Percent Free Cortisol Research Articles

Serum Free Cortisol Fraction in Healthy and Septic Neonatal Foals

Relative cortisol insufficiency occurs in septic foals and impacts survival. Serum free (biologically available) cortisol concentration might be a better indicator of physiologic cortisol status than serum total cortisol concentration in foals. In septic foals, (1) low free cortisol concentration correlates with disease severity and survival and (2) predicts disease severity and outcome better than total cortisol concentration. Fifty-one septic foals; 11 healthy foals; 6 healthy horses. In this prospective clinical study, foals meeting criteria for sepsis at admission were enrolled. University-owned animals served as healthy controls. Basal and cosyntropin-stimulated total cortisol concentration and percent free cortisol (% free cortisol) were determined by chemiluminescent immunoassay and ultrafiltration/ligand-binding methods, respectively. Group data were compared by ANOVA, Mann-Whitney U-tests, and receiver operator characteristic curves. Significance was set at P < .05. Basal % free cortisol was highest in healthy foals at birth (58 ± 8% mean ± SD), and was higher (P ≤ .004) in healthy foals of all ages (33 ± 6 to 58 ± 8%) than in adult horses (7 ± 3%). Cosyntropin-stimulated total and free cortisol concentrations were lower (P ≤ .03) in foals with shock (total = 6.2 ± 8.1 μg/dL; free = 3.5 ± 4.8 μg/dL versus total = 10.8 ± 6.0 μg/dL; free = 6.9 ± 3.3 μg/dL in foals without shock) and in nonsurvivors (total = 3.8 ± 6.9 μg/dL; free = 1.9 ± 3.9 μg/dL versus total = 9.1 ± 7.7 μg/dL; free = 5.5 ± 4.4 μg/dL in survivors). Free cortisol was no better than total cortisol at predicting disease severity or outcome in septic foals. Serum free cortisol is impacted by age and illness in the horse. There is no advantage to measuring free over total cortisol in septic foals.

NUMERICAL SOLUTION FOR CORTISOL EQUILIBRIUM AND MAXIMAL CORTISOL SECRETION RATES IN HUMAN SEPTIC SHOCK AND HEALTHY CONTROL SUBJECTS.

Septic shock (SS) is associated with an increase in total and free cortisol along with a disproportionate increase in percent free cortisol, due in part to decreased serum concentrations of cortisol-binding globulin (CBG) and albumin. Relative adrenal insufficiency (RAI) is often seen in septic shock and is biochemically defined by a cortisol increment Objective Keenan et al proposed a set of three differential equations describing a dynamic model for free cortisol secretion and clearance rates, which incorporates the reactions of free cortisol with CBG and albumin, under non-steady-state conditions. We sought to assess maximal cortisol secretion rates in SS and in control subjects using numerical techniques to solve for cortisol equilibrium in the serum compartment and for cortisol secretion and clearance rates. Methods Plasma total and free cortisol, serum CBG, and albumin were measured in subjects with SS (n = 45), subjects with sepsis (S, n = 19), and in healthy controls (HC, n = 10) at 0, 30, and 60 minutes after 250 μg cosyntropin. Numerical solution for cortisol secretion rates used group-specific KA determined by least squares solution and assumed a uniform, maximal cortisol secretion rate to provide a least squares solution for secretion and clearance to fit observed data points. Results The group-specific KA was significantly higher in SS versus S and HC (148, 99, and 78 μM, p Conclusions SS and RAI are associated with a reversible increase in KA, contributing to an increase in percent free cortisol. Maximal cortisol secretion rates are elevated in SS, including RAI subjects. The distribution of the normal range of maximal secretion rates (CV = 48%) suggests that application of numerical solution to non-steady-state conditions, such as the cosyntropin stimulation test, may be useful in distinguishing absolute and relative adrenal insufficiency.

