Species distribution of testosterone-binding globulin

Comparison of rabbit androgen binding protein with testosterone estradiol binding globulin—I. Physical and chemical properties

Rabbit epididymal androgen binding protein (rbABP) and serum testosterone estradiol binding globulin (rbTeBG) were purified and their physicochemical properties compared. Both proteins bound dihydrotestosterone (DHT) with high affinity. Both contained two components, Heavy (H) and Light (L), and their molecular weights and pI values were comparable. rbABP and rbTeBG were different with regard to their ConA-Sepharose binding property. rbABP was not bound by ConA-Sepharose while rbTeBG was found and retained by this lectin; thus, rbABP and rbTeBG differed in their carbohydrate structure. Peptide mapping on SDS-PAGE indicated that the H components of rbABP and rbTeBG were distinct even though they showed a high degree of homology. By contrast, the L components of these two proteins appeared to be identical. The structure of the steroid binding sites of these two proteins was analyzed by peptide mapping of [1,2(3)H]17 beta hydroxy-androsta-4,6-dien-3-one photoaffinity labeled protein. The size distribution of radioactive peptide fragments generated appeared to be identical for these two proteins. However, the distribution of labeled peptides was slightly different when examined by high pressure liquid chromatography (HPLC). The observations suggest that the differences between rbABP and rbTeBG might reside not only in carbohydrate moieties but also in their amino acid sequences.

The effect of estradiol and progesterone on the sexual behavior of ovariectomized mares

Daily treatment (5 days) with estradiol resulted in increased levels (p less than 0.05) of proceptive behavior in ovariectomized as compared to control mares (N = 8 per treatment) within 4 hr of injection and for the 4 subsequent days. Ejaculations occurred more often (p less than 0.05) in estrogen-treated mares on days 2-5, but the number of precopulatory investigations by the stallions was not altered. Progesterone treatment resulted in an absence of sexual behavior except in one mare on Day 1. Control mares exhibited varying levels of sexual interest. The concurrent administration of estradiol and progesterone produced a biphasic effect on proximity-related behaviors. Proximity behaviors were initially (Day 1) greater and subsequently less in the group treated with both hormones than in the group treated with estradiol alone. Injections of free estradiol resulted in a shorter latency to effect for two measures of proceptivity than did injections of estradiol benzoate. A dose response test for progesterone showed no effect with 0, 1, or 10 mg, but 100 mg was inhibitory (p less than 0.05). These results demonstrated that within 4 hr estradiol stimulated, while progesterone inhibited estrous behavior in ovariectomized mares and that concurrent administration of estradiol and progesterone produced a biphasic effect, first enhancing, then suppressing some aspects of the estrous response. The relatively short latency to action of all treatments and the biphasic effect of concurrent estradiol and progesterone may be attributable to low level, endogenous hormones.

Physiologic properties of steroid hormone-binding proteins in avian blood

The physiologic properties of steroid hormone-binding proteins have been partially characterized in plasmas of 23 avian species (8 orders and 12 families). A specific sex hormone-binding protein (SBP) with high affinity and low capacity, as found in amphibians and some reptiles and mammals, could not be identified in any of the avian species investigated. In addition SBP appeared to be totally absent in the blood of posthatching and juvenile stages of two species, and in the embryonic blood of three species. For birds it is concluded that sex steroid hormones circulate bound to plasma albumins with low affinity (Kd = 10(-5) mol/liter) and very high capacity. There are two protein-binding systems for corticosterone in the blood of all species investigated, including samples collected from embryos. One is saturable and specific with low capacity (10(-8) -10(-9) mol/liter) and high affinity (Kd = 10(-7) -10(-9) mol/liter), whereas the other is a nonspecific component with very high capacity and low affinity (Kd = 10(-5) mol/liter). Specificity studies show that the high-affinity binding system for corticosterone also binds progesterone with virtually identical affinity, whereas testosterone and estradiol are bound with lower affinity. These data suggest that the high-affinity binding protein in avian blood has physiologic properties similar to mammalian corticosteroid-binding globulin (CBP).

