A glucocorticoid-responsive mutant androgen receptor exhibits unique ligand specificity: therapeutic implications for androgen-independent prostate cancer

The cortisol/cortisone-responsive AR (AR(ccr)) has two mutations (L701H and T877A) that were found in the MDA PCa human prostate cancer cell lines established from a castrated patient whose metastatic tumor exhibited androgen-independent growth. Cortisol and cortisone bind to the AR(ccr) with high affinity. In the present study, we characterized the structural determinants for ligand binding to the AR(ccr). Our data revealed that many of the C17, C19, and C21 circulating steroids, at concentrations that are found in vivo, functioned as effective activators of the AR(ccr) but had little or no activity via the wild-type AR or GRalpha. Among the synthetic glucocorticoids tested, dexamethasone activated both GRalpha and AR(ccr), whereas triamcinolone was selective for GRalpha. In MDA PCa 2b cells, growth and prostate-specific antigen production were stimulated by potent AR(ccr) agonists such as cortisol or 9alpha-fluorocortisol but not by triamcinolone (which did not bind to or activate the AR(ccr)). Of the potential antagonists tested, bicalutamide (casodex) and GR antagonist RU38486 showed inhibitory activity. We postulate that corticosteroids provide a growth advantage to prostate cancer cells harboring the promiscuous AR(ccr) in androgen-ablated patients and contribute to their transition to androgen-independence. We predict that triamcinolone, a commonly prescribed glucocorticoid, would be a successful therapeutic agent for men with this form of cancer, perhaps in conjunction with the antagonist casodex. We hypothesize that triamcinolone administration would inhibit the hypothalamic-pituitary-adrenal axis, thus suppressing endogenous corticosteroids, which stimulate tumor growth. Triamcinolone, by itself, would not activate the AR(ccr) or promote tumor growth but would provide glucocorticoid activity essential for survival.

Structural basis for the glucocorticoid response in a mutant human androgen receptor (AR(ccr)) derived from an androgen-independent prostate cancer

The crystal structure of a mutant androgen receptor (AR) ligand-binding domain (LBD) in complex with the agonist 9alpha-fluorocortisol has been determined at 1.95 A resolution. This mutant AR contains two mutations (L701H and T877A) and was previously reported as a high-affinity cortisol/cortisone responsive AR (AR(ccr)) isolated from the androgen-independent human prostate cancer cell lines MDA PCa 2a and 2b (Zhao et al. Nature Med. 2000, 6, 703-6). The three-dimensional structure of the AR(ccr) LBD complexed with 9alpha-fluorocortisol shows the typical conformation of an agonist-bound nuclear receptor in which helix 12 is precisely positioned as a "lid" for the ligand-binding pocket. Binding of 9alpha-fluorocortisol to the AR(ccr) involves favorable hydrogen bond patterns on the C17 and C21 substituents of the ligand due to the mutations at 701 and 877 in the AR(ccr). Our studies provide the first structural explanation for the glucocorticoid activation of AR(ccr), which is important for the development of new therapeutic treatments for androgen-independent prostate cancer.

Endothelial cell dysfunction in mice after transgenic knockout of type 2, but not type 1, 11beta-hydroxysteroid dehydrogenase

BACKGROUND

11beta-Hydroxysteroid dehydrogenase (11betaHSD) isozymes catalyze the interconversion of active and inactive glucocorticoids, allowing local regulation of corticosteroid receptor activation. Both are present in the vessel wall; here, using mice with selective inactivation of 11betaHSD isozymes, we test the hypothesis that 11betaHSDs influence vascular function.

