Showing papers on "Pregnenolone published in 1978"
TL;DR: When given orally to rats, trilostane inhibits corticosterone and aldosterone production and elevates circulating levels of pregnenolone at doses lower than those that produce adrenal hypertrophy or inhibit gonadal steroidogenesis.
224 citations
207 citations
TL;DR: The block in steroid biosynthesis caused by intravenous injection of human chorionic gonadotropin (hCG) was beyond pregnenolone synthesis, and was not dependent on impairment of cyclic AMP formation and availability.
196 citations
TL;DR: The observed patterns of immunoprecipitation and inhibition of catalytic activity indicated that the two P -450 proteins are immunochemically different from each other.
131 citations
TL;DR: A highly reactive and reliable assay has been developed for the conversion of cholesterol to pregnenolone and it is shown that the addition of adrenal ferredoxin readily restores full ferric high spin type spectrum of the substrate-bound P -450 scc or, together with cholesterol and Tween 20, restores the CO-spectrum of the P - 450 scc.
102 citations
TL;DR: The negative effects of LH and hCG on Leydig cell responses result from the combination of receptor loss and enzymatic defect(s), attributable to the local inhibitory effects of steroids, such as estrogens, that are formed during the acute tcsticular response to gonadotropin.
Abstract: The regulation of testicular endocrine function by hormonal mechanisms depends upon the integrated actions of gonadotropins (LH, FSH and prolactin) and steroids (estrogen and androgen) upon the Leydig cell Withdrawal of gonadotropic support by hypophysectomy causes partial loss of LH receptors and testosterone responses, whereas cyclic AMP responses are normal or increased Thus, the major effects of hypophysectomy are on processes beyond receptor activation and cyclic AMP formation Treatment with FSH increases LH receptors and testosterone responses to hCG, and reduces the elevated cyclic AMP responses to hCG in vitro In FSH-treated hypophysectomized rats, direct inhibitory actions of estrogen upon LH receptors and testosterone responses are demonstrable, indicating that intratesticular regulation of androgen biosynthesis could be exerted by locally formed estrogen
While low concentrations of LH are necessary for maintenance of Leydig cell function, elevation of plasma LH by treatment with LHRH or exogenous gonadotropin has a marked negative effect on LH receptors and subsequent steroidogenic responses Such hormone-induced loss of LH receptors leads to decreased sensitivity of the Leydig cell to gonadotropin, an effect that is most evident after subcutaneous treatment with hCG More acute increases in plasma gonadotropin are followed by a post-receptor lesion in the steroidogenic pathway, with loss of the maximum testosterone response during stimulation by gonadotropin or cyclic AMP in vitro The retention of pregnenolone responses and the accumulation of progesterone and 17-hydroxylated steroids in partially desensitized Leydig cells indicates that a transitory block of the 17–20 desmolase step is rcsponsible for the second lesion in receptor-depleted Leydig cells Thus, the negative effects of LH and hCG on Leydig cell responses result from the combination of receptor loss and enzymatic defect(s), attributable to the local inhibitory effects of steroids, such as estrogens, that are formed during the acute tcsticular response to gonadotropin
80 citations
TL;DR: The cycloheximide-sensitive process in sterol metabolism appeared related to the transfer of non-polar sterols such as cholesterol within the mitochondria to a region in close proximity to the enzyme.
Abstract: Steroidogenesis by adrenal mitochondria from endogenous precursors is stimulated by corticotropin (ACTH) and is sensitive to the protein-synthesis inhibitor cycloheximide. In the present investigation the effect of cycloheximide treatment on the metabolism of a number of analogues of the normal steroidogenic substrate, i.e. cholesterol, by rat adrenal mitochondria was studied. It was observed that the metabolism of analogues such as desmosterol, 26-norcholest-5-en-3beta-ol and 5-cholen-3beta-ol (that is with non-polar alkyl side chains like cholesterol), was sensitive to cycloheximide treatment. By contrast, the metabolism of those analogues with polar groupings on the side chain, i.e., 20alpha-, 24-, 25- and 26-hydroxycholesterols was insensitive to pretreatment with cycloheximide. The binding of added sterol to the cytochrome P-450 component of the mitochondrial sterol desmolase was studied. Similar studies on the equilibration time on addition of exogenous sterols to achieve maximum rates of pregnenolone production were also made. Both studies show that cholesterol, a non-polar sterol, penetrated slowly through the mitochondrial milieu to reach the cytochrome P-450 reaction centre whereas 24- and 26-hydroxycholesterols rapidly attained the enzymic environment. The cycloheximide-sensitive process in sterol metabolism appeared related to the transfer of non-polar sterols such as cholesterol within the mitochondria to a region in close proximity to the enzyme. The importance, and possible mechanism of action, of the cycloheximide-sensitive factor in the control of adrenal steroidogenesis is discussed.
