The effect of dexamethasone on urinary acidification.

Although it is well recognized that mineralocorticoids enhance renal acid excretion, the effect of glucocorticoids on renal acidification is unclear. Oral administration of dexamethasone to six healthy volunteers for 1 week at a daily dose of 4.5 mg was associated with mild respiratory alkalosis and a small but statistically significant increase in baseline urine pH. However, neither the ability to lower urine pH nor to excrete titratable acid and ammonium after NH4Cl acid-loading was altered. Administration of a single intravenous dose of dexamethasone sodium phosphate (7.5 mg) was associated with a significant rise in urine pH and potassium excretion and decreased titratable acid, ammonium , and phosphorus excretion in the absence of changes in blood acid-base status, creatinine clearance, or urine flow.     

Effects of aldosterone on the urinary excretion of total and non-dialyzable hydroxyproline

In order to explore the role of mineralocorticoids on collagen metabolism, the effects of aldosterone on the urinary excretion of total and non dialyzable hydroxyproline (HYPRO) was studied in rats. The administration of aldosterone in sesame oil, 75 microgram/100 g body weight to adrenalectomized rats maintained on 1% NaCl solution as drinking fluid and 1 mg of cortisone subcutaneously daily, provoked elevation of total and non dialyzable HYPRO in urine (P less than 0.001), when compared to similarly treated adrenalectomized rats receiving sesame oil but no aldosterone. Both groups showed a normal growth curve and had similar urinary excretion of creatinine. The effects of aldosterone are opposed to the known lowering effects of glucocorticoids on HYPRO excretion and may suggest an effect of aldosterone on collagen turnover. Alternatively, aldosterone may modify the metabolism or excretion of HYPRO in an opposite manner to that of glucocorticoids.     

Glucocorticoids increase salt appetite by promoting water and sodium excretion

Glucocorticoids [e.g., corticosterone and dexamethasone (Dex)], when administered systemically, greatly increase water drinking elicited by angiotensin and sodium ingestion in response to mineralocorticoids [e.g., aldosterone and deoxycorticosterone acetate (DOCA)], possibly by acting in the brain. In addition, glucocorticoids exert powerful renal actions that could influence water and sodium ingestion by promoting their excretion. To test this, we determined water and sodium intakes, excretions, and balances during injections of Dex and DOCA and their coadministration (DOCA+Dex) at doses commonly employed to stimulate ingestion of water and sodium. In animals having only water to drink, Dex treatment greatly increased water and sodium excretion without affecting water intake, thereby producing negative water and sodium balances. Similar results were observed when Dex was administered together with DOCA. In animals having water and saline solution (0.3 M NaCl) to drink, Dex treatment increased water and sodium excretion, had minimal effects on water and sodium intakes, and was associated with negative water and sodium balances. DOCA treatment progressively increased sodium ingestion, and both water and sodium intakes exceeded their urinary excretion, resulting in positive water and sodium balances. The combination of DOCA+Dex stimulated rapid, large increases in sodium ingestion and positive sodium balances. However, water excretion outpaced total fluid intake, resulting in large, negative water balances. Plasma volume increased during DOCA treatment and did not change during treatment with Dex or DOCA+Dex. We conclude that increased urinary excretion, especially of water, during glucocorticoid treatment may explain the increased ingestion of water and sodium that occurs during coadministration with mineralocorticoids.     

Effect of starvation, alloxan diabetes and adrenalectomy on Na+ K+-ATPase of the mucosa of the small intestine of rat.

The dietary stress conditions such as starvation influenced Na+K+-ATPase activity which increased steadily above normal fed levels between the starvation periods of 24--48 hr. Also, an increased enzyme level was observed in alloxan diabetic rats and administration of insulin to diabetic rats led to a tendency towards a lowering of Na+K+-ATPase. Adrenalectomy brought about a lowering of Na+K+-ATPase activity from those of normals while the administration of hydrocortisone induced an enhancement. The results indicate that both starvation and diabetic conditions might cause a stress-like activation of adrenal cortex resulting in increased levels of glucocorticoids which in turn activate the intestinal Na+K+-ATPase activity.     

