Transcortin Concentrations Research Articles

Cortisol and transcortin in human seminal plasma and amniotic fluid as estimated by modern specific assays

Cortisol concentrations in human seminal plasma, as estimated by the very specific Amersham 'Amerlite' luminescence immunoassay, were 176 +/- 43 (85-260) nmol/l, that is, 63.7 +/- 15.5 (31-94) ng/ml (mean +/- SD, n = 21). This is about 60% of random levels in blood serum and is the first description of cortisol in seminal fluid. In human amniotic fluid at 16-22 weeks of gestation, cortisol concentrations were lower, at 72.6 +/- 14.6 (63-124) nmol/l, that is, 29.3 +/- 5.3 (23-45) ng/ml (n = 21). Concentrations were about 15% of random maternal serum levels in the second trimester of pregnancy. The cortisol concentrations in both fluids were considerably higher than those reported for saliva, which has a mean of about 10 nmol/l. Transcortin (corticosteroid binding globulin, CBG), has been found in human seminal plasma and amniotic fluid for the first time. Concentrations were low, with values up to 12 micrograms/ml, with no significant difference between the two fluids, when using the IRE-Megenix monoclonal iodinated radioimmunoassay. Transcortin concentrations were about 10% of levels in non-pregnant blood serum, compared with about 0.1% for saliva. The higher concentrations of transcortin could perhaps account for the greater diffusion of cortisol into seminal plasma and amniotic fluid. The presence of beta-endorphin, ACTH and cortisol in amniotic fluid, seminal fluid, ovarian follicular fluid, endometrial fluid and gastric fluid may possibly, indicate the existence of a small paracrine ACTH-cortisol axis in the relevant secretory tissues.

Hypothalamic Pituitary Adrenal Function during Critical Illness: Limitations of Current Assessment Methods

Activation of the hypothalamic-pituitary-adrenal (HPA) axis represents one of several important responses to stressful events and critical illnesses. Despite a large volume of published data, several controversies continue to be debated, such as the definition of normal adrenal response, the concept of relative adrenal insufficiency, and the use of glucocorticoids in the setting of critical illness. The primary objective was to review some of the modulating factors and limitations of currently used methods of assessing HPA function during critical illness and provide alternative approaches in that setting. This was a critical review of relevant data from the literature with inclusion of previously published as well as unpublished observations by the author. Data on HPA function during three different forms of critical illnesses were reviewed: experimental endotoxemia in healthy volunteers, the response to major surgical procedures in patients with normal HPA, and the spontaneous acute to subacute critical illnesses observed in patients treated in intensive care units. The study was conducted at an academic medical center. Participants were critically ill subjects. There was no intervention. The main measure was to provide data on the superiority of measuring serum free cortisol during critical illness as contrasted to those of total cortisol measurements. Serum free cortisol measurement is the most reliable method to assess adrenal function in critically ill, hypoproteinemic patients. A random serum free cortisol is expected to be 1.8 microg/dl or more in most critically ill patients, irrespective of their serum binding proteins. Because the free cortisol assay is not currently available for routine clinical use, alternative approaches to estimate serum free cortisol can be used. These include calculated free cortisol (Coolens' method) and determining the free cortisol index (ratio of serum cortisol to transcortin concentrations). Preliminary data suggest that salivary cortisol measurements might be another alternative approach to estimating the free cortisol in the circulation. When serum binding proteins (albumin, transcortin) are near normal, measurements of total serum cortisol continue to provide reliable assessment of adrenal function in critically ill patients, in whom a random serum total cortisol would be expected to be 15 microg/dl or more in most patients. In hypoproteinemic critically ill subjects, a random serum total cortisol level is expected to be 9.5 microg/dl or more in most patients. Data on Cosyntropin-stimulated serum total and free cortisol levels should be interpreted with the understanding that the responses in critically ill subjects are higher than those of healthy ambulatory volunteers. The Cosyntropin-induced increment in serum total cortisol should not be used as a criterion for defining adrenal function, especially in critically ill patients. The routine use of glucocorticoids during critical illness is not justified except in patients in whom adrenal insufficiency was properly diagnosed or others who are hypotensive, septic, and unresponsive to standard therapy. When glucocorticoids are used, hydrocortisone should be the drug of choice and should be given at the lowest dose and for the shortest duration possible. The hydrocortisone dose (50 mg every 6 h) that is mistakenly labeled as low-dose hydrocortisone leads to excessive elevation in serum cortisol to values severalfold greater than those achieved in patients with documented normal adrenal function. The latter data should call into question the current practice of using such doses of hydrocortisone even in the adrenally insufficient subjects.