Steroid dynamics in the rabbit

Male rabbits were infused at a constant rate with 3H-androstenedione/14C-estrone (n = 5) or 3H-testosterone/14C-estradiol-17 beta (n = 3) for 3 1/2 hr and blood samples were obtained over the last hour and analyzed for radioactivity as androstenedione (A), testosterone (T), estrone (E1), estradiol-17 beta (E2 beta) and estradiol-17 alpha (E2 alpha). The mean value for the metabolic clearance rate of androstenedione (MCRA) was 85 +/- 10 l/day/kg, which was significantly greater than the mean MCRE1 59 +/- 10 l/day/kg. MCRT, 42 +/- 8 l/day/kg, and MCRE2 beta, 45 +/- 9 l/day/kg were not different. The conversion ratio of androstenedione to testosterone (CRA,T) was greater than CRT,A but for the estrogens, CRE2 beta, E1 was greater than CRE1,E2 beta. CRE2 beta, E2 alpha was greater than CRE1,E2 alpha. The overall aromatization of androstenedione to estrone, the fraction of 3H-androstenedione infused into the blood and measured as 3H-estrone in blood [( rho]A,E1BB) was 0.0005 +/- 0.0001 and for [rho]T,E2 beta BB was 0.0012 +/- 0.0006. In the rabbit both sex hormone binding globulin (SHBG) and albumin binding may effect the MCRs, and peripheral aromatization of androgens occurs to a far lesser degree than in humans and primates.

Purification and characterization of the sex steroid binding protein from macaque serum. Comparison with the human protein

The sex steroid binding protein (SBP) of Macaca mulatta and Macaca nemestrina sera has been purified to homogeneity and chemically characterized. The native protein is a glycoprotein having a molecular weight of approximately 88 000 and is composed of two similar subunits of molecular weight 47 000 as estimated by sodium dodecyl sulfate gel electrophoresis. One molecule of 5 alpha-dihydrotestosterone is bound per dimer with a KD equal to 1.6 nM at 11 degrees C. Isoelectric focusing patterns reveal the presence of at least 12 different forms of dimeric SBP molecules probably resulting from the presence of different amounts or types of carbohydrate side chains. The data indicate a very close similarity in molecular and steroid-binding properties to human SBP and establish the macaque monkey as a valuable animal model to study the physiological role of SBP in humans.

Testosterone-binding protein in a seasonally breeding amphibian

The concentration of testosterone and dihydrotestosterone (DHT) in the plasma of Taricha granulosa rises markedly during the season when androgen-dependent epigamic structures and behaviors recrudesce. During this season (June-October), the physiological characteristics of the testosterone-binding globulin (TeBG) remain unchanged. Competitive binding studies indicate that TeBG binds fairly specifically to testosterone and DHT. The dissociation constant (5 X 10(-8) M) and binding capacities (ranging from 6 to 12 ng androgen bound/ml plasma) were determined using the charcoal adsorption procedures. Because the binding capacity of TeBG remains unchanged when the concentrations of androgens increase, the proportion of testosterone and DHT bound to TeBG is drastically lower during the breeding season, compared to the nonbreeding season. Furthermore, bilateral castration of male newts apparently reduces the binding capacity of TeBG, but Silastic implants of androgen fail to restore the binding capacity.

The presence of androgen-binding protein in the guinea-pig testis, epididymis and epididymal fluid