METHODS AND RESULTS

Thoracic aortas were obtained from weight-matched male wild-type (MF1x129 cross(+/+)), 11betaHSD1(-/-), and 11betaHSD2(-/-) mice. mRNA for both isozymes was detected in wild-type aortas by RT-PCR. 11betaHSD activity in aortic homogenates (48.81+/-4.65% conversion) was reduced in both 11betaHSD1(-/-) (6.36+/-2.47% conversion; P<0.0002) and 11betaHSD2(-/-) (24.71+/-3.69; P=0.002) mice. Functional responses were unaffected in aortic rings isolated from 11betaHSD1(-/-) mice. In contrast, aortas from 11betaHSD2(-/-) mice demonstrated selectively enhanced constriction to norepinephrine (E(max) 4.28+/-0.56 versus 1.72+/-0.47 mN/mm; P=0.004) attributable to impaired endothelium-derived nitric oxide activity. Relaxation responses to endothelium-dependent and -independent vasodilators were also impaired. To control for chronic renal mineralocorticoid excess, MF1 mice were treated with fludrocortisone (16 weeks) but did not reproduce the functional changes observed in 11betaHSD2(-/-) mice.

CONCLUSIONS

Although both 11betaHSD isozymes are present in the vascular wall, reactivation of glucocorticoids by 11betaHSD1 does not influence aortic function. Mice with 11betaHSD2 knockout, however, have endothelial dysfunction causing enhanced norepinephrine-mediated contraction. This appears to be independent of renal sodium retention and may contribute to hypertension in 11betaHSD2 deficiency.

Insulin and mineralocorticoids influence on extrarenal potassium metabolism in chronic hemodialysis patients

Insulin-mineral corticoids effects on extrarenal K+ metabolism in dialysis patients. During the inter-dialytic interval in dialyzed patients, hydrogen and potassium ions are regulated by extrarenal mechanisms. We studied the hormonal and acidotic effects on the extrarenal potassium metabolism, in selected, anuric and stable, hemodialysis patients. Fifteen patients, were grouped according to the mean mid-week pre-dialysis K+ over the past 12 months: > 6.0 mEq/L (G1, n=5), = 5.1-6.0 mEq/L (G2, n=5), < or = 5.0 mEq/L (G3, n=5). After a mid-week hemodialysis session and 12 h fasting, they received 1 g/Kg glucose p.os (A). Insulin, aldosterone, renin, pH, HCO3-, glucose, body weight, blood pressure and heart rate were measured before and 60' after the meal. We recorded the same parameters, except insulin, in 15 patients, similarly grouped, before hemodialysis (T0) and on 3 consecutive off dialysis days (T1-T3); G1 received fluorohydrocortisone (FHC) 0.1 mg-0.3 mg/day, according to body weight and G3 spironolactone (SLT) 200 mg per day. G2 were controls (B). (A) A significant rise in glycemia (81 +/- 23 to 157 +/- 52 mg/dL, P<0.001) and insulin (11.8 +/- 6.2 to 46.8 +/- 19.5 microU/mL, P<0.001), with a drop in K+ (5.1 +/- 0.6 to 4.8 +/- 0.7 mEq/L, P=0.001) and aldosterone (453 +/- 373 to 383 +/- 364 pg/mL, P<0.01), were noted at T60 vs. T0, in all groups. Insulin levels correlated negatively (r=-0.54, P<0.04) to serum K+ at T60, in all patients. (B) No major pH, HCO3 and aldosterone changes were observed in the 3 groups. Despite that, K+ dropped in G1 by FHC (6.7 +/- 0.9 to 5.9 +/- 0.6 mEq/L, P<0.05), rose in G3 by SLT (4.4 +/- 0.4 to 5.4 +/- 0.3 mEq/L, P<0.05) and remained unchanged in controls (5.8 +/- 0.2 to 5.8 +/- 0.6 mEq/L), (T0 vs T3 pre-dialysis values). Glucose significantly lowered K+ by promoting adequate insulin secretion. Drugs affecting aldosterone action significantly influenced potassium metabolism. Acid-base balance was not important in K+ handling in steady state anuric dialysis patients.

