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Biomedical subjects

E R Simpson

Publications and source records attributed to E R Simpson.

At least 235 records · Page 13Linked to original sources
PubMed1984

Induction of synthesis of bovine adrenocortical cytochromes P-450scc, P-45011 beta, P-450C21, and adrenodoxin by prostaglandins E2 and F2 alpha and cholera toxin.

To further elucidate the mechanisms by which ACTH (adrenocorticotropin) exerts its long-term action to maintain normal levels of adrenocortical cytochromes P-450 and related enzymes, the abilities of cholera toxin and prostaglandins E2 and F2 alpha to induce the synthesis of cytochromes P-450scc, P-45011 beta, and P-450C21 and adrenodoxin have been examined. These effectors stimulate the production of cyclic AMP and thus steroidogenesis in the adrenal cortex. Using bovine adrenocortical cells in primary monolayer culture, we have shown that treatment with cholera toxin results in increased synthesis of cytochromes P-450scc and P-45011 beta and adrenodoxin, similar to the effect observed upon ACTH treatment. Prostaglandins E2 and F2 alpha are less effective at inducing the synthesis of the mitochondrial cytochromes P-450, and do not seem to induce the synthesis of adrenodoxin. Furthermore, cholera toxin was found to be less effective at inducing the synthesis of microsomal cytochrome P-450C21 than ACTH, and no more effective than the prostaglandins. Thus, while it appears that elevation of cyclic AMP levels is a necessary step leading to increased synthesis of adrenocortical forms of cytochrome P-450, the detailed mechanism of this induction will be found to be different for each of the different enzymes.

Adrenal Cortex↗
PubMed1984

Regulation of aromatase activity of cultured adipose stromal cells by catecholamines and adrenocorticotropin.

Adipose tissue is the major site of estrogen formation in postmenopausal women. We have previously reported (Simpson, E.R., Ackerman, G.E., Smith, M.E. and Mendelson, C.R. (1981) Proc. Natl. Acad. Sci. (U.S.A.) 78, 5690-5694; Mendelson, C.R., Cleland, W.H., Smith, M.E. and Simpson, E.R. (1982) Endocrinology 111, 1077-1085) that aromatase activity of human adipose stromal cells in culture is stimulated by glucocorticoids and by dibutyryl cyclic AMP (Bt2-cAMP). In order to establish which physiological factors might stimulate aromatase activity of these cells by activation of adenylate cyclase, we have investigated the roles of adrenocorticotropin (ACTH) and isoproterenol to increase cyclic AMP levels and stimulate the aromatization of androstenedione. In the presence of methylisobutylxanthine (MIX), ACTH stimulated cyclic AMP formation and aromatase activity in a time- and concentration-dependent manner. The concentration of ACTH required for half-maximal stimulation was approximately 10(-8) M. Isoproterenol, in the presence of MIX, stimulated cyclic AMP formation in a time- and concentration-dependent fashion, and also stimulated aromatase activity. These effects of isoproterenol appeared to be mediated by binding of the agonist to a population of beta-adrenergic receptors. On the basis of these and our previous studies, we suggest that ACTH may play an important role in stimulating estrogen formation by human adipose tissue, both directly, and by stimulating the adrenal cortex to produce both substrate, androstenedione, and inducing agent, namely cortisol.

1-Methyl-3-isobutylxanthine↗
PubMed1984

Identification and characterization of cDNA clones specific for cholesterol side-chain cleavage cytochrome P-450.

Two overlapping cDNA clones (pBSCC-1 and pBSCC-2) bearing inserts approximately equal to 425 and approximately equal to 950 base pairs long, respectively, which are specific for bovine cholesterol side-chain cleavage cytochrome P-450 (P-450scc), have been identified by using two differential hybridization screening procedures followed by hybrid-selected RNA translation. By using these cloned cDNAs as hybridization probes, an RNA species was identified that had the properties expected of mRNA specific for P-450scc with respect to tissue specificity, corticotropin (ACTH)-mediated regulation of synthesis, and size of the protein product synthesized in vitro. In RNA samples obtained from bovine adrenal cortex, from bovine corpus luteum, and from cultured bovine adrenocortical cells, it was found that P-450scc is encoded by mRNA species approximately equal to 2000 bases long, a majority of which are polyadenylylated. P-450scc mRNA was not detected in RNA samples prepared from bovine heart, liver, and kidney. Treatment of cultured bovine adrenocortical cells with ACTH resulted in the appearance of elevated levels of P-450scc mRNA within 8 hr. Thus, ACTH promotes the enhancement of P-450scc gene transcription or acts to stabilize the transcripts. When pBSCC-2 cDNA was used to probe high molecular weight bovine DNA following treatment with restriction endonucleases, a simple pattern of hybridization was observed indicating that P-450scc may be encoded by a single gene.