Androgen-binding protein (ABP) is present in the guinea-pig testis, epididymis and epididymal fluid. Guinea-pig ABP sediments as an approx. 4.6S species on sucrose gradients containing 0.01 M KCl. Electrophoresis on non-denaturing polyacrylamide gels indicated that specific androgen binding was present in epididymal cytosol, but not in plasma. Time-course studies indicated that binding equilibrium is approached in about 2.5 h; the dissociation half-time of [3H]5 alpha-DHT from guinea-pig ABP is 5.64 +/- 0.62 h (n = 6) at 4 degrees C. The relative affinities of some steroids for guinea-pig ABP in relation to 5 alpha-DHT = 1 are: testosterone = 0.55 +/- 0.13 (n = 4), estradiol = 0.14 +/- 0.03 (n = 4), the anti-androgen cyproterone acetate = 0.0025 +/- 0.0002 (n = 3). Guinea-pig ABP exhibited an equilibrium dissociation constant of 6.34 +/- 0.52 nM (n = 3) at 4 degrees C and there were 3.43 +/- 0.78 (n = 3) pmoles of binding sites per mg of protein when homogenates of the whole epididymis were assayed. The concentration of ABP was lowest in the caput-corpus region of the epididymis, highest in the proximal cauda, and intermediate in the distal cauda. Essentially all of the ABP present in the distal cauda was intraluminal, as evidenced by the fact that flushing of the duct eliminated most of the [3H]5 alpha-DHT binding activity.

Uptake and retention of androgens by the rat ventral prostate and consideration of their use as site directing agents

Elucidation of the mechanism whereby androgens are accumulated selectively by the prostate may help in the design of drugs for the treatment of prostatic cancer. The uptake and retention of [3H]testosterone, following intraperitoneal injection, by various tissues in the 24 hr castrate rat has been studied over an extended time course. The selectivity with which prostate, as compared with blood or other tissues, accumulated 3H was shown to be dose-dependent. At a low dose (0.15 microgram), selective prostatic accumulation was greater in 24 hr castrate and diethylstilboestrol-treated rats than in normal animals. Testosterone, 5 alpha-dihydrotestosterone and oestradiol, radioactively labelled, were each administered to 24 hr castrate rats by intraperitoneal injection. Specific prostatic accumulation of radioactivity was more dependent on steroid structure at a low dose than at a high dose (0.6 mg) and at the low dose (0.15 microgram) followed the order testosterone greater than 5 alpha-dihydrotestosterone greater than or equal to oestradiol. This order was surprising in view of the androgen receptor binding affinities of these steroids. It is concluded that small quantities of material could be directed with the greatest specificity to the prostate of castrate or diethylstilboestrol-treated animals if attached to testosterone. Androgens would be more useful for site-directed radiopharmaceuticals than cytotoxic agents.

Binding of testosterone, 5 alpha-dihydrotestosterone and 5 alpha-androstane (3 alpha- and 3 beta-), 17 beta-diols to serum proteins in the rat

Experiments with polyacrylamide gel electrophoresis at steady state conditions, indicated that testosterone, 5 alpha-dihydrotestosterone, 3 alpha-androstanediol and 3-beta-androstanediol bound only to albumin in rat serum. The extent of binding of several C19-steroids to serum proteins was measured in rat blood utilizing equilibrium dialysis. The values for the adult male rat were as follows (mean +/- SEM): testosterone 78.3 +/- 0.4% 5 alpha-dihydrotestosterone 81.8 +/- 0.4%, 3 alpha-androstanediol 95.5 +/- 0.1%; 3 beta-androstanediol 95.2 +/- 0.1%. The values for the latter two are significantly higher than those for the first two which in turn differ significantly from each other. The values for adult female and castrated male serum samples were not significantly different from those of the normal male. The results obtained for the extent of binding of C19-steroids in a 5-g% albumin solution (which is similar to male rat serum albumin concentration) did not differ significantly from values for serum indicating that the binding in the latter is due primarily to albumin. The KA's for C19-steroid binding to albumin were: testosterone 2.22 X 10(4)l/mol; 5 alpha-dihydrotestosterone 3.46 X 10(4)l/mol; 3 alpha-androstanediol 1.36 X 10(5)l/Mol and 3 beta-androstanediol 1.20 XC 10(5)l/mol. When correlated to our previously reported metabolic clearance rats (MCR) it was concluded that binding to serum proteins does not account for the significant difference between the MCR for testosterone and 5 alpha-dihydrotestosterone but may account for the lower MCR's for the 3 alpha- and 3 beta-androstanediols.

