Showing papers on "Pregnenolone published in 1970"
TL;DR: The hypothesis that ACTH controls steroidogenesis by determining the rate of efflux of mitochondrial pregnanolone and hence the extent of the feedback inhibition by pregnenolone of its own synthesis is found to be consistent with the data obtained.
148 citations
TL;DR: The lipid: buffer distribution coefficients calculated for progesterone and pregnenolone were much higher than those calculated for the steroids related to the androgens and corticosteroids.
74 citations
TL;DR: The secretory function of both human ovaries was studied simultaneously by comparing the concentrations of several steroids in the effluent blood from the two ovaries with their concentrations in the blood of mice lacking ovaries.
Abstract: The secretory function of both human ovaries was studied simultaneously by comparing the concentrations of several steroids in the effluent blood from the two ovaries with their concentrations in the
65 citations
64 citations
TL;DR: Results suggested that Δ5-3β-hydroxysteroid dehydrogenase activity may be rate-limiting in the over-all reaction and that the inhibitory effects of the cyclic nucleotide on conversion of pregnenolone to progesterone in adrenal subcellular preparations were primarily related to actions on the dehydration.
56 citations
TL;DR: Tritiated cholesterol, pregnenolone, progesterone and testosterone were injected intravenously into adult male rats and the radioactivity in the seminiferous tubules was always significantly lower than in the interstitial tissue, the difference being most marked in the case of cholesterol.
Abstract: Tritiated cholesterol, pregnenolone, progesterone and testosterone were injected intravenously into adult male rats. They were killed from 30 min to 10 days after the injection of cholesterol, and from 2 to 30 min after the other steroids. The interstitial tissue of the testis was separated by free hand dissection from the seminiferous tubules. The tissue samples were dried, weighed, combusted in closed glass ampules and the tritium gas was subsequently counted in a metal cathode internal gas counter. Pregnenolone, progesterone and testosterone behaved equally, producing maximal radioactivity in both tissue compartments between 2 and 5 min after the injection, but the maximal radioactivity appeared at 24 hr after the cholesterol injection. The radioactivity in the seminiferous tubules was always significantly lower than in the interstitial tissue, the difference being most marked in the case of cholesterol. Very low or negligible counts were obtained in the seminiferous tubules throughout the cholesterol ...
55 citations
TL;DR: The results indicate that the ratio between 3-sulphates of 17β-hydroxysteroids and the corresponding 17-ketosteroids in plasma is determined by the NADH/NAD+ ratio in the liver cell cytoplasm.
Abstract: Ethanol intake has been shown to cause a rapid increase of the concentration of androst-5-ene-3β,17β-diol 3-sulphate and a simultaneous decrease of the concentration of dehydroepiandrosterone sulphate in plasma. The ratio between the 17β-hydroxysteroid and the 17-ketosteroid increased with the ethanol concentration up to 30–50 mg ethanol/100 ml blood when a 6 to 10-fold increase was obtained. The ratios between the 3-sulphates of 5α-androstane-3α, 17β-diol and androsterone and between the monosulphates of 5α-androstane-3β,17β-diol and 3β-hydroxy-5α-androstan-17-one also increased during ethanol metabolism. Deuterium was rapidly incorporated into the D-ring of the three C19 steroid diols, reaching about 20 atom per cent excess 10 to 20 min after oral administration of 0.1 g [1-2H2]ethanol per kg body weight. The concentrations of steroids with a sulphate group at C-17 did not change and deuterium was not incorporated into these steroids or into the 17-ketosteroid sulphates. The ratio between the 3-sulphates of 5-pregnene-3β,20α-diol and pregnenolone increased only slightly and incorporation of deuterium into the side chain of the C21 diol reached a maximum of about 4 atom per cent excess about 1 hour after the ethanol administration.
The results indicate that the ratio between 3-sulphates of 17β-hydroxysteroids and the corresponding 17-ketosteroids in plasma is determined by the NADH/NAD+ ratio in the liver cell cytoplasm. They also indicate that the 3-sulphate of 5-pregnene-3β,20α-diol is not formed from pregnenolone sulphate at the same site or with the use of the same coenzyme molecules as the 17β-hydroxysteroids.
55 citations
TL;DR: It has been established that under in, vivo conditions the fetal testis synthesizes androgens and that apparently the pathway pregnenolone → 17a-hydroxypregnenolones → dehydroepi-androsterone → androstenedione/5-androstene-3β, 17β-diol → testosterone is preferred.
