Plasma Sex Steroid-binding Protein Research Articles

Tudy on sex steroid-binding proteins (with emphasize on 17 -estradiol) in plasma of female and juvenile kutum (Rutilus frisii kutum)

A sex steroid-binding protein (SBP) that binds to 17 b-estradiol with high affinity and moderate capacity was identified in the plasma of female and juvenile of kutum (Rutilus frisii kutum) sampled during the early stage of gonadal maturation in October and prior to spawning in March. Mean maximum specific binding (Bmax) and equilibrium dissociation constant (Kd) of the fish were as follows: In early stage of gonadal development (October), Bmax= 5800±970 fmol E2/m gprotein, Kd 4.1±0.6nM, and prior to spawning (March) Bmax= 4000±895 fmol E2/mgprotein, Kd 2.9±0.3nM. In juvenile sampled in October Bmax= 1600±130 fmol E2/mg protein, Kd 2.1±0.2n M and in March samples Bmax= 3500±780 fmol E2/mg protein, Kd 2.2±0.2nM. Plasma estradiol binding characteristics of the adult samples in October and March differed from the juvenile samples in having both Bmax and Kd significantly higher than juveniles. Plasma SBP levels displayed a moderate correlation with GSI (r2= 0.52) and CF (r2= 0.51) and a weak correlation with HSI (r2 = 0.28). Affinity was moderately correlated with CF (r2 = 0.68) and HIS (r2 = 0.50). A strong correlation was obtained between Bmax and Kd, high Bmax values coincided with high Kd values and vice versa.

Binding of alkylphenols and alkylated non-phenolics to the rainbow trout ( Oncorhynchus mykiss) plasma sex steroid-binding protein

Alkylphenols are well-known endocrine disrupters, mediating effects through the estrogen receptor (ER). Although the estrogenic properties of the alkylphenols are well documented, alternative mechanisms of action are poorly described. In the present work, the interaction of a range of alkyl-substituted phenols and alkyl-substituted non-phenolics with the rainbow trout ( Oncorhynchus mykiss) sex steroid-binding protein (rtSBP) were determined by competitive ligand-binding studies. The role of alkyl chain length and branching, substituent position, number of alkylated groups, and the requirement of a phenolic ring structure were assessed. The results showed that the rtSBP binds to most chemical structures tested, although the highest affinity was obtained for mono-substituted alkylphenols with a chain length of four to eight methyl groups. Interestingly, rtSBP binding was also observed for non-phenolic compounds such as 4- t-butylcyclohexanol and 4- t-butylnitrobenzene suggesting that the rtSBP has a broad binding specificity for alkylphenols and alkylated non-phenolics.

Effluents from oil production activities contain chemicals that interfere with normal function of intra- and extra-cellular estrogen binding proteins

Some environmental pollutants have the ability to alter the endocrine function in fish through interaction with the estrogen receptor (ER). Many of these chemicals are also able to interfere with the endocrine system through other mechanisms of action, however. The plasma sex steroid-binding protein (SBP), which is involved in regulating circulating levels of endogenous sex steroids, has recently been proposed to contribute to pollutant induced disruption of endocrine homeostasis. The objective of the present work was to determine whether industrial effluents contain chemicals that are able to modulate the endocrine system through interference with the function of the ER and SBP using in vitro biological assays (bioassays) from rainbow trout. The results show that solid phase extracts of process water (produced water) from an oil production facility in the North Sea and a land-based oil refinery contain chemicals that are able to induce estrogenic effects as well as displace natural sex steroid 17beta-estradiol from the SBP. The bioactive chemicals were found to be partly resistant to biological degradation, but the identity of the chemicals was not determined. The alkylphenol 4-tert-butylphenol, which is known to occur in effluents from various oil production facilities, was found to be estrogenic and displace 17beta-estradiol from the SBP and may thus contribute to the observed endocrine disrupting activity.

Binding of xenoestrogens to the sex steroid-binding protein in plasma from Arctic charr ( Salvelinus alpinus L.)