69 citations
TL;DR: The data indicate that in prepubertal obesity, maturation of adrenal gland function (chiefly the delta 5 pathway), is notably enhanced, whereas gonadal secretion of estradiol is impaired in the presence of high levels of FSH and PRL.
Abstract: Plasma levels of gonadotropins, PRL, T4, and adrenal and gonadal steroids were measured in two groups of 7- to 9-yr-old and 10- to 11-yr-old obese prepubertal girls, and were compared to those found in groups of nonobese girls of the same age. The data found in normal weight subjects confirm the data reported in the literature, showing a significant rise between the 7- to 9- and 10- to 11-yr groups, of FSH, pregnenolone, dehydroepiandrosterone, testosterone, and estradiol plasma levels, while LH, PRL, T4, cortisol, progesterone, 17-hydroxyprogesterone (17P), and androstenedione remained constant. In the obese subjects, pregnenolone and dehydroepiandrosterone levels are notably higher than in the normal girls, in the same range as those found in adult women; furthermore, they show no rise between the two age groups. The obese prepubertal groups had significantly higher progesterone, androstenedione, and PRL levels in comparison with those observed in girls of normal weight, but 17- hydroxyprogesterone, cor...
63 citations
TL;DR: When expressed in terms of the cytochrome P450 content, the rate of pregnenolone formation is high, suggesting that cholesterol side-chain cleavage in human placenta is in an activated state.
59 citations
TL;DR: It is suggested that translocation of cholesterol between different sterol pools occurs within the mitochondria, and potential intracellular effectors that could be of importance in the movement or regulation of mitochondrial cholesterol include bivalent metallic ions, prostaglandins, cyclic nucleotides, polyamines and polylysine.
54 citations
TL;DR: It is proposed that cytochalasin B enhances the availability of cholesterol bound to HDL for steroidogenesis by Y-1 adrenal cells by increasing the levels of cAMP at concentrations that lead to maximal steroidogenesis.
Abstract: The cytochalasins stimulate steroid secretion of Y-1 adrenal tumor cells two-to threefold. The order of potencies is cytochalasin E is greater than D is greater than B, but the maximum response is the the same and always less than with ACTH. Like that with ACTH, the stimulation has a rapid onset, is easily reversible, is inhibited by cucloheximide and aminoglutethimide, and occurs at a stage before pregnenolone. Although the cytochalasin, like ACTH, produce cell rounding, it is shown that this morphological change is not necessarily coupled to steridogenesis. Unlike ACTH, cytochalasin B does not measurably increase cellular levels of cAMP at concentrations that lead to maximal steroidogenesis. The cytochalasin B-induced stimulation of steroidogenesis, unlike the short-term ACTH effect, fails to occur in the absence of serum. This lack of response can be corrected by even low concentrations of human high density lipoproteins (HDL) but not by low density lipoproteins (LDL). We, therefore, propose that cytochalasin B enhances the availability of cholesterol bound to HDL for steroidogenesis by Y-1 adrenal cells.
TL;DR: Testicular steroid concentrations were determined in testes from 16 patients, 10 of whom had been treated with estrogen 1–5 days before orchiectomy, and no effect of estrogen treatment on testicular concentrations of steroids was observed, despite the previously established decline in levels of these steroids in the spermatic veins of similar patients.