Adrenal Cortex↗
PubMed1984

Cholesterol synthesis by human fetal hepatocytes: effects of hormones.

In previous investigations, we found high rates of cholesterol synthesis in human fetal liver tissue, second only to rates in fetal adrenal tissue. Previous estimates of the amount of cholesterol in the fetus derived from the maternal compartment are in the range of 20%. Thus, the liver may be the principal source of circulating lipoproteins in the human fetus, as is true in the human adult. Low density lipoprotein is the major source of cholesterol used for fetal adrenal steroidogenesis; therefore, it follows that factors regulating cholesterol synthesis in the human fetal liver may indirectly control the rate of steroid secretion by the adrenal cortex. The purpose of the present investigation was to determine if hormones, particularly those produced by the fetal-placental unit, might serve to stimulate cholesterol synthesis in the human fetal liver. The rate of cholesterol biosynthesis was determined by measuring the rate of incorporation of [3H]water into [3H]cholesterol in hepatocytes maintained in culture or by determination of the specific activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in microsomal preparations from human fetal liver. The addition of dexamethasone (10(-10) - 10(-6)M) stimulated cholesterol synthesis up to 2- to 4-fold between days 2 and 6 of exposure. When human fetal liver cells were maintained in the presence of dexamethasone (10(-7)M), the activity of 3-hydroxy-3-methylglutaryl coenzyme A reductase in microsomal fractions was stimulated 4-fold compared to that in control cells. Cortisol also stimulated cholesterol biosynthesis in a concentration-dependent manner. The addition of 17 beta-estradiol (E2) to the culture medium resulted in stimulation of cholesterol biosynthesis in a concentration-dependent manner from 10(-10) - 10(-7)M. The rate of cholesterol synthesis when E2 was present (10(-7)M) was 4-fold greater than that in untreated cells. Stimulation of cholesterol synthesis by E2 was maintained between 2-7 days of incubation with E2. Estrone, estriol, and E2 (10(-6)M) caused similar increases (3- to 4-fold) in the rates of cholesterol synthesis in human fetal hepatocytes. Finally, progesterone in concentrations greater than 10(-6) M significantly stimulated cholesterol synthesis in human fetal liver cells. In contrast, other hormones and factors, including insulin, glucagon, PRL, GH, dehydroepiandrosterone and its sulfate, epidermal growth factor, fibroblast growth factor, T3, (Bu)2cAMP, and cholera toxin, had no effect on the rate of cholesterol synthesis in human fetal liver cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Cells, Cultured↗
PubMed1983

Evidence for the presence of cholesterol side chain cleavage cytochrome P-450 and adrenodoxin in fresh granulosa cells. Effects of follicle-stimulating hormone and cyclic AMP on cholesterol side chain cleavage cytochrome P-450 synthesis and activity.

The synthesis of cholesterol side chain cleavage cytochrome P-450 (cytochrome P-450scc) and adrenodoxin was studied both in freshly harvested bovine granulosa cells and in granulosa cells maintained in primary monolayer culture. In addition, the action of follicle-stimulating hormone (FSH) and cyclic AMP analogs to stimulate the synthesis of cytochrome P-450scc was investigated in cultured cells. Precursor forms of cytochrome P-450scc and adrenodoxin were immunoisolated from a cell-free translation system directed by RNA prepared from freshly obtained granulosa cells that were not luteinized. Furthermore, the presence of cytochrome P-450scc in lysates of granulosa cells freshly obtained from very small follicles (containing less than 0.1 ml of follicular fluid) and in mitochondria of freshly obtained granulosa cells was demonstrated by using an immunoblotting technique. Continuous treatment of cultured granulosa cells with FSH or with cyclic AMP analogs (dibutyryl cyclic AMP or 8-bromo cyclic AMP) for 72 h increased incorporation of [35S]methionine into immunoprecipitable cytochrome P-450scc. Moreover, FSH, dibutyryl cyclic AMP, and 8-bromo cyclic AMP stimulated pregnenolone production by cultured granulosa cells (2.3-, 4.0-, and 7.5-fold increase over control, respectively), indicative of an increase in cholesterol side chain cleavage activity. The results of this study demonstrate for the first time the presence of two components of the cholesterol side chain cleavage system in freshly obtained granulosa cells, and provide direct evidence for the trophic effect of FSH and its presumed mediator, cyclic AMP, on the synthesis of cytochrome P-450scc in granulosa cells.

