Radioimmunological determination of apparent free cortisol concentration: some physiological and clinical applications

Hypothalamic-pituitary adrenal function in end-stage non-alcoholic liver disease

Patients with end-stage liver disease have significant mortality often associated with intercurrent episodes of bleeding or sepsis. Intact adrenal function is essential in such situations. In order to test the hypothesis that adrenal insufficiency might be present in severe liver disease, hypothalamic-pituitary adrenal function was evaluated in patients with end-stage liver disease awaiting transplantation. The study had a prospective, open comparative design with patients restricted to those having non-alcoholic liver disease in order to avoid the confounding direct effects of alcohol on adrenocortical function. Fifty-one consecutive patients with end-stage, non-alcoholic liver disease undergoing evaluation for liver transplantation and 40 healthy controls were studied. Patients who had used corticosteroids (n = 8) or who were unable to complete the investigations (n = 5) were excluded leaving 38 patients eligible for analysis. Adrenal function was evaluated under basal conditions by single morning measurements of plasma total and free cortisol, corticosteroid-binding globulin, dehydroepiandrosterone sulfate and by adrenal stimulation indirectly using insulin-induced (0.1 U/kg, i.v.) hypoglycaemia and/or directly by adrenocorticotrophic hormone (ACTH); 250 micrograms tetracosactrin, i.v.) stimulation. Compared with healthy controls, patients with liver disease had a 64% reduction in maximal increments of plasma cortisol to indirect adrenal stimulation via insulin-induced hypoglycaemia and a 39% reduction to direct adrenal stimulation by ACTH (all P < 0.001). There was a significant negative correlation between the severity of underlying liver disease as assessed by Child-Pugh scores and peak control responses to ACTH (r = -0.647, P < 0.0001) and insulin-induced hypoglycaemia (r = -0.597, P < 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

Measurement of plasma free steroids by direct radioimmunoassay of ultrafiltrate in association with the monitoring of free components with [14C]glucose

We describe a modified method of centrifugal ultrafiltration using the Grace MPS-3 device for the measurement of plasma free (unbound) steroids (cortisol, testosterone, estradiol, and prednisolone). Plasma was incubated with [14C]glucose to monitor the movement of free components, applied to the MPS-3 and centrifuged. Steroid concentration of ultrafiltrate was directly measured by radioimmunoassay, and multiplied by the ratio of [14C]glucose count (dpm) in plasma to [14C]glucose count (dpm) in ultrafiltrate. The data by this method correlated well with those obtained by equilibrium dialysis. Our results of free steroid in healthy volunteers and patients with various diseases were comparable with the previously reported values. This procedure showed the advantages of small sample volume, rapid separation and the ability to process a large number of samples in a single run.

Type A, test performance and salivary cortisol

Forty first year medical students, previously screened for the presence or absence of the Type A behavior pattern, collected saliva samples for four days leading up to the first major examination of their medical school course. It was observed that the day of the examination produced substantially different patterns of salivary cortisol concentrations for Type A and non-A subjects, depending on their level of performance. The Type A subjects who scored above the median on the examination showed higher concentrations of salivary cortisol than Type A subjects who scored below the median. The reverse of this pattern was found for non-A subjects. Visual analog scale ratings of subjective stress showed no behavior pattern effects and a very low correlation with the salivary cortisol concentrations. The results support the view that the occurrence of physiological arousal associated with the Type A behaviour pattern is intermittent and dependent on situational factors such as expectation of success and actual success. This is consistent with conceptualizing the Type A pattern as a strategy for resource allocation which may be elective, rather then the behavioural manifestation of an automatic physical response to stress.

Hormones in saliva

Since the collection of saliva is noninvasive, nonstressful and usually very convenient there have been many recent studies examining the clinical relevance of measuring various hormones in saliva. It now appears that the measurement of most unconjugated steroids in saliva will provide clinically useful data whereas the measurement of conjugated steroids, thyroid hormones, and protein hormones is unlikely to be clinically relevant. The key factors determining whether the salivary concentration of a hormone or drug is likely to be clinically relevant are the mechanisms by which the material enters the saliva; the "free to protein bound" ratio for the material; and the structure of the material, i.e., its molecular weight, polarity and the presence of ionizable groups.

Apparent free cortisol concentrations in patients with anorexia nervosa at different stages of the disease

We have measured the total cortisol concentration (TC) and the apparent free cortisol concentration (AFCC) in plasma samples of 17 patients with anorexia nervosa (AN) at different stages of the disease, in basal conditions and after suppression test. We measured free cortisol values directly by a RIA method in dialyzed plasma samples after an equilibrium dialysis system. We have found significantly elevated TC and AFCC values in basal conditions and after suppression test only in the group of patients in the severe stage of the disease. In addition, a significant (p less than 0.05) correlation existed between percent loss of ideal body weight TC and AFCC values after suppression test. Our results suggest that the hypothalamus-pituitary-adrenal axis may be grossly impaired only in the severe stage of AN.

A simplified ultrafiltration method for determination of serum free cortisol

We describe the suitability of the Amicon MPS-1 centrifugal ultrafiltration device and the YMB membrane for measuring free cortisol in serum. The method combines two independent assays: total cortisol and the ultrafiltrate fraction of added [3H]cortisol. The unbound fraction is determined in 0.25-0.30 ml of ultrafiltrate collected from 0.6 to 1 ml of serum that has been equilibrated with [3H]cortisol at 37 degrees C for 20 min. The assay is rapid (less than 1 h), practical ( no more than 0.6 ml of serum is necessary) and repeatable (CV: 3.8% within-assay and 12.2% in different assays). Error introduced in free cortisol measurement due to dilution effects in dialysis is systematically defined, and the effect of tracer purity on the ultrafiltration method is examined. Dialyzed sera from normal men and women, from patients with Cushing's disease and adrenal insufficiency, and from pregnant women gave ultrafiltration results that accurately duplicated those obtained by previous dialysis.