Abstract: A method is described for the simultaneous radioimmunoassays of pregnenolone, progesterone, 17α-hydroxyprogesterone, androstenedione, testosterone and 5α-dihydrotestosterone in 100 mg samples of human testis tissue. The specificity is illustrated by determining the chromatographic elution profiles of steroid extracts by radioimmunoassay. The C.V. of individual assays were assessed by analysing 5 samples taken from the same testis, and illustrates the high reproducibility of the method, and homogeneity of samples. The stability of endogenous testicular steroids was assessed in relation to time at room temperature, and marked changes in composition occurred within 5 h, indicating the limitations in using autopsy samples. Testicular steroid concentrations were determined in testes from 16 patients, 10 of whom had been treated with estrogen (polyestradiol phosphate) 1–5 days before orchiectomy. No effect of estrogen treatment on testicular concentrations of steroids was observed, despite the previously established decline in levels of these steroids in the spermatic veins of similar patients.
TL;DR: When the 3β-hydroxysteroid dehydrogenase activity of chorionmicrosomes was compared with that of placental microsomes, the specific activities were found to be of the same order of magnitude, and the substrate, nucleotide specificity and steroid binding properties were almost identical.
TL;DR: Urinary steroids from a patient with 17α-Hydroxylase deficiency syndrome have been identified and it is probable that the 11-oxygenated 21-deoxysteroids are principally formed by microbial 21- dehydroxylation of the tetrahydro metabolites of corticosterone secreted into the bile.
TL;DR: Results represent definite evidence of cortisol and testosterone formation in vitro by embryonic and very young chick adrenals by incubating with homogenates of adrenal gland from 17- and 21-day-old chick embryos and chickens.
TL;DR: Dogfish testes were incubated with radioactive progesterone, pregnenolone, and testosterone, and both free and conjugated metabolites were examined, and steroid glucuronide formation was insignificant and very large amounts of solvolysable steroids were isolated from all incubations.
TL;DR: Electrofocusing of a highly-purified preparation of bovine adrenocortical cytochrome P-450(scc) showed a single peak of enzyme activity at pH 6.8, which support the assumption that a single species of enzyme catalyzes all the three steps of the reaction, i.e., 20-hydroxylation, 22-hydoxylation and cleavage of carbon chain between carbon-20 and carbon-22.
TL;DR: The conclusion is that active metabolism of sulfated steroids occurs in human and boar testes and is known to be quantitatively important in the testes of the two species studied.
TL;DR: The data support the two-cell theory for oestradiol synthesis, for granulosa cells do not appear to undertake steroid conversion via the 5-unsaturated pathway, but aromatize androgens known to be produced by thecal cells.
Abstract: Human granulosa cells from Graafian follicles aspirated 3-4 h before the expected time of ovulation were incubated with various steroid substrates, including pregnenolone, androstenedione, testosterone and dehydroepiandrosterone (DHA). Steroid production after 3 and 10 h of incubation was determined by radioimmunoassay. Progesterone and 17alpha-hydroxyprogesterone were the major products of granulosa cells in control short-term cultures with endogenous substrates. The addition of pregnenolone increased the synthesis of progesterone and 17alpha-hydroxyprogesterone compared with the controls, although the response varied considerably between paired short-term cultures. Little or no oestradiol-17beta was produced from endogenous precursors or short-term cultures to which pregnenolone had been added; one follicle, however, produced similar amounts of oestradiol-17beta in the control cultures and after incubation with pregnenolone. When granulosa cells were cultured with various amounts of androstenedione, DHA or testosterone, large amounts of oestradiol-17beta were produced, especially in short-term cultures in which larger amounts of substrate were added. Progesterone production continued and progesterone was synthesized more rapidly or in greater amounts in some short-term test cultures than in the controls. The results indicate that human granulosa cells are one source of oestradiol-17beta during the preovulatory phase. The data support the two-cell theory for oestradiol synthesis, for granulosa cells do not appear to undertake steroid conversion via the 5-unsaturated pathway, but aromatize androgens known to be produced by thecal cells. It is also suggested that either androgens or oestradiol-17beta stimulate progesterone production by granulosa cells, at least in vitro.
TL;DR: The presence of a heat stable protein in the cytosol of adrenal, testicle and ovary, which specifically binds cholesterol and some of its derivatives, but which does not recognize the compounds without the side chain of cholesterol is reported.
TL;DR: It seems unlikely that calcium is the agent primarily responsible for mediating the ACTH-induced steroidogenic effect at the mitochondrial level, but it may be possible to amplify the effects of ACTH on steroidogenesis through an increase in intraadrenal calcium.
