Free steroids

A convenient route to steroidal aziridines from the diaxial IN3-olefin adducts, e.g., (99), which undergo elimination with lithium aluminum hydride, was developed by Galle and Hassner. Upon treatment with trialkyl phosphite, these adducts are converted to A-phosphorylated aziridines which are reduced by lithium aluminum hydride to the free steroidal aziridine. 

Gels are obtained for concentrations shown in the temperature-concentration phase diagram (Figure 1). Electron spin resonance (ESR) shows (10) that for a given temperature only a fraction (p) of the initial steroid concentration is transferred from the solution to the gel network. The picture of this gel is thus of a supersaturation gel there is a dynamic equilibrium between free molecules in solution and aggregated steroid molecules included in the long objects which constitute the gel network. The free steroid molecules concentration at a temperature where the gel state is stable is (1-p), while C p is the steroid concentration within the solid-iike gel aggregates. 

Free steroids that do not bind with plasma proteins enter target cells by passive diffusion and bind with cytoplasmic soluble-binding proteins (acceptor region), forming a steroid-protein complex. This enters the nucleus, where it interacts with steroid receptors on chromatin. 

System (4) has been reported for the quantitative determination of steroids in health and disease [143], Prior to analysis, free steroids were removed from the sample. Conjugated steroids were enzymatically hydrolyzed, and the liberated products extracted into 1 3 tetrahydrofuran-ethyl ether. The extract was evaporated, the residue dissolved in acetic acid, and then oxidized with sodium bismuthate. The final product was acetylated or formulated, and subjected to GC analysis along with the standard. A stabilized column of 4% LAC-2R-446 and 1% 85% phosphoric acid on... 

It is a halogen free steroid and highly active corticosteroid for topical application. 

Bufogenins or Bufagins These are nitrogen-free steroidal lactones that are heart toxins found in toad venom. They have no chemical resemblance to bufotenine whatsoever. 

We measure unconjugated 18-OHF by GC-MS [62]. Values for 18-OHF (measured in the free steroid fraction) are typically <150 pg/24 h for normals and > 500 pg/24 h for patients with GRA or adenoma [39]. Another important diagnostic analyte in the hydrolyzed extract is 18-oxo-THF patients with GRA have values > 15 pg/24 h compared to the normal value of < 5 pg/24 h. Selected ratios are reported for GRA, including a cortisol 18-oxygenation quotient, which is the 18-OHF cortisol ratio, giving a value about 4 for normals and >25 for patients with GRA (Table 5.3.10) and 18-oxo-THF(xl00) THF + 5aTHF, which is < 0.2 for normals and > 1.0 for those with GRA. 

Electrolytes total activity free Steroids Thyroxine free... 

Substituting [B] for the concentration of bound steroid, [F] for the concentration of free steroid, and [Rtot] = [R] + [SR] for the total number of receptor sites, this relationship can be rewritten as ... 

When only limited amounts of cells are available (e.g., of human leukocytes for estimation of corticoid receptors or of human skin fibroblasts for estimation of androgen receptors) an estimation of receptors in separated cell fractions might not be feasible. Total numbers of binding sites per cell may be obtainend if different concentrations of suitable highly specific ligands are used and incubation conditions of intact cells are carefully calibrated. In addition a good separation between medium with free steroid or steroids loosely adsorbed to the cell surface and steroid bound to the receptor inside the cell is essential. 

Nuclear magnetic resonance spectroscopy can be used to distinguish between the phosphate esters of steroids. The free steroids can be distinguished by infra-red spectrophotometry, but the phosphate esters are sufficiently polar to give rise to absorption bands that dominate the IR spectra and make distinction difficult. The NMR spectra of these steroid esters are not subject to this interference, and although they may be very difficult to interpret, they do provide the necessary distinction. 

Most of the work reported with amino-substituted steroids has been concerned with the removal of the nitrogen function from the molecule. Interest has centred mainly on the peculiarities of the reaction between nitrous acid and steroidal primary amines. The naturally-occurring steroidal alkaloids have been studied mainly with a view to establishing their structures and usefulness as sources of nitrogen-free steroids, and are not included in the present survey. 

