Adrenocorticotrophin-induced hypertension: effects of mineralocorticoid and glucocorticoid receptor antagonism

Treatment of Hypertension Because of Immunosuppressive Therapy After Solid Organ Transplantation-Pharmacological Approach

ABSTRACT

Solid organs transplantation procedures have been performed for more than half a century. Growing knowledge of immune response and development of new immunosuppressive regimens guarantee more and more successful outcomes. However, many of the applied drugs lead to cardiovascular complications, the most frequent of which is hypertension. This article describes epidemiology, pathogenetic mechanisms, and treatment of hypertension induced by immunosuppressive medication. The main impact is focused on drugs belonging to the following groups: calcineurin inhibitors, the inhibitors of the mammalian target of rapamycin, and glucocorticosteroids. We analyze the mechanism of action of the main hypertensive drugs and their influence on the reversing hypertonic action of the immunosuppressive agents. In the absence of current guidelines addressing this problem, this article is an attempt to fill the gap, helping clinicians to choose proper medication.

Histone deacetylase inhibition ameliorates hypertension and hyperglycemia in a model of Cushing's syndrome

Cushing's syndrome (CS) caused by hypercortisolism is occasionally accompanied by metabolic disorders such as hypertension, diabetes mellitus (DM), dyslipidemia, and central obesity. Thus morbidity and mortality, observed in cardiovascular disease, are elevated in patients with CS. We hypothesized that HDAC inhibition (HDACi) decreased transcriptional activity of glucocorticoid receptor (GR), which ameliorates hypertension and hyperglycemia in patients with CS. To establish an animal model of hypercortisolism, Sprague-Dawley rats were infused with adrenocorticotropic hormone (ACTH, 40 ng/day) or dexamethasone (Dex, 10 μg/day) via osmotic minipumps for 4 wk. Expression of GR target genes was determined by quantitative real-time PCR (qRT-PCR). GR enrichment on specific loci, and across the whole genome, was analyzed by chromatin immunoprecipitation (ChIP) and ChIPseq, respectively. HDACi decreased blood pressure and expression of ion regulators in the kidneys of ACTH-infused rats. Additionally, HDACi reduced deposition of polysaccharide, fasting blood glucose level, glucose intolerance, and expression of gluconeogenesis genes in the livers and kidneys of ACTH- and Dex-infused rats. Among class I HDACs, HDAC1 and HDAC3 interacted with GR. HDAC1 knockdown resulted in increased level of acetylation and decreased transcriptional activity of GR. GR recruitment on the promoters of 2,754 genes, which include ion transporters, channels, and gluconeogenic genes, was significantly decreased by MS-275, a class I HDAC inhibitor. These results indicate that HDACi ameliorates hypertension and hyperglycemia in a model of CS by decreasing the transcriptional activity of GR via elevating its level of acetylation.

Blockade of glucocorticoid receptors with RU486 attenuates cardiac damage and adipose tissue inflammation in a rat model of metabolic syndrome

Glucocorticoids are stress hormones that modulate metabolic, inflammatory and cardiovascular processes. We recently characterized DahlS.Z-Lepr(fa)/Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive (DS) and Zucker rats, as a new animal model of metabolic syndrome (MetS). We have now investigated the effects of glucocorticoid receptor (GR) blockade on cardiac and adipose tissue pathology and gene expression, as well as on glucose metabolism in this model. DS/obese rats were treated with the GR blocker RU486 (2 mg kg(-1) per day, subcutaneous) for 4 weeks beginning at 9 weeks of age. Age-matched homozygous lean (DahlS.Z-Lepr(+)/Lepr(+), or DS/lean) littermates of DS/obese rats served as controls. Treatment of DS/obese rats with RU486 attenuated left ventricular (LV) fibrosis and diastolic dysfunction, as well as cardiac oxidative stress and inflammation, without affecting hypertension or LV hypertrophy. Administration of RU486 to DS/obese rats also inhibited the upregulation of GR and 11β-hydroxysteroid dehydrogenase type 1 (11β-HSD1) expression at the mRNA and protein levels in the heart; it attenuated adiposity and adipose tissue inflammation, as well as the upregulation of GR and 11β-HSD1 mRNA and protein expression in adipose tissue; it ameliorated fasting hyperinsulinemia as well as insulin resistance and glucose intolerance. Our results thus implicate the glucocorticoid-GR axis in the pathophysiology of MetS, and they suggest that GR blockade has therapeutic potential for the treatment of this condition.