Abstract: The importance of calcium in the ACTH-induced increase in adrenal mitochondrial pregnenolone synthesis was evaluated. In mitochondria prepared in the absence of EDTA and albumin, calcium enhanced the binding of cholesterol to cytochrome P- 450 and subsequent pregnenolone synthesis. Although these effects of calcium were slightly greater in control than in ACTH-treated mitochondria, a sizeable effect of ACTH remained even at high calcium levels (500 μM). In mitochondria prepared from adrenals homogenized in fluid containing EDTA and albumin, ACTH-induced effects on pregnenolone synthesis were relatively poor unless calcium was added to the incubation mixture. High concentrations of added calcium (500 μM or greater) obviated the need for the labile protein required for ACTH-induced effects in intact mitochondria, presumably by disrupting mitochondria and allowing an “unrestrained” interaction of cholesterol with cytochrome P-450. Thus, cholesterol-rich mitochondria from ACTH plus cycloheximide-treated rats ...
TL;DR: Testes from three species of anuran Amphibia, Bufo marinus, Rana catesbeiana, and Rana esculenta were incubated with radioactive pregnenolone, progesterone, and testosterone, and it is possible that at least some of these compounds arise from a biosynthetic pathway not involving testosterone.
TL;DR: In vitro steroid metabolism was investigated in Xenopus laevis vitellogenic follicles and full-grown follicles, finding that 10 to 50 times more estrogens were found to be associated with follicular envelopes.
TL;DR: It is demonstrated that angiotensin stimulates aldosterone biosynthesis at a point prior to pregnenolone formation, and the conversion of deoxycorticosterone to ald testosterone was enhanced (P).
TL;DR: Very small amounts of delta4-3 oxo products were formed suggesting a deficiency of 3beta-hydroxy-steroid-dehydrogenase activity in the testes of these 8 men, possibly related to the derangement of their spermatogenic function.
Abstract: Androgen biosynthesis in the testis may be analyzed in some detail by means of techniques of in vitro incubation of small testicular biopsy specimens with suitable radiolabelled precursors. Sixty-six tissue specimens from 33 patients who underwent bilateral testicular biopsies because of infertility were incubated in vitro with [3H]pregnenolone in order to investigate the possibility of abnormalities in their steroid biosynthetic activity. As a normal control, testicular tissue obtained by testicular biopsy from a young normal volunteer was used. The distribution of metabolites in the incubates of testes from 8 infertile men differed greatly from the remaining 25 patients and the normal control. The major steroids formed from pregnenolone by the testes of those 8 men were 17-hydroxypregnenolone, dehydroepiandrosterone, 20alpha-dihydropregnenolone and and 20alpha-dihydro-17-hydroxypregnenolone. Very small amounts of delta4-3 oxo products (progesterone, 17-hydroxyprogesterone, androstenedione and testosterone) were formed suggesting a deficiency of 3beta-hydroxy-steroid-dehydrogenase activity in the testes of these 8 men, possibly related to the derangement of their spermatogenic function.
TL;DR: Studies employing an antibody to P-450 demonstrate that no immunochemical similarity exists between the two P- 450s, either by the Ouchterlony technique or by inhibition study of the catalyzed reactions by the comparable antibody.
Abstract: Publisher Summary This chapter provides information on the purification of adrenal cytochrome P-450. Two different kinds of cytochrome P-450 play an essential role as oxygenative enzymes in steroid hormone biosynthesis of adrenocortical mitochondria. One is P-450scc, which is responsible for the conversion of cholesterol to pregnenolone. The other is P-45011β, which catalyzes 11β-hydroxylation of 11-deoxycorticosteroids. In the method that is described in the chapter, the activity of P-450scc and P-45011β is assayed conveniently at 37° with radioactive substrate by measuring the formation of pregnenolone from cholesterol and of corticosterone from DOC, respectively. The reaction catalyzed by each P-450 proceeds in the presence of molecular oxygen, NADPH, a ferredoxin (adrenodoxin), and an electron-transferring flavoprotein (adrenodoxin reductase). Studies employing an antibody to P-450 demonstrate that no immunochemical similarity exists between the two P-450s, either by the Ouchterlony technique or by inhibition study of the catalyzed reactions by the comparable antibody. The activity of P-450 can be measured by using the reaction system composed with NADPH, adrenodoxin, adrenodoxin reductase, the substrate, and molecular oxygen.
