The role of vascular steroid receptors in the control of vascular contractility and peripheral vascular resistance

Coincidence of Large Adrenal Cyst and Prominent Hyporeninemic Hyperaldosteronism

A 67-year-old Japanese woman who had end-stage renal disease was referred to our hospital for kidney transplantation. Abdominal CT revealed a large adrenal mass with inhomogeneity. She had a history of hospitalization for stroke and heart failure and exhibited prominent hyporeninemic hyperaldosteronism. Histological examination of the resected tumor with anti-CYP11B2 antibody indicated that she had a vascular endothelial cyst with primary aldosteronism (PA) due to multiple adrenocortical micronodules. This report implicates the pathological interaction between adrenal vascular cysts and PA-mediated vascular damage of the adrenal vein.

Echocardiographic and biomarker evidence of plasma volume expansion after short-term steroids administered orally in cats

Background

Steroids administered PO and intramuscularly are associated with development of congestive heart failure in cats without prior signs of heart disease, but criteria to identify cats at increased risk for steroid‐induced heart failure are not established.

Hypothesis

Cats administered steroids PO for 5 to 7 days will develop increased N terminal pro‐B‐type natriuretic peptide (NT‐proBNP) concentration and heart size.

Animals

Ten client‐owned cats.

Methods

Observational cohort study. Cats intended to initiate at least a 5‐day course of steroids administered PO were consecutively recruited.

Results

Steroids administered PO to cats are not associated with differences in absolute concentration of NT‐proBNP (baseline: 49 pmol/L [range, 24‐1013]; after steroids: 85 pmol/L [range, 46‐1367]; P = .23), blood pressure (baseline: 145 mm Hg [range, 116‐163]; after steroids: 145 mm Hg [range, 115‐230]; P = .94), nor blood glucose concentration (baseline: 125 mg/dL [range, 92‐254]; after steroids: 144 mg/dL [range, 114‐307]; P = .43), but are associated with increased median left atrial dimension (baseline: 1.26 cm [range, 0.96‐2.03; after steroids: 1.38 [range, 1.03‐2.20]; P = .02) and mean left ventricular internal diameter (baseline: 1.55 cm [standard deviation—SD, 0.28; after steroids: 1.72 cm [SD, 0.28]; P = .03). Six of 10 (60%) cats had a percentile change in NT‐proBNP >60% after steroids, and 3 of 8 (38%) cats with baseline BNP <100 pmol/L had an NT‐proBNP >100 pmol/L after steroids.

Conclusions and Clinical Importance

Increased heart size and percentage change in individual NT‐proBNP concentration suggests plasma volume expansion secondary to steroids administered PO in cats. A serial assessment of an individual cat's change in NT‐proBNP might be clinically useful for judging risk for volume expansion.

Glucocorticosteroids for sepsis in children. A protocol for a systematic review

BACKGROUND

Sepsis is the primary diagnosis in more than 8% of all critically ill children and sepsis is among the ten leading causes of death in children <10 years. Glucocorticosteroids are currently recommended in septic children with fluid or catecholamine resistant refractory shock. Glucocorticosteroids are widely used for severe sepsis in paediatric intensive care units worldwide. However, the evidence on the clinical effects of glucocorticosteroids for sepsis in children is unclear.

METHODS

We will perform a systematic review with meta-analysis and Trial Sequential Analysis of randomised clinical trials. We will include randomised clinical trials assessing the effects of glucocorticosteroids vs placebo or no intervention as an add-on therapy to standard care for sepsis in children. For the assessment of harms, we will also include quasi-randomised studies and observational studies identified during our searches for randomised clinical trials.

DISCUSSION

This review will seek to assess whether glucocorticosteroids indeed have their therapeutic place in the standard treatment for sepsis in children.

Adrenocortical function in hypotensive patients with end stage renal disease

BACKGROUND

Sustained hypotension among patients with end stage renal disease on dialysis (ESRDh) varies from 5.0% to 12.0%. Despite their role in the regulation of blood pressure (BP) corticoadrenal hormones have been poorly investigated.

OBJECTIVES

This study aims to detect adrenal insufficiency in ESRDh and follow their clinical outcome.

METHODS

Fifty ESRDh and 30 healthy volunteers were studied. In all cases basal blood and saliva were obtained. Synthetic ACTH (25μg) was injected intramuscularly and at 30min saliva was collected. Circulating ACTH, renin, cortisol and aldosterone were measured and steroids were also assessed in saliva by immunoassay.