8-Bromo Cyclic Adenosine Monophosphate↗
PubMed1983

Effect of adrenocorticotropin on steroid 21-hydroxylase synthesis and activity in cultured bovine adrenocortical cells. Increased synthesis in the absence of increased activity.

The action of adrenocorticotropin (ACTH) to stimulate synthesis of steroid 21-hydroxylase was studied in bovine adrenocortical cells maintained in primary culture. Continuous treatment with ACTH (1 microM) caused an increased incorporation of [35S]methionine into cytochrome P-450C21 (21-hydroxylase cytochrome P-450); a maximum value (15-fold increase) was attained 24 h after initiation of ACTH treatment. Also, a 3-fold increase in cytochrome P-450C21 synthesis was observed in a cell-free translation system programmed by RNA isolated from cells that were exposed to ACTH for 24 h. The rate of synthesis of cytochrome P-450C21 declined after longer periods of treatment of the cells with ACTH. The increase in synthesis of cytochrome P-450C21 was associated with an increase (3-6 fold) in both total cytochrome P-450 content and in the type I absorbance change induced by 17 alpha-hydroxyprogesterone in microsomes prepared from ACTH-treated cells, as compared with that in microsomes from control cells. By contrast, ACTH did not act to increase steroid 21-hydroxylase activity in cultured intact cells, as determined by the rate of secretion of cortisol and 11-deoxycortisol, after addition of 17 alpha-hydroxyprogesterone to the medium. Similarly, there was no difference in steroid 21-hydroxylase activity in postmitochondrial supernatant fractions prepared from non-treated or ACTH-treated cells. Cytochrome P-450C21 was found to be synthesized as a form identical in molecular weight to the mature form. These results are indicative that ACTH acts to stimulate the synthesis of steroid 21-hydroxylase, yet is without a demonstrable effect on the activity of this enzyme which is high throughout the time period of the experiment.

Adrenal Cortex↗
PubMed1983

Regulation of human fetal testicular secretion of testosterone: low-density lipoprotein-cholesterol and cholesterol synthesized de novo as steroid precursor.

The results of the present investigation support the conclusion that low-density lipoprotein (LDL)-cholesterol facilitates androgen synthesis in human chorionic gonadotropin (hCG)-treated human fetal testicular tissue in vitro. Moreover, the number of LDL receptors and the rate of de novo synthesis of cholesterol are high during the period of active fetal testicular steroidogenesis and fall with advancing gestational age, suggestive of regulation by hCG.

Androstenedione↗
PubMed1983

Induction of 17 alpha-hydroxylase (cytochrome P-450(17)alpha) activity by adrenocorticotropin in bovine adrenocortical cells maintained in monolayer culture.

Using bovine adrenocortical cells in monolayer culture it has been shown that treatment with adrenocorticotropin (ACTH) causes a dramatic increase in 17 alpha-hydroxylase activity. In postmitochondrial supernatant fractions (PMS) prepared from cells maintained in culture, there was a 15-fold increase in 17 alpha-hydroxylase activity 36 h following initiation of ACTH treatment compared with the activity measured in PMS prepared from control cells. In the continued presence of ACTH, 17 alpha-hydroxylase activity declined; however, even after 60 h of exposure to ACTH, 17 alpha-hydroxylase activity was eight times higher than that present in control cells. The dramatic increase in 17 alpha-hydroxylase activity provides an explanation for the previously observed phenomenon that following initiation of ACTH treatment of bovine adrenocortical cells in monolayer culture there is a shift in the pattern of corticosteroid secretion from approximately equal amounts of cortisol and corticosterone to almost exclusively cortisol. Thus, the modulation of 17 alpha-hydroxylase activity by ACTH action appears to serve a key regulatory role in the pattern of corticosteroid production. Soluble cytosolic factors apparently do not participate in the regulation of 17 alpha-hydroxylase activity in the bovine adrenal cortex. Increases in the magnitude of substrate-induced absorbance changes are indicative that the increase in 17 alpha-hydroxylase activity is due, at least in part, to an elevation of cytochrome P-450(17)alpha synthesis.