Is the mineralocorticoid receptor in Brown Norway rats constitutively active?

In a previous study using corticosterone treatment of adrenalectomized rats, we hypothesized that mineralocorticoid receptor (MR)-related mechanisms are constitutively active and that glucocorticoid receptor (GR)-mediated mechanisms are more efficient in Brown Norway rats compared to Fischer 344 (F344) rats. In order to discriminate the mineralocorticoid from the glucocorticoid actions exerted by corticosterone, F344 and Brown Norway adrenalectomized rats were treated with increasing doses (1, 5 and 25 microg/ml of drinking water) of deoxycorticosterone (DOC, MR-specific ligand) or RU 28362 (GR-specific ligand). These rats were compared with long-term adrenalectomized (ADX) untreated rats and sham-ADX rats. This study confirms our previous results, notably the lack of effect of ADX on body weight and fluid intake in Brown Norway rats. Moreover, DOC treatment had no effect in Brown Norway rats whereas the higher dose restored fluid intake of the F344 ADX group to sham values. These results support the hypothesis of a constitutive activation of the MR and therefore the insensitivity of this receptor to its ligand in Brown Norway rats. Alternatively, RU 28362 treatment induced greater weight loss, decrease in food intake, anxiolysis, thymus involution, and decrease in plasma transcortin concentration and pituitary corticosteroid receptor densities in Brown Norway rats than in F344 rats, which is consistent with greater efficiency of GR mechanisms in Brown Norway rats than in F344 rats. Therefore, these strains are of great utility to disentangle MR and GR effects on complex phenotypes.

A Preliminary Study of Circadian Serum Cortisol Concentrations in Response to a 72-hour Fast in Rheumatoid Arthritis Patients not Previously Treated with Corticosteroids

The aim of the study was to investigate the effects a 72-h fast upon serum total and free cortisol concentrations in RA patients not previously treated with glucocorticoids. Total serum cortisol and transcortin concentrations were measured in four RA patients with active disease at 4-h intervals during two 24-h periods (1200 h-1200 h), the first while eating a normal diet (fed state) and the second during the last 24 h of a 72-h water fast. Free cortisol concentrations were calculated from the total cortisol and transcortin values. The 3-day fast increased overall 24-h free and total cortisol concentrations by 50% and 35%, respectively. This was due largely to a marked increase in nocturnal serum cortisol concentrations during fasting, particularly at 0400 h, when mean total and free cortisol levels were increased by 170% and 260% compared to the fed state. Between 2000 and 0800 h overall total- and free cortisol concentrations were increased by 72% and 99%, respectively. These results suggest that an increase in nocturnal concentrations of cortisol occurs in response to fasting in RA patients not previously treated with glucocorticoids. These increases may mediate the beneficial clinical response previously found in studies of longer fasting periods in RA patients.

Strain differences in corticosteroid receptor efficiencies and regulation in Brown Norway and Fischer 344 rats.

During the dark phase of the diurnal cycle, and during recovery from restraint stress, Brown Norway (BN) rats secrete less corticosterone than Fischer 344 (F344) rats. These strains also display different levels of corticosteroid receptors in the hippocampus, and of plasma transcortin. Because corticosteroid receptors, plasma transcortin and corticosterone secretion are mutually regulated, we examined brain and pituitary mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) expression and some of the parameters modulated by these receptors (i.e. body and thymus weight, fluid intake, plasma transcortin) in BN and F344 rat strains, by comparing the effects of either hormone deprivation by long-term (21 days) adrenalectomy (ADX), or chronic elevation of corticosterone given in drinking fluid to ADX rats. In BN rats, body weight gain and fluid intake were insensitive to corticosterone deprivation, suggesting that MR-related mechanisms are constitutively active in this strain. Body weight (b.w.) gain, plasma transcortin and thymus weight were reduced to a greater extent by chronic corticosterone in BN rats than in F344 rats, possibly as a consequence of higher free, active fraction of plasma corticosterone due to lower plasma transcortin concentrations and/or a greater efficiency of GR-related mechanisms in BN rats. F344 rats displayed twofold higher brain and pituitary MR levels than BN rats, whereas tissue-and strain-specific regulations were observed for GR levels. The differences in MR levels observed between BN and F344 strains cannot completely explain the differences in corticosterone actions, suggesting that strain differences in response to ADX or corticosterone treatment result from variable receptor efficiencies.