Studies on arterial mineralocorticoid and glucocorticoid receptors: evidence for the translocation of steroid-cytoplasmic receptor complexes to cell nuclei

The high affinity binders for mineralocorticoids and glucocorticoids, previously reported by us as present in arterial cytosol have been further characterized. The results of this study demonstrate that these binders translocate under appropriate conditions to cell nuclei as complexes with mineralocorticoids and glucocorticoids, respectively. Thus, they exhibit a fundamental property of steroid receptors. This provides evidence for the presence in the arterial wall of a molecular mechanism(s) for the in-situ action of both mineralocorticoids and glucocorticoids.     

Effect of hydrocortisone and dexamethasone on xylose uptake by isolated rat soleus muscle.

To determine the effects of glucocorticoids on sugar uptake, xylose uptake by isolated rat soleus muscle of bilaterally adrenalectomized animals was studied. The results indicate that in vitro addition of 10-4 M hydrocortisone, dexamethasone or hydrocortisone sodium succinate had no inhibitory effect on basal xylose uptake. In the presence of both low and high medium insulin, the above steroids failed to inhibit insulin-stimulated uptake. When the concentration of hydrocortisone sodium succinate was increased to 10-2 M, insulinstimulated uptake was decreased. The results thus indicate that glucocorticoids at concentrations observed under physiological or pathological conditions do not inhibit basal or insulin-stimulated sugar uptake.     

Adrenalectomy Blocks the Compensatory Increases in UT-A1 and AQP2 in Diabetic Rat Kidney

In normal rats we showed that glucocorticoids participate in the downregulation of UT-A1 protein abundance in the inner medullary tip and in lowering of basal and vasopressin-stimulated facilitated urea permeability in terminal IMCDs. To examine the relevance of this response to a rat model of human disease, we studied rats with uncontrolled diabetes mellitus (DM) induced by streptozotocin (STZ), since these rats have increased corticosterone production and urea excretion. We found that at 3 days of DM, UT-A1 protein abundance is downregulated in the inner medullary tip compared to pair-fed control rats, while DM for more than 7 days caused an increase in UT-A1. To test whether adrenal steroids could be a mechanism contributing to the latter increase, we studied adrenalectomized rats (ADX), ADX rats given STZ to induce diabetes (ADX + STZ), and ADX + STZ rats receiving exogenous aldosterone or dexamethasone. In contrast to control rats, UT-A1 protein abundance was not increased by prolonged DM in the ADX rats. Aquaporin 2 (AQP2) was not increased in the inner medullas of 10-day DM rats either. However, UT-A1 protein abundance was significantly reduced in the inner medullary tips from both diabetic aldosterone-treated (40 ± 2%) and dexamethasone-treated (43 ± 2%) ADX rats compared to diabetic ADX rats without steroid replacement. AQP2 was unaffected by steroid hormone treatments. Thus, both mineralocorticoids and glucocorticoids downregulate UT-A1 protein abundance in rats with uncontrolled diabetes mellitus for 10 days. These results suggest that: 1) the increase in UT-A1 observed in DM is dependent upon having adrenal steroids present; and 2) adrenal steroids are not sufficient to enable the compensatory rise in UT-A1 to a steroid-deficient diabetic animal.     

Renal excretion and saline intake during post-stress immobilization period in rats

An experiment in which the rats access either to 0.5% or 1.5% saline was designed in order to further characterise the relationship between sodium intake and renal excretion after acute immobilization stress. A saline solution for 3 days was provided to the rats previous to the experimental day. On that day, after finishing acute immobilization stress, all variables under observation were measured every 6 h for 24 h. These periods were denominated as follows: T1 (12.00 to 18.00 h), T2 (18.00 to 24.00 h), T3 (24.00 to 06.00 h) and T4 (06.00 to 12.00 h). Acute immobilization stress reduced sodium renal excretion in both T1 and T2. Sodium intake in acute immobilization stress rats was lower than in control rats during all observed periods, while the urine volume was only reduced in the stressed animals in T1. These results were similar in both saline solution concentrations. A good correlation was observed between sodium intake and sodium excretion in control rats having access to either 0.5% or 1.5% saline as well as in stressed rats having access to 0.5% saline, this correlation was not observed in stressed rats with 1.5% saline. This suggests that stress impaired the renal capability of rats to handle high sodium but not a slight sodium overload. The inability of the kidney to excrete sodium may be critical to reduce sodium intake after acute immobilization stress.     