Phase shifts in circadian rhythmicity of total, free corticosterone and transcortine plasma levels in hypothyroid male Japanese quails

Control, radiothyroidectomized, and methimasol-treated short day (6L:18D; beginning of light at 0700) male Japanese quails were studied with regard to their circadian rhythmicity of total, free corticosterone and transcortine plasma level. In the controls, the peak of total and free corticosterone coincided with the maximal corticosterone binding capacity of transcortine; these parameters can be characterized by similar daily rhythm. In hypothyroid birds a synchronous phase shift of these parameters has been observed. In methimasol-treated animals the phase shift of the circadian rhythmicity was 6-8 hr, and in the radiothyroidectomized group 12 hr, respectively. According to the degree of hypothyroidism the metabolic clearance rate (MCR) of corticosterone decreased. This effect leads to the phase shift of total corticosterone rhythm, and the shift includes not only free, but also transcortine concentration.

Use of saliva for monitoring unbound free cortisol levels in serum

In order to verify the clinical usefulness of saliva in assessing the adrenocortical function, we measured saliva cortisol levels by a radioimmunoassay after extraction with dichloromethane, and compared the results with the levels of serum unbound cortisol determined by the method of equilibrium dialysis. Paired samples of saliva and serum were obtained from 10 healthy male volunteers. Morning levels of saliva cortisol and serum unbound cortisol were 0.99 +/- 0.42 and 1.56 +/- 0.54 microgram/100 ml, respectively, where serum total cortisol was 19.28 +/- 3.56 microgram/100 ml. A well-defined diurnal rhythm and a greater response to ACTH stimulation were observed in saliva cortisol than in serum total cortisol. Kinetic study of injected cortisol revealed almost identical values for the compartments of saliva cortisol and serum unbound cortisol. The correlation coefficient (r) between the levels of saliva cortisol and serum unbound cortisol was 0.893 (p less than 0.001, n = 150). From these results we concluded that the measurement of saliva cortisol can be used sufficiently to monitor unbound free concentrations in serum.

The relationship between unbound and total cortisol: its usefulness in detecting CBG abnormalities

The relationship between unbound and total cortisol has been studied in patients with a variety of clinical conditions. We report on a simple, rapid and reliable method for evaluating the percentage unbound cortisol in serum or plasma which can be used in conjunction with total plasma cortisol to obtain a more complete understanding of the patients' adrenal status. Comparison of a patient's percentage unbound and total cortisol with a nomogram showing the normal relationship between percentage unbound and total cortisol indicates the patient's concentration of cortisol binding globulin. The concentration of unbound cortisol, the biologically active moiety, is the product of the percentage unbound and total cortisol concentration. The following values for the unbound cortisol concentration (microgram/dl) were obtained (mean +/- S.D.). Twenty-four normal subjects, 8--10 a.m., 1.2 +/- 0.4; 14 women receiving an oral contraceptive, 1.4 +/- 0.5; 6 patients with adrenal insufficiency, 0.2 +/- 0.1; 9 hyperthyroid patients, 1.7 +/- 0.8; 5 acute ill patients, 3.8 +/- 2.4; and a patient with Cushing's syndrome, 6.1. In normal subjects the values decreased at 4 p.m. (0.4 +/- 0.1) and after dexamethasone administration (0.1 +/- 0.1), and increased following the intravenous injection of adrenocorticotropic hormone (3.6 +/- 0.7). In pregnant women the unbound cortisol increased as the pregnancy progressed, first trimester: 1.2 +/- 0.3, second trimester: 1.6 +/- 0.2, third trimester: 2.4 +/- 0.5.

A source of error in equilibrium dialysis

Equilibrium dialysis is often used to study the binding of steroids to proteins. With this technique it is customary to determine the percent bound and unbound steroid in the sample, the affinity constant for the steroid-protein binding reaction, and the concentration of binding sites on the protein. Investigators have used many different ratios of dialysis buffer to sample volumes in their experiments assuming that the equilibrium in the post-dialysis sample was the same as existed before dialysis. Chemical equilibrium expressions for the system before and after dialysis indicate that during dialysis the concentration of steroid in the sample decreases resulting in a new equilibrium in which the percent bound and unbound are different from the original sample. The magnitude of the difference between the pre- and post-dialysis systems is proportional to the ratio of dialysis buffer to sample volumes. Accurate values for the affinity constant and binding site can be obtained only if this change in the equilibrium is considered.

Progressively elevated levels of biologically active (free) cortisol during pregnancy by a direct radioimmunological assay of diffusible cortisol in an equilibrium dialysis system

The measurement of free cortisol would be preferable with respect to the total hormone content, since it yields more reliable information about the plasma levels of the biologically active cortisol. We have developed a new method for the determination of the apparent free plasma cortisol concentration (AFCC) by means of direct radioimmunological measurement of dialyzed cortisol. The AFCC was measured in 23 plasma pools obtained from normal pregnant women at various gestational times and in 18 nonpregnant women. The mean AFCC was 19.5 +/- 7.1 ng/ml in pregnant women and 9.0 +/- 6.2 ng/ml in nonpregnant women (p less than 0.005). The percent of free cortisol (%FC) showed a progressive increase during pregnancy reaching the lower limits of the normal range at the third trimester. However, the mean of %FC was significantly lower (p less than 0.005) in pregnant women than in nonpregnant women. Our data show a progressive increase of biologically active cortisol during pregnancy.