Effect of spironolactone on electrolytes, renin, ACTH and corticosteroids in the rat

CS-3150, a Novel Nonsteroidal Mineralocorticoid Receptor Antagonist, Shows Preventive and Therapeutic Effects On Renal Injury in Deoxycorticosterone Acetate/Salt-Induced Hypertensive Rats

The present study was designed to assess both preventive and therapeutic effects of (S)-1-(2-Hydroxyethyl)-4-methyl-N-[4-(methylsulfonyl) phenyl]-5-[2-(trifluoromethyl) phenyl]-1H-pyrrole-3-carboxamide (CS-3150), a novel nonsteroidal mineralocorticoid receptor antagonist, on renal injury in deoxycorticosterone acetate (DOCA)/salt-induced hypertensive rats (DOCA rats). From 7 weeks of age, DOCA was subcutaneously administered once a week for 4 weeks to uninephrectomized rats fed a high-salt diet. In experiment 1, CS-3150 (0.3-3 mg/kg) was orally administered once a day for 4 weeks coincident with DOCA administration. In experiment 2, after establishment of renal injury by 4 weeks of DOCA/salt loading, CS-3150 (3 mg/kg) was orally administered once a day for 4 weeks with or without continuous DOCA administration. In experiment 1, DOCA/salt loading significantly increased systolic blood pressure (SBP), which was prevented by CS-3150 in a dose-dependent manner. Development of renal injury (proteinuria, renal hypertrophy, and histopathological changes in glomeruli and tubule) was also suppressed by CS-3150 with inhibition of mRNA expression of fibrosis, inflammation, and oxidative stress markers. In experiment 2, under continuous DOCA treatment, CS-3150 clearly ameliorated existing renal injury without lowering SBP, indicating that CS-3150 regressed renal injury independent of its antihypertensive action. Moreover, CS-3150 treatment in combination with withdrawal of DOCA showed further therapeutic effect on renal injury accompanied by reduction in SBP. These results demonstrate that CS-3150 not only prevents but also ameliorates hypertension and renal injury in DOCA rats. Therefore, CS-3150 could be a promising agent for the treatment of hypertension and renal disorders, and may have potential to promote regression of renal injury.

Traumatic brain injury regulates adrenocorticosteroid receptor mRNA levels in rat hippocampus

Glucocorticoid activation of two types of adrenocorticosteroid receptors (ACRs), the mineralocorticoid receptor (MR) and glucocorticoid receptor (GR), influences the vulnerability of hippocampal neurons to insult. To examine the potential impact of ACR activation following traumatic brain injury (TBI), the current study assesses regulation of MR and GR expression and glucocorticoid levels following controlled cortical impact (CCI). Male Sprague-Dawley rats were pretreated for 48 h with vehicle, the MR antagonist spironolactone, or the GR antagonist mifepristone (RU486). On day three, subjects were sham-operated or injured by unilateral CCI. In situ hybridization analysis determined that pretreatment with either MR antagonist spironolactone or GR antagonist RU486 increased 24-h hippocampal GR mRNA levels in sham-operated animals only, suggesting that MR and GR regulation of GR mRNA is suppressed following TBI. Injury decreased GR mRNA levels in the ipsilateral dentate gyrus of all pretreatment groups and bilaterally increased MR mRNA levels in CA3 of antagonist-pretreated animals. One day post-injury, plasma corticosterone levels were comparable in sham and injured animals pretreated with vehicle. A separate group of animals that did not receive pretreatment injections prior to sham operation or injury were included for a 24-h time course analysis of plasma ACTH and corticosterone levels. Injury increased hypothalamic-pituitary-adrenal (HPA) activation for approximately 6 h following injury. These results indicate that hippocampal ACR mRNA levels and HPA activation are altered by TBI. Regulation of MR and GR expression following TBI may influence hippocampal neuron viability by modulating glucocorticoid signaling after injury.

Adrenocorticosteroid receptor blockade and excitotoxic challenge regulate adrenocorticosteroid receptor mRNA levels in hippocampus

The mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) are glucocorticoid-activated transcription factors essential for maintenance of cellular homeostasis. Differential activation of these adrenocorticosteroid receptors (ACR) is thought to influence neuronal viability, particularly under challenging cellular conditions. The present study is designed to determine the effects of receptor blockade and excitotoxic insult on MR and GR mRNA expression and neuronal viability in hippocampus. Male Sprague--Dawley rats were pretreated for 48 hr with vehicle, MR antagonist spironolactone (SPIRO) (50 mg/kg, twice daily, s.c.), or GR antagonist RU486 (25 mg/kg, twice daily, s.c.) and subsequently injected with saline or the glutamate analog kainic acid (KA) (12 mg/kg i.p.). Twenty-four hr post-insult, MR and GR mRNA levels were assessed by in situ hybridization analysis, and hippocampal neurons were counted to assess KA-induced cell loss. MR blockade with SPIRO increased basal MR mRNA levels in hippocampal subregions CA1, CA3, and dentate gyrus (DG) and increased basal GR mRNA levels in CA3. GR blockade with RU486 increased basal GR mRNA levels in CA3. The excitotoxin KA decreased MR mRNA levels in CA1 and CA3, decreased GR mRNA levels in DG, and negated all antagonist-induced increases of ACR mRNAs. Cell counts quantifying KA damage indicated increased CA3 vulnerability to KA insult after treatment with MR antagonist spironolactone but demonstrated no significant cell loss in any other group or region. These results demonstrate dynamic regulation of hippocampal MR and GR mRNAs after ACR antagonist treatment and kainate toxicity, underscoring the potential importance of MR and GR availability to neuronal viability after insult.

