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Both pregnenolone and 17-OH-pregnenolone were found to be higher in the plasma of patients with poorly controlled congential adrenal hyperplasia than in normal subjects. The plasma levels of these precursor steroids were significantly correlated with urinary 17-ketosteroid and pregnanetriol excretion and with plasma testosterone. The mechanism where by plasma pregnenolone and 17-OH-pregnenolone levels are elevated in patients with 21-hydroxylase deficiency is unknown, but the phenomenon of product inhibition is suggested as a possible explanation. As 17-OH-pregnenolone in plasma is almost entirely of adrenal origin, its measurement promises to be useful in the management of patients with congenital adrenal hyperplasia. Acute stimulation with ACTH caused negligible changes in the plasma levels of pregnenolone and 17-OH-pregnenolone and failed to distinguish between overly, appropriately, and under-treated patients. However, following repeated stimulation with repository ACTH, the steroid levels rose. These findings indicate limited adrenal responsiveness to ACTH following chronic glucocorticoid treatment of congenital adrenal hyperplasia, even in under-treated patients, and suggest that normal precursor steroid levels in plasma and normal 17-ketosteroid and pregnanetriol excretion can only be achieved by the suppression of total steroidogenesis to less than that occurring in normal subjects.
A radioimmunoassay method has been developed for the simultaneous determination of pregnenolone, pregnenolone sulfate, dehydroepiandrosterone(DHA) and dehydroepiandrosterone sulfate (DHA sulfate). The method consists of the following procedures: 1) ether extraction of unconjugated compounds, 2) extraction of sulfates fromaqueous residue with ethyl acetate, 3) solvolysis with sulfuric acid at 40 degree C for 60 minutes, 4) celite column chromatography to separate individual compounds, 5) radioimmunoassay. Efficiencies of solvolysis for pregnenolone sulfate and DHA sulfate are 94 and 80%, Precision and accuracy studies have shown that the assays of sulfates as well as unconjugates are reproducible and accurate. Specificity was ascertained by parallelism and linearity studies. No interfering substance was detected in appreciable quantity. Plasma levels of these four compounds were determined in specimens obtained from 15 normally ovulating women. To represent the whole menstrual cycle, samples were taken 8 days before LH peak (LH-8), the day of LH peak (LH = O) and 8 days after LG peak (LH+8). Plasma contents of these compounds (geometric mean in ng/ml and 95% confidence limits in parentheses) are as follows: pregnenolone, LH-8: 1.33 (1.02-1.74), LH = 0: 1.45 (1.22-1.72), LH+8: 1.88(1.70-2.21); pregnenolone sulfate, LH-8: 70.0 (55.9-89.2), LH = 0 57.5 (40.0-82.7), LH+8: 102 (81.5-129); DHA, LH-8: 5.38 (3.90-7.43), LH = 0: 4.90 (3.58-6.79), LH+8: 4.58 (3.12-6.83), DHA sulfate, LH-8: 1480 (1110-1980), LH = 0: 1570 (1150-2140), LH+8: 1590 (1150-2190). Both pregnenolone and pregnenolone sulfate levels of 8 days after LH peak are significantly higher than those of other two days. Conversely, plasma DHA and DHA sulfate levels fluctuate over wide range with no consistent trend.
Plasma levels of the delta5-pregnenes, pregenolone and 17-OH-pregnenolone, were measured in patients with disordered steroidogenesis. While 17-OH-pregnenolone was within the normal range in patients with hypercortisolemia due to Cushing's disease, ectopic ACTH or adrenal adenrenal adenoma, 4 of 6 patients with an adrenal carcinoma had elevated levels of this precursor. Thus, elevated plasma 17-OH-pregnenolone levels in patients with Cushing's syndrome indicate adrenal carcinoma, although a normal value does not exclude this diagnosis. Abnormal resistance of delta5-pregnenes to suppression with dexamethasone proved useful in detecting the presence of residual tumor in the post-operative evaluation of adrenal carcinoma. Basal plasma pregnenolone was within the normal range in 19 of 20 patients with Cushing's disease and was invariably normal in patients with other varieties of hypercortisolism. Since acute administration of ACTH causes marked elevation of delta5-pregnene levels while patients with chronic ACTH excess (Cushing's disease and ectopic ACTH production) have normal levels, it is suggested that ACTH has a chronic influence on the intraadrenal utilization of delta5-pregnenes in addition to stimulating their formation. In pre-menopausal women with idiopathic hirsutism, basal levels of both delta5-pregnenes were elevated (P less than 0.001). Following dexamethasone administration the absolute decrease in delta5-pregnenes levels was greater than that seen in normal subjects. This observation indicates that the metabolism of delta5-pregnenes is abnormal in patients with idiopathic hirsutism.
