Corticosterone Binding Capacity Research Articles

Hormetic effects of gamma radiation on the stress axis of natural populations of meadow voles (Microtus pennsylvanicus)

We tested the hypothesis that low doses of gamma radiation have beneficial, hormetic effects on the stress axis (the hypothalamic-pituitary-adrenocortical axis) of free-ranging meadow vole populations (Microtus pennsylvanicus). Voles were exposed to chronic gamma radiation from a 137Cs field irradiator. In isolated populations, voles received one of three treatments over a four-year period: Controls (0.19-0.42 microGy/h--levels that were 2-5x above background levels [0.1 microGy/h] and live-trapped in all years--1982--1985), low doses (22.6 microGy/h--50-200x background, live-trapped from November 1982--April 1985), or high doses (3,840 microGy/h--40,000x background, live-trapped from November 1983--April 1985). Voles exposed to a low dose had levels of free and total corticosterone that were significantly higher than those in the control or high-dose groups. Differences in response to radiation between the sexes were apparent for maximum corticosterone-binding capacity, with females exposed to low doses having higher binding capacity than control or high-dose females, whereas males exposed to low doses had lower binding capacity than control or high-dose males. Low-dose voles had higher counts of neutrophils than either the controls or high-dose voles; hematocrit was greater in the controls than in irradiated voles. These results indicate that voles display a hormetic response to radiation, wherein low doses of an otherwise harmful agent produce a beneficial effect. The stimulation of the stress axis resulting in the increased secretion of glucocorticoids, which may protect against the excessive actions of the immune and inflammatory responses, may be a key mechanism producing this effect.

Abnormalities of hypothalamic-pituitary-adrenal and hypothalamic-somatotrophic axes in Fawn-Hooded rats.

Fawn-Hooded (FH) rats show central and peripheral abnormalities in serotoninergic functions and have attracted attention as an animal model of some pathologies, including depression and hypertension. In addition, these rats show a reduced growth rate. As the hypothalamic-pituitary-adrenal (HPA) axis has been implicated in both depression and hypertension, and the hypothalamic-somatotrophic (HSM) axis has a major role in growth, these two endocrine axes were characterised in FH rats as compared with outbred Sprague-Dawley (SD) rats in basal conditions. FH rats showed normal serum ACTH and corticosterone concentrations, but reduced serum corticosterone binding capacity. At a central level, normal expression of mRNA for glucocorticoid type II receptors in the hippocampal formation and mRNA for corticotrophin-releasing factor (CRF) in the paraventricular nucleus of the hypothalamus were observed in FH rats, whereas expression of mRNA for CRF in the central nucleus of the amygdala was enhanced compared with the expression in SD rats. Serum GH concentrations were normal in FH rats, IGF-I tended to be lower, and mRNA for somatostatin (SRIF) in the periventricular nucleus of the hypothalamus was significantly lower in FH rats than in SD rats. The reduced SRIF gene expression in rats with normal or slightly reduced GH and IGF-I, respectively, might be secondary to a defective central and peripheral response to IGF-I, compatible with the reduced growth of FH rats. The present results suggest that FH rats have abnormalities in both HPA and HSM axes that might be related to some of their physiopathological characteristics.

Permanent upregulation of hippocampal mineralocorticoid receptors after neonatal administration of ACTH-(4–9) analog ORG 2766 in rats

The development of brain corticosteroid receptors may be permanently modified by perinatal hormone treatments, in particular by hormones of the hypothalamic-pituitary-adrenal axis. Changes in binding characteristics of corticosteroid receptors were investigated in rats treated subcutaneously with 1 μg/g body wt of the ACTH-(4–9) analog peptide ORG 2766 once daily at postnatal days 1, 3 and 5. [ 3H]Corticosterone (CORT) binding capacity ( B max) and affinity ( K d) were determined at 1-, 2- and 3-weeks old and adult ages in the hippocampal cytosol by using saturation analysis. Mineralocorticoid type receptor (MR) and glucocorticoid receptor (GR) sites were measured separately with single-point analysis applying a selective glucocorticoid ligand RU 28362 saturating GR. An increase in [ 3H]CORT binding capacity was found during postnatal development which remained permanently high up to adult age. Separate analysis of MR and GR expression indicated that the increment in the number of corticoid receptor sites was due to an increase in number of MRs in both the young and adult rats. It was concluded that neonatal injections of ACTH-(4–9) peptide resulted in a permanent and selective upregulation of hippocampal MRs, which may underlie the previously observed increased vigilance and novelty-induced behavioral reactivity of the peptide-treated adult rats (Felszeghy, K., Sasvári, M. and Nyakas, C., Horm. Behav., 27 (1993) 380–396). © 1997 Elsevier Science B.V. All rights reserved.