Close association of urinary excretion of aquaporin-2 with appropriate and inappropriate arginine vasopressin-dependent antidiuresis in hyponatremia in elderly subjects

The present study was undertaken to determine whether urinary excretion of aquaporin-2 (AQP-2) participates in the involvement of arginine vasopressin (AVP) in hyponatremia less than 130 mmol/L in 33 elderly subjects (> or =65 yr old) during the last 5-yr period. Subjects were separated into euvolemic hyponatremia groups: 13 with hypopituitarism, 8 with syndrome of inappropriate secretion of antidiuretic hormone (SIADH), 8 with mineralocorticoid-responsive hyponatremia of the elderly, and 4 with miscellaneous diseases. Approximately 40% of those with hyponatremia was derived from hypopituitarism, but severe hyponatremia was found in the patients with SIADH and mineralocorticoid-responsive hyponatremia of the elderly. Plasma AVP levels remained relatively high despite hypoosmolality and were tightly linked with exaggerated urinary excretion of AQP-2 and antidiuresis in the 3 groups of patients, except for one miscellaneous one. An acute water load test verified the impairment in water excretion, because the percent excretion of the water load was less than 42% and the minimal urinary osmolality was not sufficiently diluted. Also, plasma AVP and urinary excretion of AQP-2 were not reduced after the water load. The inappropriate secretion of AVP was evident in the patients with SIADH and hypopituitarism, and hydrocortisone replacement normalized urinary excretion of AQP-2 and renal water excretion in those with hypopituitarism. In contrast, the appropriate antidiuresis seemed to compensate loss of body fluid in the patients with mineralocorticoid-responsive hyponatremia of the elderly, who lost circulatory blood volume by 7.3% (mean). Fludrocortisone acetate increased renal sodium handling and body fluid, resulting in the reduction in AVP release and urinary excretion of AQP-2 in mineralocorticoid-responsive hyponatremia of the elderly. These findings indicate that urinary excretion of AQP-2 may be a more sensitive measure of AVP effect on renal collecting duct cells than are plasma AVP levels, and that increased urinary excretion of AQP-2 shows exaggerated AVP-induced antidiuresis in hyponatremic subjects in the elderly. In addition, mineralocorticoid-responsive hyponatremia of the elderly has to be carefully differentiated from SIADH in elderly subjects.

Effects of the mineralocorticoid fludrocortisone on fibrinolytic function in healthy subjects

Recent evidence suggests that the renin-angiotensin-aldosterone system (RAAS) may participate in the regulation of fibrinolytic function. Angiotensin II (Ang II) is the primary candidate to mediate this inter-relationship, since this peptide is capable of stimulating plasminogen activator inhibitor-1 (PAI-1) in vitro and in vivo. It has been suggested that aldosterone may also modulate fibrinolysis, possibly by interacting with Ang II. The present study therefore investigates the effect of short-term treatment with the synthetic mineralocorticoid fludrocortisone (F) on fibrinolytic function. Ten healthy male volunteers, aged 25 to 30 years, on a constant intake of 160-180 mmol Na(+) and 60-80 mmol K(+), were studied on a control day (C1), after two days of oral administration of F (0.1 mg b.d.), and again three days after cessation of F (C2). F was associated with a marked decrease in plasma renin activity (PRA) from 0.91 +/- 0.45 ng ml(-1) h(-1) to 0.34 +/- 0.29 ng ml(-1) h(-1) (p=0.005), which returned to the baseline range at C2 (0.65 +/- 0.45 ng ml(-1) h(-1); p=0.032). The experimental protocol was not associated with significant changes in the activity or antigen concentration of tissue plasminogen activator (t-PA). PAI-1 exhibited a circadian rhythm with highest values at 0800 hours (41.8 +/- 9.1 ng/ml), decreasing by 1230 hours (22.6 +/- 5.9 ng/ml), with a further decrease at 1630 hours (12.3 +/- 3.1 ng/ml). At all three time points, PAI-1 remained unchanged by the mineralocorticoid. Our results therefore do not support a major mineralocorticoid effect on PAI-1. However, our study does not exclude a modulatory role of F, since unchanged PAI-1 could be observed in spite of a marked suppression of the RAAS.