Acid-base and endocrine effects of aldosterone and angiotensin II inhibition in metabolic acidosis in human patients

Chronic metabolic acidosis (CMA) in human beings is characterized by increased renin-angiotensin-aldosterone (RAA) activity and cortisol secretion as well as nitrogen wasting. The purpose of this study was to examine whether and to what extent increased RAA activity (i.e., angiotensin II or aldosterone) regulates acid-base equilibrium in CMA and thus might co-determine the severity of acidosis. CMA was induced in 8 normal subjects by oral NH4Cl administration (2.1 mmol/kg body weight per day) for 7 days, followed by a 7-day period of spironolactone (100 mg, 4 times a day by mouth), followed by a 4-day period of spironolactone and losartan (100 mg, every day by mouth). NH4Cl feeding was continued during all study periods. Spironolactone resulted in exacerbation of acidosis ((HCO3)p decreased from 19.8+/-0.4 mmol/L to 17.7+/-0.6 mmol/L, P<.005) because of a large increase in endogenous acid production, as evidenced by significant increases in net acid excretion (116 to 185 mmol/day, P<.005), urinary anion gap (+31 mEq/day, P<.05), and sulfate excretion (+32 mEq/day, P<.05). Plasma potassium increased from 4.2 to 4.6 mmol/L (P<.05) because of decreased urinary potassium excretion (from 108 to 92 mmol/day, P<.05). Plasma angiotensin II, cortisol, aldosterone, urinary aldosterone, urinary tetrahydrocortisol, free cortisol, and nitrogen excretion increased significantly. The subsequent addition of losartan to spironolactone administration resulted in further exacerbation of acidosis ((HCO3)p decreased to 15.7+/-0.4 mmol/L, P<.05) and hyperkalemia (5.0 mmol/L, P<.05) with no change in plasma anion gap. Renal potassium excretion decreased from 92 to 73 mmol/day (P<.05) on day 1. Exacerbation of acidosis was accounted for by a renal mechanism, as evidenced by the significant decrease in net acid excretion and unchanged urinary unmeasured anion and nitrogen excretion. We conclude the following: (1) AT-1 blockade by losartan exacerbates acidosis by inducing a distal-tubular acidification defect. Angiotensin II is an important modulator of the renal acid excretory response to CMA in human beings. (2) Inhibition of aldosterone action by spironolactone in CMA results in an increase in endogenous acid production and exacerbates acidosis by a non-renal mechanism that is mediated, at least in part, by exacerbated hyperglucocorticoidism.

Effect of dietary cardiac glycosides on blood pressure regulation in rats

To investigate the possible physiological significance of dietary cardiac glycosides in blood pressure regulation, the blood pressure of normal Sprague Dawley rats raised on a regular diet, which naturally contains large amounts of Na+-pump inhibitors, was compared with that of rats on a purified synthetic diet, which contains no Na+-pump specific inhibitors, and with that of rats on a synthetic diet supplemented with 10 µg·mL-1ouabain or 10 µg·mL-1convallatoxin in the drinking water. After 6 weeks on the synthetic diet, the systolic blood pressure in the synthetic diet group was significantly elevated (145 ± 5 vs. 128 ± 4 mmHg, P < 0.05). At 10 weeks it reached a plateau (154 ± 3 vs. 122 ± 3 mmHg, P < 0.05). Plasma renin activity and Na+level were significantly higher in animals fed synthetic diets than in the regular diet group (P < 0.01). Administration of either losartan or lisinopril or a switch to a low salt synthetic diet (0.03% sodium) normalized the synthetic diet-induced high blood pressure. Supplementation of the synthetic diet with the cardiac glycosides delayed the onset of the increase in blood pressure for 4 weeks. Plasma aldosterone levels were approximately doubled in the cardiac glycoside-treated groups. Higher plasma Na+levels and hematocrit values present in the synthetic diet group were normalized by the glycoside supplements. These results suggest that supplemental dietary cardiac glycosides exert bidirectional effects on blood pressure regulation through actions that modulate extracellular fluid and electrolyte balance.Key words: cardiac glycosides, convallatoxin, ouabain, ouabain-like substance, purified synthetic diet, high blood pressure, renin-angiotensin system.