Glucocorticoid-induced hypertension

Glucocorticoid-induced hypertension is a common clinical problem that is poorly understood, thus rendering treatment strategies sub-optimal. This form of hypertension has been commonly thought to be mediated by excess sodium and water reabsorption by the renal mineralocorticoid receptor. However, experimental and clinical data in both humans and animal models suggest important roles for the glucocorticoid receptor as well, in both the pathogenesis and maintenance of this hypertension. The glucocorticoid receptor is widely expressed in a number of organ systems relevant to blood pressure regulation, including the kidney, the brain and the vasculature. In vitro studies in isolated kidney tissues as well as in vascular smooth muscle and vascular endothelial cells have attempted to elucidate the molecular physiology of glucocorticoid-induced hypertension, but have generally been limited by the inability to study signaling pathways in an intact organism. More recently, the power of mouse genetics has been employed to examine the tissue-specific contributions of vascular and extra-vascular tissues to this form of hypertension. Here we review recent developments in our understanding of the pathogenesis of glucocorticoid-induced hypertension.

Glucocorticoid-induced hypertension and the nitric oxide system

Glucocorticoid hormones, both naturally occurring and synthetic, have long been recognized as a major cause of hypertension. There are well-described experimental models of glucocorticoid-induced hypertension, such as adrenocorticotropic hormone- and dexamethasone-induced hypertension in rats, although the exact mechanism of glucocorticoid-induced hypertension remains unclear. It was initially considered to be due to mineralocorticoid receptor activation but more recent studies have not supported this notion. Current evidence demonstrates the importance of the nitric oxide (NO) system and interactions between NO and reactive oxygen species in the development of glucocorticoid-induced hypertension. This review highlights the pathways contributing to NO deficiency, which encompass the availability of l-arginine, endothelial NO synthase function and the extent of NO inactivation during oxidative stress.

How do glucocorticoids cause hypertension: role of nitric oxide deficiency, oxidative stress, and eicosanoids

The exact mechanism by which glucocorticoid induces hypertension is unclear. Several mechanisms have been proposed, although there is evidence against the role of sodium and water retention as well as sympathetic nerve activation. This review highlights the role of nitric oxide-redox imbalance and their interactions with arachidonic acid metabolism in glucocorticoid-induced hypertension in humans and experimental animal models.

Mineralocorticoid and Glucocorticoid Receptors Stimulate Epithelial Sodium Channel Activity in a Mouse Model of Cushing Syndrome

Experiments in Cushing patients and healthy control subjects receiving adrenocorticotropic hormone (ACTH) indicate that transient renal sodium retention may contribute to the generation of hypertension. Here we have investigated the effect of chronic ACTH infusion on renal sodium handling in adult male C57BL/6J mice using selective antagonists to dissect mineralocorticoid and glucocorticoid receptor–mediated pathways. Mice were infused via osmotic minipump with ACTH (2.5 μg/d) or saline for 2 weeks before being anesthetized for renal function experiments. ACTH caused an increase in blood pressure and a reduction in fractional sodium excretion associated with enhanced activity of the epithelial sodium channel. Given separately, spironolactone and RU38486 blunted the pressor response to ACTH and the increased epithelial sodium channel activity; combined mineralocorticoid and glucocorticoid receptor blockade was required to resolve the response to ACTH excess. Dietary sodium depletion also prevented ACTH-induced hypertension. The effect of increased sodium reabsorption in the distal nephron is offset by downregulation of Na-K-Cl cotransport in the loop of Henle. Sodium excretion is normalized chronically, but blood pressure remains high; acute blockade of V1 receptors and α1 adrenoceptors in combination restored blood pressure to control values. In summary, ACTH excess promotes renal sodium reabsorption, contributing to the increased blood pressure; both glucocorticoid and mineralocorticoid receptor pathways are involved. These data are relevant to conditions associated with overactivity of the hypothalamic-pituitary-adrenal axis, such as obesity and chronic stress.