Success of surgery for primary aldosteronism judged by residual autonomous aldosterone production

Since February 1996 we have prospectively assessed residual adrenal autonomy by the fludrocortisone suppression test (FST) in 23 patients 3 months after unilateral adrenalectomy for Conn syndrome and in 45 patients after a longer interval. In regard to blood pressure, 36 (53%) patients were cured of hypertension and the remaining 32 (47%) patients had improved hypertension control at the time of their latest postoperative clinical assessment. In regard to the outcome of surgery, patients who achieved normal suppressibility of aldosterone were regarded as cured, and those who had greater suppressibility after surgery were considered improved. Time since surgery for the whole group averaged 26 months. By these biochemical criteria, 42 patients (62%) were cured by surgery, and the rest improved; 16 (76%) of 21 women were cured, and 26 (55%) of 47 men. The women (mean +/- SD age 47 +/- 11 years) were significantly (p < 0.05) younger than the men (52 +/- 9 years). Preoperative aldosterone levels before and after FST were similar in the cured and improved groups and fell significantly (p < 0.01) in both groups following surgery. After surgical reduction of autonomous aldosterone production, mean plasma renin activity levels increased sixfold in the cured group and threefold in the improved group. Surgical mortality in this group of 68 patients with Conn syndrome was zero.

Effect of mineralocorticoid activity on transtubular potassium gradient, urinary [K]/[Na] ratio, and fractional excretion of potassium

Clinical assessment of potassium derangements may require evaluation of mineralocorticoid status. Several indirect indices of mineralocorticoid activity based on renal electrolyte excretion have been proposed and include the transtubular potassium gradient, urinary [K]/[Na] ratio, and renal fractional excretion of potassium. We studied the impact of high mineralocorticoid activity versus blocked mineralocorticoid activity on these indices in otherwise normal subjects who ingested a defined diet. Eight normal subjects received either fludrocortisone or spironolactone for 4 days. After a washout period of > or = 2 weeks, each subject then received the opposite regimen. Subjects ingested an identical high-potassium diet during both experimental periods. The renal fractional excretion of potassium and transtubular potassium gradient were calculated using standard formulas. Fludrocortisone caused an increase in body weight and no significant reduction in serum potassium concentration, while spironolactone decreased body weight and increased plasma potassium concentration. After 1 or 2 days of treatment with fludrocortisone, the average values for all urinary indices of mineralocorticoid activity were significantly higher than after 1 or 2 days of treatment with spironolactone. However, the differences between these indices in the fludrocortisone and spironolactone test periods diminished by day 3 and were nonexistent by day 4. In conclusion, the transtubular potassium gradient, [K]/[Na] ratio, and renal fractional excretion of potassium reflect acute changes in mineralocorticoid activity. However, these indices do not discriminate between states of high and low mineralocorticoid activity lasting longer than 2 to 3 days.

Ambulatory 24-hour blood pressure recordings in patients with Parkinson's disease with or without fludrocortisone

Orthostatic hypotension is often associated with patients suffering from Parkinson's disease. Only few studies have been published about the ambulatory blood pressure in patients with Parkinson's disease. Fludrocortisone has been used in management of orthostatic hypotension. This study was made to determine the Circadian rhythm of blood pressure in healthy elderly people, in Parkinson's disease patients without orthostatic hypotension and Parkinson's disease patients with fludrocortisone medication for orthostatic hypotension. Ambulatory 24-hour blood pressure recordings were made in 20 elderly Parkinson's disease patients and 21 healthy elderly persons. Eight of the Parkinson's disease patients were on fludrocortisone (Florinef) therapy because of orthostatic hypotension. The mean daytime systolic blood pressure of Parkinson's disease patients without fludrocortisone was 123 mmHg and the mean nighttime systolic blood pressure was 121 mmHg. There was no significant difference between daytime and nighttime systolic blood pressure (Figure 1). Diastolic blood pressure in this group was significantly higher during the day (68 mmHg) than at night (63 mmHg) (Figure 2). The daytime blood pressure of control patients was 135/74 mmHg and at night 127/69 mmHg (Figures 1, 2). The blood pressure of Parkinson's disease patients with fludrocortisone was higher at night (156/83 mmHg) than during the day (134/77 mmHg) (Figures 1, 2). The daytime and nighttime systolic and diastolic blood pressure was significantly lower by non-fludrocortisone Parkinson patients than the blood pressure of fludrocortisone Parkinson patients (Figures 1, 2).