53 citations
TL;DR: In this article, the conversion of 20α-hydroxy-cholesterol to (22R)-22-hydroxymethylpolysilicon (22S)-20α,22-dihydroxycholesterol and pregnenolone was investigated.
50 citations
TL;DR: In vitro steroid biosynthesis in the 700 g supernatant fraction of the male-phase ovotestis of Ariolimax californicus was investigated and it was shown that the following sequence occurred in male- phases: Cholesterol → pregnenolone → 17a-hydroxypregnenolones → dehydroepiandrosterone → androstenedione.
49 citations
TL;DR: Tissue that had been stored at -20 degrees C was still capable of metabolizing pregnenolone to androsta-5,16-dien-3beta-ol and no radioactivity was incorporated into androst-5-en-3 beta-ol used to trap any corresponding (14)C-labelled compound formed from [4-( 14)C]pregnenolones.
Abstract: 1. The metabolism of [4-(14)C]pregnenolone to androst-16-enes has been studied in short-term incubations of boar testis tissue. With fresh tissue androsta-5,16-dien-3beta-ol (8%) and 5alpha-androst-16-en-3beta-ol (2%) were formed. Tissue that had been stored at -20 degrees C was still capable of metabolizing pregnenolone to androsta-5,16-dien-3beta-ol. 2. NADPH was essential for the formation of androsta-5,16-dien-3beta-ol from pregnenolone; NADH had less activity and ATP was not necessary for the reaction. 3. [4-(14)C]Androsta-5,16-dien-3beta-ol, prepared biosynthetically from [4-(14)C]pregnenolone, was shown to be converted by boar testis preparations into androsta-4,16-dien-3-one (31%) if NAD(+) was present or into 5alpha-androst-16-en-3beta-ol (4%) if NADPH was present. 4. 17alpha-Hydroxyandrost-4-en-3-one and 3beta,17alpha-dihydroxypregn-5-en-20-one were considered as possible precursors for androst-16-ene formation, but both were shown to be ineffective. 5. No radioactivity was incorporated into androst-5-en-3beta-ol used to trap any corresponding (14)C-labelled compound formed from [4-(14)C]pregnenolone.
TL;DR: Although the reduction of androstenedione to testosterone was markedly impaired, estrone reduction to estradiol was essentially normal, suggesting that the defective enzyme is specific for some rather than all 17-ketosteroids.
Abstract: Testes of the Stanley-Gumbreck pseudohermaphrotic (Ps) rat secrete only 12–25% as much testosterone as normal (Nl) rats. To explain the mechanism of this defect, minces of testes from Ps and Nl animals were incubated with 14C-steroids, and radioactive testosterone precursors wereisolated by reverse isotope dilution. Pregnenolone, 17-hydroxyprogesterone and androstenedione were converted to testosterone in Nl testes, but in testes from Ps rats androstenedione was the predominant steroid isolated, indicating defective 17β-hydroxysteroid dehydrogenase. This enzyme defect was not corrected by treatment of Ps rats with HCG or by addition of a TPNH generating system to the incubation flasks. Although the reduction of androstenedione to testosterone was markedly impaired, estrone reduction to estradiol was essentially normal, suggesting that the defective enzyme is specific for some rather than all 17-ketosteroids. The data suggest that the enzyme defect is inherited and is unrelated to other conditions associat...
TL;DR: A speculative proposal is made that the adrenal cortical cleavage of the isohexyl moiety of the cholesterol side-chain may proceed via 20α-hydroperoxide formation followed by enzymic rearrangement to 20α, 22 R -dihydroxycholesterol, which then undergoes bond cleavage between C-20 and C-22 to yield pregnenolone.
TL;DR: This chapter discusses the cholesterol side-chain cleavage enzymes in steroid hormone-producing tissues and understanding of the components of the electron transport system in this mitochondrial reaction has recently been greatly extended.