A specific sex steroid-binding protein (SBP) is believed to be involved in regulation of circulating sex steroids, steroid delivery to target cells and intracellular signalling in sex steroid-sensitive tissues. In the present work, interactions between xenoestrogens and the plasma SBP in Arctic charr ( Salvelinus alpinus L.) were determined using ligand–protein binding studies. The test compounds were all able to displace tritiated 17β-estradiol (E2) from the Arctic charr SBP (acSBP) in a competitive and dose-dependent manner. The acSBP affinities for the xenoestrogens ranged over several orders of magnitude (17β-estradiol≫ethynylestradiol (EE2)>zearalenone (ZEA)>diethylstilbestrol (DES)>genistein (GEN)>bisphenol A (BPA), 4- t-octylphenol (OP)≫ o, p′-DDT, and dieldrin (DIN)), but were consistently lower than that of 17β-estradiol (about 4×10 2–10 6-fold less potent). The relative binding affinity (RBA) for selected chemicals were independent of both gender, age and maturation status, as well as variations of acSBP binding affinity. The affinity of endogenous steroids and estrogen mimics for the acSBP shows a high correlation to the affinity for the rainbow trout SBP, thus suggesting a phylogenetically conserved ligand-binding site between closely related species. Furthermore, it is argued that interaction with the acSBP- and SBP-mediated processes may introduce novel pathways for endocrine disruption, which may work in concert with the classical receptor-mediated effects.

Interaction of estrogen mimics, singly and in combination, with plasma sex steroid-binding proteins in rainbow trout ( Oncorhynchus mykiss)

The plasma sex steroid-binding protein (SBP) is believed to be involved in regulating circulating endogenous sex steroids as well as cellular signal transduction to nuclear steroid receptors in sex steroid-sensitive tissues. In this study, a variety of estrogen mimics (EMs), which may contribute to the endocrine disrupting effects observed in fish, were tested for the ability to interact with the rainbow trout plasma sex steroid-binding protein (rtSBP) either singly or in binary combinations. The EMs ethynylestradiol, diethylstilbestrol, 4-hydroxytamoxifen, genistein, zearalenone, 4- t-octylphenol, bisphenol A and o,p′-DDT were all able to displace 1,2,4,6,7-[ 3H]estradiol from the sex steroid-binding site at the rtSBP ( K d=2.1±0.5 nM, B max=2963±303 fmol estradiol/mg protein) in a dose-dependent and competitive manner. The plastizicer n-butyl benzyl phthalate only displayed weak binding affinity for the rtSBP, whereas the pesticide dieldrin was not able to compete for the high affinity estradiol-binding sites in plasma. None of the compounds tested was able to clearly promote the binding of the others when given in combination, indicating that synergy did not occur at the ligand-SBP binding level. The rtSBP binding affinity for EMs ranged over several orders of magnitude, but were consistently lower than those for the endogenous sex steroids (about 10 2–10 6 less potent). The results suggest that the presence of rtSBP may potentially modulate the bioavailability of EMs to estrogen receptors relative to each other and to the endogenous sex steroids themselves. Since the binding of the endogenous ligands is reversible, SBP-bound estrogens (or androgens) potentially may also become displaced by potent EMs.

Human Sex Hormone-binding Globulin Promoter Activity Is Influenced by a (TAAAA)n Repeat Element within an Alu Sequence

Sex hormone-binding globulin (SHBG) is the major sex steroid-binding protein in human plasma and is produced by the liver. Plasma SHBG levels vary considerably between individuals and are influenced by hormonal, metabolic, and nutritional factors. We have now found that a (TAAAA)(n) pentanucleotide repeat, located within an alu sequence at the 5' boundary of the human SHBG promoter, influences its transcriptional activity in association with downstream elements, including an SP1-binding site. Furthermore, SHBG alleles within the general population contain at least 6-10 TAAAA repeats, and the transcriptional activity of a human SHBG promoter-luciferase reporter construct containing 6 TAAAA repeats was significantly lower than for similar reporter constructs containing 7-10 TAAAA repeats when tested in human HepG2 hepatoblastoma cells. This difference in transcriptional activity reflected the preferential binding of a 46-kDa liver-enriched nuclear factor to an oligonucleotide containing 6 rather than 7-10 TAAAA repeats. Thus, a (TAAAA)(n) element within the human SHBG promoter influences transcriptional activity in HepG2 cells and may contribute to differences in plasma SHBG levels between individuals.