CONCLUSION

The Parkinson's disease patients were non-dippers and with fludrocortisone the blood pressure was higher at night than on day. On day, the blood pressure of the Parkinson's disease patients with fludrocortisone elevated to the level of controls.

Rapid effects of corticosteroids on cytosolic protein kinase C and intracellular calcium concentration in human distal colon

Recent studies from our laboratory have reported rapid (< 1 min) non-genomic activation of potassium recycling, Na+-H+ exchange, protein kinase C (PKC) activity and PKC-sensitive Ca2+ entry by mineralocorticoids in mammalian distal colonic epithelium. Previous studies from other laboratories have described stimulation of the Na+-H+ exchanger by PKC activation. Here a rapid non-genomic effect of aldosterone on PKC activity and intracellular free calcium [Ca2+]i is demonstrated in human distal colonic epithelium. Rapid activation (after 15 min incubation) of basal PKC activity was observed in cytosolic fractions of human colonic epithelium by aldosterone, fludrocortisone and deoxycorticosterone acetate (DOCA). PKC activation was inhibited by the specific PKC inhibitor bisindolylmaleimide (GF109203X). The glucocorticoid hydrocortisone failed to activate PKC activity. Aldosterone induced a rapid increase in [Ca2+]i in isolated human colonic crypts. This stimulatory effect on [Ca2+]i was inhibited by the PKC inhibitor chelerythrine chloride. Hydrocortisone and dexamethasone similarly failed to increase [Ca2+]i. These results indicate that intracellular signalling for aldosterone involves changes in [Ca2+]i via activation of PKC. Since stimulation of PKC activity and increase in [Ca2+]i are apparent at normal circulating levels of aldosterone, our findings may have important physiological implications and prompt a reassessment of mineralocorticoid effects on electrolyte homeostasis.

Targeted disruption of the mouse gene encoding steroidogenic acute regulatory protein provides insights into congenital lipoid adrenal hyperplasia

An essential component of regulated steroidogenesis is the translocation of cholesterol from the cytoplasm to the inner mitochondrial membrane where the cholesterol side-chain cleavage enzyme carries out the first committed step in steroidogenesis. Recent studies showed that a 30-kDa mitochondrial phosphoprotein, designated steroidogenic acute regulatory protein (StAR), is essential for this translocation. To allow us to explore the roles of StAR in a system amenable to experimental manipulation and to develop an animal model for the human disorder lipoid congenital adrenal hyperplasia (lipoid CAH), we used targeted gene disruption to produce StAR knockout mice. These StAR knockout mice were indistinguishable initially from wild-type littermates, except that males and females had female external genitalia. After birth, they failed to grow normally and died from adrenocortical insufficiency. Hormone assays confirmed severe defects in adrenal steroids-with loss of negative feedback regulation at hypothalamic-pituitary levels-whereas hormones constituting the gonadal axis did not differ significantly from levels in wild-type littermates. Histologically, the adrenal cortex of StAR knockout mice contained florid lipid deposits, with lesser deposits in the steroidogenic compartment of the testis and none in the ovary. The sex-specific differences in gonadal involvement support a two-stage model of the pathogenesis of StAR deficiency, with trophic hormone stimulation inducing progressive accumulation of lipids within the steroidogenic cells and ultimately causing their death. These StAR knockout mice provide a useful model system in which to determine the mechanisms of StAR's essential roles in adrenocortical and gonadal steroidogenesis.

Effect of fludrocortisone and spironolactone on sodium and potassium losses in secretory diarrhea

The response of the colon to aldosterone is believed to be an important adaptive mechanism to excessive sodium losses in diarrhea. However, the degree to which mineralocorticoid activity actually influences fecal output of sodium in people with diarrhea is unknown. To gain insight into this question, 10 normal people were treated with placebo, fludrocortisone (an aldosterone agonist), and spironolactone (an aldosterone antagonist) during three experimental periods lasting nine days. On days 5-8, diarrhea was induced by ingestion of phenolphthalein. Diet was controlled. Fecal sodium was 40 meq/day on placebo and 29 meq/day on fludrocortisone, consistent with mineralocorticoid stimulation of intestinal sodium absorption. However, contrary to our expectations, spironolactone therapy was also associated with a fall in fecal sodium output, to 28 meq/day. To explain this paradoxical effect of spironolactone, we suggest that sodium depletion caused by spironolactone's natriuretic action on the kidney caused the release of an unknown stimulant of intestinal sodium absorption, whose action more than overcame the reduced colonic absorption resulting from inhibition of aldosterone activity by spironolactone. This interpretation implies that the intestinal adaptation to sodium depletion in diarrhea involves both aldosterone and an aldosterone independent factor, working in concert to reduce fecal sodium output.