Abstract: Publisher Summary This chapter discusses the cholesterol side-chain cleavage enzymes in steroid hormone-producing tissues. There is now little doubt that cholesterol is the obligatory precursor of steroid hormones produced by the ovary, testis, adrenal, and placenta. In these tissues, cholesterol can be metabolized to pregnenolone and progesterone, and the cleavage of the cholesterol side chain appears to be the first reaction in the degradation of cholesterol to steroid hormones. This cleavage reaction is common to all steroidogenic tissue and seems to involve hydroxylation of the cholesterol molecule at C-20 and C-22. This results in an overall side-chain cleavage leading to pregnenolone formation. The cholesterol side-chain cleavage enzyme system occurs in mitochondria and has the characteristics of a mixed-function oxidase requiring NADPH and molecular oxygen for its activity. The relevant enzymes have been resolved, and understanding of the components of the electron transport system in this mitochondrial reaction has recently been greatly extended.
TL;DR: Pathways leading from pregnenolone to androstenedione (the delta-4, and the delta-5 pathways) similar to those operating in the mammalian ovary, have been demonstrated to operate in the ovary of Tilapia.
TL;DR: The steroid-synthetic capacity of the mature testis of the teleost Gobius paganellus was studied in vitro by incubating the tissue with pregnenolone-4-14C of four different specific activities for four different time intervals.
TL;DR: The hypothesis that gonadal steroids inhibit gonadotrophin secretion in both young and adult animals implies that the gonads are capable of adult activity before puberty, an assumption which has yet to be proved.
Abstract: Identification of 5α-Androstane-3α, 17β-diol as a Principal Metabolite of Pregnenolone in Rat Ovary at Onset of Puberty
TL;DR: The cessation of progesterone secretion, which precedes parturition and lactogenesis at the end of pregnancy, is partly due to the redirected metabolism of pregnenolone towards 20α-hydroxypregn-4-en-3-one as the secreted end product, which is super-imposed on the already declining rate of net Δ4-steroid release by the ovary.
Abstract: 1. The activity of 20α-hydroxy steroid dehydrogenase in rat ovarian corpora lutea increased at least 50-fold between 2 days before and 2 days after parturition, and then fell gradually during lactation. The activity of 3β-hydroxy Δ5-steroid dehydrogenase decreased by 50% at parturition but remained constant at other times. 2. The 20α-hydroxypregn-4-en-3-one/progesterone concentration ratio in the ovary fell tenfold between 1 day before and 1 day after parturition, in contrast with the increase of the ratio for these steroids in plasma. 3. Pregnenolone was metabolized in intact cells or cell-free systems either to pregn-5-ene-3β,20α-diol and then to 20α-hydroxypregn-4-en-3-one by 20α-hydroxy steroid dehydrogenase and 3β-hydroxy Δ5-steroid dehydrogenase respectively, or directly to progesterone by the latter enzyme. The relative activities of these pathways appeared to reflect the relative amounts of the two enzymes and the concentrations of their respective coenzymes NADPH and NAD+. 4. From these and other observations it was concluded that the cessation of progesterone secretion, which precedes parturition and lactogenesis at the end of pregnancy, is partly due to the redirected metabolism of pregnenolone away from progesterone and towards 20α-hydroxypregn-4-en-3-one as the secreted end product. This is primarily the consequence of the sharp increase in the activity of 20α-hydroxy steroid dehydrogenase. This mechanism is super-imposed on the already declining rate of net Δ4-steroid release by the ovary. 5. A relationship of these pathways to subcellular compartments of luteal cells is proposed.
TL;DR: The in vitro metabolism of radioactive androstenedione, pregnenolone and progesterone by rat placental homogenates has been studied and the metabolites of pregnenolate and progestersone were quantitatively and qualitatively similar.
Abstract: The in vitro metabolism of radioactive androstenedione, pregnenolone and progesterone by rat placental homogenates has been studied. No estrogens were isolated but there was extensive ring A reduction of each compound. From the androstenedione incubations, 3α-hydroxy-5α-androstan-17-one, 3β-hydroxy- 5α-androstan-17-one, 5α-androstane-3α,17β-diol and 5α-androstane-3β,17β-diol were isolated by paper chromatography and identified by thin layer chromatography and the reverse isotope dilution technique. The metabolites of pregnenolone and progesterone were quantitatively and qualitatively similar. From these incubations 3α-hydroxy-5α-pregnan-20-one and 5α-pregnane-3α,20β-diol were isolated and identified. In the presence of a progesterone trap, progesterone- 7α-3H was found following the incubation of pregnenolone-7α-3H, demonstrating the presence of a 3β-ol-dehydrogenase Δ4–5-isomerase enzyme system. (Endocrinology 87: 151, 1970) ATTEMPTS to evaluate possible endocrine functions of the rat placenta during pre...