Binding of Xenobiotics to Hepatic Estrogen Receptor and Plasma Sex Steroid Binding Protein in the Teleost Fish, the Common Carp (Cyprinus carpio)

Competitive receptor binding assays have been suggested as an in vitro screening tool for assessing the activity of alleged estrogenic substances. In this study, we determined the ability of steroidal and nonsteroidal substances to inhibit the binding of [3H]17β-estradiol (E2) to the hepatic estrogen receptor (ER) and the plasma sex steroid binding protein (SBP) of the teleost fish, the common carp (Cyprinus carpio). The objectives of the study were (1) to characterize ER binding in the liver cytosol of male and female carp, (2) to establish complete [3H]E2 displacement curves from carp ER for a range of natural and xenobiotic substances and to compare the ligand data of carp ER with published data from other vertebrate species to reveal possible species differences, and (3) to determine the interaction of natural and xenobiotic substances with the steroid binding site of SBP in carp plasma. The results indicate the presence of a single class of estrogen binding sites with high affinity and limited capacity in liver cytosol of carp. The various test agents showed partly quantitative differences in their binding affinities, with the xenobiotics generally showing limited ability to displace [3H]E2 from the hepatic ER or from plasma SBP of carp. However, we found no evidence that a compound is an ER ligand exclusively in one species. The findings of this study indicate that interspecies extrapolation of steroid receptor binding data is possible on a yes/no basis but not on a quantitative basis.

Interaction of environmental chemicals with the plasma sex-steroid binding protein in the spotted seatrout

We have recently purified and characterized a high-affinity sex-steroid binding protein (SBP) with a mol weight of 135 kDa from the plasma of the spotted seatrout ( Cynoscion nebulosus). The SBP shows high affinity for 17-estradiol (Kd ∼3 nM), and testosterone (Kd ∼6 nM), and competition studies demonstrate that other endogenous steroids including 11-ketotestosterone (the teleostean androgen), progesterone, pregnenolone, cortisol and the maturation-inducing steroid (17α, 20β, 21-trihydroxy-4-pregnen-3-one) bind with much lower affinities, and are essentially unbound at their physiological concentrations. The binding of a variety of estrogenic chlorinated pesticides, polychlorinated biphenyl (PCB) congeners and alkyl phenols to the seatrout SBP were examined in competition assays. The most potent compounds tested were the hydroxylated polychlorinated biphenyl (PCB) congeners (IC50 ∼1 μM) followed by methoxychlor, nonylphenol and several DDT isomers, with IC 50s of approximately 4–8 μM. Interestingly, several of the naturally occurring phytoestrogens were inactive in this assay system. Scatchard analysis confirmed that the active compounds inhibit ligand binding through competitive mechanisms and that exposure to combinations of chemicals results in additive, and not synergistic, binding activities.

Interactions of 16α-[ 18F]-fluoroestradiol (FES) with sex steroid binding protein (SBP)

Fluorine-18 16α-Fluoroestradiol ([ 18F]- FES) is a positron-emitting tracer for the estrogen receptor that is used for positron emission tomography (PET) studies of tumor tissues rich in the estrogen receptor. The role of the sex steroid binding protein (SBP or SHBG) in the transport of the [ 18F]-FES to the estrogen-receptor-rich tissue in breast cancer patients in vivo was investigated. To determine the extent to which [ 18F]-FES is bound to SBP in the blood, we performed a series of studies using blood samples obtained from patients undergoing [ 18F]-FES PET scans. The binding of [ 18F]-FES to the SBP was measured using a simple protein precipitation assay. The binding of [ 18F]-FES metabolites to SBP was also measured. These measurements showed that the tracer was distributed between albumin and SBP, and the binding capacity of SBP was sufficient to ensure that the protein was not saturated when the tracer was fully mixed with the plasma; however, local saturation of SBP may occur when [ 18F]-FES is administered intravenously. Typically about 45% of [ 18F]-FES in circulating plasma was bound to SBP, but this fraction was dependent on the concentration of SBP in plasma. The transfer of the tracer between the two proteins was rapid, complete in less than 20 s at 0°C, suggesting that the equilibrium was maintained under most circumstances and that local saturation resolved quickly when blood from the injection site entered the central circulation. These data suggest that SBP binding of [ 18F]-FES is significant and will affect the input function of the tracer for any model that is used for the quantitative evaluation of [ 18F]-FES uptake in PET studies. Estimates of equilibrium binding in blood samples are sufficient to characterize [ 18F]-FES binding to SBP in the circulation.