Brain cells of the male rhesus monkey accumulate 3H-testosterone or its metabolites

Autoradiography was used to localize target cells for 3H-testosterone or its labeled metabolites in the brain of the rhesus monkey. Two castrated males were injected intravenously with 3H-testosterone (2 mCi/monkey) and were killed 1 hour later. In both animals, neurons that concentrated radioactivity in their nuclei were located in a well-circumscribed system that included the bed nucleus (n.) of the stria terminalis, medial preoptic n., suprachiasmatic preoptic n., anterior hypothalamic area, ventromedial hypothalamic n., cortical, medial, and basal accessory amygdaloid n., mesencephalic reticular n., and periaqueductal gray matter. In contrast to reports in some nonprimate mammalian species, little or no cellular labeling was observed in the lateral septum, arcuate n.-median eminence, motor nuclei of cranial nerves, or spinal cord.

Identification of a novel sex steroid binding protein

We describe a cytoplasmic steroid binding protein in the chick oviduct which has intriguing characteristics. This protein binds [3H]estradiol with high affinity (Kd = 30 X 10(-9) M) and limited capacity (300 fmol/mg of cytosol protein). It sediments at 8 S in low-salt sucrose density gradients and at 4 S in high-salt gradients. Unlike the estrogen receptor, however, this protein also binds progesterone, R5020, testosterone, and 5 alpha-dihydrotestosterone with similar affinities and in a competitive manner. Moreover, it is not translocated to the nucleus by the in vivo administration of these sex steroids. The protein is only present in estrogen-responsive tissue, and like the sex steroid receptors, its synthesis appears to be regulated by estrogen.

Androgen transport proteins: physical properties, hormonal regulation, and possible mechanism of TeBG and ABP action

The physical properties and hormonal regulation of testosterone estradiol binding globulin (TeBG) and androgen binding protein (ABP) are reviewed. Brief mention is made of prostatic binding protein. The discussion focuses on the mechanism of action for these proteins in androgen secretion, transport, and absorption and androgen binding models. Speculations are presented for the functional significance of these proteins.

Hormonal and immunological aspects of the phylogeny of sex steroid binding plasma protein

Sex steoid binding plasma protein (Sbp) in man and in monkeys binds the androgens dihydrotestosterone and testosterone and the estrogen estradiol with high affinity (Kd approximately 0.5, 1, and 2 nM, respectively). Detailed studies of steroid binding specificity give the same results in all primates, except that in humans and chimpanzees estrone does not compete for dihydrotestosterone binding. In other mammals, Sbps of Artiodactyla and Lagomorpha have the same range of affinities for androgens but they do not bind estradiol to any significant extent (Kd > 280 nM). The dog has an unusual Sbp (Kd for dihydrotestosterone, 7.1 nM; for estradiol, 125 nM), and rodents do not have a specific dihydrotestosterone-binding plasma protein. Gel filtration and immunoelectrophoretic experiments have been performed with a monospecific antiserum against human Sbp. The results indicate variable crossreactivities with Sbps of primates (from complete in chimpanzee and gorilla to weak in Prosimii). No crossreaction was observed with specific androgen-binding plasma proteins of other species. These results suggest the evolutionary emergence of bifunctional Sbp.

Preliminary characterization of a new androgen-binding protein in human seminal plasma

In order to obtain comparative analysis between the steroid binding proteins from blood serum and seminal plasma, fresh samples were incubated and assayed in parallel with the following tritiated steroids: dihydrotestosterone, testosterone, cortisol, progesterone and estradiol. Thereafter, and using techniques such as (1) polyacrilamide disk gel electrophoresis with elution of proteins from the gel slices, (2) ammonium sulphate precipitation, (3) enzymatic hydrolysis, and (4) gel filtration on Sephadex G-100, there was a resemblance in the electrophoretic patterns confirming the presence in both fluids of proteins like TeBG, CBG, and Albumin, previously described in blood serum. In seminal fluid, but not in blood serum, another small protein with androgen binding capacity was found and its preliminary characterization demonstrated: disappearance with enzymatic treatment, low molecular weight, negative charge, and precipitation range with ammonium sulphate from 30 to 35%. Its elution profile on Sephadex G-100 was contaminated with albumin.