Does glucocorticoid receptor blockade exacerbate tissue damage after mineralocorticoid/salt administration?

Mineralocorticoid receptor (MR) antagonism reverses established inflammation, oxidative stress, and cardiac fibrosis in the mineralocorticoid/salt-treated rat, whereas withdrawal of the mineralocorticoid deoxycorticosterone (DOC) alone does not. Glucocorticoid receptors (GRs) play a central role in regulating inflammatory responses but are also involved in cardiovascular homeostasis. Physiological glucocorticoids bind MR with high affinity, equivalent to that for aldosterone, but are normally prevented from activating MR by pre-receptor metabolism by 11beta-hydroxysteroid dehydrogenase 2. We have previously shown a continuing fibrotic and hypertrophic effect after DOC withdrawal, putatively mediated by activation of glucocorticoid/MR complexes; the present study investigates whether this effect is moderated by antiinflammatory effects mediated via GR. Uninephrectomized rats, drinking 0.9% saline solution, were treated as follows: control; DOC (20 mg/wk) for 4 wk; DOC for 4 wk and no steroid wk 5-8; DOC for 4 wk plus the MR antagonist eplerenone (50 mg/kg.d) wk 5-8; DOC for 4 wk plus the GR antagonist RU486 (2 mg/d) wk 5-8; and DOC for 4 wk plus RU486 and eplerenone for wk 5-8. After steroid withdrawal, mineralocorticoid/salt-induced cardiac hypertrophy is sustained, but not hypertension. Inflammation and fibrosis persist after DOC withdrawal, and GR blockade with RU486 has no effect on these responses. Rats receiving RU486 for wk 5-8 after DOC withdrawal showed marginal blood pressure elevation, whereas eplerenone alone or coadministered with RU486 reversed all DOC/salt-induced circulatory and cardiac pathology. Thus, sustained responses after mineralocorticoid withdrawal appear to be independent of GR signaling, in that blockade of endogenous antiinflammatory effects via GR does not lead to an increase in the severity of responses in the mineralocorticoid/salt-treated rat after steroid withdrawal.

Role of xanthine oxidase in dexamethasone-induced hypertension in rats

1. Glucocorticoid-induced hypertension (GC-HT) in the rat is associated with nitric oxide-redox imbalance. 2. We studied the role of xanthine oxidase (XO), which is implicated in the production of reactive oxygen species, in dexamethasone-induced hypertension (dex-HT). 3. Thirty male Sprague-Dawley rats were divided randomly into four treatment groups: saline, dexamethasone (dex), allopurinol plus saline, and allopurinol plus dex. 4. Systolic blood pressures (SBP) and bodyweights were recorded each alternate day. Thymus weight was used as a marker of glucocorticoid activity, and serum urate to assess XO inhibition. 5. Dex increased SBP (110 +/- 2-126 +/- 3 mmHg; P < 0.001) and decreased thymus (P < 0.001) and bodyweights (P" < 0.01). Allopurinol decreased serum urate from 76 +/- 5 to 30 +/- 3 micromol/L (P < 0.001) in saline and from 84 +/- 13 to 28 +/- 2 micromol/L in dex-treated (P < 0.01) groups. 6. Allopurinol did not prevent dex-HT. This, together with our previous findings that allopurinol failed to prevent adrenocorticotrophic hormone induced hypertension, suggests that XO activity is not a major determinant of GC-HT in the rat.