Endocrinology of the carbohydrate-deficient glycoprotein syndrome type 1 from birth through adolescence.

The carbohydrate-deficient glycoprotein (CDG) syndrome type 1 is a genetic multisystem disorder, characterized by hypoglycosylation of glycoproteins and presenting with neurologic impairment. In 12 girls and 14 boys, we confirmed the diagnosis of CDG syndrome type 1 by immune-isoelectric focusing of serum sialotransferrins, and we examined the endocrine status singly or sequentially, including a 16-y follow-up of the index cases, a pair of monozygotic girls. Serum FSH levels were normal in newborns and prepubertal children, but elevated in female toddlers and teenagers, as well as in adolescent males. Serum LH concentrations displayed an analogous age-dependent pattern. In adolescent girls, serum estradiol remained low. FSH bioactivity was low normal, as was the bioactive/immunoreactive FSH ratio. However, exogenous gonadotropins evoked an estradiol response and induced ovarian follicular growth. Male patients virilized at puberty; however, testicular volume was subnormal. The thyroid axis was hallmarked by thyroid-binding globin deficiency and, during infancy, increased serum TSH concentrations. A subgroup of female patients presented hypersomatotropism and/or hyperprolactinemia. During adolescence, the index cases responded to glucagon with normal glycemic, but exaggerated insulin and paradoxically augmented growth hormone responses. The hypothalamo-pituitary area appeared intact on magnetic resonance imaging. Circulating IGF-1 levels were in the lower normal range and transcortin concentrations decreased. In conclusion, a study of endocrine aspects of a major glycosylation disorder revealed an age-dependent constellation, including hypergonadotropic hypogonadism with deficient FSH rather than LH action; transient hyperthyrotropinemia; inconsistent hyperprolactinemia; hyperglycemia-induced growth hormone release; deficiencies of hormone-binding glycoproteins and possibly decreased insulin sensitivity, thus pointing to the importance of glycoprotein glycosylation for pediatric endocrinology.

Ventromedial hypothalamic lesions inhibit corticosteroid feedback regulation of basal ACTH during the trough of the circadian rhythm.

We have determined the effects of bilateral electrolytic lesions of the ventromedial hypothalamus (VMH) on activity in the hypothalamo-pituitary-adrenal (HPA) system. Acutely, during the first 5 days, lesions of the anterior-medial VMH caused loss of the diurnal rhythms in food intake and plasma corticosterone (B) levels. Plasma B concentrations were elevated during the time of the normal trough of the basal diurnal rhythm in HPA axis activity and the diurnal rhythm in food intake was abolished, in agreement with the results of others. Consistent with hyperactivity in the HPA axis, lesioned rats had increased adrenal weight, decreased thymus and body weights and decreased plasma transcortin concentrations. To determine how lesions of the VMH provoke these increases in activity of the HPA system, the sensitivity of ACTH in adrenalectomized, lesioned rats to replacement with exogenous B was determined under basal conditions during the trough (morning-AM) and peak (evening-PM) of the diurnal rhythm in HPA axis activity. ACTH in lesioned rats in the AM was insensitive to feedback over the very low range of plasma B of 1-4 micrograms/dl, whereas sham-lesioned controls exhibited the normal, high sensitivity of ACTH to B at this time of day. There was no difference between the sensitivity of ACTH to this low range of B in the PM in VMH- and sham-lesioned rats. Two to 5 weeks after VMH lesions, as found by others, mean daily plasma B levels did not differ from sham-lesioned controls; however, plasma B during the AM was still mildly elevated in these rats. Inhibition of plasma B in the PM by dexamethasone was less effective in lesioned rats. Although HPA system responses to hypoglycemia, corticotropin-releasing factor and ACTH were normal, the lesioned rats exhibited obesity, hyperinsulinemia, hyperglycemia, hypertension and tachycardia, all signs consistent with mild hyperactivity of the PHA axis. Occupancy of type I, high-affinity corticosteroid receptors is known to control basal activity of the HPA system during the trough of the diurnal rhythm and to interact with glucocorticoid receptors to affect basal activity during the peak of the diurnal rhythm and during AM stress. We conclude that VMH lesions disrupt transmission of inhibitory signals, mediated by occupancy of type I corticosteroid receptors, that are initiated by a B feed-back site.