RESULTS

Fifteen ESRDh achieved steroid responses not different than healthy volunteers; four had primary adrenal insufficiency; six had secondary adrenal insufficiency; nine had selective hypoaldosteronism and sixteen secondary hyperaldosteronism. The years on dialysis did not differ among subgroups. ROC analysis defined the following cut-offs for basal cortisol to predict adrenal insufficiency: in serum ⩽232.0nM (sensitivity (S) 100.0% and specificity (E) 90.0%); in saliva ⩽4.4nM (100.0% S and E). Basal aldosterone cut-off values to predict hyperaldosteronism were: in serum >500.0pM and saliva >60.0pM (100.0% S and E, for both). For the prediction of hypoaldosteronism the basal serum aldosterone was ⩽260.0pM (100% S; 53% E) and in saliva it was ⩽20.1pM (100% S; 58.5% E). Three patients with primary adrenal insufficiency and six with secondary adrenal insufficiency improved general clinical condition and normalized BP on steroids. One patient died before initiation of steroid therapy.

CONCLUSION

Adrenal function should be assessed in ESRDh in order to unmask adrenal insufficient states.

Cardiovascular effects of Boophone disticha aqueous ethanolic extract on early maternally separated BALB/C mice

ETHNOPHARMACOLOGICAL RELEVANCE

There are a number of reports from traditional medical practice in Zimbabwe and neighboring countries and few in vitro studies suggesting an effect with extracts of Boophone disticha in some forms of anxiety disorder.

AIM OF THE STUDY

In order to validate the use of Boophone disticha in treatment of anxiety, this study was set to determine the effects of the plant extracts on blood pressure (BP) and heart rate (HR) in adult BALB/c mice subjected to repeated early maternal separation (MS) stress.

MATERIALS AND METHODS

To test whether early life stress increases anxiety in mice, non-invasive tail cuff method was used to examine the autonomic nervous system activity by assessing cardiovascular reactivity and response to acute mixing stress (AMS) and restraint stress (RS) in adult mice subjected to early postnatal stress as compared to control. AMS-induced cardiovascular response was then evaluated in adult MS mice treated with Boophone disticha as compared to vehicle and diazepam.

RESULTS

Comparisons of the BP and HR measurements indicated that MS significantly reduced AMS-induced HR responses in BALB/c mice when compared with control. Boophone disticha treatment significantly reduced AMS-induced BP response in BALB/c MS mice as compared to vehicle and diazepam treatments.

CONCLUSIONS

Our findings demonstrate for the first time that postnatal stress can induce short-term changes in the sensitivity of the cardiovascular system to subsequent stress which can be reduced by treatment with a freeze dried aqueous ethanolic extract of Boophone disticha.

Knockout of the vascular endothelial glucocorticoid receptor abrogates dexamethasone-induced hypertension

BACKGROUND

Glucocorticoid-mediated hypertension is incompletely understood. Recent studies have suggested the primary mechanism of this form of hypertension may be through the effects of glucocorticoids on vascular tissues and not to excess sodium and water re-absorption as traditionally believed.

OBJECTIVE

The goal of this study was to better understand the role of the vasculature in the generation and maintenance of glucocorticoid-mediated hypertension.

METHODS

We created a mouse model with a tissue-specific knockout of the glucocorticoid receptor in the vascular endothelium.

RESULTS

We show that these mice are relatively resistant to dexamethasone-induced hypertension. After 1 week of dexamethasone treatment, control animals have a mean blood pressure (BP) increase of 13.1 mmHg, whereas knockout animals have only a 2.7 mmHg increase (P < 0.001). Interestingly, the knockout mice have slightly elevated baseline BP compared with the controls (112.2 ± 2.5 vs. 104.6 ± 1.2 mmHg, P = 0.04), a finding which is not entirely explained by our data. Furthermore, we demonstrate that the knockout resistance arterioles have a decreased contractile response to dexamethasone with only 6.6% contraction in knockout vessels compared with 13.4% contraction in control vessels (P = 0.034). Finally, we show that in contrast to control animals, the knockout animals are able to recover a significant portion of their normal circadian BP rhythm, suggesting that the vascular endothelial glucocorticoid receptor may function as a peripheral circadian clock.