Strain-dependent differences in hippocampal glucocorticoid binding capacity and active avoidance in the mouse

Maximal individual [ 3H]corticosterone binding capacity in the hippocampus was lower in C57BL/6 mice than in BALB/c mice, and positively correlated with active avoidance learning in the two strains. Moreover, a parallel difference in the activity of hypothalamo-pituitary adrenocortical axis (HPAA) was found, consisting in a level of plasma corticosterone in C57BL/6 higher than in BALB/c mice. These results confirm the genetically determined differences in behavior of C57BL/6 and BALB/c mice, and demonstrate their association with differences in hippocampal corticosterone binding capacity, pointing to a functional relationship between the behavioral and neuroendocrine parameters.

Population Ecology and Physiology of the Common Rock Rat, Zyzomys argurus (Rodentia: Muridae) in Tropical Northwestern Australia

The common rock rat, Zyzomys argurus , undergoes a marked seasonal change in abundance in rocky habitats of tropical Australia. Four local populations had highest numbers between the late-dry (September) and mid-wet (January) periods before undergoing a three- to four-fold decrease by the end of the wet season (April). Densities differed between these populations; one population disappeared in April. Immature individuals were more abundant in September when recruitment appeared maximal; the population decline is attributable to mortality in all age categories. Both sexes were reproductively active throughout the year, but pregnant females were most abundant in April. Litter size ranged from one to six and heavier females had more embryos. Gene frequencies of Z. argurus were significantly different between the wet (January and April) and dry (July and September) seasons and the ephemeral population had different gene frequencies from the others. Differences also occurred in concentration of plasma corticosterone, maximum corticosterone-binding capacity, and corticosteroid-binding globulin-bound corticosterone. In January, individuals in all local populations had normal body weight and albumin levels, and enlarged tail bases (a fat store). They also had elevated levels of free corticosterone, neutrophils, incidence of Salmonella , and total leucocyte count; lymphocyte to neutrophil ratios differed between populations. These data indicate that populations at differing densities and in average nutritional state had greater levels of physiological and pathological stress factors in the wet season suggesting that exogenous rather than endogenous factors control stress.

Concentration of Free Glucocorticoids in Plasma and Mortality in the Australian Bush Rat (Rattus fuscipes Waterhouse)

We investigated the adrenocortical response to the stress of capture and anesthesia, and its association with seasonal mortality patterns in the Australian bush rat ( Rattus fuscipes ). In females, there were two marked seasonal peaks in the concentration of total corticosterone B of stressed plasma, one in the summer breeding period and the other in winter, a time of high mortality in females. The increase in summer was matched by a greater increase in maximum corticosterone-binding capacity of plasma so that free, biologically active, corticosterone B in plasma remained low. At the time of winter mortality, total corticosterone B exceeded maximum corticosterone-binding capacity and free corticosterone B in plasma was much higher than at other times. In males, total corticosterone B in plasma was much lower than in females during the summer period when mortality of males was high but maximum corticosterone-binding capacity was even lower, so that free corticosterone B in plasma was much higher than at other times. A similar increase in some males occurred at the time of winter mortality. The association of higher free corticosterone B in plasma and high mortality suggest an excessive adrenocortical response to stress causing increased susceptibility to disease, as in some dasyurid marsupials.

Corticosteroid receptors in liver cytosol of the clawed toad, Xenopus laevis: Daily and seasonal variations