21.12 A throw-and-catch pattern in postural sway doesnot exclude continuous feedback control

Heritability of the variation of the plasma concentrations of total and unbound cortisol, cortisol binding globulin (CBG), and dehydroepiandrosterone sulfate (DHEA-S) was investigated in 20 monozygotic (MZ) and 20 dizygotic (DZ) male twin pairs. Three plasma samples collected between 8 am and 9:30 am were pooled for the assays. Heritability was calculated from the intraclass correlation [2(rMZ - rDZ)]. The mean age, total and unbound cortisol, CBG, and DHEA-S were not significantly different between the MZ and DZ groups of twins. The heritability index for variability of the plasma content of steroids was 45.4% (p < .05) for total cortisol, 50.6% (P < .05) for unbound plasma cortisol, 57.8% (P < .05) for DHEA-S, and 32.4% (P > .05) for CBG. The data were analyzed by factor analysis, and heritability estimates were corrected for factors including age, smoking, drinking, exercise, and degree of obesity. These factors did not account for the variation in hormone values in twin pairs. Factor analysis of the three quantitative measurements, cortisol, percent free cortisol, and DHEA-S, provides no evidence for shared factors. The correlation coefficients between age and CBG and total and unbound plasma cortisol concentrations were insignificant. The correlation coefficient between total plasma cortisol levels and CBG was 0.57, which indicates that CBG accounts for 32% of the variation of plasma cortisol concentrations. The results suggest that genetic factors have a decided influence on the variation of the concentration of cortisol of DHEA-S in normal adult men.

Free and total cortisol levels in semelparous and iteroparous chinook salmon

Total cortisol, free cortisol and percent free cortisol were all significantly higher in semelparous male chinook salmon Oncorhynchus tshawytscha than in iteroparous and immature fish. The findings suggest that the regulation of both total and free cortisol concentrations may play key roles in mediating the post‐spawning death of semelparous Pacific salmon.

Hormone profiles in humans experiencing military survival training

Background: Clinical models of the human response to intense, acute stress have been limited to laboratory settings or cross sectional characterizations. As a result, data about the sensitivity of the human neuroendocrine activation to realistic stressors of varying magnitudes are limited. The U.S. Army survival course offers a unique opportunity to examine, in a controlled manner, the human response to acute, realistic, military stress. Methods: Salivary data were collected in 109 subjects at baseline during four stress exposure time points and at recovery. Serum data was collected at baseline and recovery in 72 subjects and at baseline and during stress exposure in a subgroup of subjects ( n = 21). Results: Cortisol significantly increased during the captivity experience and was greatest after subjects’ exposure to interrogations. Cortisol remained significantly elevated at recovery. Testosterone was significantly reduced within 12 hours of captivity. Reductions of both total and free T4 and of total and free T3 were observed, as were increases in thyrotropin. Conclusions: The stress of military survival training produced dramatic alterations in cortisol, percent free cortisol, testosterone, and thyroid indices. Different types of stressors had varying effects on the neuroendocrine indices. The degree of neuroendocrine changes observed may have significant implications for subsequent responses to stress.

Reduced plasma cortisol binding to albumin in ocular hypertension and primary open-angle glaucoma

Purpose. To compare plasma cortisol binding as well as total plasma cortisol, free cortisol and percent free cortisol in normals, ocular hypertensives and primary high pressure open-angle glaucomas. Methods. Blood samples were obtained on outpatient visits of 18 normals, 19 ocular hypertensives and 18 primary open-angle glaucomas. Plasma cortisol binding was determined after the endogenous steroids were removed by charcoal absorption. Scatchard analysis was used to determine both the affinity of binding and the cortisol binding capacity of corti-costeroid binding globulin and albumin. Plasma total and free cortisol were measured by radioimmunoassay. Results. Both the ocular hypertensive and the open-angle glaucomas in comparison to normals were found to have a highly significant reduced cortisol binding capacity to albumin (p = 0.006) with a borderline significantly increased binding affinity to plasma corticosteroid binding globulin (p = 0.0495) and no significant difference in binding affinity to albumin or cortisol binding capacity to plasma globulin. Both the ocular hypertensives and the open-angle glaucomas in comparison to normals were found to have significantly elevated levels of free cortisol (p = 0.012) and percent free cortisol (p = 0.003). Multivariate analyses showed that the reduced cortisol binding capacity to albumin was significantly associated with an increased percent free cortisol, with ocular hypertension and open-angle glaucoma and with male gender. Conclusion. Both ocular hypertension and primary open-angle glaucoma are associated with elevated levels of plasma free cortisol which are related to a reduced cortisol binding capacity to albumin.

