A competitive protein binding radioassay for deoxycorticosterone in human plasma

Measurement of free glucocorticoids: quantifying corticosteroid binding capacity and its variation within and among mammal and bird species

Plasma glucocorticoid (CORT) levels are one measure of stress in wildlife and give us insight into natural processes relevant to conservation issues. Many studies use total CORT concentrations to draw conclusions about animals' stress state and response to their environment. However, the blood of tetrapods contains corticosteroid-binding globulin (CBG), which strongly binds most circulating CORT. Only free CORT (CORT not bound by CBG) leaves the circulation and exerts biological effects on CORT-sensitive tissues. Measuring free CORT concentrations provides insight to an animal's stress response that cannot be revealed by simply measuring total CORT. To calculate free CORT concentrations in plasma or serum samples, one needs three measurements: the binding affinity of CBG for CORT (which varies by species), the total CORT concentration in the sample and the maximum corticosteroid binding capacity (MCBC) of CBG in the sample. Here, we detail the measurement of CBG binding capacity. We compare and contrast the three main methods to measure MCBC: charcoal, cell harvester and dialysis. Each is defined by the means by which free and bound CORT are separated. We weigh the relative merits and challenges of each. We conclude that sample volume, species and taxon binding specificity, and availability of equipment are the primary considerations in selecting the appropriate separation method. For most mammals, the charcoal method is recommended. For birds, the harvester method has critical advantages over the charcoal method. The dialysis method is widely regarded as the gold standard and has lower equipment costs but is more time-intensive and costly in terms of radioactive isotope needed and is less suited to processing large numbers of samples. The binding capacity of CBG varies tremendously within and among the bird and marine mammal species studied, and we discuss the implication of this variation for understanding the role of stress in wildlife.

Seasonal changes in glucocorticoid and testosterone concentrations in free-living arctic ground squirrels from the boreal forest of the Yukon

We examined how glucocorticoid and testosterone concentrations changed from spring to summer by livetrapping free-living populations of arctic ground squirrels (Spermophilus parryii). The primary glucocorticoid was found to be cortisol, with corticosterone below measurable concentrations in most individuals. Livetrapping elicited a strong stress response in both sexes: breeding males and females trapped in spring had free cortisol concentrations 4 and 34 times, respectively, those of base-line animals. The maximum corticosteroid-binding capacity (MCBC) was unaffected by trapping and was about 3 times higher in breeding females than in breeding males. Over the active season, MCBC values were lowest in all male classes (juveniles, nonreproductive adults, and reproductive adults), being less than half those in all female classes; pregnant females had values approximately twice those of juvenile females. However, free cortisol concentrations were similar in all female classes and in juvenile males and about half those in adult males. Livetrapping increased testosterone concentrations in males over those found in samples from base-line males, and testosterone concentrations did not affect MCBC values. Testosterone concentrations in livetrapped animals differed significantly among male classes, with nonreproductive males maintaining concentrations 64% of those in breeding males and 10 times those in juveniles.

Deoxycorticosterone secretion by the human ovary

Progesterone (P), deoxycorticosterone (DOC), estradiol-17 beta (E2) and cortisol (F) were determined simultaneously in the peripheral and the ovarian veins in 13 patients. Blood was collected either by direct sampling during laparotomy (12 patients) or by selective catheterization (1 patient). In all ovarian effluents P and E2 levels were significantly higher than in the peripheral vein. This was also true for DOC except in one ovarian effluent. The gradient was higher on the side of the corpus luteum-bearing ovary. P and E2 levels were correlated in ovarian as well as in peripheral veins. In ovarian effluents, DOC gradients were only significantly correlated with P levels (r = 0.63; P less than 0.01) suggesting a metabolic relationship between the two steroids.

Lack of prolactin involvement in corticosteroid secretion

In mammals prolactin can modify adrenal steroidogenesis. Its trophic effect on adrenal cells where prolactin receptors have been identified suggest a direct impact upon corticosteroid biosynthesis. In man, this role of prolactin remains controversial. The purpose of our study was to investigate the effects of chronic hyperprolactinemia on basal and stimulated corticosteroid hormone secretion. Seven women with untreated chronic hyperprolactinemia (HPRL) were included in the study. In each of them, a beta 1-24 ACTH test was performed on a normal and low Na+ diet for 4 days. Basal and ACTH-stimulated cortisol, aldosterone, deoxycorticosterone and 17 hydroxyprogesterone secretion were not significantly different in HPRL and NPRL women. These results do not support evidence for any significant role of prolactin upon corticosteroid biosynthesis in man. They also suggest that prolactin is not the pituitary factor which modulates ACTH or low Na+ diet stimulated corticosteroid secretion.

Synthesis of 7 alpha- and beta-carboxymethyl derivatives of cortisol, corticosterone, deoxycorticosterone and cortisone. Immunogenic properties of cortisol, corticosterone and deoxycorticosterone derivatives

7 alpha- and 7 beta-Carboxymethylderivatives of cortisol, corticosterone and deoxycorticosterone have been synthetized. After coupling to bovine serum albumin, they were used to elicit antibodies in rabbits. Highly specific antisera were obtained which may possibly be used for a direct radioimmunoassay of these steroids in human and rodent plasma. In the case of the derivatives of cortisol and corticosterone and stereoisomery of the coupling had an effect on the affinity and the specificity of the antisera. In all immunized rabbits the antisera obtained with the 7 alpha-derivative had a higher affinity and a narrower specificity than the antiserum obtained with the 7 beta-derivative.

Celite multi-column chromatography for the simultaneous separation of progesterone, deoxycorticosterone and 17 alpha-hydroxyprogesterone from small plasma or tissue samples

A rapid, inexpensive and reliable chromatographic method has been developed for the simultaneous separation of progesterone, deoxycorticosterone and 17 alpha-hydroxyprogesterone on 15-cm Celite columns using n-heptane-benzene-methanol-water (100:35:80:20) as mobile phase. Six columns can be run in parallel within an hour with the assistance of nitrogen pressure. There is negligible column-to-column or batch-to-batch variation with consistent high recoveries. Columns are easily and quickly prepared and being inexpensive are disposable which is important when working with radioactivity. Using this method three important corticosteroids can be rapidly and reliably isolated from 20-30 small plasma or tissue samples per day.

Radioimmunoassays for aldosterone and deoxycorticosterone in plasma and urine

Radioimmunoassays for aldosterone and deoxycorticosterone (DOC) are described in which a simple separation procedure using ammonium sulfate stabilization of bound steroid and extraction of free steroid into toluene scintillant allows an "in vial" assay without mechanical separation of the two phase system. Extraction and thin layer chromatographic methods for purification of aldosterone and DOC are free of solvent and plate blank effects. Normal values are given for unconjugated aldosterone and DOC in urine, for aldosterone and DOC in plasma and for aldosterone 18-glucuronide in urine.