In postmetamorphic Xenopus laevis liver cytosol the glucocorticoid binding capacity R o and the dissociation constant K d were determined. The receptor assay included an incubation period of 24 hr at 0–4° with sodium molybdate to stabilize the receptor. Dexamethasone, triamcinolone acetonide, and corticosterone as tritiated ligands were compared regarding the R 0 (67.6, 57.2, and 30.7 fmol/mg protein), the K d (3.54, 0.56, and 9.03 n M), and the rate of dissociation in young specimens of X. laevis. In adult toads the [ 3H]dexamethasone receptor binding capacity was threefold higher in females than in males (153.86 ± 12.19, 54.29 ± 4.5 fmol/mg protein)—with about the same K d (3.97 ± 0.57, 4.08 ± 0.28 n M). Young toads were kept under an artificial light regime (light from 600 to 1800 hr) and dexamethasone binding was measured every 3 hr. Unlike K d , R 0 showed a significant diurnal variation with maximal values at 600 and 1800 hr, which occurred about 9 hr after a maximal level of corticosterone in serum was reached (900, 2100). Seasonal variations of the [ 3H]dexamethasone and [ 3H]corticosterone binding capacity were different in both sexes of adult X. laevis. Maximal values in males were found in June/July and October/November. In females, the R 0 was increased in the second half of the year with the maximum in August (275.5 ± 45.02 fmol/mg protein). No correlation between R 0 and the concentration of corticosterone or aldosterone existed.

Enhanced corticosterone-binding capacity in plasma after stimulation of the rat adrenal cortex: the possibility of a simultaneous release of protein and corticosterone.

Exposure of rats to either footshock or handling stress produced a significant increase in both plasma corticosterone concentration and specific binding capacity. Non-specific binding was eliminated using the synthetic glucocorticoid, dexamethasone. The increase in both plasma corticosterone and specific binding capacity was biphasic following exposure to footshock. Adrenalectomy and pretreatment with betamethasone abolished both phases of the enhanced binding capacity and plasma steroid concentration. Intraperitoneal injection of ACTH (1-24) in animals pretreated with betamethasone resulted in a biphasic rise in plasma concentrations of corticosterone but only the initial increase in binding capacity. Dissociation constant (Kd) values, determined by Scatchard analysis, for adrenalectomized and betamethasone-pretreated animals were 546 and 556 pmol/l respectively. These values were significantly different from the Kd in animals with functional adrenals (631 pmol/l). The results are discussed in the light of a possible specific corticosteroid-binding globulin (CBG) like binding protein of adrenal origin released in conjunction with corticosterone. This binding protein has a lower affinity for corticosterone and a shorter half-life than CBG.

Effects of progesterone induced postmaturity on CBG and pituitary-adrenal activities in the rat foetus.

CBG and pituitary-adrenal activities were investigated in intact rat foetuses, in newborns spontaneously delivered by vaginal way and in postmature foetuses from mothers with delayed parturition caused by daily progesterone injection from day 20 of gestation. The postmature foetuses had lower body weights and higher adrenal weights on day 22, 23 and 24 of gestation than newborns of the same conceptional age. The corticosterone binding capacity of the plasma as well as the binding capacity of CBG for corticosterone decreased in intact foetuses for the last 3 days of gestation and stayed very low in pups from day 0 to day 8 postpartum. These parameters decreased more slowly in postmature foetuses; however, the differences between the latter and intact foetuses or newborns were not statistically significant. Similar evolution occurred in intact pregnant and suckling females as well as in females with prolonged gestation. The fall in CBG activity in normal rat pups and the subsequent rise in free steroids could explain a sharp decrease in plasma ACTH levels as well as the drop in adrenal and plasma corticosterone concentration. In foetuses with prolonged gestation, the same phenomenon did not occur. Stress conditions produced by maintaining growing foetuses in utero and the development of severe jaundice maintained high ACTH levels. In contrast, the fall in adrenal and plasma corticosterone concentrations in spite of the high level of circulating ACTH could be mainly due to the progesterone inhibition of the steroidogenic activity of the foetal adrenals.

A direct method for determination of the time integral of corticosterone availability in interstitial fluid of rats

A novel method for direct determination of the time integral of free corticosterone levels in interstitial fluid was used to measure corticosterone availability at rest and during free-operant shock-avoidance (SA) training in male rats. The method employs a subcutaneously implanted device to continuously accumulate the free hormone at a rate proportional to local concentration. The proportional rate of accumulation is maintained by providing mass-action corticosterone binding capacity within the device such that the device establishes a diffusion gradient for free corticosterone. The rate of uptake is limited so as to avoid disturbing equilibrium between free and bound hormone in the environment of the device. Corticosterone accumulation increased to 3× baseline during SA and was dexamethasone suppressible. These findings demonstrate the utility of a method uniquely combining specific measurement of free hormone with time integration to yield estimates of hormone availability during behavioral performance by an untethered subject. The method is suggested to be applicable to measurement of an extremely wide variety of drugs and hormones, under generally nonconstraining conditions.