Changes in plasma sex steroid-binding protein levels associated with ovarian recrudescence in the spotted seatrout (Cynoscion nebulosus).

Adult spotted seatrout were sampled from the wild during the period of their yearly gonadal recrudescence to study the association of plasma sex steroid-binding protein (SBP) levels with seasonal reproductive development. Plasma SBP levels were estimated by Scatchard analysis of the binding of radiolabeled testosterone to seatrout plasma. Plasma SBP levels were lowest in regressed females, with a mean binding capacity of 310 +/- 18 nM. SBP levels increased slightly with the appearance of cortical alveolar-stage oocytes and continued increasing throughout the period of early and late vitellogenesis to reach peak values of 468 +/- 46 nM in fish undergoing final oocyte maturation. The steroid dissociation constant increased from 4.80 +/- 0.19 nM in fish with regressed ovaries to 6.58 +/- 0.76 nM in fish having completed ovarian recrudescence. The male sample size was too small to permit examination of stage-dependent changes in SBP levels during testicular recrudescence. However, neither the overall mean binding capacity nor mean binding affinity differed significantly between male (n = 14) and female fish (n = 81) in this study. Plasma SBP levels were not directly correlated with plasma levels of either testosterone or estradiol, but there was a strong correlation (r2 = 0.67, p < 0.001) between plasma testosterone binding capacity and the steroid dissociation constant. Changes in mean SBP levels were associated with changes in mean gonadosomatic index, hepatosomatic index, and plasma estradiol concentration, suggesting that the plasma SBP may have an important role in the reproductive cycle of the female spotted seatrout.

Direct evidence for the localization of the steroid-binding site of the plasma sex steroid-binding protein (SBP or SHBG) at the interface between the subunits.

Complete dissociation of dimeric plasma sex steroid-binding protein (SBP or SHBG) was obtained in 6 M urea at 10 degrees C. Removal of urea resulted in the refolding of monomers, followed by reformation of dimeric SBP, which migrates with the same mobility as the native protein. Dimerization does not require Ca+2 or steroid. Renatured monomers yield dimers with dissociation constants for 5 alpha-dihydrotesterone (DHT) and 17 beta-estradiol (E2) indistinguishable from those of native human SBP. This phenomenon was also demonstrated by mixing human and rabbit SBPs that, upon renaturation, form a hybrid dimer composed of one human subunit and one rabbit subunit. The hybrid binds both DHT and E2 in contrast to rSBP, which only binds the androgen. Therefore, we conclude that (1) docking of the two subunits creates an asymmetric steroid-binding site located at the interface between the subunits, and (2) only one face of the dimer defines the specificity for binding E2 by encompassing portion of a structural motif that recognizes the flat ring A of E2. The remaining portion, which recognizes the saturated ring A of DHT, is shared by both faces of the dimer. Because native monomers do not exist alone, the often-asked question of whether the SBP monomer binds steroid can be considered meaningless; steroid-binding activity is expressed only in the dimeric state. Finally, formation of the hybrid indicates that SBP dimerization represents a conserved event during the molecular evolution of SBP, suggesting that the structural elements responsible for dimerization will be homologous in SBPs from other species.