The role of the glucocorticoid receptor in mineralocorticoid/salt-mediated cardiac fibrosis

The pathophysiological consequences of excess mineralocorticoid for salt status include hypertension, vascular inflammation, and cardiac fibrosis. Mineralocorticoid receptor (MR) blockade can both prevent and reverse established inflammation and fibrosis due to exogenous mineralocorticoids or endogenous glucocorticoid activation of the MR. Glucocorticoids also exert potent antiinflammatory effects via glucocorticoid receptors (GR) in the vascular wall. We propose that GR signaling may ameliorate mineralocorticoid/salt-induced vascular inflammation and fibrosis in the mineralocorticoid/salt model. In the present study, the role of GR in the mineralocorticoid/salt model was explored in uninephrectomized rats that were maintained on 0.9% saline solution to drink and treated as follows: control (CON), no further treatment; deoxycorticosterone (DOC; 20 mg/wk) for 4 wk (DOC4); DOC for 8 wk (DOC8); DOC for 8 wk plus the GR antagonist RU486 (2 mg/d) wk 5-8 (DOC8/RU486); and DOC for 8 wk plus RU486 and the MR antagonist eplerenone (EPL; 50 mg/kg.d) for wk 5-8 (DOC8/RU486+EPL). DOC treatment significantly increased systolic blood pressure, cardiac fibrosis, inflammation (ED-1-positive macrophages and osteopontin), and mRNA for markers of oxidative stress (p22phox, gp91phox, and NAD(P)H-4). GR blockade reduced the DOC-mediated increase in systolic blood pressure and the number of infiltrating ED-1-positive macrophages but had no effect on fibrosis, oxidative stress, or osteopontin mRNA levels. EPL reversed DOC-induced pathology in the absence or presence of GR blockade. Thus, blocking agonist activity at the GR neither enhances nor attenuates the fibrotic response, although it may modulate systolic blood pressure and macrophage recruitment in the mineralocorticoid/salt model.

How does salt retention raise blood pressure?

A critical question in hypertension research is: How is long-term blood pressure controlled? Excessive NaCl ingestion or NaCl retention by the kidneys and the consequent tendency toward plasma volume expansion lead to hypertension. Nevertheless, the precise mechanisms linking salt to high blood pressure are unresolved. The discovery of endogenous ouabain, an adrenocortical hormone, provided an important clue. Ouabain, a selective Na+ pump inhibitor, has cardiotonic and vasotonic effects. Plasma endogenous ouabain levels are significantly elevated in approximately 40% of patients with essential hypertension and in animals with several forms of salt-dependent hypertension. Also, prolonged ouabain administration induces hypertension in rodents. Mice with mutant Na+ pumps or Na/Ca exchangers (NCX) and studies with a ouabain antagonist and an NCX blocker are revealing the missing molecular mechanisms. These data demonstrate that alpha2 Na+ pumps and NCX1 participate in long-term regulation of vascular tone and blood pressure. Pharmacological agents or mutations in the alpha2 Na+ pump that interfere with the action of ouabain on the pump, and reduced NCX1 expression or agents that block NCX all impede the development of salt-dependent or ouabain-induced hypertension. Conversely, nanomolar ouabain, reduced alpha2 Na+ pump expression, and smooth muscle-specific overexpression of NCX1 all induce hypertension. Furthermore, ouabain and reduced alpha2 Na+ pump expression increase myogenic tone in isolated mesenteric small arteries in vitro, thereby tying these effects directly to the elevation of blood pressure. Thus, endogenous ouabain, and vascular alpha2 Na+ pumps and NCX1, are critical links between salt and hypertension. New pharmacological agents that act on these molecular links have potential in the clinical management of hypertension.

Glucocorticoid receptor blockade disinhibits pituitary-adrenal activity during the stress hyporesponsive period of the mouse

During postnatal development, mice undergo a period of reduced responsiveness of the pituitary-adrenal axis, the stress hyporesponsive period (SHRP), which is largely under control of maternal signals. The present study was designed to test the hypothesis that this quiescence in hypothalamic-pituitary-adrenal (HPA) activity is mediated by glucocorticoid feedback. For this purpose, the role of mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) in control of HPA activity was examined during the SHRP and in response to 24 h of maternal deprivation. Nondeprived or deprived (24 h) CD1 mice on postnatal d 8 were injected sc at 16 and 8 h before testing with the MR antagonist RU28318 or the GR antagonist RU38486. The results showed that, in nondeprived mice, blockade of GR rather than MR triggered a profound increase in anterior pituitary proopiomelanocortin mRNA, circulating ACTH, and corticosterone concentrations. In contrast, CRH mRNA in hypothalamus and GR mRNA in hippocampus and hypothalamus were decreased. Blockade of the GR during the deprivation period amplified the rise in corticosterone induced by maternal deprivation, whereas it reversed the deprivation effect on the other HPA markers, leading to profound increases in plasma ACTH, proopiomelanocortin mRNA expression in the anterior pituitary, CRH mRNA expression in the paraventricular nucleus, and MR mRNA expression in the hippocampus, but not in GR mRNA expression in the hippocampus and paraventricular nucleus. In conclusion, the data suggest that control of postnatal pituitary-adrenal activity during the SHRP involves GR-mediated feedback in the anterior pituitary, which is further potentiated in the absence of the mother.

