Effects of adrenalectomy on hormone action on hepatic glucose metabolism. Impaired glucagon activation of glycogen phosphorylase in hepatocytes from adrenalectomized rats.

The effects of adrenalectomy on glucagon activation of liver glycogen phosphorylase and glycogenolysis were studied in isolated hepatocytes. Adrenalectomy resulted in reduced responsiveness of glycogenolysis and phosphorylase to glucagon activation. Stimulation of cAMP accumulation and cAMP-dependent protein kinase activity by glucagon was unaltered in cells from adrenalectomized rats. Adrenalectomy did not alter the proportion of type I and type II protein kinase isozymes in liver, whereas this was changed by fasting. Activation of phosphorylase kinase by glucagon was reduced in hepatocytes from adrenalectomized rats, although the half-maximal effective concentration of glucagon was unchanged. No difference in phosphorylase phosphatase activity between liver cells from control and adrenalectomized rats was detected. Glucagon-activated phosphorylase declined rapidly in hepatocytes from adrenalectomized rats, whereas the time course of cAMP increase in response to glucagon was normal. Addition of glucose (15 mM) rapidly inactivated glucagon-stimulated phosphorylase in both adrenalectomized and control rat hepatocytes. The inactivation by glucose was reversed by increasing glucagon concentration in cells from control rats, but was accelerated in cells from adrenalectomized rats. It is concluded that impaired activation of phosphorylase kinase contributes to the reduced glucagon stimulation of hepatic glycogenolysis in adrenalectomized rats. The possible role of changes in phosphorylase phosphatase is discussed.     

葆包牡丹碱对垂体前叶组织块释放促肾上腺皮质激素的刺激效应

本实验利用垂体组织块离体灌流技术,观察到γ－氨基丁酸Ａ受体拮抗剂荷包牡丹笃切除双侧肾上腺９６ｈ后的大鼠垂体前叶ＡＣＴＨ的分泌具有强烈的刺激作用。但同样浓度的荷包牡丹笃分离的垂体前叶细胞的ＡＣＴＨ分泌无影响,提示肾上腺切除后,γ－氨基丁酸在垂体前叶直接或通过间接途径抑制ＡＣＴＨ分泌。     

Roles of adroxazine, a new heterocyclic hormone of the adrenals, and leucogenenol, a thymothyroid hormone, in the formation of blood cells

Treatment of normal rats with the thymothyroid hormone leucogenenol accelerates the rate at which the 'functional' cells, neutrophils, red blood cells and lymphocytes, develop in the bone marrow from their corresponding committed precursor cells. Following the initial treatment of normal rats with leucogenenol, there is a temporary elevation in the bone marrow of the relative concentrations of myeloblasts, rubriblasts and lymphoblasts. It has now been found that bilaterally adrenalectomized rats have a different response from normal rats to treatment with leucogenenol. Although treatment of bilaterally adrenalectomized rats with leucogenenol accelerates the rate of development of their functional cells, the initial injection of leucogenenol is followed by a temporary decrease in the relative concentrations of myeloblasts, rubriblasts and lymphoblasts in their bone marrow. Additionally, adrenalectomized rats treated concurrently with tritiated thymidine and leucogenenol show a significant lower percentage of labeled cells in their bone marrow than do correspondingly treated normal rats. These results indicate that adrenalectomized rats have a lower than normal concentration of stem cells in their bone marrow that can be committed to become functional cells. Treatment with adroxazine, a new recently isolated heterocyclic hormone of the adrenals, causes adrenalectomized rats to respond as normal rats to the injection of leucogenenol. There is a temporary elevation of myeloblasts, rubriblasts and lymphoblasts in their bone marrow as well as a normal increase in the percentage of cells that are labeled following concurrent treatment with tritiated thymidine and leucogenenol. It may be concluded that treatment with adroxazine increases the rate of replication of uncommitted bone marrow stem cells while treatment with leucogenenol increases the rate at which committed cells develop into their respective functional cells. A scheme is presented to show the suggested roles that leucogenenol and adroxazine play in regulating the formation of blood cells.     