Structure of mouse protein S as determined by PCR amplification and DNA sequencing of cDNA

The cDNA sequence of mouse protein S was derived by conventional PCR amplification from liver mRNA, initially using primers derived from the human cDNA sequence, followed by direct DNA sequencing. Seven overlapping PCR fragments covering all of the mature protein, part of the propeptide, and the 3′ noncoding region were generated and sequenced. In some cases primers based upon the human cDNA sequence were ineffective. Subsequent successful amplification with mouse-derived primers to the same regions and comparison of the mouse and human sequences in these regions suggest that the failure of the human primers was due to insufficient degree of heterospecies identity. The mouse protein S cDNA sequence of the coding region shares 82% identity to human. The 3′ noncoding region of mouse protein S cDNA has several small deletions and insertions compared to human protein S cDNA. Mature mouse protein S consists of 634 amino acids in a single polypeptide chain and displays domain organization similar to that for other species. The amino acid sequence of mouse protein S is about 80% identical to that of other species. Eleven glutamic acid residues were found in the amino terminal region and are predicted to be sites of γ-carboxylation. Amino acid residues #80244 are defined as four cysteine-rich repeat sequences homologous to epidermal growth factor. The remainder of the molecule is homologous to plasma sex steroid binding protein. The mouse protein S contains two potential N-glycosylation sites at positions #458 and 468 and is lacking the putative glycosylation site at #490 found in human protein S.

Influence of hypophysectomy, castration, fasting, and spermiation on SBP concentration in male rainbow trout ( Oncorhynchus mykiss)

The influence of different experimental and physiological conditions on sex steroid binding protein (SBP) concentrations in the blood (and in hepatic and testicular cytosols) has been studied on male rainbow trout. SBP was measured with a specific binding assay. The aim was to further understanding of regulation of the SBP and in particular to determine the respective influences of reproductive and metabolic status. Twelve days after hypophysectomy, pituitary and steroid hormones were dramatically decreased and SBP concentrations were significantly lowered in blood (−32%) and in hepatic cytosol (−46%) while the binding protein concentration remained constant in testicular cytosol. Castration of maturing animals did not influence SBP concentration in blood and liver cytosol. Toward the end of the reproductive cycle, a dramatic decrease (−80%) of plasma SBP concentration occurred that appears independent of androgen changes that take place during this period, but is concomitant with a rapid increase of plasma growth hormone (GH) levels (and possibly secondary to a natural arrest of food intake). Long-term fasting that increases endogenous GH but decreases plasma IGFs (insulin-like growth factors) concentrations also induces a limited but significant decrease in SBP concentration. Treatment of intact control trout with recombinant bovine GH (1 μg/g wt, twice a week, for 6 weeks) increased plasma IGF concentrations but did not significantly increase SBP levels. These results suggest that in mature male trout, testicular androgens have little or no influence on SBP regulation. GH levels or liver GH responsiveness and IGF might be involved in SBP regulation. This would, in part, explain the large decrease in SBP around spermiation in trout.

In vivo and in vitro studies on sex steroid binding protein (SBP) regulation in rainbow trout ( oncorhynchus mykiss): Influence of sex steroid hormones and of factors linked to growth and metabolism

The respective roles of sex steroids and hormones related to growth and metabolism, on SBP regulation have been studied in rainbow trout. In vivo, oestradiol (E2) supplementation induces a slow but significant increase of plasma SBP concentration. Testosterone or cortisol injections have no effect. In vitro, the steroid binding protein that accumulates in incubation medium of hepatic cell primary cultures has been characterized and found to be similar to blood SBP. Its production is increased by addition of E2 (maximum: + 300%). This effect develops slowly over several days of culture and is dose dependent; as little as 1–10 nM E2 is effective. Recombinant rainbow trout GH (rtGH)—0.01 to 1 μg/ml—also increases SBB accumulation as compared to control cells and seems to maintain SBP production over culture duration. In preliminary experiments, (1) insulin-like growth factor (IGF) and SBP concentrations were found to change inversely after a 4 days stimulation with increasing concentrations of GH; (2) recombinant human IGF 1 (250 ng/ml) tended to be inhibitory when SBP production was expressed per mg of total cellular protein, and a micromolar concentration of bovine insulin was clearly inhibitory. Other hormones tested in vitro: triiodothyronine (10–1000 nM), thyroxine (100 nM), 17α,20β-dihydroprogesterone (10–2000 nM), and testosterone (1–1000 nM) did not influence SBP concentration in hepatic cells culture media.