Feedback sensitivity of the rat hypothalamo-pituitary-adrenal axis and its capacity to adjust to exogenous corticosterone.

Chronic stress causing elevated morning (AM) corticosterone (B) concentrations of 2-8 micrograms B/dl does not appear to inhibit subsequent activity in the hypothalamic-pituitary-adrenal (HPA) axis, a surprising finding in view of the known depression in AM basal ACTH by only 3 micrograms B/dl in adrenalectomized rats. To distinguish between the possibilities that either intact rats are less sensitive to B feedback than adrenalectomized rats, or that chronic stress facilitates responses in the HPA axis, we elevated basal B levels in young male rats with slow-release B pellets in the absence of stress. Between 4-6 days after implantation of B pellets at three doses that elevated basal AM (diurnal trough) plasma B to approximately 1.2, 4, and 10 micrograms/dl, we studied basal ACTH and B at trough (AM) and peak evening (PM) times of the diurnal cycle, as well as the responses to the stress of restraint and blood collection from the tail at each time of day. We also determined mean daily plasma B, insulin, and glucose from samples collected at six intervals during the day. Adrenal, thymus, and body wts were measured as were transcortin (CBG) and adrenal phenylethanolamine-N-methyl transferase activity. Compared to controls implanted with wax pellets, all doses of B inhibited adrenal wt and AM stress responses and tended to inhibit pituitary ACTH content and adrenal phenylethanolamine-N-methyl transferase activity. Inhibition with the middle dose B pellet was close to maximally effective for these endpoints. Plasma glucose and thymus wt were significantly decreased and insulin was significantly increased in the middle and highest B pellet groups, with significantly greater effects at the highest dose. The gain in body wt and transcortin concentrations were significantly decreased only in the highest dose groups, in which mean daily plasma B was approximately 10 micrograms/dl, a level that clearly overwhelmed the capacity of the adrenocortical system to respond to any stimulus tested. By contrast, rats with low and middle dose B pellets appeared to adjust HPA axis function by decreasing the peak diurnal increase in B, so that 24-h mean B levels did not differ from control, and were maintained at approximately 5 micrograms/dl. Both of these groups also had inhibited ACTH responses to stress applied during the diurnal trough (AM). By contrast, neither group had inhibited ACTH responses to stress applied during the diurnal peak (PM). We conclude that: 1) The HPA axis of intact rats is extremely sensitive to exogenous B.(ABSTRACT TRUNCATED AT 400 WORDS)