Increased follicular fluid total and free cortisol levels during the luteinizing hormone surge

To determine the changes in follicular fluid (FF) total and free cortisol during the LH surge in naturally ovulating women. Twenty-six women having diagnostic laparoscopy during the follicular phase of normal menstrual cycles were selected. Blood samples were collected 1 day before, the day of, and 1 day after surgery and the results of serum E2 and LH were used to divide the cycles retrospectively into pre- and post-LH surge groups. Follicular fluid was collected during laparoscopy. Serum P, total and free cortisol, and FF volume, E2, P, total cortisol, and free cortisol were measured on the day of surgery. Median serum and FF P levels were significantly higher in the post-LH surge group compared with the pre-LH surge group (0.54 versus 1.54 ng/mL [1.7 versus 4.85 nmol/L] and 5.03 versus 28.0 micrograms/mL [15.8 versus 88.0 mumol/L], respectively). Follicular fluid volume also increased significantly after the surge (2.5 versus 4.5 mL). Median serum total and free and percent free cortisol were higher after the surge, although not significantly. In contrast, FF total, free, and percent free levels increased dramatically between pre- and post-LH surge samples (4.41 versus 43.6 ng/mL [16.0 versus 158 nmol/L], 0.138 versus 6.68 ng/mL [0.5 versus 24.2 nmol/L], and 3.3% versus 15.0%, respectively; P < 0.05). An increase in total and free cortisol occurs in the follicle during the LH surge. Cortisol and its regulation by 11 beta-hydroxysteroid dehydrogenase therefore may exert a physiologic role in oocyte maturation or ovulation.

Corticosteroid-binding globulin (CBG) production by hepatic and extra-hepatic sites in the ovine fetus; effects of CBG on glucocorticoid negative feedback on pituitary cells in vitro

Plasma cortisol levels increase in fetal sheep during late gestation and this is associated with an increase in plasma corticosteroid-binding globulin (CBG) concentrations. However, the relative tissue sources of plasma CBG, the ontogeny of its biosynthesis and glycoform composition have not been established in the ovine fetus. Therefore we examined whether changes in plasma corticosteroid binding capacity (CBC) in fetal sheep during late gestation were associated with different patterns of glycosylation and reflected changes in tissue CBG expression. Since free cortisol is considered the bioactive fraction, we measured changes in the percent and absolute free cortisol in fetal plasma during late gestation. In order to examine whether CBG alters cortisol negative feedback at the level of the fetal pituitary, we also examined the effect of exogenous CBG in mediating the glucocorticoid-induced suppression of basal and corticotrophin-releasing hormone (CRH)-stimulated ACTH release from fetal pituitary cells in culture. The mean free cortisol concentration in plasma was not different between days 15 and 20 prior to parturition, and between 5 and 10 days prepartum, although it did rise between these times. Plasma CBC in chronically catheterized fetuses rose from 23.3 +/- 4.6 ng/ml at day 115 to 86.5 +/- 20.8 ng/ml at term and then decreased rapidly after birth. Between day 125 and day 140 of pregnancy approximately 10% of fetal plasma CBG was retarded by Concanavalin-A chromatography. This proportion increased at birth and attained adult values of > 70% by one month of age. By Northern blotting the relative levels of CBG mRNA in the fetal liver did not change between days 100 and 125, then increased significantly at day 140, but declined at term and in newborn lambs. CBG mRNA was undetectable in total RNA from lung, kidney, hypothalamus and placentomes, but was present in the fetal pituitary at days 125 and 140. Reverse transcription-PCR was used to confirm the presence of CBG mRNA in pituitary tissue from term fetuses. In cultures of term fetal pituitary cells, added CBG attenuated the cortisol- but not the dexamethasone-mediated suppression of basal and CRH-stimulated ACTH release. We conclude that in fetal sheep there is an increase in the corticosteroid binding capacity of plasma during late pregnancy which regulates, in part, free cortisol levels in the circulation. The liver is the major site of CBG biosynthesis in the fetus and at least until day 140 of gestation the rise in plasma CBC is associated with an increase in hepatic CBG mRNA levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Alcohol and other dietary factors in relation to serum hormone concentrations in women at climacteric