TL;DR: It is suggested that during sexual maturation the testicular biosynthesis of active 5-ane androgen(s) proceeds via5-ane precursors with the help of age and gonadotropin-dependent 5-anes 3beta-oxidoreductase.
Abstract: The in vivo influence of gonadotropins on the activities of oxidoreductases of androst-5-ane and androst-5-ene steroids and pregnenolone was examined in testes from young rats. Animals were given daily injections of human CG for 5 days starting at 20 days of age and the testicular 12,000 × g supernatants were assayed for steroid oxidoreductase activities. Marked increases (up to 8-fold) were noted in the rate of oxidation of the 3β-hydroxyl of 3β-hydroxy-5β-androstan- 17-one, 3β-hydroxy-5α-androstan-17-one, 5aandrostane- 3β,17β-diol, dehydroepiandrosterone, and pregnenolone, and in the 3-keto reduction of 17β-hydroxy- 5α-androstan-3-one, 17β-hydroxy-5β-androstan- 3-one, 5β-androstane-3,17-dione, and 5α-androstane- 3,17-dione. The hormone response required a certain amount of time as no response was detected until 72 h after the first injection. As little as 1 IU hCG/injection resulted in significant increases in 3β-oxidoreductase (3β-HSD) activities. FSH and TSH gave no significant increases and 25 μg NIH...
01 Jan 1978
TL;DR: This chapter illustrates gonadotropin receptors and regulation of interstitial cell function in the testis and ovary and shows how the endocrine and reproductive functions of the gonads are preserved and regulated by the actions of follicle-stimulating hormone and luteinizing hormone.
Abstract: Publisher Summary This chapter illustrates gonadotropin receptors and regulation of interstitial cell function in the testis. Synchronized or directly united formation of hormone receptors and characteristic biosynthetic pathways has been examined in the fetal testis and appears to be a probable mode of segregation into other endocrine intended tissues. The endocrine and reproductive functions of the gonads are preserved and regulated by the actions of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) and in some species, these are also influenced by prolactin. The control of steroid production by LH is believed to operate mainly through stimulation of the conversion of cholesterol to pregnenolone at the mitochondrial level in the testis and ovary. Receptor sites for LH and hCG in the testis and ovary have been identified and characterized by binding studies with labeled gonadotropins, most commonly employing I-labeled hCG. The demonstration of gonadotropin receptor sites by radioisotopic methods was initially performed by in vivo binding studies with radio-iodinated LH or hCG. The specific activity of labeled peptide hormones should be measured by bioassay or radioligand-receptor assay.
TL;DR: It is suggested that estradiol-17 beta is a feedback inhibitor of 3 beta-hydroxysteroid dehydrogenase-isomerase, the enzyme complex that converts pregnenolone to progesterone, a necessary step in the initiation of GVBD.
Abstract: Increasing doses of estradiol-17 beta added to in vitro incubations inhibited pregnenolone-induced germinal vesicle breakdown in Rana pipiens ovarian follicles. The inhibition was reversed with increasing concentrations or pregnenolone added to the medium. Because no evidence of estradiol-17 beta inhibition or interaction with progesterone-induced GVBD was observed, the effect of estradiol-17 beta on the conversion of 3H-pregnenolone to 3H-progesterone was investigated. Estradiol-17 beta in doses as low as 10(-7) M significantly inhibited the conversion of 3H-pregnenolone to 3H-progesterone in follicles incubated in vitro. It is suggested that estradiol-17 beta is a feedback inhibitor of 3 beta-hydroxysteroid dehydrogenase-isomerase, the enzyme complex that converts pregnenolone to progesterone, a necessary step in the initiation of GVBD.
TL;DR: The effect of ascorbic acid deficiency on adrenal hydroxylation of cholesterol and deoxycorticosterone in guinea pigs was studied and it was concluded that the level of asCorbate in the adrenals might be of some importance for the capacity to convert cholesterol into pregnenolone.