Influence of tryptophan on the activity of acetylcholinesterase in the brain of well-fed normal and adrenalectomized rats

Eight hours after a single tube-feeding of tryptophan the activity of acetylcholinesterase in the cerebral hemisphere of well-fed (non-fasted) normal and adrenalectomized rats was 28 and 53% higher, respectively, compared to the corresponding water-fed control. On the other hand, the enzyme activity in the cerebellum of both normal and adrenalectomized rats remained essentially unchanged following tryptophan administration. Pretreatment of adrenalectomized rats with actinomycin-D totally abolished the tryptophan-mediated stimulation of cerebral acetylcholinesterase activity. The pattern of response of cerebral acetylcholinesterase in well-fed adrenalectomized rats over a period of 24-hr following a dose of tryptophan was found to be biphasic.     

The role of tryptophan 2,3-dioxygenase in the hormonal control of tryptophan metabolism in isolated rat liver cells. Effects of glucocorticoids and experimental diabetes.

The metabolism of L-tryptophan by isolated liver cells prepared from control, adrenalectomized, glucocorticoid-treated, acute-diabetic, chronic-diabetic and insulin-treated chronic-diabetic rats was studied. Liver cells from adrenalectomized rats metabolized tryptophan at rates comparable with the minimum diurnal rates of controls, but different from rates determined for cells from control rats 4h later. Administration of dexamethasone phosphate increased the activity of tryptophan 2,3-dioxygenase (EC 1.13.11.11) 7-8-fold, and the flux through the kynurenine pathway 3-4-fold, in cells from both control and adrenalectomized rats. Increases in flux through kynureninase (EC 3.7.1.3) and to acetyl-CoA can be explained in terms of increased substrate supply from tryptophan 2,3-dioxygenase. The metabolism of tryptophan was increased 3-fold in liver cells isolated from acutely (3 days) diabetic rats, with a 7-8-fold increase in the maximal activity of tryptophan 2,3-dioxygenase. The oxidation of tryptophan to CO2 and metabolites of the glutarate pathway increased 4-5-fold, consistent with an increase in picolinate carboxylase (EC 4.1.1.45) activity. Liver cells isolated from chronic (10 days) diabetic rats metabolized tryptophan at rates comparable with those of cells from acutely diabetic rats, but with a 50% decrease in the activity of tryptophan 2,3-dioxygenase. The proportion of flux from tryptophan 2,3-dioxygenase to acetyl-CoA, however, was increased by 50%; this was indicative of further increases in the activity of picolinate carboxylase. Administration of insulin partially reversed the effects of chronic diabetes on the activity of tryptophan 2,3-dioxygenase and flux through the kynurenine pathway, but had no effect on the increased activity of picolinate carboxylase. The role of tryptophan 2,3-dioxygenase in regulating the blood tryptophan concentration is discussed with reference to its sensitivity to the above conditions.     

荷包牡丹碱对垂体前叶组织块释放促肾上腺皮质激素的刺激效应

本实验利用垂体组织块离体灌流技术,观察到－氨基丁酸Ａ受体拮抗剂荷包牡丹碱对切除双侧肾上腺９６ｈ后的大鼠垂体前叶ＡＣＴＨ的分泌具有强烈的刺激作用。但同样浓度的荷包牡丹碱对分离的垂体前叶细胞的ＡＣＴＨ分泌无影响。提示肾上腺切除后,－氨基丁酸在垂体前叶直接或通过间接途径抑制ＡＣＴＨ分泌。     

Effects of adrenalectomy on CRH regulation of ACTH release: adenylate cyclase activity, cyclic AMP-dependent protein kinase activity and ACTH release

Corticotropin releasing hormone (CRH) stimulation of ACTH release and cyclic AMP-mediated events involved in the control of ACTH release were compared in sham-operated and adrenalectomized rats. CRH-stimulated adenylate cyclase activity was decreased in pituitary homogenates from adrenalectomized animals. CRH-stimulated cyclic AMP accumulation was essentially abolished and CRH-stimulated cyclic AMP-dependent protein kinase (A-kinase) activity was decreased in freshly prepared anterior pituitary cells from adrenalectomized animals. Basal and CRH-stimulated ACTH release was elevated in these cells. Since ACTH release is increased in adrenalectomized rats despite the down regulation of CRH-linked pituitary mechanisms, we speculate that the site of action of disinhibition by corticosterone of ACTH release (or synthesis) following adrenalectomy is distal to the generation of cyclic AMP and/or that non-CRH mediated mechanisms assume a greater role in ACTH regulation following adrenalectomy.     

The metabolism of L-tryptophan by liver cells prepared from adrenalectomized and streptozotocin-diabetic rats.