Study of the transcortin binding to human endometrium plasma membrane

Transcortin complexed with progesterone was shown to bind specifically to the plasma membrane of human decidual endoterium. The binding reaction was characterized by a high affinity (an apparent K d value was (1.0±0.2) · 10 −10 mol/1) and high selectivity: such human serum proteins as albumin, orosomucoid, transferrin, thyroxine-binding globulin and sex hormone-binding globulin did not compete with transcortin for the membrane binding sites. Transcortin binding to the membrane was steroid-dependent: transcortin-cortisol complex bound to the membranes substantially more weakly than transcortin-progesterone, and specific bindig of transcortin devoid of steriod was not detected. Using a radioimmunoassay, we have measured the concentration of endogenous transcortin in highly purified membrane preparations solubilized with sodium cholate. It was found that an extensive washing of decidual strips with a physiological buffer prior to the membrane isolation resulted in a decrease of the endogenous transcortin level along with an increase of the specific membrane binding of exogenous 125I-labeled transcortin. Affinity chromatography on immobilized transcortin was used to isolate transcortin-binding components from 125I-labeled, cholate-solubilized plasma membrane of decidual endometrium. Along with lipid components, the structure of which was not investigated, a 125I-labeled transcortin-binding sialoglycoprotein with a minimal M r of 20.0±1.5 kDa and a p I of approx. 3.3 was detected. In the presence of transcortin, this sialoglycoprotein could be precipitated with a monospecific antitranscortin antiserum. Using hydroxylapatite as a separating agent, the interaction of transcortin, and the membrane sialogly-coprotein in model systems containing the two proteins and various steroid hormones was studied. It was found that the membrane sialoglycoprotein displayed a higher affinity for transcortin-progesterone than for transcortin-cortisol (the K δ values were, respectively, 2·10 −11 and 7·10 −11 mol/l) and it did not bind transcortin complexed with testosterone.

Determination of transcortin in serum by polyethylenglycol enhanced immunonephelometry. A comparison with equilibrium dialysis and radioimmunoassay

A method for immunonepholometric determination of transcortin has been developed. It is based upon a polyethylenglycol (PEG) enhanced immunonephelometric response using a commercial transcortin antiserum in the assay. It was found that pretreatment of the serum samples with 10% (w/v) PEG 6000 was a necessity in order to obtain satisfactory low blank values. The immunonephelometric assay showed a good correlation with transcortin concentrations as calculated from cortisol binding experiments ( r = 0.9501, n = 26). The intraassay coefficient of variation for a standard serum was found to be 3.2% ( n = 50) and for a pregnancy serum pool 2.6% ( n = 50). The interassay coefficient of variation in ten consecutive analyses of thirteen samples was found to be 7.4%. The sensitivity allows detection of transcortin in 5 μl of serum. The average concentration in male serum was 35 mg/l ( n = 55), in female serum 36 mg/l ( n = 55) and in serum from third trimester pregnant women 81 mg/l ( n = 30) which agrees with the results in previously published reports.

Characterization of Corticosterone Feedback Regulation of ACTH Secretiona

Adrenalectomy-induced increases in ACTH secretion in rats are returned to normal by an action of corticosterone on the brain, not on the pituitary. Five days after adrenalectomy with constant steroid replacement, the concentration of free corticosterone in plasma which reduces plasma ACTH by 50% is approximately 0.8 nM. By contrast, the concentration of free plasma corticosterone required for 50% reduction of thymus wet weight or plasma transcortin concentration (both targets for glucocorticoid action) is about 4.5 nM. These results suggested that the inhibition of ACTH by corticosterone might be mediated by association of the steroid with high affinity, type I corticosteroid receptors, whereas the inhibition of thymus weight and transcortin might be mediated by association of the steroid with lower affinity, type II receptors. The results of studies comparing the ability of corticosterone, dexamethasone and aldosterone to inhibit adrenalectomy-induced ACTH secretion support the hypothesis that basal ACTH secretion in rats is mediated by association of corticosterone with type I receptors.

Circadian rhythm in the membrane of circulating human blood cells: microviscosity and number of benzodiazepine binding sites. A search for regulation by plasma ions, nucleosides, proteins or hormones.

Circadian rhythms in both the number of peripheral type binding sites for benzodiazepines in platelet membranes and the microviscosity of the erythrocyte membrane were demonstrated in 7 healthy men. Neither variable appeared to be linked to each other, or regulated by the plasma concentrations of total or free cortisol, testosterone, potassium, magnesium, calcium, cAMP, cGMP or proteins or by the erythrocytic concentration of magnesium or potassium or by the plasma cAMP:cGMP ratio or by the ratio of intra-erythrocyte:plasma concentrations of potassium or magnesium. A highly significant negative correlation was found between the microviscosity of the erythrocyte membrane and the activity of the membrane-bound enzyme, methyltransferase I. Such a correlation was validated both on raw data and on 24 hr-means (r = 0.84; P less than 0.01). A circadian rhythm in the activity of this enzyme was also demonstrated. Moreover, a highly significant correlation was also found between plasma transcortin concentration (TRC) and microviscosity (r = 0.50, P less than 0.01), and between TRC and methyltransferase I activity (r = 0.61, P less than 0.01). Such findings may constitute clues towards the understanding of the regulation of the circadian rhythm in the fluidity of the red blood cell membrane in man and guide future steps with regard to the role of this rhythm upon the availability of drug binding sites at the cell surface.