Effect of 6-hydroxydopamine on in vitro hippocampal corticosterone binding capacity in the male rat.

Adult male rats were injected with 6-hydroxydopamine, either into the lateral brain ventricle or directly into the dorsal hippocampus. They were adrenalectomized 5-7 days later, and following an additional 24 hours, the specific in vitro 3H-corticosterone binding capacity of dorsal hippocampal slices was determined by estimation of uptake of radioactivity by the nuclear fraction. Specific corticosterone binding was reduced by 40-50% in both experimental groups, as compared to vehicle-treated controls. These results suggest that the maintenance of normal dorsal hippocampal corticosterone binding capacity is dependent upon the integrity of endogenous brain catecholaminergic neural systems.

Hippocampal cell nuclear binding of corticosterone following 5,7-dihydroxytryptamine

Adult male rats were injected into the lateral brain ventricle with 5,7-dihydroxytryptainine (5,7-DHT). They were adrenalectomized 5–7 days later and, following an additional 24 h, the specific in vitro [ 3H]corticosterone binding capacity of dorsal hippocampal slices was determined by estimation of uptake of radioactivity by the nuclear fraction. Specific corticosterone (CS) binding was reduced by 50–70% in the neurotoxin-treated as compared to vehicle-injected animals. Brain serotonin and 5-hydroxyindoleacetic acid concentrations were depleted by 50–70% in the 5,7-DHT-injected rats. These results suggest that the maintenance of normal dorsal hippocampal CS binding capacity is dependent upon the integrity of endogenous brain serotoninergic neuronal systems.

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 radiothyrodectomized 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.

Corticosterone binding capacity increases in contralateral hippocampus after partial unilateral hippocampectomy

After unilateral dorsal hippocampectomy the binding of [ 3H]corticosterone to cytosol receptors in contralateral hippocampus was measured. For estimation of binding capacity the adrenals were removed bilaterally 24 h prior to sacrifice. The apparent maximal binding capacity (B max) for corticosterone in the contralateral hippocampus lobe was increased by 74 and 41%, respectively, 10 and 20 days after surgery. The data reveal a novel aspect of steroid receptor capacity control. It is suggested that compensation of altered amounts of receptor sites is an intrinsic property of the hippocampal corticosterone receptor system.

Effect of subtotal inhibition of liver development on plasma transcortin in chick embryo

The relationship between liver weight and the concentration of plasma transcortin (CBG) was investigated in ovo during early chick embryo development. As measured by equilibrium dialysis, corticosterone-binding capacity increased in parallel with liver weight. Early prevention of normal hepatic endodermal cell progression at the 9- to 12-somite stage inhibited liver development subtotally. In the operated embryos, a good correlation between CBG activity in plasma and liver weight was observed: (1) the liver weight of the operated embryos was 78% lower than in the controls of the same age (12 days old) and (2) the CBG activity in plasma compared to the same controls was 85% lower. Previous experiments ( B. Martin and J. M. Gase, 1979, J. Steroid Biochem. 10, 553–556) showed that plasma transcortin is synthesized by embryonic chick liver in vitro. Present data provide evidence that in ovo, the major if not the sole source of plasma transcortin is the liver.

AUTOSYNCHRONIZATION OF RAT LIVER CELLS WITH ENDOGENOUS CORTICOSTERONE AFTER PARTIAL HEPATECTOMY

AbstractAfter adrenalectomy in adult male rats 3H‐TdR incorporation into the liver parenchymal cells is increased 4–8 times and the mitotic index rises from 0–31 % to 1–3%; this is inhibited by corticosterone. After hepatectomy the serum corticosterone level increases from 18 μg/100 ml to 57 μg/100 ml. The corticosterone binding capacity of the serum declines from 2–06 to 0–17. The activity of tyrosine transaminase doubles, whereas the incorporation of 3H‐TdR into the liver cells is decreased by a factor of 5–7. Thereafter the binding capacity increases again and reaches, 24 hr after operation, a value of 3–82. The tyrosine transaminase activity and the serum corticosterone content return to normal. 3H‐TdR incorporation, however, increases by a factor of 7‐7 of the initial value. We concluded that in the first few hours after partial hepatectomy corticosterone blocks the liver cells in G1 and an accumulation of the cells occurs at this cell cycle phase. Folio wing the binding of the corticosterone by serum proteins a little later the liver cells enter the S‐phase synchronously.