1. The metabolism of L-tryptophan by liver cells prepared from fed normal, adrenalectomized and streptozotocin-diabetic rats was studied. 2. At physiological concentrations (0.1 mM), the rate of oxidation of tryptophan by tryptophan 2,3-dioxygenase was 3-fold greater in liver cells from diabetic rats than in those from fed rats. In liver cells from diabetic rats, oxidation of tryptophan to CO2 and metabolites of the glutarate pathway was increased 7-fold. Quinolinate synthesis was decreased by 50%. These findings are consistent with an increase in picolinate carboxylase activity. 3. Rates of metabolism of 0.1 mM-tryptophan by hepatocytes from fed and adrenalectomized rats were similar. 4. In all three types of cell preparation, fluxes through tryptophan 2,3-dioxygenase with 2.5 mM-tryptophan were 7-fold greater than those obtained with 0.1 mM-tryptophan. Tryptophan 2,3-dioxygenase and kynureninase fluxes in hepatocytes from fed and adrenalectomized rats were comparable, whereas those in liver cells from diabetic rats were increased 2.5-fold and 3.3-fold respectively. Picolinate carboxylase activities of liver cells from diabetic rats were 15-fold greater than those of cells from fed rats, but rates of quinolinate synthesis were unchanged. 5. It is concluded that: (i) adrenal corticosteroids are not required for the maintenance of basal activities of the kynurenine pathway, whereas (ii) chronic insulin deficiency produces changes in both the rate of oxidation and metabolic fate of tryptophan carbon.     

Effect of a varying corticosteroid allowance on the cAMP content of limbic system structures of the rat brain

A study was made of the effect of adrenalectomy and substitution therapy in the absence of adrenals on the cAMP content in the hypothalamus, hippocamp and striate body of the rat brain. It was shown that in sham adrenalectomized animals, the concentration of cAMP in the brain structures under study did not differ from the characteristics recorded in the control group. Adrenalectomy in rats was followed by a significant reduction of the nucleotide in all the structures, namely in the hypothalamus by 89.5%, and in the hippocamp and striate body by 30.3 and 30.5%, respectively. Application of substitution therapy (5 mg hydrocortisone per 100 mg body mass) prevented the decreased content of cAMP seen in the adrenalectomized rats, with its magnitude being within the limits recorded in the intact animals. Doca was little effective in this aspect.     

Alterations in response of rat white adipocytes to insulin, noradrenaline, corticotropin and glucagon after adrenalectomy. Correction of these changes by adenosine deaminase.

1. Adipocytes isolated from rats 6--9 days after adrenalectomy had significantly increased sensitivity to insulin action against noradrenaline-stimulated lipolysis. In the presence of adenosine deaminase there was no significant difference in insulin sensitivity between cells from adrenalectomized and sham-operated rats. 2. Adipocytes from adrenalectomized rats had decreased lipolytic responses to all concentrations of noradrenaline and glucagon tested and a decreased lipolytic response to low but not high concentrations of corticotropin. There was no difference in lipolytic response to theophylline after adrenalectomy. Adenosine deaminase corrected the differences in response to noradrenaline and glucagon resulting from adrenalectomy. 3. In the presence of adenosine deaminase rates of lipolysis, after stimulation by high concentrations of noradrenaline, glucagon, corticotropin or theophylline, were the same in cells from adrenalectomized or sham-operated rats. 4. These findings and previously reported effects of adenosine and adrenalectomy on adipocyte function are discussed. It is proposed that changes in adipocyte hormone responsiveness after adrenalectomy may result from changes in adenosine metabolism or release.     

Effect of prostaglandin E1 administration on the heart glycogen synthase and phosphorylase systems

The effects of intravenous administration of PGE₁ on the glycogen synthase and phosphorylase system in rat heart were studied.Unlike the consistent effects of PGE₁ on glycogen synthase in liver, the response in heart was variable. A significant decrease in the per cent synthase occurred in fasted intact rats while a significant increase was seen in adrenalectomized hydrocortisone treated fasted rats. No significant effect was seen on the synthase system in either fed intact or fasted adrenalectomized rats.Phosphorylase activity was increased significantly following PGE₁ administration in fed intact rats and slightly increased in adrenalectomized fasted rats. The phosphorylase system was not affected in fasted intact and fasted adrenalectomized rats given glucocorticoid replacement. With our present state of knowledge an adequate explanation for the response of these heart enzymes to PGE₁ under the various conditions of this study does not appear possible.     