In contrast to most receptors, most ligand-free steroid receptors are not membrane bound. They can be cytoplasmic or nuclear, depending on the receptor and the time scale. At a given instant, ERs are mostly nuclear, like the nuclear receptors. Eor the other receptors, the amount of nuclear localization is PR > MR > AR and GR. However, the dynamic picture is that receptors are shuttling back and forth across the nuclear membrane (53)... 

According to the classical view of metabolism the hormones are synthesized as free steroids in endocrine tissues and prepared for excretion in urine by peripheral metabolism and conjugation. This view had to be modified upon the isolation of dehydroepiandrosterone sulfate from adrenal tumor [307]. Thus dehydroepiandrosterone sulfate, a steroid conjugate, was shown to be secreted by the adrenal tissue. Isotopic methods also pointed in the same direction. Lieberman et al. [304], using... 

Metabolic studies carried out with isotopically labeled dehydroepi-androsterone sulfate [312] showed that this conjugated steroid may follow an indirect metabolic pathway initiated by the hydrolysis of the sulfate group. In the course of the metabolism the conjugated steroid thus becomes a free steroid first and the free steroid may undergo further metabolism. On the other hand, dehydroepiandrosterone sulfate may follow a direct metabolic pathway without a break of the ester group. 

Conjugated Estrogens Esterified Estrogens Estrone, Equilin and 17a-dihyroeuilin (free steroids) 15M X 0.25mm I.D. fused Silica capillary bonded with G19 (0.25 pm) Hydrogen 220 FID 3-O-Methylestrone USP (24, pp. 681 and 683)... 

Isobe et al. [20] extended the seope by analysing both estrogens like estradiol, estrone, and estriol, and their sulfate and glucuronide eonjugates in river water, lake water, and STP samples. SPE in eombination with negative-ion LC-ESl-MS-MS in SRM mode was used. Method deteetion limits between 0.1 and 3.1 ng/1 were reported. While the free steroids and some of the sulfates were deteeted in environmental samples, most of the eonjugates were below the deteetion hmit. 

The sample-pretreatment method applied in the regulatory analysis of steroids to some extent depends on the matrix. Urine is first submitted to an enzymatic hydrolysis step in order to convert the steroid conjugates into free steroids. The next step for all matrices is a liquid extraction or LLE, generally followed by a clean-up of the extract by SPE. The sample is then injected into the LC-MS system. In most studies, an IS is added prior to the sample pretreatment. This IS can be an analogue, but more recently isotopically-labelled IS are used more frequently. 

Steroid hormones (e.g., cortisol and estrogen) are hydro-phobic and insoluble in water. These hormones circulate in plasma, reversibly bound to transport proteins (e.g., cortisol-binding globulin and sex-hormone binding globulin) with only a small fraction free or unbound available to exert physiological action.The half-life of steroid hormones is 30 to 90 minutes. Free steroid hormones, being hydrophobic, enter the cell by passive diffusion and bind with intracellular receptors either in the cytoplasm or the nucleus. ... 

Only a small fraction (1% to 2%) of imconjugated testosterone exists fireely (non-protein bound) in serum or plasma. None of the conventional assay methods, including RIA, is sufficiently sensitive to quantify the free steroid directly in a protein-free ultrafiltrate of plasma. Instead, the free steroid is estimated in plasma by adding a known amount of radiolabeled compound to the sample and allowing labeled and unlabeled compounds to reach equilibrium in their competition for the same binding sites on the proteins. Bound and free radiolabeled fractions are then separated and the ratio of free labeled to total labeled compound is determined. At equilibrium, this ratio is taken as a measure of the free testosterone fraction. An estimate of serum free testosterone can then be calculated by multiplying the free testosterone fraction by the total testosterone concentration. 

In the equilibrium dialysis/ultrafiltration method for determining free testosterone in blood, a sample is first equilibrated with radioactive testosterone. Free steroid is then separated from bound steroid by filtration through an anisotropic, hydrophilic ultrafiitration membrane. The driving force for ultrafiltration is provided by centrifugation at 1000 to 2000 xg. Filtrate containing free steroid collects in the filtrate cup, whereas protein-bound steroid remains above the filter. Radioactivity in the filtrate is a measure of... 

Hammond GL, Nisker JA, Jones LA, Siiteri PK. Estimation of the percentage of free steroid in undiluted serum by centrifugal ultrafiltration-dialysis. J Biol Chem 1980 255 5023-6. 

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