Differentiation of sex steroid-binding protein in adult rhesus monkeys

Several species of primates have sex differences in sex steroid-binding protein (SBP), female adults having higher serum binding capacities (micrograms of dihydrotestosterone bound per deciliter) than male adults, e.g., male humans, 1.28 +/- 0.4; human females, 2.86 +4- 0.9; Macaca nemestrina male animals, 5.62 +/- 1.24; Macaca nemestrina female animals, 11.07 +/- 1.85 (means +/- standard deviations). SBP correlates inversely with metabolic clearance rates of testosterone (T). The sex difference was identified in rhesus monkeys, six per group, evaluated 4 years after postpubertal castration: male animals 3.95 +/- 1.14; female animals 5.85 +/- 0.98 (p less than 0.05). Estradiol-17 beta (E2) pellets producing physiologic levels of E2 in female monkeys obliterated the sex difference by increasing SBP in male animals. After withdrawal of E2, physiologic levels of T in male monkeys produced a marked decrease in SBP levels (p less than 0.01), and the sex difference reappeared; castrated female animals and prenatally androgenized female animals responded similarly to T (2.81 +/- 0.81 and 2.64 +/- 0.49, respectively). Both values were greater (p less than 0.05) than that of the male group (2.02 +/- 0.33). These data suggest that the sex steroid milieu influences the binding capacity of SBP for potent androgens in adulthood but that the differentiation of the SBP sex in rhesus monkeys is determined by factors other than prenatal androgen exposure.

Breech delivery: evaluation of the method of delivery on perinatal results and maternal morbidity

A retrospective study of 460 single-gestation infants in breech position was conducted at the University of Colorado Medical Center to assess the impact of a policy for the selection of cases for vaginal delivery. Among infants weighing more than 2,500 grams, there was an increase in the cesarean section rate from 13% to 54%, with an associated increase in maternal morbidity from 7% to 15%. This occurred with no significant reduction in adverse perinatal outcome. However, a case-by-case review suggests that more frequent and timely cesarean sections would have further reduced perinatal morbidity and deaths among term infants. Among the infants weighing 2,500 grams or less there was an increase in cesarean births from 5% to 55% following the introduction of the strict criteria for vaginal delivery. Among the infants weighing 1,501 to 2,500 grams there was no significant difference in survival between the cesarean and vaginally delivered patients. Although infants weighing 501 to 1,500 grams delivered by cesarean section survived more frequently than did those delivered vaginally, the differences in perinatal deaths may have been due to a higher birth weight in the cesarean-delivered infants or an over-all improvement in neonatal intensive care for infants of very low birth weight.

Transport of protein-bound steroid hormones into liver in vivo

The unidirectional influx of 3H-gonadal (progesterone, dihydrotestosterone, testosterone, estradiol) and adrenal (aldosterone, cortisol) steroid hormones into liver was studied with a tissue-sampling single-injection technique in barbiturate-anesthetized rats. Liver uptake of the steroid hormone was measured relative to [14C]butanol, a highly diffusible reference, after a single pass through the liver. Portal flow (1.4 ml.min-1.g-1) under the experimental conditions was measured with 3H2O. The extraction of unidirectional influx of all six steroid hormones was 70-100% after a bolus portal injection of labeled steroid in Ringer solution (0.1% albumin). Steroid transport was nonsaturable because 35 muM concentrations of unlabeled hormone resulted in no inhibition of liver transport. The plasma proteins (albumin and specific globulins) in serum from human (male, female, pregnancy), rat (male), and guinea pig (pregnancy) sources inhibited the liver clearance of the respective steroid hormones to a variable extent. In all cases albumin-bound steroid hormone was freely cleared by liver and, in the case of cortisol or estradiol, the fraction bound to a specific globulin was also transported into liver.