The effect of a large dose (1000 mg) of iv cortisol-hemisuccinate on circulating steroid concentrations in five women, 28--34 weeks, gestational age, is reported. Maternal concentrations of estriol, 16 alpha-hydroxyprogesterone, 17 alpha-hydroxyprogesterone, progesterone, 20 alpha-dihydroprogesterone, delta 5-pregnenolone, delta 5-pregnenolone sulfate, dehydroepiandrosterone sulfate, and cortisol were measured by RIA before and at 8 and 12 h after iv cortisol infusions at 0 and 8 h. Data were evaluated by repeated measure analysis of variance. Estriol and 17 alpha-hydroxyprogesterone suppressed initially (P less than 0.05) and suppressed further with retreatment and increased treatment time (P less than 0.05). Dehydroepiandrosterone sulfate and progesterone suppressed initially (P less than 0.05) but did not suppress further with retreatment and increased treatment time (P greater than 0.05). delta 5-Pregnenolone and delta5-pregnenolone sulfate increased initially (P less than 0.05) but did not increase further (P greater than 0.05). Concentrations of 16 alpha-hydroxyprogesterone and 20 alpha-dihydroprogesterone were unchanged by cortisol infusion initially (P greater than 0.1) and with retreatment and increased treatment time (P greater than 0.1).
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Trace amounts of labelled pregnenolone were added to the slices of veriliscent tumor from human adrenal gland in order to study the stepwise conversion of the steroid into androstenedione, 11betaOH-androstenedione and their intermediats--17-alpha-OH pregnenolone, dehydroepiandrosterone, progesterone, and 17-alpha-OH-progesterone. The definite sequence was observed in the maximal incorporation of pregnenolone label into 17-alpha-OH-pregnenolone (2-5 min of incubation) leads to dehydroepiandrosterone (5-15 min) leads to androstenedione (10-20 min). Incorporation of the pregnenolone label into 17-alpha-OH-pregnenolone and dehydroepiandrosterone was distinctly higher than into progesterone and 17-alpha-OH-progesterone in all the experiments within all the studied periods of incubation. The data obtained suggest that in viriliscent tumors of adrenal gland conversion of pregnenolone into androgens proceeded as follows: pregnenolone leads to 17-alpha-OH-pregnenolone leads to dehydroepiandrosterone leads to androstenedione. When formation of androstenedione and 11beta-OH-androstenedione from pregnenolone and progesterone was analyzed during the experiment it was shown that 11-beta-OH-androstenedione was mainly formed via androstenedione and the hormone was the end product of the androgen synthesis.
Pregnenolone synthesis was estimated in whole adrenal homogenates incubated in the presence of cyanoketone (2alpha-cyano-4,4,17alpha-trimethyl-androst-5-en-17beta-ol-3-one). The yield of pregnenolone depended on the type of incubation medium employed. Both Ca++ and bovine serum albumin (BSA) markedly stimulated the rate of pregnenolone synthesis as did NADPH or NADPH generating system. Aminoglutethimide added in vitro inhibited cholesterol sidechain cleavage activity. Ether stress in vivo stimulated pregnenolone synthesis in vitro, and hypophysectomy of 24 hours duration resulted in a decrease. Cortisone administration for 8 days reduced the formation of pregnenolone by rat adrenal homogenates, an effect prevented by concomitant treatment with ACTH. Similarly, hypophysectomy of 8 days duration resulted in a marked diminution of pregnenolone synthesis and ACTH replacement reversed this effect. Changes in pregnenolone synthesis were paralleled by changes in corticosterone and total steroid production.
The metabolism of 7-(3)H-pregnenolone was studied in vitro using 16 human breast carcinomas. All mammary tumors transformed pregnenolone to progesterone. All estrogen receptor poor tumors and 4 out of 8 estrogen receptor rich tumors converted pregnenolone to 17-hydroxypregnenolone. Five estrogen receptor poor tumors showed the presence of 17,20-lyase as evidenced by formation of dehydroepiandrosterone and androstenedione. In two estrogen receptor poor tumors, conversions of pregnenolone to progesterone, 17-hydroxy pregnenolone, dehydroepiandrosterone, androstenedione and finally to estradiol was documented, providing a hypothetical pathway for steroid metabolism in human breast cancer. The conversion of pregnenolone to 17-hydroxypregnenolone was significantly less in receptor rich tumors and was totally absent in 4 receptor rich tumors with estrogen receptors of over 45 fmol/mg protein.
Antiserum was generated in a rabbit against pregnenolone-16 alpha-carboxyethyl thioether conjugated to bovine serum albumin. The antibody, used for the assay of pregnenolone in extracts of serum and tissue homogenates, proved sufficiently specific to allow direct assay of extracts without chromatography. Sensitivity, defined as that point on the standard inhibition curve equal to the lower value 2 SD from the mean radioactivity bound to antibody in the buffer control (zero hormone) tubes, was 0.02 ng. The accuracy was confirmed by the recovery of known amounts of pregnenolone added to serum and aqueous buffer medium. The inter- and intra-assay coefficients of variation were respectively 10.6% and 9.1%. Specificity was confirmed by checking cross reactivity of various steroids and by finding comparable pregnenolone levels in samples before and after chromatography. The administration of aminoglutethimide to rats resulted in the reduction of ovarian and serum pregnenolone levels. Administration of isoxazole, on the other hand, caused an increase in both serum and tissue pregnenolone levels. These findings are in agreement with accepted views of the action of these two metabolic blocking agents.