Nitric Oxide Donation Lowers Blood Pressure in Adrenocorticotrophic Hormone‐Induced Hypertensive Rats

Adrenocorticotrophic hormone (ACTH) elevates systolic blood pressure (SBP) and lowers plasma reactive nitrogen intermediates in rats. We assessed the ability of NO donation from isosorbide dinitrate (ISDN) to prevent or reverse the hypertension caused by ACTH. In the prevention study, male Sprague Dawley rats were treated with ACTH (0.2 mg/kg/day) or saline control for 8 days, with either concurrent ISDN (100 mg/kg/day) via the drinking water or water alone. Animals receiving ISDN via the drinking water were provided with nitrate-free water for 8 hours every day. In the reversal study ISDN (100 mg/kg) or vehicle was given as a single oral dose on day 8. SBP was measured daily by the indirect tail-cuff method in conscious, restrained rats. ACTH caused a significant increase in SBP compared with saline (P < 0.0015). In the prevention study, chronic administration of ISDN (100 mg/kg/day) did not affect the SBP in either group. In the reversal study, ISDN significantly lowered SBP in ACTH-treated rats at 1 and 2.5 hours (132 +/- 3 mmHg (1 h) and 131 +/- 2 mmHg (2.5 h) versus 143 +/- 3 mmHg (0 h), P < 0.002), but not to control levels. It had no effect in control (saline treated) rats. In conclusion, the lowering of SBP by NO donation is consistent with the notion that ACTH-induced hypertension involves an impaired bioavailability or action of NO in vivo.

Glucocorticoids and the kidney. Review Article

Glucocorticoids are widely used by nephrologists for their immunomodulatory and anti-inflammatory effects. The present review considers three aspects of glucocorticoids with which nephrologists may be less familiar: (i) renal metabolism; (ii) effects on renal haemodynamics; and (iii) effects on blood pressure as they relate to the kidney.

Lipopolysaccharide reverses adrenocorticotrophic hormone-induced hypertension in the rat

Lipopolysaccharide (LPS) was used to stimulate nitric oxide (NO) release and investigate the effect of endogenous NO on adrenocorticotrophic hormone (ACTH)-induced hypertension in rats. After preliminary studies to determine the appropriate dose of LPS, 40 male Sprague-Dawley rats were treated with ACTH (200 microg/kg/day, s.c.) or saline (sham) for 8 days and then given a single dose of LPS (10 mg/kg, i.p.) or saline. ACTH treatment was continued for a further 5 days. Systolic blood pressure (SBP) was measured daily using the tail cuff method. Results were expressed as the mean +/- SEM. ACTH treatment significantly increased SBP (from 105 +/- 3 to 129 +/- 4 mmHg; p<0.05), whereas saline had no effect on SBP. The ACTH-induced increase in SBP was reversed by LPS injection (from 125 +/- 6 to 102 +/- 7 mmHg; p<0.05). SBP was also decreased in sham + LPS-treated rats compared with that of sham + saline-treated rats (p<0.05), but the SBP change in response to LPS was greater in ACTH-treated than in sham-treated rats (-23 vs. -8 mmHg; p<0.05). These data are compatible with the notion that reduced NO availability plays a role in ACTH-induced hypertension.