The permissive effects of glucocorticoid on hepatic gluconeogenesis. Glucagon stimulation of glucose-suppressed gluconeogenesis and inhibition of 6-phosphofructo-1-kinase in hepatocytes from fasted rats

Production of [14C]glucose from [14C]lactate in the perfused livers of 24-h fasted adrenalectomized rats was not stimulated by 1 nM glucagon but was significantly increased by 10 nM hormone. Crossover analysis of glycolytic intermediates in these livers revealed a significant reduction in glucagon action at site(s) between fructose 6-phosphate and fructose 1,6-bisphosphate as a result of adrenalectomy. Site(s) between pyruvate and P-enolpyruvate was not affected. In isolated hepatocytes, adrenalectomy reduced glucagon response in gluconeogenesis while not affecting glucagon inactivation of pyruvate kinase. A distinct lack of glucagon action on 6-phosphofructo-1-kinase activity was noted in these cells. When hepatocytes were incubated with 30 mM glucose, lactate gluconeogenesis was greatly stimulated by glucagon. A reduction in both sensitivity and responsiveness to the hormone in gluconeogenesis was seen in the adrenalectomized rat. These changes were well correlated with similar impairment in glucagon action on 6-phosphofructo-1-kinase activity and fructose 2,6-bisphosphate content in hepatocytes from adrenalectomized rats incubated with 30 mM glucose. These results suggest that adrenalectomy impaired the gluconeogenic action of glucagon in livers of fasted rats at the level of regulation of 6-phosphofructo-1-kinase and/or fructose 2,6-bisphosphate content.     

Adipocyte G-proteins and adenylate cyclase. Effects of adrenalectomy.

Steroid hormones modulate the ability of cells to respond to hormones that act via cyclic AMP. In adipocytes of adrenalectomized rats, cyclic AMP accumulation and lipolysis in response to adrenaline are attenuated. However, the mechanism(s) of these effects are poorly understood. The effects of altered glucocorticoid status in vivo on the steady-state amounts of components of the hormone-sensitive adenylate cyclase were analysed in rat adipocytes. beta-Adrenergic receptors were analysed by using radioligand binding and immunoblotting with an anti-receptor antiserum. Neither the amount of radioligand binding nor the amount of beta-adrenergic-receptor peptide (Mr 67,000) was altered by adrenalectomy, whereas treatment of adrenalectomized rats with dexamethasone was found to increase both parameters by more than 25% with respect to the control. Forskolin-stimulated adenylated cyclase activity was unchanged in membranes isolated from adipocytes of adrenalectomized rats, but was decreased (50%) in those from dexamethasone-treated rats. The alpha-subunit of Gs was probed by using cholera-toxin-catalysed ADP-ribosylation. Immunoblotting was used to analyse the steady-state amounts of G-protein beta-subunits (beta-G35/36). Adrenalectomy was associated with decreases in the steady-state amounts of alpha-Gs (30%) and beta-G35/36 (50%). Dexamethasone treatment of adrenalectomized animals partially restored the lipolytic response of adipocytes to adrenaline and the amounts of alpha-Gs, increased the amounts of beta-G35/36 subunits from 50% to 150% of control values, increased beta-adrenergic receptors by more than 25% and decreased adenylate cyclase activity (50%). These results suggest that the steady-state amounts of components of hormone-sensitive adenylate cyclase are differentially regulated by glucocorticoids.     

Metabolic and immunological responses associated with in vivo glucocorticoid depletion by adrenalectomy in mature Swiss albino rats

The study is undertaken to determine the effect of adrenal corticosteroid depletion after adrenalectomy on carbohydrate, protein and fat metabolism as well as maturation and functional efficacy of the immunocompetent cells. Beside biochemical and hematological parameters, whether in vivo glucocorticoid depletion has any modulatory effects on splenic macrophage responses to bacterial challenge with regards to intracellular killing, nitric oxide release and cellular integrity, were determined. Major findings of our study indicate that blood glucose, urea and total inorganic phosphate levels showed a time dependent increase in adrenalectomized rats compared to control. Total glycogen content in liver was decreased gradually due to adrenal corticosteroid insufficiency. Hematological parameters like hemoglobin concentration, hematocrit value, total leukocyte count and differential count were also found to increase in the adrenalectomized group with respect to intact group. From the functional study of immunocompetent cells, intracellular killing capacity of splenic macrophages recovered from control and adrenalectomized rats after 10 and 20 days of adrenalectomy showed no significant alteration; however, the function of splenic macrophages recovered from rats after 30 days of adrenalectomy showed altered response. Nitric oxide released from splenic macrophages of adrenalectomized rats was less than that of control animal even after stimulation with lipopolysaccharide. DNA fragmentation assay showed a lesser degree of fragmentation of splenic macrophages obtained from adrenalectomized rats indicating, apoptotic death of cells in this group decreases. Adrenal corticosteroid insufficiency due to adrenalectomy interferes with metabolic and hematopoietic functions and modulates the development and maintenance of normal immunitary status, which in turn influences the inflammatory response.     