Renal sodium retention in cirrhotic rats depends on glucocorticoid-mediated activation of mineralocorticoid receptor due to decreased renal 11beta-HSD-2 activity

Downregulation of the renal glucocorticoid-metabolizing enzyme 11beta-hydroxysteroid dehydrogenase type 2 (11beta-HSD-2) during liver cirrhosis may allow activation of the mineralocorticoid receptor (MR) by glucocorticoids and contribute to sodium retention. We tested this hypothesis in male Wistar rats with decompensated liver cirrhosis and ascites 7 wk after bile duct ligation (BDL). Renal 11beta-HSD-2 mRNA, protein, and activity were significantly decreased in decompensated rats. The urinary Na(+)/K(+) ratio was reduced by 40%. Renal epithelial sodium channel (ENaC) mRNA and immunostaining were only slightly affected. Complete metabolic studies, including fecal excretion, showed that the BDL rats had avid renal sodium retention. Treatment of the BDL rats with dexamethasone suppressed endogenous glucocorticoid production, normalized total sodium balance and renal sodium excretion, and reduced ascites formation to the same degree as direct inhibition of MR with K-canrenoate. Total potassium balance was negative in the BDL rats, whereas renal potassium excretion was unchanged. In the distal colon, expression of ENaC was increased in BDL rats. Fecal potassium excretion was increased in cirrhotic rats, and this was corrected by treatment with K-canrenoate but not dexamethasone. We conclude that development of sodium retention and decompensation in cirrhotic rats is associated with downregulation of renal 11beta-HSD-2 activity and inappropriate activation of renal sodium reabsorption by endogenous glucocorticoids. In addition, the overall potassium loss in the BDL model is due to increased fecal potassium excretion, which is associated with upregulation of ENaC in distal colon.     

Biological Activity of Fractions Obtained by Differential Centrifugation of the Bovine Adrenal Cortex

This study is an attempt to correlate adrenocortical hormonal activity with various cell fractions obtained by homogenization and differential centrifugation of bovine adrenocortical tissue. Bioassays involving the decrease in circulating eosinophils and sodium retention were employed for the estimation of the glucocorticoids and mineralocorticoids respectively. The supernatant was the most active fraction in both bioassays, while the microsome and mitochondrial fractions demonstrated varying degrees of activity. The total nitrogen, lipide phosphorus, and cholesterol contents of the fractions were determined. The microsome fraction contained a relatively higher amount of lipide phosphorus and a marked amount of cholesterol.     

肾上腺皮质激素对心房钠尿肽基因表达的促进作用

给完整的及切除肾上腺的雌性 Wistar 大鼠分別注射地塞米松、去氧皮质酮或地塞米松加去氧皮质酮;冷酚法提取心房总 RNA,用α-~(32P)标记的大鼠心房肽 cDNA 探针与之杂交。完整大鼠接受地塞米松和切除肾上腺后接受地塞米松加去氧皮质酮的大鼠,心房肽基因转录产物增加2倍,其余组无显著变化。结果提示糖皮质激素可促进心房肽基因表达,但此作用依赖于盐皮质激素的同时存在,单纯盐皮质激素不能增强该基因的表达。     

Protective effect of corticosteroids on intercellular junction

Actions of adrenocortical hormones on intercellular communication in salivary gland cells of Chironomus plumosus were studied by means of electrophysiological measurements. Glucocorticoids have an effect maintaining junctional communication, while mineralocorticoids have an effect blocking it. When glucocorticoids in their proper concentration are previously applied to the cells, they can prevent the block of junctional communication which should be produced by EGTA, lipase and trypsin. Mineralocorticoids prevail in competitive action between glucocorticoids and mineralocorticoids on junctional communication. The interaction between glucocorticoids and uncoupling agents, and between glucocorticoids and mineralocorticoids on junctional communication were discussed at the level of the cell membrane.     