The nitric oxide system in glucocorticoid-induced hypertension

The blood pressure-raising effects of adrenocortical steroids with predominantly glucocorticoid activity, both naturally occurring and synthetic, are well known. Recent evidence suggests that the nitric oxide system plays a key role in the hypertension produced by glucocorticoids. Glucocorticoid actions at various sites in the nitric oxide synthase (NOS) pathway may result in elevated blood pressure. These include: alterations in l-arginine availability or transport; NOS2 and NOS3 downregulation; reduced cofactor bioavailability; NOS uncoupling; a concomitant elevation in reactive oxygen species and removal of nitric oxide (NO) from the vascular environment; alterations in whole body antioxidant status; and erythropoietin induced resistance to NO.

Mutations in aldosterone synthase gene of Milan hypertensive rats: phenotypic consequences

Using in vitro and in vivo methods, we have demonstrated increased sensitivity of adrenocortical steroidogenesis to ACTH in Milan hypertensive (MHS) compared with normotensive (MNS) rats and have investigated whether this is caused by mutations of steroidogenic enzymes. Genes encoding aldosterone synthase (CYP11B2) and 11beta-hydroxylase (CYP11B1) in MHS and MNS have been cloned and sequenced. Nucleotide 752 (G) in exon 4 of MHS CYP11B2 differs from that of MNS (A); CYP11B1 sequences were identical. The nucleotide 752 mutation caused a Q251R substitution in the amino acid sequence of MHS CYP11B2. The phenotype of MHS CYP11B2 alleles, when expressed in COS-1 cells, differed from that of MNS alleles. The relative activities of the three reactions catalyzed by CYP11B2 (11beta-hydroxylation of deoxycorticosterone, 18-hydroxylation of corticosterone, and dehydrogenation of 18-hydroxycorticosterone) were estimated after incubation of transfected cells with [(14)C]deoxycorticosterone and analysis of radioactivity associated with deoxycorticosterone, corticosterone, 18 hydroxycorticosterone, and aldosterone. Both 11- and 18-hydroxylase activities were lower (19 and 12%, respectively; P < 0.01 and P < 0.05) in cells transfected with MHS compared with MNS alleles, whereas 18-oxidase activity was 42% higher (P < 0.01). To assess the significance of the CYP11B2 mutation in vivo, DNA from F2 hybrid MHS x MNS rats was genotyped. MHS alleles were associated with lower urine volumes in both sexes, lower ventricle weights in male rats, but no difference in systolic or diastolic blood pressures between the sexes. We conclude that a mutation in CYP11B2 may affect aldosterone secretion in MHS; however, under normal environmental circumstances, we were unable to demonstrate any influence of this mutation on blood pressure.

Glucocorticoid-induced hypertension: from mouse to man

1. Adrenocorticotrophic hormone (ACTH) raises blood pressure in humans, sheep, rat and mouse. In rat and humans, but not sheep, the hypertension can be explained by glucocorticoid excess. 2. In both rat and humans, the hypertension is associated with a rise in cardiac output and renal vascular resistance. 3. In both rat and humans, the nitric oxide system is implicated in glucocorticoid hypertension. 4. In both rat and humans, hypertension due to naturally occurring glucocorticoids is not prevented by drugs that block classical glucocorticoid or mineralocorticoid receptors. 5. Abnormalities in glucocorticoid metabolism may contribute to some forms of 'essential' hypertension.

L-arginine partially reverses established adrenocorticotrophin-induced hypertension and nitric oxide deficiency in the rat

BACKGROUND

L-arginine treatment prevents adrenocorticotrophin (ACTH) induced hypertension in the rat. This study examined whether L-arginine treatment could reverse established ACTH hypertension and its effects on markers of decreased NO activity.

METHODS

Sixty-four male Sprague-Dawley rats were randomly divided into 6 groups given 12 days of treatment: (1) sham (0.9% NaCl, 0.5 ml/kg, subcutaneously, sc, n = 16); (2) ACTH (0.5 mg/kg/day, sc, n = 16); (3) sham + L-arginine (0.6% in food, from treatment day 8 onwards, n = 10); (4) ACTH + L-arginine (n = 10); (5) sham + D-arginine (0.6% in food, from T 8 onwards) (n = 6); and (6) ACTH + D-arginine (n = 6). Systolic blood pressure, water intake, urine volume, and body weight were measured every second day. At the end of the experiments, plasma and urinary nitrate/nitrite (NOx), plasma amino acid concentrations (in groups 1-4), and urinary cyclic guanosine monophosphate (cGMP) concentrations were measured.