TL;DR: The combination of reaction inhibition and of incorporation of tritium into cholesterol 20α-hydroperoxide and 20α, 22R-dihydroxycholesterol suggest that both be important intermediates in the biosynthesis of pregnenolone from cholesterol.
TL;DR: It is investigated in two non-lactating goats, five and twelve weeks pregnant, whether progesterone could be produced by the normal mammary gland when pregnenolone was provided and, if so, its quantitative significance.
Abstract: EARLIER work by R. B. H. and J. L. L. suggested that in addition to its ability to extract progesterone1, normal mammary tissue may also have the capacity of synthesizing it (ref. 2 and unpublished results of R. B. H. and J. L. L.). We have therefore investigated in two non-lactating goats, five and twelve weeks pregnant, whether progesterone could be produced by the normal mammary gland when pregnenolone was provided and, if so, its quantitative significance.
TL;DR: Epididymal spermatozoa did not contribute to the observed metabolism of steroid substrates by epididymic tissue, and DHEA did not increase when cofactors were added to the incubation medium or when animals were injected with human chorionic gonadotrophin (HCG).
Abstract: Tissue slices of the rabbit epididymis, incubated in Krebs-Ringer bicarbonate buffer, converted pregnenolone to 17-hydroxypregnenolone and dehydroepiandrosterone, progesterone to 17-hydroxyprogesterone and allopregnanolone, dehydroepiandrosterone to Δ5- androstenediol, and testosterone to androstenedione. The conversion by rabbit epididymal slices of pregnenolone to 17-hydroxypregnenolone and DHEA did not increase when cofactors were added to the incubation medium, nor did it change when the animals were injected with human chorionic gonadotrophin (HCG). Epididymal spermatozoa did not contribute to the observed metabolism of steroid substrates by epididymal tissue.(Endocrinology 87: 646, 1970)
TL;DR: It is concluded that corticosteroid ‘feedback receptors’ may exist, both in the hypothalamus and anterior pituitary, and failure to suppress ACTH release by some of cortICosteroids when implanted in the infundibular region or anterior pituitsary seems to depend on their solubility in the brain and pituitARY tissues and on the amount of steroids implanted rather than on the structure of the molecule.
Abstract: In order to elucidate the localization and specificity of corticosteroid feedback receptors in the hypothalamo-hypophyseal system, various steroids were implanted in the median eminence and the anterior pituitary of female rats and their effects on stress-induced ACTH release were investigated. Suppression of ACTH release was observed after the implantation of dexamethasone, cortisol, corticosterone, 11-dehydro-corticosterone and 11-deoxycorticosterone (DOC) in the anterior median eminence. 11-Deoxycortisol (Reichstein’s substance S), tetrahydrocortisol, pregnenolone, progesterone, and testosterone were ineffective when implanted in this region. Infundibular dexamethasone, cortisol and 11-deoxycorticosterone implants suppressed ACTH release, while other steroids were not effective. Dexamethasone and 11-deoxy-corticosterone also suppressed ACTH release when implanted bilaterally in the anterior pituitary. It is concluded that corticosteroid ‘feedback receptors’ may exist, both in the hypothalamus and anterior pituitary. Failure to suppress ACTH release by some of corticosteroids when implanted in the infundibular region or anterior pituitary seems to depend on their solubility in the brain and pituitary tissues and on the amount of steroids implanted rather than on the structure of the molecule.
TL;DR: The enzyme activities of the submicrosomal fraction which were diminished by the gradient centrifugation were largely restored by addition of the heated 105,000 × g supernatant fluid.
TL;DR: It was established that the formation of saturated steroids from 3β-hydroxy-Δ5-steroids in cyanoketone treated rats involved 3-oxo-steroid as intermediates since [3α-3H,4-14C]pregnenolone was converted into saturated steroids with loss of 3H.