High plasma levels of endothelin-1 in untreated Addison's disease

The aim of this study has been to investigate the plasma endothelin-1 (ET-1) levels in adult patients with proven Addison's disease (AD). Plasma ET-1 levels were measured in 29 subjects (17 males and 12 females, aged between 20 and 54 years): 15 of them were patients with AD and 14 were sex- and age-matched normal subjects, used as a control group. All patients with AD have been studied under basal conditions and nine of them also after 2 weeks on oral corticosteroid therapy (individual cortisol dosage ranging from 25 to 37.5 mg/day and 0.1 mg/day 9 alpha-fluorohydrocortisone). Extracted plasma ET-1 was determined by a specific radioimmunoassay using rabbit endothelin antisera. Mean ET-1 values in the patients with AD were three times higher than in normal subjects (21.09 +/- 4.38 pg/ml vs 6.72 +/- 1.74 pg/ml; p < 0.0001). Plasma ET-1 levels assayed in the patients with AD after 2 weeks of corticosteroid therapy were significantly decreased (14.47 +/- 3.7 pg/ml vs 22.8 +/- 5.2 pg/ml; -37%; p < 0.001) compared to values in untreated patients. However, the plasma ET-1 values obtained following corticosteroid therapy were still significantly higher (p < 0.001) than those detected in the control subjects. These results clearly indicate that patients with untreated AD have increased circulating ET-1 levels that may be reduced by short-term corticosteroid therapy.

Rat 11 beta-hydroxysteroid dehydrogenase type 2 enzyme is expressed at low levels in the placenta and is modulated by adrenal steroids in the kidney

The 11 beta-hydroxysteroid dehydrogenase type II enzyme (11 beta HSD2) protects the non-discriminating mineralocorticoid receptor from occupation by glucocorticoids. In man the enzyme is also highly expressed in the placenta where it is thought to also protect the fetus from the high circulating levels of maternal glucocorticoids. Mutations in the HSD11B2 gene have recently been shown to account for the syndrome of apparent mineralocorticoid excess. In the present study we have used a rat 11 beta HSD2 cDNA to study the distribution and regulation of this enzyme. The rat protein is highly homologous to the mouse, rabbit and human enzymes, except for the carboxy-terminal region which displays extensive divergence between species beyond residue 382. Northern blot analysis of rat total RNA showed that the single copy gene is highly expressed in kidney and adrenal with lower levels in the colon; surprisingly, there was no detectable signal in the placenta. There was also no detectable mRNA in the liver, heart, hippocampus, testis, thymus and pancreas. Nuclease protection analysis revealed the presence of moderate 11 beta HSD2 message levels in the parotid and exceedingly low levels in the placenta. Regulation studies showed that administration of dexamethasone, deoxycorticosterone and 9 alpha-fluorocortisol to adrenalectomized rats for 7 days increased renal enzyme activity 33%-50%, while message levels decreased 35%-70%, suggesting that the increased enzyme activity may represent activation of latent enzyme.

Usefulness of tilt table test with normal saline infusion in management of neurocardiac syncope in children