Plasma Sex Steroid-Binding Protein in Mature Heifers: Effects of Reproductive Status, Nutritional Level, and Porcine Growth Hormone, and Estradiol-17β Treatments1

In heifers, the specific 5 alpha-dihydrotestosterone (5 alpha-DHT) binding to sex steroid-binding protein (SBP) was 53 nM in midluteal phase and was 20% lower (p less than 0.05) in early luteal phase. In ovariectomized heifers on a high (H) or a low (L) energy diet, SBP bound testosterone with high specificity and estradiol-17 beta (E2) with a lower specificity; the affinity constant with 5 alpha-DHT was similar in the two groups independent of diet (Ka = 1.0 and 1.3 x 10(9) x M-1 for H and L heifers, respectively). Electrophoretic mobility of SBP was not affected by undernutrition. The specific 5 alpha-DHT binding to SBP in anestrous heifers compared to heifers in early luteal phase was 17% lower 18 days after cessation of ovarian activity (p less than 0.05) and 35% lower after 78 days of anestrus (p less than 0.001). Specific 5 alpha-DHT binding to SBP was 33% lower (p less than 0.001) in L heifers than in H heifers (40 nM). Porcine growth hormone (pGH) and E2 injections increased specific 5 alpha-DHT binding to SBP in both H and L heifers, but the effect depended on diet. Simultaneous injections of pGH and E2 increased specific binding in H heifers (p less than 0.02), whereas it had no effect in L heifers. We conclude that SBP binding capacity varies with ovarian activity in heifers and that nutritional status is one factor of regulation of SBP binding capacity because it affects binding and modifies the SBP response to stimulating factors such as pGH and E2.

The plasma sex steroid binding protein (SBP or SHBG). A critical review of recent developments on the structure, molecular biology and function

Significant developments have taken place within the past five years on the characterization, molecular biology and function of the plasma sex steroid-binding protein, SBP (or sex hormone binding globulin, SHBG). During the span of that time, amino acid sequences of two SBPs have been established, amino acid residues in the steroid-binding site have been identified, the structure of the human SBP gene has been deduced and evidence for the possible existence of a SBP membrane receptor has been presented. This review covers the salient aspects of these and other developments including a critical analysis of the various proposed models and interpretations with regards to the structure, evolution, molecular biology and function of SBP.

Effects of hormones on SBP mRNA levels in human cancer cells

The human plasma sex steroid binding protein (SBP) has been previously shown to be synthesized in liver cells. The hormonal regulation studies of hepatic SBP mRNA demonstrate that it is controlled by estradiol, antiestrogen tamoxifen, dihydrotestosterone, triiodothyronine and insulin in a similar way as secreted SBP. The metabolic inhibitor cycloheximide was unable to prevent the estrogen or thyroid hormone induced increase in SBP mRNA. The slight stimulation of SBP synthesis by estradiol suggests that non-steroidal factors may be involved in its regulation and that the estrogen regulatory mechanism could also be partly post-transcrptional. In endometrial (Ishikawa cells) and prostatic (LNCaP cells) carcinoma cells, SBP mRNA has been detected suggesting that SBP may play a role in the uptake and intracellular mechanism of action of sex steroid in target cells.

Effect of testosterone on regulation of the level of sex steroid-binding protein mRNA in monkey (Macaca fascicularis) liver

Two specific oligonucleotide probes complementary to different regions of human sex steroid-binding protein (SBP) cDNA were used to study the levels of hepatic monkey SBP mRNA during different hormonal states. In females the SBP mRNA level was higher than in males and paralleled the serum SBP level. After castration, the SBP concentration increased in the serum but was reduced after testosterone treatment. In contrast, the hepatic SBP mRNA level decreased after castration and was restored by testosterone treatment. These results suggest a high homology of the nucleotide sequence between human and monkey SBP mRNAs. The changes in liver SBP mRNA levels may explain the sex difference in plasma SBP concentrations, but mechanisms other than the regulation of transcription may regulate the plasma concentration in monkeys.