The influence of transcortin on adrenocorticotropin-stimulated corticosterone production in monolayer cultured rat adrenal cells.

To verify the influence of the protein binding status of steroids adjacent to adrenal cells on steroidogenesis, the effect of transcortin, a specific binding protein of cortisol or corticosterone, on adrenocorticotropin (ACTH)-stimulated corticosterone production in monolayer cultured rat adrenal cells was studied. The transcortin in concentration of 5 x 10(-7) M was loaded with 0, 2.5, 5 and 10 pg/ml ACTH-(1-24), and the cells were incubated for 2 and 4 hours. Since molar concentrations of corticosterone produced in the medium were below the transcortin concentration at all levels of stimulation, protein-unbound corticosterone in the medium may have been largely reduced by the addition of transcortin. However, the total corticosterone production was not influenced by the transcortin added to the medium. It was speculated that protein-unbound steroid within the concentration range modulated by transcortin in the area surrounding the adrenal cells may not affect adrenal steroidogenesis.

Transcortin and vitamin D-binding protein levels in mouse serum.

The influence of age, sex and strain on the serum concentration of transcortin (corticosteroid-binding globulin) and vitamin D-binding protein (DBP) in mice was investigated. The effect of age was studied in two strains, C57BL/6JPfd and BALB/cmHeAPfd. The concentration of transcortin and DBP increased with age. In young animals the concentration of each protein showed a significant strain difference, which disappeared in older mice for DBP, but not for transcortin. In 7-day-old animals, no sex difference was observed for either protein, but in older animals a clear sex difference was found for transcortin. Adult males tended to have somewhat higher levels of DBP than adult females, but this difference was significant only on day 70. The variation in transcortin and DBP levels was further investigated in a large number of mouse strains. The DBP concentration did not markedly vary among strains (5.98-9.65 mumol/l in males and 5.08-8.85 mumol/l in females). Transcortin, however, showed marked strain variations, ranging from 0.72 to 2.06 mumol/l in males and from 1.02 to 4.55 mumol/l in females and there was a significant correlation (r = 0.66, n = 26, P less than 0.001) between the mean transcortin levels in males and females of different strains. Interstrain variation was much higher than intrastrain variation or variation among related strains, suggesting that the transcortin concentration is largely controlled by genetically determined factors. There was a significant correlation (r = 0.82, n = 9, P less than 0.01) between the mean corticosterone and transcortin concentrations (measured at 21.00 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Transcortin and α 2u-globulin messenger rna activities during turpentine-induced inflammation in the rat

Previously we have shown that the serum concentration of transcortin and α 2u-globulin markedly decreases during turpentine-induced inflammation. In the present study transcortin and α 2u-globulin mRNA from healthy rats and from animals with inflammation was translated in a rabbit reticulocyte lysate system. Female rats had higher levels of translatable transcortin mRNA than male animals and the level of mRNA for transcortin and α 2u-globulin decreased rapidly during inflammation. These results indicate that the sex difference in the serum level of transcortin and the changes in serum transcortin and α 2u-globulin during inflammation are mainly determined by differences in the mRNAs in the liver.

Prednisolone disposition and protein binding in oral contraceptive users.