The effect of foetal decapitation on the antenatal development of the enzymes monoamine oxidase and catechol O-methyl transferase in rabbit foetuses

The development of the enzymes monoamine oxidase and catechol O-methyl transferase in rabbit foetuses was studied. The adrenocortical system of the rabbit foetuses was inactivated by hypophysectomy on the 18th day of foetal age. The hypophysectomy of the foetuses by decapitation in utero resulted in marked increases in the activities of the enzymes monoamine oxidase and catechol O-methyl transferase in most of the body organs determined 12 days after the operation. A single administration of adrenocorticotropic hormone or hydrocortisone to the decapitated foetuses reduced the activities of both the enzymes studied in most of the body organs. The results suggest that glucocorticoids present in the circulation of foetal animals act as inhibitory factor for enzymes of catecholamine degradation. The inactivation of glucocorticoidogenesis by removal of the hypophysis takes away this rate-limiting control and highly significant increases in the activities of the enyzmes monoamine oxidase and catechol O-methyl transferase occur.     

Immobilization stress elevates IP(3) receptor mRNA in adult rat hearts in a glucocorticoid-dependent manner

Gene expression of the type 1 and 2 inositol 1,4,5-trisphosphate (IP(3)) receptors in the rat cardiac atria and ventricles and their possible modulation by single immobilization stress was studied. Single immobilization stress significantly elevated mRNA levels for both types of these receptors. To evaluate the involvement of glucocorticoids in the modulation of the gene expression of IP(3) receptors by immobilization stress, we used adrenalectomized and/or hypophysectomized rats. Since adrenalectomy and/or hypophysectomy completely abolished increase in IP(3) receptor's mRNA levels after the immobilization, we conclude that immobilization stress elevates mRNA of type 1 and 2 IP(3) receptors, mainly through the glucocorticoid responsive element.     

Effects of hypophysectomy and immobilization stress on S-adenosylmethionine levels in rat adrenal glands

Rat adrenal S-adenosylmethionine (SAM) levels and phenylethanolamine-N-methyltransferase (PNMT) activity were measured under conditions of hypophysectomy and stress. A new dual-label radioenzymatic assay for SAM is presented which eliminates problems found to exist with previous methods. Strain-specific differences in both PNMT and SAM were found, as well as sex differences in SAM levels. Immobilization stress resulted in an increase in adrenal SAM and PNMT activity, while hypophysectomy decreased both. The distribution of SAM between cortex and medulla did not change with either hypophysectomy or stress. Hypophysectomized Fisher rats were found to be capable of increasing PNMT activity in the absence of increased SAM levels.     

Existence of cardiac PNMT mRNA in adult rats: elevation by stress in a glucocorticoid-dependent manner

Phenylethanolamine N-methyltransferase (PNMT) is the enzyme that synthesizes epinephrine from norepinephrine. The aim of this study was to determine potential PNMT gene expression in the cardiac atria and ventricles of adult rats and to examine whether the gene expression of this enzyme is affected by immobilization stress. PNMT mRNA levels were detected in all four parts of the heart, with the highest level in the left atrium. Both Southern blot and sequencing verified the specificity of PNMT detected by RT-PCR. Single immobilization for 2 h increased gene expression of PNMT in both atria and ventricles. In atria, this effect was clearly modulated by glucocorticoids, because either adrenalectomy or hypophysectomy prevented the increase in PNMT mRNA levels in response to immobilization stimulus. This study establishes, for the first time, that PNMT gene expression occurs in cardiac atria and also, to a small extent, in ventricles of adult rats. Immobilization stress increases gene expression in atria and ventricles. This increase requires an intact hypothalamus-pituitary-adrenocortical axis, indicating the involvement of glucocorticoids.     