Adrenal Cortex↗
PubMed1983

Aromatization of androgens by human adipose tissue in vitro.

Stromal cells prepared from adipose tissue of women were maintained in monolayer culture to study the regulation of aromatase activity by hormones. Aromatase activity was stimulated 20-100-fold by dexamethasone. Half-maximal stimulation of aromatase activity was attained at a dexamethasone concentration of 2.5 nM. The stimulatory effect of dexamethasone was apparent after a preincubation time of 4 h, and stimulation was maximal after 24 h of preincubation. The stimulatory effect of dexamethasone was observed only when fetal calf serum also was present in the culture medium. Of the various steroids tested, dexamethasone was the most potent in stimulating aromatase activity. Cytosolic fractions prepared from stromal cells that had been maintained in monolayer culture were found to contain a homogeneous population of sites that specifically bound [3H]-dexamethasone with relatively high affinity (Kd = 2.9 nM) and low capacity (38 fmol/mg of protein). The stimulatory effect of dexamethasone on aromatase activity was prevented by simultaneous incubation with cortisol 21-mesylate (0.1-10 microM), a compound known to block the binding of glucocorticosteroids to cytoplasmic receptors. These findings are suggestive that glucocorticosteroids act to increase aromatase activity in stromal cells by binding to a glucocorticosteroid receptor. This presumably results in the induction of synthesis of specific proteins, perhaps the form of cytochrome P-450 involved in aromatization, or else NADPH-cytochrome P-450 reductase. Aromatase activity was also stimulated by dibutyryl cyclic AMP ( (Bu)2cAMP). In contrast to the stimulation by dexamethasone, the effect of (Bu)2cAMP was diminished by 70% when fetal calf serum (15%) was present in the culture medium. Aromatase activity of cells incubated with (Bu)2cAMP continued to increase over an 8 day period, at which time, enzyme activity was increased by 200-fold. Aromatase activity of stromal cells maintained in the presence or absence of serum was unaffected after incubation for 5 days with oFSH, hCG, bPRL, hGH or soterenol. On the other hand, incubation of cells for 5 days with cholera toxin (10 micrograms/ml) or 1-methyl-3-isobutylxanthine (0.1 mM) resulted in a marked increase in aromatase activity; the effect of these agents was diminished greatly when serum was present in the culture medium. The findings that serum inhibited the stimulation of aromatase activity by (Bu)2cAMP and that the time courses of aromatase induction by (Bu)2cAMP and dexamethasone were markedly different are suggestive that different molecular events mediate aromatase induction by glucocorticosteroids and cyclic AMP.

Adipose Tissue↗
PubMed1983

Effects of ACTH on steroidogenesis in bovine adrenocortical cells in primary culture--increased secretion of 17 alpha-hydroxylated steroids associated with a refractoriness in total steroid output.

The long-term effects of ACTH on steroidogenesis in bovine adrenocortical cells maintained in primary culture have been investigated. Cells in monolayer culture were incubated in the presence or absence of ACTH for up to 72 h, and the steroid content of the incubation medium was assayed at 12 h intervals. During the first 12 h, adrenocortical cells incubated in the presence of ACTH (10(-9) M and 10(-6) M) produced substantially more cortisol and corticosterone than did cells incubated in the absence of ACTH. The production of steroidogenic intermediates such as pregnenolone, progesterone, and 17 alpha-hydroxypregnenolone, as well as 17 alpha-hydroxyprogesterone, 11-deoxycortisol, and 11-deoxycorticosterone also was increased by short-term (12 h) treatment with ACTH. Thereafter, corticosteroid production by cells incubated in the continued presence of ACTH decreased in a time and concentration dependent fashion. The maximal rate of cortisol production by cells incubated in the presence of ACTH (10(-9) M and 10(-6) M) for 72 h was only one third that of cells incubated in the presence of ACTH for 12 h. More dramatically, by 36 h, corticosterone secretion by cells incubated in the presence of ACTH (10(-6) M) declined to less than 20% of that of nontreated cells, and the production of 11-deoxycorticosterone was no longer detectable. ACTH also induced refractoriness in the production of other C21-steroids (pregnenolone, progesterone, 17 alpha-hydroxypregnenolone, 17 alpha-hydroxyprogesterone, and 11-deoxycortisol) as well as of C19-steroids (dehydroepiandrosterone, androstenedione, and 11 beta-hydroxyandrostenedione). The ACTH-induced refractoriness in the production of C21-steroids lacking a 17 alpha-hydroxyl group occurred earlier than that of 17-hydroxylated C21-steroids. Despite the decline in total corticosteroid production, the long term effect of ACTH was to enhance the relative secretion of 17 alpha-hydroxylated steroids and C19-steroids. Adrenocortical cells incubated for 72 h in the presence of ACTH continued to secrete cortisol, 17 alpha-hydroxyprogesterone, 11-deoxycortisol, and 11 beta-hydroxyandrostenedione in increased amounts. In fact, 11-deoxycortisol became a major secretory product of the ACTH-refractory adrenocortical cell. These results are indicative that ACTH acts in diverse manners on the bovine adrenocortical cell to affect corticosteroid secretion. The initial stimulation of corticosteroid production appears to be reflective of an increase in overall substrate (cholesterol) utilization and probably is mediated, in part, by an increase in cholesterol side chain cleavage activity. The secretion of 17 alpha-hydroxysteroids and C19-steroids is enhanced further by an action of ACTH to increase 17 alpha-hydroxylase activity and possibly also 17,20-lyase activity. The ACTH-induced refractoriness in corticosteroid production, on the other hand, appears to result primarily from a decline in precursor (cholesterol) utilization.