Head-up tilt test has been useful in evaluating children with neurocardiac syncope. In this study patients with positive baseline and isoproterenol tests had repeat tilt testing done after normal saline infusion. If the symptoms persisted, the test was then repeated with phenylephrine infusion. Of the 101 patients studied, 58 (57%) had a positive tilt sign. Normal saline infusion was given to 53 patients. Three patients were excluded because of structural heart disease. Fifty patients (aged 14 +/- 4 years) comprised the study group. Forty-two (84%) of 50 patients had a negative repeat tilt sign after normal saline infusion, and these patients were treated with 0.5 to 1 gm of salt three times a day and/or fludrocortisone (20 patients). Of the 8 (16%) patients who did not respond to normal saline infusion, 5 had negative results when given phenylephrine and were treated with pseudoephedrine. Follow-up data on 42 patients (range 4 to 40 months, median 18 months) showed that all 35 patients who responded to normal saline were either asymptomatic or had improved. Two patients were successfully treated with pseudoephedrine; however, two patients in this group required pacemaker therapy. We conclude that (1) normal saline infusion mitigates the hemodynamic effects of neurocardiac syncope, (2) high-salt diet treatment in these patients was economical and effective, and (3) failure to respond to normal saline test may indicate a less favorable prognosis.

Determinants of cardiac fibrosis in experimental hypermineralocorticoid states

Uninephrectomized rats maintained on 1.0% NaCl to drink and infused with aldosterone (0.75 microgram/h) for 8 wk have previously been shown to develop hypertension, cardiac hypertrophy, and cardiac fibrosis. In the present study we have shown that K+ supplementation (1.0% NaCl plus 0.4% KCl drinking solution) alters neither the interstitial nor the perivascular fibrotic response to mineralocorticoid treatment. Second, rats receiving 0.75 microgram/h 9 alpha-fluorocortisol, a mineralocorticoid and glucocorticoid agonist, respond with hypertension and cardiac fibrosis without cardiac hypertrophy. Finally, intracerebroventricular infusion of the mineralocorticoid receptor antagonist RU-28318 blocks blood pressure elevation, but not cardiac hypertrophy or fibrosis, when aldosterone is coinfused peripherally. We conclude that the myocardial fibrosis observed in response to chronic mineralocorticoid elevation and salt loading is a humorally mediated event independent of hypokalemia, hypertension, and cardiac hypertrophy. It remains to be determined whether the fibrosis observed in the presence of excess salt represents a direct (e.g., cardiac) effect of mineralocorticoid hormones or one mediated via a primary action on classical epithelial aldosterone target tissues (e.g., kidney).

Effect of exogenous mineralocorticoid on platelet cytosolic calcium in normal humans

We tested the hypothesis that the fludrocortisone in doses sufficient to elevate blood pressure (BP) in normal subjects would increase platelet cytosolic calcium. Eight normal volunteers were given 0.8 mg fludrocortisone daily for 7 days (short protocol). Eight other normal volunteers ingested the drug for 6 weeks (long protocol). In the short protocol, fludrocortisone increased platelet cytosolic calcium and body weight by day 3, while BP was increased by day 7. In the long protocol, platelet cytosolic calcium was increased after 1 week, returned to basal values by 3 weeks and remained at that level for the rest of the study. Stimulation of the subjects' platelets ex vivo with thrombin and vasopressin led to a significant increase in intracellular free calcium concentration; however, fludrocortisone treatment did not alter the calcium response to either agonist. Fludrocortisone decreased serum potassium, plasma renin activity, plasma noradrenaline concentration and serum ionised calcium. These changes, as well as the BP increase, reverted to basal values when the drug was discontinued. We next incubated human platelets with fludrocortisone (1.4 nmol/l) and found a significant increase in cytosolic calcium by 30 min. The data suggest that a blood pressure-raising dose of mineralocorticoid leads to a transient (days to weeks) increase in platelet cytosolic calcium. Platelet cytosolic calcium and blood pressure are dissociated in that cytosolic calcium increases before the BP increase and later decreases to lower values, while the BP increase is sustained. Mineralocorticoid also has a direct effect on platelet cytosolic calcium in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocortical steroids increase renal thiazide diuretic receptor density and response