Effect of the exercise-induced increase in glucocorticoids on endurance in the rat

To investigate the effect of the increase in glucocorticoids during exercise on endurance, rats were either sham operated (SO) or adrenalectomized. All adrenalectomized rats were given a subcutaneously implanted corticosterone pellet at the time of adrenalectomy. Adrenalectomized rats were injected with corticosterone (ADX Cort) or corn oil (ADX) 5 min before exercise. Rats were killed at rest or after running on a treadmill (21 m/min, 15% grade) until exhaustion. SO rats ran 138 +/- 6 min compared with 114 +/- 9 min for ADX Cort and 89 +/- 8 min for ADX. All differences in run times were significant (P less than 0.05). Corticosterone levels were similar in exhausted SO and ADX Cort groups. ADX exhausted rats had corticosterone levels similar to resting values in SO and ADX rats. Inhibition of the rise in glucocorticoids during exercise had no effect on liver glycogen, liver adenosine 3',5'-cyclic monophosphate, plasma insulin, blood glucose, lactate, glycerol, or 3-hydroxybutyrate, plasma norepinephrine, or red quadriceps and soleus glycogen. Plasma free fatty acids were significantly depressed at exhaustion in ADX rats compared with SO. These data show that glucocorticoids exert effects within the time frame of a prolonged exercise bout and play a role in increasing endurance.     

The effects of adrenalectomy on the alpha-adrenergic regulation of cytosolic free calcium in hepatocytes

We have previously published that bilateral adrenalectomy in the rat reduces the Ca2+-mediated alpha-adrenergic activation of hepatic glycogenolysis, while it increases the cellular calcium content of hepatocytes. In the experiments presented here, the concentration of cytosolic free calcium (Ca2+i) at rest and in response to epinephrine was measured in aequorin-loaded hepatocytes isolated from sham and adrenalectomized male rats. We found that in adrenalectomized rats the resting Ca2+i was elevated, the rise in Ca2+i evoked by epinephrine was reduced, and the rise in 45Ca efflux that follows such stimulation was depressed. Furthermore, the slope of the relationship between Ca2+i and calcium efflux was decreased 60% in adrenalectomized. Adrenalectomy did not change Ca2+ release from intracellular calcium pools in response to IP3 in saponin-permeabilized hepatocytes. The EC50 for inositol 1,4,5-triphosphate and the maximal Ca2+ released were similar in both sham and adrenalectomized animals. Finally, the liver calmodulin content determined by radioimmunoassay was not significantly different between sham and adrenalectomized rats. These results suggest that 1) adrenalectomy reduces calcium efflux from the hepatocyte, probably by an effect on the plasma membrane (Ca2+-Mg2+)-ATPase-dependent Ca2+ pump and thus alters cellular calcium homeostasis; 2) adrenalectomy decreases the rise in Ca2+i in response to epinephrine; 3) this decreased rise in Ca2+i is not due to defects in the intracellular Ca2+ storage and mobilization processes; and 4) the effects of adrenalectomy on cellular calcium metabolism and on alpha-adrenergic activation of glycogenolysis are not caused by a reduction in soluble calmodulin.     

Adroxazine, a hormone of the adrenals that stimulates the rate of replication of bone marrow stem cells

Treatment of normal animals with the thymothyroid hormone, leucogenenol, increases the rate at which appropriate committed precursor cells of the bone marrow develop sequentially into their corresponding functional cells: neutrophils, lymphocytes and red blood cells. Hence following treatment with leucogenenol, at a time that is dependent on the quantity of leucogenenol injected, there is a temporary increase in the bone marrow of the relative concentrations of early forms of committed cells such as myeloblasts. However, following treatment of bilaterally adrenalectomized rats with leucogenenol the early forms of committed cells in the bone marrow, such as myeloblasts, instead of showing a temporary relative increase show a temporary significant decrease in concentration. A new compound, adroxazine, C34H65NO2, was isolated from the methanol extract of bovine adrenal tissue. This compound, on injection into bilaterally adrenalectomized rats, causes leucogenenol to have the same effect on the development of their bone marrow cells as it does in normal rats. Adroxazine is present in the cortex of the adrenals and in blood serum. It is suggested that the population of primitive replicating cells is controlled by the concentration of adroxazine in the serum.     