Transport of steroid hormones through the rat blood-brain barrier. Primary role of albumin-bound hormone

These studies were undertaken to investigate (a) the permeability properties of the blood-brain barrier (BBB) to the major gonadal and adrenal steroid hormones, and (b) the role of the binding proteins of plasma (albumin and specific globulins) in the regulation of BBB steroid hormone transport. The permeability of the BBB to [(3)H]-labeled progesterone, testosterone, estradiol, corticosterone, aldosterone, and cortisol, was measured relative to [(14)C]butanol, a freely diffusable reference, in the barbiturate anesthetized rat using a tissue sampling-single injection technique. The isotopes were rapidly injected in a 200-mul bolus of Ringer's solution (0.1 g/dl albumin) via the common carotid artery and the percent extraction of unidirectional influx of hormone was determined after a single pass through brain: progesterone, 83+/-4%; testosterone, 85+/-1%; estradiol, 83+/-3%; corticosterone, 39+/-2%; aldosterone, 3.5+/-0.8%; and cortisol, 1.4+/-0.3%. The selective permeability of the BBB was inversely related to the number of hydrogen bonds each steroid formed in aqueous solution and directly related to the respective 1-octanol/Ringer's partition coefficient. When the bolus injection was 67% human serum, >95% of the labeled steroid was bound as determined by equilibrium dialysis. However, the influx of the steroids through the BBB was inhibited by human serum to a much less extent than would be expected if only the free (dialyzable) hormone was transported; progesterone, estradiol, testosterone, and corticosterone transport was inhibited 18, 47, 70, and 85% respectively, or in proportion to the steroid binding to plasma globulins. Rat serum (67%) only inhibited the transport of these four hormones, 0, 13, 12, and 69%, respectively, reflecting the absence of a sex hormone-binding globulin in rat plasma. However, neonatal rat serum (67%) inhibited progesterone, testosterone, and estradiol transport 0, 0, and 91%, respectively, consistent with the presence of an estradiol-binding protein in neonatal rat serum. The binding of steroid hormone to bovine albumin in vitro (as determined by equilibrium dialysis) was compared to albumin binding in vivo (as determined by the single injection technique). The ratio of apparent dissociation constant in vivo, K(D)(app), to the in vitro K(D) was: >>200 for progesterone, >200 for testosterone, 120 for estradiol, and 7.7 for corticosterone. Assuming the steady-state condition, the K(D)(app)/K(D) was found to be proportional to the BBB permeability for each steroid. These data demonstrate (a) the selective permeability properties of the BBB to the major steroid hormones is proportional to the tendency of the steroid to partition in a polar lipid phase and is inversely related to the number of hydrogen bond-forming functional groups on the steroid nucleus; (b) the presence of albumin in serum may bind considerable quantities of steroid hormone, but exerts little inhibitory effects on the transport of steroids into brain, whereas globulin-bound hormone does not appear to be transported into brain to a significant extent. Therefore, the hormone fraction in plasma that is available for transport into brain is not restricted to the free (dialyzable) fraction, but includes the larger albumin-bound moiety.

Comparative studies of the ethynyl estrogens used in oral contraceptives: effects with and without progestational agents on plasma androstenedione, testosterone, and testosterone binding in humans, baboons, and beagles

The effects of ethynylestradiol or mestranol given in cyclic fashion, with and without a progestational compound (norethindrone acetate, dl-norgestrel, or megestrol acetate), on plasma androgens and their binding were examined in adult women, female baboons, and beagles. The two estrogens are equivalent in their effect, and there were essentially no dose-related differences over the range examined. In human subjects, the estrogens increased total testosterone and testosterone binding, and decreased free testosterone. In baboons, estrogen produced a transient decrease in total testosterone and an increase in binding. The levels of progestational agents used did not affect total testosterone in humans, as is commonly observed with commercial agents, but did decrease it in baboons. Percentage binding was decreased in both species by the 19-nor compounds, but not by megestrol. Androstenedione levels were unaffected in human subjects, but effects of both estrogens and progestins were seen in baboons. Because of the very low levels of androgens in female beagles, this species did not lend itself well to a study of this kind. However, an increase in testosterone binding was induced by estrogen even in the absence of testosterone/estrogen-binding globulin.