Adrenal Cortex↗
PubMed1983

Decline in the concentration of low-density lipoprotein-cholesterol in human fetal plasma near term.

Fetal plasma levels of lipoprotein-cholesterol were quantified during the latter stages of normal human gestation to ascertain whether a relationship exists between fetal adrenal steroid production and the concentration of plasma lipoprotein-cholesterol. It was found that total cholesterol and low-density lipoprotein (LDL)-cholesterol levels in fetal plasma declined progressively from 33 to 42 weeks of gestation. At 41 to 42 weeks of gestation, the fetal plasma concentrations of total cholesterol (53 +/- 3 mg/dL, mean +/- SEM) and of LDL-cholesterol (28 +/- 2 mg/dL) were significantly lower (P less than 0.001) than those at 33 to 34 weeks of gestation (73 +/- 7 mg/dL and 49 +/- 6 mg/dL, respectively). However, there were no fluctuations in the plasma concentrations of high-density lipoprotein (HDL)-cholesterol during this period of fetal development. The fetal plasma levels of dehydroepiandrosterone sulfate (DS), the major secretory product of the fetal adrenals, rose significantly between 33 and 42 weeks of gestation. Since LDL-cholesterol is utilized as substrate for fetal adrenal steroidogenesis, it is suggested that the increasing rate of growth and steroid production by the fetal adrenals near term is causally related to the significant decline in the concentration of both LDL-cholesterol and total cholesterol in fetal plasma during normal human development.

Cholesterol↗
PubMed1983

Steroidogenic refractoriness of bovine adrenocortical cells to dibutyryl cyclic AMP.

The long-term effects of dibutyryl cyclic AMP [(Bu)2-cAMP] on steroidogenesis in bovine adrenocortical cells maintained in primary culture were investigated. During the first 36 h, total steroid production by cells incubated with (Bu)2-cAMP increased progressively. Thereafter, however, there was a marked fall in steroid output. During the first 36 h adrenocortical cells incubated in the presence of (Bu)2-cAMP produced substantially more C19-steroids and 17 alpha-hydroxylated C21-steroids than did cells incubated in the absence of (Bu)2-cAMP. By 48 h, however, such steroid secretion by cells incubated in the continued presence of (Bu)2-cAMP declined toward control levels. By contrast, the secretion of corticosterone and 11-deoxycorticosterone was consistently less by cells maintained in the presence of (Bu)2-cAMP than by cells maintained in its absence. These results suggest that refractoriness results, at least in part, from events which occur distal to the formation of cAMP. The action of ACTH and (Bu)2cAMP to promote the secretion of 17 alpha-hydroxylated C21-steroids and C19-steroids, on the other hand, appears to reflect an increase in the rate of cholesterol side-chain cleavage, as well as an increase in 17 alpha-hydroxylase and possibly also 17, 20-lyase activities.

Adrenal Cortex↗
PubMed1983

Effect of prostaglandins on steroid secretion by human fetal adrenal tissue.