Suppressive effect of adrenalectomy on growth of L1210 leukemic cells in ascites

This study was designed to evaluate the effect of adrenalectomy on growth of L1210 leukemic cells in ascites of BDF1 mice. Varying doses of 1.5 x 10(4), 5.0 x 10(5), and 1.5 x 10(6) viable tumour cells were inoculated intraperitoneally into groups of either adrenalectomized or sham-operated mice. At days 4 to 7 after the inoculation, adrenalectomized mice inoculated with 1.5 x 10(4) or 5.0 x 10(5) tumour cells had a smaller number of tumour cells in ascites than sham-operated controls. However, after inoculation of 1.5 x 10(6) cells, no significant differences were found at days 2 to 4 between adrenalectomized and sham-operated mice. The growth retardation by adrenalectomy was not observed in adrenalectomized mice supplemented with 4 or 6 micrograms dexamethasone per day per mouse. It suggested that the ablation of glucocorticoids was at least partially responsible for the growth retardation observed in adrenalectomized mice. Cell kinetic analysis revealed that the difference in a potential doubling time could not explain these results. Tumour retention in the peritoneal cavity was measured using [125I]-iododeoxyuridine-labelled tumour cells as a tracer. At days 4 to 6 after inoculation of 5.0 x 10(5) labelled cells, radioactivity in the peritoneal cavity in adrenalectomized mice was about 70 per cent of that in sham-operated mice. This ratio was almost equivalent to the ratio of the number of cells in ascites of adrenalectomized mice to that of sham-operated ones. Consequently, growth retardation observed in adrenalectomized mice resulted from an increase in tumour cell migration and/or in tumour cell death, but not from an increase in doubling time.     

Adrenal modulation of the inhibitory effect of corticotropin releasing factor on feeding

Corticotropin releasing factor (CRF) reduces food intake in rats after central administration. In these studies we examined whether the adrenal gland and the vagus were involved in CRF suppression of intake. One hour intake was reduced by a 5 μg (ICV) injection of CRF in sham but not adrenalectomized rats maintained on 0.9% NaCl. In a separate experiment on rats maintained on tap water, the inhibitory effect of CRF (5 μg) lasted at least 4 hours in sham rats whereas adrenalectomized rats did not significantly differ from controls. These experiments suggest that the adrenal gland modulates the feeding response to CRF. As replacement with corticosterone (0.75 mg/kg) in total adrenalectomized rats did not restore responsiveness to 5 or 10 μg of CRF, we next studied whether the adrenal medulla was responsible for the decreased responsiveness to CRF. In rats lacking the adrenal medulla only, food intake was reduced by a 5 μg injection of CRF; in sham rats, intake was significantly reduced by doses as low as 0.1 μg of CRF. An additional experiment examined the effect of gastric vagotomy on the CRF feeding response. Vagotomized rats were as responsive to 5 and 10 μg injections of CRF as sham rats, which suggests that the effect is not dependent on the vagus nerve. These findings indicate that the adrenal gland, primarily the medulla, plays an intermediate role in the reduction of food intake caused by central injections of CRF. This conclusion is consistent with the known effect of CRF on adrenomedullary discharge.     

Changes in glucocorticoid receptors in different regions of brain of immature and mature male rats

Specific cytosolic binding for synthetic glucocorticoid dexamethasone was studied in several brain regions (hypothalamus, hippocampus, caudate nucleus, cerebellum, cerebral cortex) of immature (3-week) and mature (26-week) male rats, intact and adrenalectomized. A significant regional difference was observed in the concentration of in vitro [3H] dexamethasone binding in the brain of adrenalectomized rats at both ages, with the highest levels in the hippocampus. A marked decrease in specific binding was observed in all brain regions of adrenalectomized mature rats as compared to immature. The dexamethasone binding was significantly lower in all brain regions of normal intact animals as compared to adrenalectomized rats in both ages.