Glucocorticoid-Induced Prenatal Modification of GABA-ergic Regulation of the Responsiveness of the Hypothalamo-Hypophyseal-Adrenocortical System to Stress in Rats

We studied the effects of introduction of exogenous glucocorticoids within the prenatal period (seven subcutaneous injections of hydrocortisone acetate, 50 mg/kg, daily, on the 15th–21st pregnancy days, or two injections on the 16th and 18th days) on the state of the hippocampal GABA-ergic system and the hypothalamo-hypophyseal-adrenocortical system (HHAS) of adult rats under conditions of acute stress (1-h-long immobilization): effects of pre-stress injection of an agonist of GABA_B receptors, baclofen (10 mg/kg, 30 min before immobilization), were also examined. The activity of glutamate decarboxylase and binding of ³H-GABA were the indices characterizing the state of the former regulatory system, while the content of catecholamines in the hypothalamus and the level of hormones of the adrenal cortex characterized the state of the latter system. Prenatal introduction of hydrocortisone acetate resulted in weakening of the adrenocortical reaction to acute stress in adult offspring males; post-stress changes in the noradrenaline level in the hypothalamus and the activity of glutamate decarboxylase in the hippocampus, as well as stress-related activation of GABA_B receptors, were absent in these animals. Adult females subjected to the prenatal influence of hydrocortisone acetate, vice versa, demonstrated a greater reaction of the adrenal cortex to stress; this occurred against the background of suppression of the activity of glutamate decarboxylase in the hippocampus and preserved activity of GABA_B receptors. Our study shows that modifying influences, which exogenous glucocorticoids applied within the prenatal period exert on the GABA-ergic regulation of the responsiveness of the HHAS to stress, are characterized in adult offspring of rats by a significant sex-related dependence. Neirofiziologiya/Neurophysiology, Vol. 37, No. 3, pp. 244–249, May–June, 2005.     

Effect of hydrocortisone and dexamethasone on xylose uptake by isolated rat soleus muscle

To determine the effects of glucocorticoids on sugar uptake, xylose uptake by isolated rat soleus muscle of bilaterally adrenalectomized animals was studied. The results indicate that in vitro addition of 10⁻⁴ M hydrocortusine, dexamethasone or hydrocortisone sodium succinate had no inhibitory effect on basal xylose uptake. In the presence of both low and high medium insulin, the above steroids failed to inhibit insulin-stimulated uptake. When the concentration of hydrocortisone sodium succinate was increased to 10⁻² M, insulin-stimulated uptake was decreased. The results thus indicate that glucocorticoids at concentrations observed under physiological or pathological conditions do not inihibit basal or insulin-stimulated sugar uptake.     

Extra-adrenal glucocorticoids and mineralocorticoids: evidence for local synthesis, regulation, and function

Glucocorticoids and mineralocorticoids are steroid hormones classically thought to be secreted exclusively by the adrenal glands. However, recent evidence has shown that corticosteroids can also be locally synthesized in various other tissues, including primary lymphoid organs, intestine, skin, brain, and possibly heart. Evidence for local synthesis includes detection of steroidogenic enzymes and high local corticosteroid levels, even after adrenalectomy. Local synthesis creates high corticosteroid concentrations in extra-adrenal organs, sometimes much higher than circulating concentrations. Interestingly, local corticosteroid synthesis can be regulated via locally expressed mediators of the hypothalamic-pituitary-adrenal (HPA) axis or renin-angiotensin system (RAS). In some tissues (e.g., skin), these local control pathways might form miniature analogs of the pathways that regulate adrenal corticosteroid production. Locally synthesized glucocorticoids regulate activation of immune cells, while locally synthesized mineralocorticoids regulate blood volume and pressure. The physiological importance of extra-adrenal glucocorticoids and mineralocorticoids has been shown, because inhibition of local synthesis has major effects even in adrenal-intact subjects. In sum, while adrenal secretion of glucocorticoids and mineralocorticoids into the blood coordinates multiple organ systems, local synthesis of corticosteroids results in high spatial specificity of steroid action. Taken together, studies of these five major organ systems challenge the conventional understanding of corticosteroid biosynthesis and function.