Abstract: The 3β-hydroxy-Δ5-steroid oxidoreductase inhibitor 2α-cyano-4,4,17α-trimethyl-5-androsten-17β-ol-3-one was administered intramuscularly to germfree and conventional, male and female, rats. Under the experimental conditions used, no steroids were found in faeces and urine from the male rats, but a large number of steroids were identified in excreta from female rats. The following 3β-hydroxy-Δ5-steroids, none of which is present in normal rats, appeared in urine and faeces from germfree and conventional cyanoketone treated female rats (chiefly as mono-sulphates): 5-androstene-3β, 17β-diol, 3β, 7α(and 7β)-dihydroxy-5-androsten-17-one, 5-androstene-3β, 7α(and 7β), 17β-triol, 3β, 16α-dihydroxy-5-androsten-17-one, 3β, 17β-dihydroxy-5-androsten-16-one, 3β-hydroxy-5,16-pregnadien-20-one, 3β-hydroxy-17α-pregn-5-en-20-one, 3β-hydroxy-5-pregnen-20-one, 3β,7α(and 7β)-dihydroxy-5-pregnen-20-one, 3β, 17α-dihydroxy-5-pregnen-20-one, 3β, 16β-dihydroxy-5-pregnen-20-one, 5-pregnene-3β, 16α, 20α-triol, 5-pregnene-3β, 17α, 20α-triol and 3β, 21-dihydroxy-5-pregnen-20-one. In addition, several saturated steroids were identified which were identical with steroids excreted by normal germfree and conventional female rats.
3β, 16α-Dihydroxy-5-pregnen-20-one normally accounts for less than 1% of the total amount of 3β, 16α-dihydroxy-5-pregnen-20-one and 3α, 16α-dihydroxy-5α-pregnan-20-one found in urine. This percentage was found to be about 70–80 in urine from cyanoketone treated germfree as well as conventional female rats. This figure is in good agreement with the extent of inhibition (75–85%) of adrenal and gonadal (testicular and ovarian) 3β-hydroxy-Δ5-steroid oxidoreductase found in experiments in vitro. It was established that the formation of saturated steroids from 3β-hydroxy-Δ5-steroids in cyanoketone treated rats involved 3-oxo-steroids as intermediates since [3α-3H,4-14C]pregnenolone was converted into saturated steroids with loss of 3H. The hepatic 3β-hydroxy-Δ5-steroid oxidoreductase active on C27 steroids was unaffected by treatment in vivo or in vitro with the cyanoketone.
TL;DR: The results show that the ovaries did not secrete detectable amounts of the steroid sulfates determined, and the conjugates circulating in the peripheral blood did not seem to be trapped by the Ovaries.
Abstract: The monosulfates of androsterone, dehydroepiandrosterone, epiandrosterone, 5-androstene- 3β,17β-diol, pregnenolone, 5-pregnene-3β,20α-diol and 5-pregnene-3β,17α,20α-triol, as well as the disulfates of 5-androstene-3β,17β-diol and 5-pregnene-3β,20α-diol, were quantified in blood plasma from normal human ovaries and in peripheral blood plasma of 6 patients. In a few instances, the progesterone concentration was determined, too. The results show that the ovaries did not secrete detectable amounts of the steroid sulfates determined. Further, the conjugates circulating in the peripheral blood did not seem to be trapped by the ovaries.
TL;DR: It is shown that amino-glutethimide in vitro could not completely inhibit cholesterol side-chain cleavage in bovine luteal tissue, as evidenced by conversion of cholesterol-l,2-3H to progesterone and LH stimulation of this phenomenon.
Abstract: Amino-glutethimide, an inhibitor of the conversion of cholesterol to pregnenolone, was employed in an attempt to elucidate a pathway for progesterone biosynthesis in which cholesterol was not an intermediate. Incubation of rat and bovine luteal tissue in Krebs-Ringer bicarbonate buffer containing amino-glutethi-mide resulted in a nearly complete inhibition of progesterone biosynthesis. Amino-glutethimide in vitro prevented acetate-l-14C incorporation into progesterone in rat luteal tissue, even in the presence of luteinizing hormone (LH); in contrast, 14C was incorporated into progesterone by bovine luteal tissue, and LH stimulated this event. Additional experiments showed that amino-glutethimide in vitro could not completely inhibit cholesterol side-chain cleavage in bovine luteal tissue, as evidenced by conversion of cholesterol-l,2-3H to progesterone and LH stimulation of this phenomenon. The in vivo administration of amino-glutethimide to rats and rabbits 1 hr before sacrifice resulted in a 4-fold or ...
TL;DR: Results are discussed in light of the suggestion that cholesterol 20α-hydroperoxide may be an intermediate in the biosynthesis of pregnenolone from cholesterol.
TL;DR: The direct metabolism of steroid sulfates and the presence of sulfatase activity in this fetal tissue and the possible significance of these findings in the developing male fetus are discussed.