Corticosterone binding to hippocampus: Immediate and delayed influences of the absence of adrenal secretion

Summary Binding of [ 3 H]corticosterone to soluble (cytosol) and cell nuclear binding sites in hippocampus of rat brain was studied in relationship to the presence or the short-term and long-term absence of endogenous corticosterone secretion. (1) Saturable binding is detectable in vivo in normal rats, but endogenous hormone, including secretion evoked by stress of injecting [ 3 H]corticosterone, can interfere with measurement of binding in vivo by both competing for binding sites and displacing bound hormone from binding sites. (2) After bilateral adrenalectomy, there is a rapid increase in available in vivo corticosterone binding sites for up to 2 h, as endogenous corticosterone levels fall, followed by a longer-term increase in total binding capacity which approaches a plateau over several days after the operation. (3) In vitro studies of uptake of [ 3 H]corticosterone both to hippocampal cell nuclei in tissue slices and to cytosol binding proteins in hippocampal homogenates also show the two post-adrenalectomy increases. The second increase begins more than 11 h after adrenalectomy, so that [ 3 H]corticosterone binding capacity either 2 or 11 h after the operation appears to reflect the capacity in intact rats in the absence of endogenous hormone. (4) Thyroidectomy and hypophysectomy, which prevent increases in serum corticosterone binding activity which follows adrenalectomy, fail to block increases in hippocampal corticosterone binding. (5) Long-term increases in hippocampal binding capacity are found in vivo as well as in vitro in both the cytosol and cell nuclear fractions. Thus, while separate mechanisms governing entry of the hormone into the cell nuclei are entirely possible, they are not required to explain the present results. (6) The in vivo dose of corticosterone in adrenalectomized rats which half-maximally saturated the hippocampal cell nuclear binding sites is estimated to be around 15 μg. This dose produces serum corticosterone levels at 10 min after injection which are in the range of resting morning levels of corticosterone in normal rats. It is concluded that the hippocampal corticosterone binding system operates within the normal daily range of endogenous corticosterone.

Kinetics of the thermal denaturation of corticosterone-binding protein in rat plasma

The corticosterone binding capacity of normal rat blood plasma after heating up to 60°C was determined by separation on Sephadex. The denaturation of corticosterone-binding protein by heat resulted in decrease of its binding capacity. The process of denaturation is strictly a first-order reaction. The rate constants of the denaturation reaction were determined for temperatures between 40 and 60°C. The temperature dependence of the rate constants obey Arrhenius' law at temperatures above 55°C, the calculated apparent energy of activation of corticosterone-binding protein being 107.08 kcal/mole.

The actions of ethinyloestradiol on the pituitary‐adrenal system of the rat

Summary . Single doses of ethinyloestradiol stimulate the pituitary adrenal axis of the female rat during quiescent conditions. . After a stimulus which releases endogenous ACTH, there is an inhibition of the release of corticosterone from the adrenal gland, but an increase in the corticosterone stored in the gland. . Ethinyloestradiol (1·0 mg/kg) injected acutely or daily for 7 days does not affect the corticosterone binding capacity of plasma in female rats, or the clearance rate of an injection of corticosterone. . Prolonged treatment with ethinyloestradiol and ACTH inhibits the pituitary‐adrenal response to a stress and to an ACTH injection, indicating a block at the adrenal and pituitary level. . The adrenal gland recovers more rapidly than the pituitary after cessation of the oestrogen treatment. . The inhibition of the pituitary‐adrenal response to stress after oestrogen is probably caused by inhibition of cholesterol synthesis as suggested by others. Oestrogens can increase corticoid secretion during non‐stress conditions, however, so precursor lack through exhaustion cannot be excluded. . It is suggested that the inhibition of the stress response after prolonged ACTH treatment is due to a decrease in sensitivity of the adrenal cortex after frequent ACTH stimulation, but the possibility that it is due to a reduction in circulating cholesterol cannot be ruled out.

The effect of long-term corticotrophin treatment on the corticosteroid-binding capacity of transcortin.

SUMMARY In rats consecutive daily doses of corticotrophin significantly reduced the corticosterone-binding capacity of transcortin as measured by the gel filtration method, even after previous removal of the adrenals or ovaries. Treatment with formalin for 14 days produced similar, though slightly lesser, changes.