The in vitro regulation of the mitochondrial conversion of cholesterol to pregnenolone in rat testis tissue has been further investigated. Pregnenolone production rates by isolated mitochondrial fractions could be stimulated by the addition of cholesterol. The stimulation was always highest in mitochondria isolated from lutropin-treated testes relative to control and cycloheximide treated testes. Addition 20- or 25-hydroxycholesterol resulted in a greater stimulation of pregnenolone production rates and these rates were unaffected by prior treatment with cycloheximide. When both cholesterol and 20- or 25-hydroxycholesterol were present in the incubation medium, pregnenolone production rates were mainly influenced by the hydroxycholesterol, even in the presence of a ten-fold excess of cholesterol. Ca2+ in vitro stimulated pregnenolone production rates from endogenous cholesterol as well as from added cholesterol. However, pregnenolone production rates in the presence of hydroxycholesterol were not influence by the addition of Ca2+ in vitro.
In order to examine the dexamethasone suppressibility of plasma pregnenolone, 9 a.m. and overnight suppression tests were performed in normal adult subjects and plasma pregnenolone levels were radioimmunoassayed. The results were as follows: 1) In the 9 a.m. test, plasma pregnenolone was suppressed to the lowest level at the time between 30 min and 2 hr after dexamethasone; 2) there was no significant difference in dexamethasone suppressibility of plasma pregnenolone between the 9 a.m. test and overnight test; 3) there was no significant difference from each other among the plasma pregnenolone levels after dexamethasone administration (0.5 mg to 3 mg) in both tests; 4) after dexamethasone administration, plasma pregnenolone was not suppressed below 40% of the basal level in both tests; 5) discussions were made about the results, comparing with those of the suppressibility of cortisol which were previously reported from this laboratory.
Eight ewes each with an autotransplanted ovary received infusions of tritium-labelled pregnenolone (41 muCi/hr) for 8 hr into the artery supplying the ovary, together with prostaglandin (PG) F-2alpha (30 mug/hr) for 3 hr beginning 2 hr after the start of the pregnenolone infusion. All animals exhibited oestrus 2-3 days after the start of the experiment. During the PGF-2alpha infusion blood flow through the ovaries was increased by 13%, but subsequently returned to pre-infusion levels. Secretion rates of endogenous progesterone and 20alpha-hydroxypregn-4-en-3-one dropped rapidly 5 hr after the PGF-2alpha infusion had started from values of 250 mug/hr and 25 mug/hr to values below 60 mug/hr and 8 mug/hr, respectively. At this time the conversion of radioactive pregnenolone to progesterone was reduced by 50% of its initial value, but the secretion of endogenous pregnenolone and the formation of radioactive metabolites other than progesterone were not diminished. In 4 control animals, which received pregnenolone only, no changes in ovarian blood flow, steroid secretion rates, or in the conversion of labelled pregnenolone were observed. These results suggest a possible involvement of PGF-2alpha in the regulation of progesterone biosynthesis by an action on the 3beta-hydroxysteroid oxidoreductase-delta5(-4) isomerase enzyme system.
Using mass spectrometric, radioisotopic, chromatographic and chemical techniques, five fatty acid esters of 3 beta-hydroxy-5-pregnen-20-one (pregnenolone) have been identified as components of the lipoidal derivatives biosynthesized in vitro with bovine adrenal mitochondria. The five compounds are: pregnenolone arachidonate, pregnenolone linoleate, pregnenolone oleate, pregnenolone palmitate, and pregnenolone stearate. The distribution of the fatty acids among these five esters is different from the previously reported (Cmelik, S.H.W., and Ley, H. (1977) Comp. Biochem. Physiol. 56B, 267-270) fatty acid composition of these organelles.
A pregnenolone-binding component has been detected in the soluble fraction of the guinea pig adrenal cortex. Enzymatic degradation studies revealed that the binding component was a protein. The binding was destroyed at 60 degrees but was not inhibited by sulfhydryl reactants. Pregnenolone was bound optimally at pH 7 to 7.5 The equilibrium association constant at 0 degrees was 10(7) M-1. The pregnenolone-binding protein had an apparent molecular weight of 58,000, as determined by gel filtration. With the exception of pregnenolone sulfate, structurally similar steroids did not interfere with pregnenolone binding. No such binding activity was detected in the guinea pig liver and kidney. Serum contained pregnenolone-binding activity which was distinguishable from the adrenal cytosol factor by a variet of physicochemical means. The physiological importance of this finding remains to be determined.