The density of the rat renal pharmacologic receptor for thiazide-type diuretics, as quantitated by the maximal specific binding of (3H)metolazone, decreased to one-third normal after adrenalectomy. Selective glucocorticoid (dexamethasone or RU-28362) replacement increased thiazide receptor density to or above the normal level over the dose range of steroid that decreased thymus weight, which served as a bioassay for glucocorticoid activity. Mineralocorticoid (fludrocortisone or aldosterone), in doses that did not decrease thymus weight, also increased thiazide diuretic receptor density to or above normal. The addition of glucocorticoid (RU-28362) to maximal aldosterone increased thiazide receptor above that produced by aldosterone alone and to threefold normal. Similarly, the addition of aldosterone to high-dose RU-28362 also increased thiazide receptor density above that produced by the glucocorticoid alone and to threefold normal. Hence, the effects of glucocorticoids and mineralocorticoids appeared to be additive. The increase in renal thiazide receptor density produced by fludrocortisone, at a dose that elicited both mineralocorticoid and glucocorticoid effects, was unrelated to the basal (prethiazide) renal excretion of sodium, potassium, chloride, or calcium. However, fludrocortisone-pretreated animals responded to bendroflumethiazide with a greater natriuresis than did controls. In addition, the magnitudes of the thiazide-elicited natriuresis and chloriuresis correlated significantly with thiazide receptor. It was concluded that both the density of the renal thiazide receptor and the quantity of sodium and chloride reabsorbed by the thiazide-sensitive Na-Cl cotransporter in the kidney are under adrenocortical regulation.

Impaired renal 11 beta-oxidation of 9 alpha-fluorocortisol: an explanation for its mineralocorticoid potency

9 alpha-Fluorocortisol (9 alpha FF) is about 200 times more potent as a mineralocorticoid than cortisol (F) in man, although it binds with the same affinity as F and aldosterone to the human mineralocorticoid receptor. The low mineralocorticoid activity of F has been shown to be due to its rapid conversion by the kidney to cortisone (E), which does not bind to the receptor. Therefore, we compared the conversion of F to E with that of 9 alpha FF to 9 alpha-fluorocortisone (9 alpha FE) by 11-hydroxysteroid dehydrogenases in man in vivo and in vitro. Single oral doses of 9 alpha FF, 9 alpha FE, and F were given to normal males, and the excretion of free 9 alpha FF, 9 alpha FE, F, and E was measured in urine. Human kidney and liver slices were incubated with unlabeled steroids, and the free 11-hydroxy- and 11-oxosteroids were quantitated after high performance liquid chromatography separation by UV absorption. Oral F (5 mg) is excreted 70% as free E and 30% as free F (percentage of free steroids only). Oral 9 alpha FF (5 mg) is excreted 90% as free 9 alpha FF and 10% as free 9 alpha FE. Free 9 alpha FF excretion is 14 times greater than that of F after ingesting an identical dose. Oral 9 alpha FE (4 mg) is also excreted 90% as 9 alpha FF and 10% as 9 alpha FE. Kidney slices convert F much faster to E than 9 alpha FF to 9 alpha FE. The conversion of 9 alpha FE to 9 alpha FF is, on the contrary, much faster than that of E to F. Thus, the equilibrium of the reaction is on the 11-oxo side for F/E and on the 11-hydroxy side for 9 alpha FF/9 alpha FE. The interconversion of both pairs of steroids is inhibited by glycyrrhetinic acid in a dose-dependent manner. Liver slices do not measurably convert 9 alpha FF to 9 alpha FE, but do rapidly convert 9 alpha FE into 9 alpha FF. Reflecting this negligible conversion of 9 alpha FF to 9 alpha FE and the low plasma-protein binding of 9 alpha FF, free urinary 9 alpha FF excretion is much higher than that of F after the same oral dose.(ABSTRACT TRUNCATED AT 400 WORDS)

[Pharmacological action of 9alpha-fluorohydrocortisone as a mineralocorticoid]

The action of 9 alpha-fluorohydrocortisone (fludrocortisone) as a potent mineralocorticoid was reviewed. Fludrocortisone shows mineralocorticoid activity as potent as aldosterone and causes sodium-retention and kaliuresis when injected intravenously in man. The duration of the action of fludrocortisone in longer than that of aldosterone. Therefore, fludrocortisone is more pertinent to clinical use than aldosterone. Fludrocortisone is administered as a mineralocorticoid in case of Addison's disease and postoperative Cushing syndrome. It is also used to relieve hyperkalemia or to ameliorate hyponatremia.