RESULTS

Sham, sham + L-arginine, and sham + D-arginine treatments did not affect blood pressure. ACTH increased systolic blood pressure (from 121 +/- 1 to 147 +/- 2 mmHg, p < 0.001, pooled control vs treatment day 12, mean +/- sem), and this was partially reversed by L-arginine (group 4: from 141 +/- 2 on day 8 to 133 +/- 1 mmHg on day 12, n = 10, p < 0.001). In contrast, D-arginine did not affect blood pressure in ACTH-treated rats (group 6). ACTH increased water intake and urine volume and decreased body weight, and L-arginine administration did not alter these parameters. ACTH decreased plasma citrulline (group 1 vs 2: 115 +/- 7 vs 67 +/- 6 micro M/L, n = 16, p < 0.001) and NOx concentrations (group 1 vs 2: 8.3 +/- 0.8 vs 4.5 +/- 0.6 microM/L, n= 10, p < 0.001) and these decreases were reversed by L-arginine treatment (group 4: citrulline 98 +/- 9 micro M/L, NOx 9.1 +/- 1.6 micro M/L, group 2 vs 4, both p < 0.05). ACTH produced marked increases in urinary cGMP excretion (group 1 vs 2: 0.5 +/- 0.1 vs 1.9 +/- 0.4 nmol/24 h, p < 0.01).

CONCLUSION

Supplementation with L-arginine partly reversed established ACTH-induced hypertension and restored plasma NOx and citrulline concentrations to levels seen in sham-treated rats. These data are consistent with previous studies suggesting that functional NO deficiency has a role in ACTH-induced hypertension in rats.

Glomerular hypertension and hyperfiltration in adrenocorticotrophin-induced hypertension in rats: the role of nitric oxide

OBJECTIVE

To determine the effects on pre- and post-glomerular vascular resistance of adrenocorticotrophin (ACTH)-induced hypertension in rats, before and after blockade of nitric oxide formation.

DESIGN

Four groups of Sprague-Dawley rats were studied. Measurements were made in ACTH- (Synacthen Depot, 0.25 mg/kg twice daily for 8 days) and sham-treated anaesthetized rats, before and after either Nomega-nitro-L-arginine (L-NNA, 6 mg/kg) or vehicle.

METHODS

Whole-kidney and single-nephron haemodynamics and function were measured. Glomerular capillary pressure was estimated from tubular stop-flow pressure measurements.

RESULTS

Blood pressure (P < 0.001), renal blood flow (RBF, P < 0.05) and glomerular filtration rate (P < 0.01) were increased following ACTH treatment compared with sham. There were no differences in either total renal, or pre- or post-glomerular vascular resistances, but stop-flow-estimated glomerular capillary pressure was elevated (P < 0.001) as was single-nephron glomerular filtration rate (SNGFR) (P < 0.001) and single-nephron blood flow (P < 0.01 ) in the ACTH- compared to the sham-treated rats. L-NNA treatment increased blood pressure by a similar extent in both ACTH- and sham-treated rats, but reduced RBF (P < 0.05) and glomerular filtration rate (GFR) (P < 0.05) more in the ACTH group; similar changes were seen in single-nephron values. L-NNA increased pre- and post-glomerular resistances to a greater extent in the ACTH group.

CONCLUSIONS

ACTH-induced hypertension produced glomerular hypertension and hyperfiltration, which may be due to nitric oxide-related vasodilatation of the renal vasculature.

Cushing, cortisol, and cardiovascular disease

Cushing's syndrome of glucocorticoid excess is named after the eminent Boston neurosurgeon Harvey W. Cushing (1869-1939). The recognition that glucocorticoid excess produces hypertension led to examination of the role of cortisol in essential hypertension, but it is only over the last decade that evidence has emerged to support the concept. Despite the widespread assumption that cortisol raises blood pressure as a consequence of renal sodium retention, there are few data consistent with the notion. Although it has a plethora of actions on brain, heart and blood vessels, kidney, and body fluid compartments, precisely how cortisol elevates blood pressure is unclear. Candidate mechanisms currently being examined include inhibition of the vasodilator nitric oxide system and increases in vasoconstrictor erythropoietin concentration.