In the present investigation we evaluated the effect of prostaglandins on the rate of steroid secretion by human fetal adrenal (HFA) tissue. Prostaglandins F2 alpha and E2 (10 micrograms/ml) were added to the culture medium in the presence or absence of ACTH (1 micrograms/ml). The medium was assayed for content of cortisol (F), dehydroepiandrosterone sulfate (DS) and pregnenolone sulfate (PS) by radioimmunoassay. When HFA tissue fragments were maintained in the absence of ACTH, F secretion was low; PGF2 alpha but not PGE2 suppressed F secretion by 60-65%. When ACTH was added to the culture medium, the secretion rate of F increased 15-fold, whereas DS and PS secretion was maintained at or near initial rates of secretion. The addition of PGF2 alpha to the culture medium containing ACTH resulted in a 80% decrease in F secretion, but PGE2 only suppressed F secretion by 50%. In contrast, PGE2 or PGF2 alpha had little effect on the rate of DS or PS secretion either in the presence or absence of ACTH. In conclusion, prostaglandins appear to inhibit the secretion of F, but not of DS or PS by the HFA.

Adrenal Glands↗
PubMed1983

Catechol-O-methyltransferase activity in erythrocytes of persons with severe thermal injury.

In the present investigation, we found that the catechol-O-methyltransferase activity (COMT) in erythrocytes of persons with severe thermal injury was strikingly increased when compared with that in erythrocytes of noninjured individuals. The specific activity of COMT in erythrocytes of burned patients was not correlated with extent of burn. Thus the echinocytes of burned persons are another example of abnormal red cells in which COMT activity is increased. This appears to be the first example of increased COMT activity in abnormal erythrocytes that is not associated with large numbers of reticulocytes.

Adult↗
PubMed1983

Regulation by ACTH of steroid hormone biosynthesis in the adrenal cortex.

In this article, current knowledge about the mechanism of action of ACTH will be reviewed. Emphasis will be placed on events which occur subsequent to binding of ACTH to its receptor, stimulation of adenylate cyclase, and activation of protein kinase. In the first part of the review, the acute action of ACTH will be discussed with emphasis on present hypotheses as to the roles of calcium, phospholipids, sterol carrier proteins, and a "labile protein" activator of cholesterol side-chain cleavage. The presumptive role of these factors to increase the binding of cholesterol to the mitochondrial cholesterol side-chain cleavage enzyme will be discussed in the light of the concept that such binding is the step in steroidogenesis which is activated during the acute response of the adrenal cell to ACTH. In the second part of the article, the long-term action of ACTH to increase the levels of steroidogenic enzymes will be reviewed. Recent evidence is indicative that ACTH causes induction of the synthesis of key steroidogenic enzymes present in both the mitochondria and the microsomes. This appears to result from transcription of genes specific for these various species of cytochrome P-450 and ancillary proteins, resulting in increased synthesis of specific forms of mRNA. Whereas the mitochondrial steroidogenic enzymes are synthesized on cytoplasmic polysomes as precursor forms of higher molecular weight, the microsomal proteins are synthesized as forms of similar molecular weight to the mature forms.

Adrenal Cortex↗
PubMed1983

Biosynthesis of cholesterol side-chain cleavage cytochrome P-450 in human fetal adrenal cells in culture.

An immunoglobulin G fraction from antiserum raised against cholesterol side-chain cleavage cytochrome P-450 (cytochrome P-450sec) purified from bovine adrenocortical mitochondria cross-reacted with human fetal adrenal cytochrome P-450sec in an Ouchterlony double diffusion system. This property of the immunoglobulin G fraction was used for the immunoisolation of cytochrome P-450sec of human fetal adrenal cells in culture. The molecular weight of the immunoisolate from [35S] methionine-labeled human fetal adrenal cells was similar to that of purified bovine adrenocortical cytochrome P-450sec (49,000). However the molecular weight of cytochrome P-450sec immuno-isolated from an in vitro translation system programmed by human fetal adrenal RNA was approximately 54,000, about 5,000 larger than that of the immunoisolate from radiolabeled cells. The rate of synthesis of cytochrome P-450sec by human fetal adrenal cells in culture, when incubated with ACTH (10(-6) M) for 36 h, was 2.5-fold greater than that by fetal adrenal cells incubated in the absence of ACTH. This result suggests that, as in the case of bovine adrenal cells, cytochrome P-450sec of human fetal adrenal tissue is synthesized as a larger molecular weight precursor which presumably undergoes processing to the mature form during translocation into the mitochondria. This synthesis is stimulated by ACTH, which is the putative trophic factor regulating human fetal adrenal steroidogenesis.

Adrenal Glands↗