Combined estrogen-progestogen oral contraceptives (OC) have been shown to alter the metabolism of certain drugs, including corticosteroids, as well as affect circulating protein concentrations. To assess these effects with regard to prednisolone, the pharmacokinetics and protein binding of this steroid were evaluated in eight female OC users and compared with results from eight male and five female non-OC users. All volunteers received 40 mg prednisolone, iv, and steroid concentrations were measured by high pressure liquid chromatography. Plasma clearance of total prednisolone in females on OC was 96 +/- 9 (SD) ml/min X 1.73 m2, significantly (P less than 0.001) lower than those in both male and female controls (205 +/- 46 and 187 +/- 22 ml/min X 1.73 m2). The prednisolone half-life and mean residence time were longer, while the steady state volume of distribution was smaller for OC users. Unbound prednisolone was measured by equilibrium dialysis, and pharmacokinetic and protein binding parameters were calculated from free prednisolone concentrations. A significantly higher (2-fold) concentration of transcortin was found in OC users. Evaluation of free prednisolone parameters showed a significantly lower clearance and decreased volume of distribution, without alteration of the mean residence time for the OC users. Dual OC effects on binding and elimination of prednisolone occur with the net result of a 2-fold increase in the area under the free concentration-time curve, indicative of a marked reduction in the biotransformation rate of the steroid.

The Effect of Cortisol, Progesterone, and Transcortin on Phytohemagglutinin-Stimulated Human Blood Mononuclear Cells and Their Interplay

The effect of transcortin on [3H]thymidine incorporation into phytohemagglutinin-stimulated human peripheral blood mononuclear cells and its influence on the well known suppressive effect of cortisol were investigated. Human transcortin by itself had no effect on thymidine incorporation between the concentrations of 0.25-1 X 10(-6) M. When transcortin was added to cortisol, the suppressive effect of cortisol decreased in proportion to the decrease in the protein-unbound cortisol concentration. We also investigated the influence of progesterone on transcortin-bound cortisol. When 0.5 and 1 X 10(-6) M transcortin, which contained 1 and 2 X 10(-7) M cortisol as a transcortin-bound form, were added to 5 X 10(-6) M progesterone, greater suppression of thymidine incorporation was observed that than produced by progesterone alone (86.1% and 81.3 for 0.5 and 1 X 10(-6) M transcortin, respectively). Moreover, when 5 X 10(-7) M transcortin containing the same amount of cortisol was added with 1, 2, and 5 X 10(-6) M progesterone, a greater suppression (92.6%, 74.1%, and 32.4% of control for 1, 2, and 5 x 10(-6) M progesterone) was demonstrated than that caused by progesterone alone (95.1%, 75.8%, and 49.5% of control for the corresponding concentrations of progesterone). This increased suppression was accompanied by an increase in the percentage of protein-unbound cortisol. These results indicate that unbound cortisol, whose concentration increases in the presence of progesterone, may be biologically active. The interaction between progesterone and cortisol may be modulated in part by the transcortin concentration.

The binding of prednisolone in human serum and to recrystallized human albumin in vitro.

1 Prednisolone binding in human serum and to recrystallized human serum albumin was measured by continuous ultrafiltration. 2 At serum concentrations of prednisolone up to 0.6 micron, 95.0% was bound but at higher concentrations the binding became non-linear falling to 80.5% at 1.8 microns. At even higher concentrations binding in serum became linear again and paralleled the binding to albumin which was linear throughout the entire range of prednisolone concentrations. 3 A binding model was proposed which included a saturable component attributable to binding to transcortin and a non-saturable binding to albumin. 4 Computer simulations using the experimentally determined binding parameters of the model indicated that binding in serum was critically dependent on transcortin concentration and almost independent of albumin concentration.

Steroid-binding proteins and testosterone level in the badger plasma during the annual cycle

Steroid-protein interactions were studied in the male badger Meles meles L. during a seasonal sexual cycle. Specific steroid-binding plasma proteins were determined by equilibrium dialysis. This study demonstrates the existence of two high-affinity steroid-binding proteins: one which has high affinity for corticosterone and saturable binding sites and resembles a transcortin-type protein, and the other which has a high affinity and limited capacity for binding DHT and could be a protein of the sex-hormone-binding protein type. The plasma concentrations of these two binding proteins fluctuate throughout the year. Transcortin concentration is not significantly higher in winter and spring than in summer and autumn. The SBP binding capacity is difficult to correlate with testosterone concentrations.

Plasma transcortin concentration in thyroidectomized chick embryos.

Concentrations of transcortin binding sites and apparent dissociation constants for corticosterone have been measured in the blood of control and thyroidectomized chick embryos. The levels of corticosterone binding are quantitatively similar in normal and thyroidectomized embryos and vary in parallel during development.