The relationships between concentrations of endogenous hormones in serum and dietary intakes of alcohol, fats, fiber, and caffeine were examined in 325 healthy Massachusetts women aged 50-60 y who reported having a normal menstrual period within the previous 12 mo. Diet was assessed by a semiquantitative food frequency questionnaire. Hormones assayed were estrone, estradiol, percent free estradiol, sex-hormone-binding globulin (SHBG), cortisol, and gonadotropins. Alcohol intake was not associated with concentrations of estrogens or gonadotropins. Neither total fat intake nor the fat composition of the diet influenced hormone concentrations. Fiber intake was positively correlated with SHBG; no associations with estrogens were seen. Caffeine intake was inversely correlated with free estradiol and positively correlated with SHBG. These data suggest that fat, fiber, and alcohol intakes of US women at climacteric are not determinants of variations in estrone and either total or percent free estradiol.

Heritability of variation of plasma cortisol levels

Heritability of the variation of the plasma concentrations of total and unbound cortisol, cortisol binding globulin (CBG), and dehydroepiandrosterone sulfate (DHEA-S) was investigated in 20 monozygotic (MZ) and 20 dizygotic (DZ) male twin pairs. Three plasma samples collected between 8 am and 9:30 am were pooled for the assays. Heritability was calculated from the intraclass correlation [2(r MZ - r DZ)]. The mean age, total and unbound cortisol, CBG, and DHEA-S were not significantly different between the MZ and DZ groups of twins. The heritability index for variability of the plasma content of steroids was 45.4% ( p < .05) for total cortisol, 50.6% ( P < .05) for unbound plasma cortisol, 57.8% ( P < .05) for DHEA-S, and 32.4% ( P > .05) for CBG. The data were analyzed by factor analysis, and heritability estimates were corrected for factors including age, smoking, drinking, exercise, and degree of obesity. These factors did not account for the variation in hormone values in twin pairs. Factor analysis of the three quantitative measurements, cortisol, percent free cortisol, and DHEA-S, provides no evidence for shared factors. The correlation coefficients between age and CBG and total and unbound plasma cortisol concentrations were insignificant. The correlation coefficient between total plasma cortisol levels and CBG was 0.57, which indicates that CBG accounts for 32% of the variation of plasma cortisol concentrations. The results suggest that genetic factors have a decided influence on the variation of the concentration of cortisol of DHEA-S in normal adult men.

Plasma free cortisol during secretory episodes.

Plasma free cortisol fractions were determined in normal men during spontaneous cortisol secretory episodes and ACTH- or exercise-provoked cortisol peaks in the physiological range. The percentage of free cortisol was measured using ultrafiltration by centrifugation at 37 C, and total cortisol concentrations were measured by RIA. The percent free cortisol varied with the time of day, as did total cortisol. It increased parallel to total cortisol increases, whether they were spontaneous, as occurring in the early morning or postprandially, or provoked by external stimulation. A highly significant positive correlation between relative increases in free and total cortisol was found throughout the experiment. As reported previously, total cortisol increases, according to their origin, did or did not reduce the effects of subsequent stimuli. The present results indicate that the variations in the percent free cortisol are not responsible for the differences in the cortisol responses to these stimuli.

Free Cortisol Index: A Rapid and Simple Estimation of Free Cortisol in Human Plasma1

A rapid and simple method for the estimation of free (nonprotein-bound) cortisol in human plasma is described. Total plasma cortisol (F) was determined by a competitive protein binding assay. An estimate of the saturation of Corticosteroid Binding Globulin was obtained by the use of "charcoal cortisol uptake" (CFU). "Charcoal cortisol uptake ratio" (CFUR) was defined as the ratio of the CFU of the unknown plasma to that of a reference serum pool. Free cortisol index (FFI) was calculated as (total plasma F) times (CFUR). Percent free cortisol and free cortisol concentration (FF) was determined by equilibrium dialysis at 37 C. 169 plasma samples with an F range of 0.8-61.2 mug/100 ml from 18 normal, 10 ACTH-stimulated, 17 estrogen-treated and 12 pregnant subjects were analyzed. A highly significant correlation between FFI and FF was found (r = 0.952). Inter-assay coefficients of variation were 7% for total plasma F and 3.5% for CFU. The method allows the rapid processing of large numbers of samples and can be performed on 0.2 ml of plasma.