Faecal dry weight and potassium are related to faecal sodium and plasma aldosterone in rats chronically fed on varying amounts of sodium or potassium chlorides

Recent studies have shown that faecal residue (dry weight) and Na and K increase with increasing levels of dietary fibre, an effect which may be related to unstirred layers that slow absorption and the flow rate of chyme through the gastrointestinal tract. Salts of Na are the primary osmotic components of chyme and influence both retention of fluid in the bowel and transit of fluid from the small to the large intestine. The present study examines the chronic effects of dietary Na and K intake on faecal Na, K and residue excretion. Male Sprague-Dawley rats were given 12-13 g feed/d (control (g/kg): Na 4, K 8.5) for 1 week, followed by a 4-week period where Na or K intake was altered (0.01-3 times control levels). These diets altered chronic (> 1 week) faecal residue excretion and affected Na and K excretion by 8-, 310- and 2100-fold respectively. Low dietary Na reduced faecal Na and residue; K excretion was doubled during week 1, but fell over weeks 2-4 despite a 4-5-fold increase in plasma aldosterone. Chronic high dietary Na increased faecal Na, residue and K despite a 60% decrease in plasma aldosterone. Chronic low dietary K decreased faecal Na, K and residue and plasma aldosterone. Chronic high dietary K did not alter faecal Na and K despite increased faecal residue and a 4-5-fold increase in plasma aldosterone. Faecal water was unchanged by diet, paralleling changes in faecal residue. Analyses of the results provide systematic models of chronic regulation of faecal Na, K and residue excretions. When plasma aldosterone is low (< 160 ng/l), weekly faecal residue excretion is equal to 3.6 g (fibre intake was 2.6-2.7 g/week)+2.6 g/mmol Na, and K excretion is equal to 0.55 mmol/mmol Na. When plasma aldosterone is high (> 1500 ng/l) weekly faecal residue excretion is equal to 2.3 g + 2.6 g/mmol Na, and K excretion is equal to 0.7 mmol/week + 0.55 mmol/mmol Na.

Influence of spironolactone on urinary prostaglandin E2 and kinin excretion in rats

Spironolactone was administered to spontaneously hypertensive rats (SHRs) in order to examine the urinary excretions of prostaglandin E2 (PGE2) and kinin. Thirteen SHRs were divided into 2 groups: 0.1 ml of sesame oil was administered to one group (the spironolactone-lactone-untreated group, n = 6) and 20 mg of spironolactone in 0.1 ml of sesame oil was administered to the other group (the spironolactone-treated group, n = 7) by the subcutaneous route for 10 days in succession. Determinations were then made of the body weight, blood pressure, urine volume, and excretion levels of Na, K, kinin and PGE2 in the 24-hour urine. After the animals had been killed by decapitation, blood samples were drawn for determination of the plasma renin activity (PRA). The results obtained indicated decreased blood pressure and increased urinary Na excretion in the spironolactone-treated group. On the other hand, the PGE2 excretion level in the 24-hour urine decreased markedly immediately after administration of spironolactone (p less than 0.05) and was maintained at lower levels up to the end of the experiment. However, the 24-hour urinary kinin levels showed similar changes in both the spironolactone-treated group and the untreated group with no significant difference between them. These findings suggest that spironolactone has a suppressive effect on urinary PGE2 excretion, the activity of which is not mediated by kinin production in the kidneys but is the result of a direct action of spironolactone itself.

Amiloride-sensitive sodium transport of the rat distal colon during early postnatal development

To evaluate developmental changes in colonic sodium transport, the sensitivity of the transepithelial potential and short-circuit current to amiloride was investigated. The amiloride-sensitive short-circuit current (IscNa), which represents the electrogenic sodium transport through Na+ channels, rose significantly from day 5, reached a peak on day 10, and entirely disappeared after weaning. The maximum rate of electrogenic, amiloride-sensitive sodium transport was 12.0 microEq/cm2 X h. The IscNa was suppressed by adrenalectomy and/or premature weaning but not by a mineralocorticoid antagonist, spironolactone. On the contrary, treatments which increase aldosterone levels in vivo (low-sodium diet, furosemide-induced natriuresis, high dietary intake of potassium) stimulated the IscNa. The effect of adrenalectomy increased during postnatal development. The sensitivity of IscNa to aldosterone was highest at the end of the weaning period. High-sodium diet, which causes a decrease in circulating aldosterone, was associated with a partial inhibition of IscNa (P less than 0.016). These data suggest that the distal colon of neonatal rats can transport sodium via an electrogenic, amiloride-sensitive mechanism and that adrenocortical hormones exert the main regulatory control of this pathway.

The relationship between tissue preparation and function; methods for the study of control of aldosterone secretion: a review

The study of the control of aldosterone synthesis and secretion by the rat adrenal gland has over the past thirty years involved the application of many different in vivo and in vitro techniques. In this review the relationship between the data that each of these methods has produced is compared. There are striking differences in overall steroid production rates, and in the qualitative nature of the steroid profile which the various methods produce. In particular, aldosterone is secreted at higher rates in vivo, and when whole tissue preparations are used in vitro, than in incubations of isolated glomerulosa cells. In addition, while corticosterone is a major product of glomerulosa tissue in vitro, the available evidence suggests that it is not a major glomerulosa product in vivo.