Half-life of plasma sex steroid-binding protein (SBP) in the primate

We have recently shown that the metabolic clearance of testosterone in plasma is directly dependent on sex steroid-binding protein (SBP or SHBG) levels [ J. steroid. Biochem. 22, 739 (1986)]. In order to further understand the relationship between these two parameters, we have measured the half-life of SBP in plasma of female rhesus monkeys. SBP was purified to homogeneity from pooled Macaca nemestrina serum, and iodinated with 125I. The labeled protein ([ 125I]nSBP) was purified by chromatography on DEAE-agarose and fractions identified as immunologically reactive against anti-human SBP were collected. Protein purity of [ 125I]nSBP was established by SDS gel electrophoresis using an unlabelled Macaca nemestrina SBP as standard. The labeled protein was infused intravenously into two different adult female Macaca mulatta (rhesus) monkeys. Plasma samples were collected at short intervals during the first 24 h after infusion, and then daily for 7–9 days. The clearance profile of labeled SBP in plasma was quantitated by radioactivity measurement and immunoprecipitation. Analysis of the results indicate that the rate of SBP clearance in plasma has two components, the t 1 2 (app) of the first component is 7.5 h ( r = 0.94), and the t 1 2 (app) of the second component is 3.95 days ( r = 0.95). Over 90% of the injected 125I-nSBP was removed from plasma within 24 h at a rate corresponding to the t 1 2 (app) of the first component. The data indicate that most of the SBP rapidly distributes into extravascular spaces during the first 24 h following infusion, and are consistent with the hypothesis that SBP may be directly involved in sex steroid hormone transport into tissues.

Effects of human chorionic gonadotropin, androgens, adrenocorticotropin hormone, dexamethasone and hyperprolactinemia on plasma sex steroid-binding protein.

This presentation reports the effects of androgens, glucocorticoids and some pituitary hormones on plasma sex steroid-binding protein (SBP). The latter was measured by a solid phase method after desteroidation of the plasma. An hCG test (1500 I.U. every other day X 7) was given to 60 boys. In the children with a normal testosterone (T) rise, plasma SBP decreased (% of basal values) either significantly (38.3 +/- 9.3%, group A; n = 29), or moderately (13.4 +/- 4.4%, group B; n = 9) or did not change (-1.6 +/- 6.4%, group C; n = 10). In the 3 infants tested at an age when SBP normally rise sharply, hCG partially prevented this rise. The administration of either fluoxymesterone (10 mg/m2 for 10 days) or depot-T (4 I.M. injections of 100 mg/m2 every 2 weeks) induced a significant drop (about 2-fold) in plasma SBP in a control group of infants or children, but did not change SBP in 3 infants with the androgen insensitivity syndrome. A single injection of 0.25 mg of ACTH did not significantly alter SBP levels. In contrast, at the end of a 3-day ACTH test (0.5 mg/m2 12 hourly X 6) SBP levels had significantly decreased (mean 35% fall) with no age or sex differences, and with no correlation with the cortisol levels reached. However, the lowering effect of ACTH on SBP levels is likely mediated by glucocorticoids, since its effect was reproduced by high doses (8 mg/day for 3 days) of dexamethasone given at once or after 3 days of treatment at lower dose (20 micrograms/kg BW). It would appear that the depressive effect of ACTH and/or dexamethasone is observed for a threshold dose of glucocorticoids (greater than 5-fold physiological levels) and a certain time (greater than or equal to 3 days) of exposure. The mechanism by which androgens and glucocorticoids lower SBP levels in vivo is not yet understood. From recent experiments, showing that both stimulate the secretion of SBP in hepatoma cells in vitro, it would appear that both hormones may alter SBP metabolism. In a selected population of hyperprolactinemic women, with normal weight and no hirsutism, plasma SBP levels were found in the normal female range. The discrepancy with previous studies in the literature may be explained by differences in the degree of hyperprolactinemia and/or associated hyperandrogenim. This study further documents the multifactorial and intricated hormonal influences involved in the regulation of plasma SBP in vivo.