Role of 11beta-hydroxysteroid dehydrogenase in nongenomic aldosterone effects in human arteries

The aim of the present study was to demonstrate rapid effects of aldosterone on the Na(+)-H(+) exchanger in strips of human vascular vessels and to determine whether 11beta-hydroxysteroid dehydrogenase enzyme (11beta-HSD) could play a protective role in this response, such as that described for the classic type I mineralocorticoid receptor (MR). The activity of 11beta-HSD isoforms 1 and 2 were measured in fetal and adult arteries. Both isoforms are present in adult and fetal vessels. However, a significant difference in the proportion of each isoform was found. Isoform 1 activity (in pmol x min(-1) x 100 mg(-1) protein) was 42+/-5 in fetal vessels and 29+/-2 in adult arteries, and isoform 2 activity was 78+/-7 in fetal and 12+/-2 in adult tissue. The nongenomic effect of aldosterone on Na(+)-H(+) exchanger activity was measured in strips of chorionic and radial uterine arteries loaded with the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5,6-carboxyfluorescein. Recordings of intracellular pH (pH(i)) were made by videofluorescence microscopy. Aldosterone (0.5 nmol/L) rapidly increased pH(i), with a half-maximal effect between 2 and 3 nmol/L in both fetal and adult vessels. Ethylisopropylamiloride, a specific inhibitor of the Na(+)-H(+) exchanger, inhibited this effect. The hormone-mediated increase in pH(i) was unaffected by spironolactone, a classic antagonist of MR, but was completely blocked by RU28318. Cortisol (up to 1 micromol/L) had no effect on pH(i), but when applied in the presence of carbenoxolone, a dramatic increase in Na(+)-H(+) exchanger activity was evident. The increments on pH(i) for each cortisol concentration were similar to those observed for aldosterone. These findings suggest that vascular 11beta-HSD plays an active role in maintaining the specificity of the rapid effects of aldosterone.

Haemodynamic mechanisms of corticotropin (ACTH)-induced hypertension in the rat

OBJECTIVES

To investigate the roles of cardiac output and systemic and regional resistances in corticotropin (ACTH)-induced hypertension in the rat

METHODS

This study consisted of three series of experiments with eight groups of male Sprague-Dawley rats (n = 132). Series 1 comprised groups 1-4, where group 1 = sham (0.9% NaCl, subcutaneous (s.c.) injection); group 2 = ACTH (0.5 mg/kg per day, s.c.); group 3 = atenolol + sham; group 4 = atenolol + ACTH treatments. Series 2 comprised groups 5 and 6, where group 5 = minoxidil + sham and group 6 = minoxidil + ACTH treatments. Series 3 comprised groups 7 and 8, where group 7 = ramipril + sham and group 8 = ramipril + ACTH treatments. Systolic blood pressure, water and food intakes, urine volume, and body weight were measured every second day. After 10 days of treatment, mean arterial blood pressure was measured by intra-arterial cannulation, and cardiac output (CO), and renal, mesenteric and hindquarter blood flows (RBF, MBF and HBF) determined using transonic small animal flowmeters.

RESULTS

ACTH treatment increased blood pressure (P < 0.001) with a rise in CO (P < 0.01) and renal vascular resistance (RVR, P < 0.05), but did not affect total peripheral resistance (TPR). Atenolol blocked the rise in CO without affecting the rise in blood pressure produced by ACTH treatment Minoxidil lowered TPR, but did not prevent the rise in blood pressure or renal vascular resistance. Ramipril blunted the rise in RVR and blood pressure without significantly affecting TPR.

CONCLUSION

Neither preventing rise in CO nor lowering TPR altered the ACTH-induced rise in blood pressure in the rat However, both the hypertension and rise in RVR were prevented by ramipril. These data suggest that increase in RVR may play a role in the pathogenesis of ACTH-induced hypertension in the rat.