the progesterone precursor pregnenolone, progesterone itself, and five ring A-reduced metabolites of progesterone were measured in 20 women with CFS and in 13 age-matched controls. To minimize the contribution of the ovary, women were either post-menopausal or in the follicular phase of the menstrual cycle (day 4-8), and progesterone levels were all well within the expected range (< or = 3.5 nmol/l). Mean values for progesterone and all of its metabolites were higher in CFS patients, the most marked being a 2.3-fold elevation in isopregnanolone (3beta,5alpha-tetrahydroprogesterone; p < or = 0.001). Progesterone levels were correlated with those of its metabolites, but even after controlling for progesterone by ANCOVA, isopregnanolone levels were still elevated (p < or = 0.001). These elevated levels of isopregnanolone could not be attributed to medications (antidepressants and anxiolytics). When the CFS patients were divided into two groups according to their Hamilton depression scale ratings, mean (+/-SD) isopregnanolone levels were higher (274+/-160 vs 197+/-119 pmol/l) in the less depressed group (ratings 2-14) than in the more depressed group (ratings 17-28), although this difference did not reach significance. Progesterone levels were negatively correlated with Hamilton depression rating scores (r=-0.56; p<0.01). These results suggest that increases in ring A-reduced progesterone metabolites, particularly isopregnanolone, are associated with CFS, and that the pathophysiology of CFS is unlikely to be due to depression.

Steroids and depression.

Patients with endogenous depression (major affective disorder) frequently have high cortisol levels, but the diurnal rhythm is usually maintained and they do not develop the physical signs of Cushing's syndrome. On the other hand, depression is a frequent feature of Cushing's syndrome regardless of etiology, and it is often relieved when the cortisol levels are reduced, by whatever means. The mechanisms of the hypercortisolemia and resistance to dexamethasone suppression commonly found in endogenous depression are poorly understood; contrary to expectations, ACTH levels are not clearly elevated. There is a striking difference in the psychiatric features seen in endogenous hypercorticism compared to those seen after exogenous administration of glucocorticoids or ACTH. This suggests that either there are other stimulating or modifying factors besides ACTH or that the steroids stimulated by ACTH or other peptides differ from those in control subjects, i.e. there may be an alteration in the metabolism of steroids in depression. Little is known about the metabolic changes or the many steroids besides glucocorticoids produced by the hyperactive steroid-producing tissue. Preliminary studies suggest that major depression may be improved by steroid suppression. It is hypothesized that steroids themselves may be important in causing and perpetuating depression.

Treatment of major depression with steroid suppressive drugs.

The hypercorticism frequently observed in major depression, unaccompanied by signs of Cushing's syndrome, is still poorly understood. One suicidal young woman, with very high cortisol levels and unusual resistance to dexamethasone suppression, is described. She was successfully treated with steroid suppressive drugs (aminoglutethimide, metyrapone), had a prompt and complete remission and has remained well for more than two years on no medication. This success prompted an on-going clinical trial of this therapy. The available drugs and a working hypothesis of their action are discussed.

Influence of 19-nortestosterone and androgens on progesterone biosynthetic enzymes in early human placental explants.

We recently showed that the production of progesterone (P4) in human placental explant culture from early gestation is enhanced by treatment with 19-nortestosterone (19-NT) or with certain androgens, namely androstenedione (A-dione), 5 alpha-androstane-3 alpha,17 beta diol (3 alpha-diol) and 5 alpha-androstane-3 beta,17 beta diol (3 beta-diol). This stimulation of P4 was explored further in this study. There was little metabolism of radioactive P4 when incubated for 24 h in the presence or absence of these steroids. The role of different steroids in the regulation of P450 cholesterol side-chain cleavage enzyme (P450scc) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) was evaluated by measuring the conversion of P4 derived from unlabelled 25-hydroxycholesterol and from labelled pregnenolone, respectively. The results showed that 19-NT, A-dione and 3 alpha-diol stimulated P450scc activity; however, 3 beta-diol was ineffective. While 19-NT and 3 beta-diol enhanced the bioconversion of pregnenolone to P4, A-dione and 3 alpha-diol were without effect. The initial rapid stimulation of P4 by 19-NT within 2 h of incubation was not blocked by concurrent treatment with cycloheximide (CH). However, after incubation for 24 h, 70% of the 19-NT-stimulated P4 was abolished by CH. During the same incubation period, P4 stimulation by A-dione, 3 alpha- and 3 beta-diol were completely blocked by treatment with CH. Thus our observations suggest that 19-NT-stimulated P4 accumulation is due to the combined effects on P450scc and 3 beta-HSD enzyme activities. A-dione and 3 alpha-diol increase biosynthesis of P4 by acting selectively on P450scc enzyme. However, the stimulatory action of 3 beta-diol on P4 is only at the level of 3 beta-HSD. Since CH blocks the stimulatory actions, the mechanism(s) by which androgens (A-dione, 3 alpha-diol and 3 beta-diol) and norandrogen (19-NT) augment the biosynthetic enzyme activities appears to be mediated by a process inhibited by CH. Since CH interference was absent during the initial rapid P4-stimulation by 19-NT, there may be a direct action of this steroid at the cellular level which is not dependent on new protein synthesis.