CONCLUSION

Our study highlights the importance of the vascular endothelial glucocorticoid receptor in several fundamental physiologic processes, namely BP homeostasis and circadian rhythm.

A critical role for vascular smooth muscle in acute glucocorticoid-induced hypertension

Although glucocorticoid (GC)-induced hypertension has commonly been attributed to promiscuous activation of the mineralocorticoid receptor by cortisol, thereby promoting excess reabsorption of sodium and water, numerous lines of evidence indicate that this is not the only or perhaps even the primary mechanism. GC induce a number of effects on vascular smooth muscle (VSM) in vitro that may be pertinent to hypertension, but their contribution in vivo is unknown. To address this question, a mouse model with a tissue-specific knockout (KO) of the GC receptor in the VSM was created and characterized. Similar to control mice, KO mice exhibited normal baseline BP and, interestingly, showed normal circadian variation in BP. When dexamethasone was administered, however, the acute hypertensive response was markedly attenuated in KO mice, and there was a trend toward a decreased chronic hypertensive response. These data suggest that the GC receptor in VSM plays a critical role in the acute hypertensive response to GC in vivo.

Modulation by the steroid/thyroid hormone superfamily of TGF-beta-stimulated VEGF release from vascular smooth muscle cells

We previously reported that transforming growth factor-beta (TGF-beta) stimulates the release of vascular endothelial growth factor (VEGF) from aortic smooth muscle A10 cells via activation of p38 mitogen-activated protein (MAP) kinase. In the present study, we investigated whether nuclear hormone receptor superfamily members affect TGF-beta-stimulated VEGF release from A10 cells. Retinoic acid or 1,25-dihydroxyvitamin D3 enhanced TGF-beta-induced VEGF release in a concentration-dependent manner, whereas dexamethasone or corticosterone suppressed TGF-beta-induced VEGF release. 1,25-Dihydroxyvitamin D3 and TGF-beta stimulated phosphorylation of p38 MAP kinase in an additive manner. SB203580, an inhibitor of p38 MAP kinase, decreased the VEGF release induced by TGF-beta or 1,25-dihydroxyvitamin D3. However, retinoic acid, dexamethasone, or corticosterone did not affect phosphorylation of p38 MAP kinase. These results indicate that retinoic acid, 1,25-dihydroxyvitamin D3, and glucocorticoids affect TGF-beta-stimulated VEGF release from aortic smooth muscle cells. The stimulatory effect of 1,25-dihydroxyvitamin D3 occurs, in part, via modification of TGF-beta-induced activation of p38 MAP kinase.

Vascular synthesis of aldosterone: role in hypertension

The author showed direct evidence that blood vessels are aldosteronogenic. The expression of CYP11B2 mRNA and synthesis of vascular aldosterone were decreased in rats treated with angiotensin converting enzyme inhibitor. Angiotensin II increased production of aldosterone in blood vessels. Vascular aldosterone and CYP11B2 mRNA levels of 2-week-old SHRSPs were significantly increased compared with that in WKY rats of the same age. High sodium intake develops and accelerates vascular injury and cardiac hypertrophy in SHRSP. Plasma aldosterone concentrations and plasma renin concentration were decreased by high salt intake in SHRSP. Aldosterone production, the expression of CYP11B2 mRNA and type I angiotensin II receptor (ATiR) mRNA in blood vessels were significantly increased by high salt intake. These results suggest that high salt intake increases aldosterone production and expression of the ATiR mRNA in the vascular tissue in SHRSP, which may contribute to the development of malignant hypertension in salt-loaded SHRSP.

Prenatal stress alters cardiovascular responses in adult rats

Environmental factors in early life are clearly established risk factors for cardiovascular disease in later life. Most studies have focused on nutritional programming and analysed basal cardiovascular parameters rather than responses. In the present study we have investigated whether prenatal stress has long-term effects on cardiovascular responses in adult offspring. Female pregnant Sprague-Dawley rats were subjected to stress three times daily from day 15 to day 21 of gestation. Litters from stressed and control females were cross-fostered at birth to control for mothering effects. When the offspring were 6 months old, blood pressure was measured in the conscious rats through implanted catheters at rest, during restraint stress and during recovery. Basal haemodynamic parameters were similar in the different groups but the pattern of cardiovascular responses during stress and recovery differed markedly between prenatally stressed (PS) and control animals. PS rats had higher and longer-lasting systolic arterial pressure elevations to restraint stress than control animals. They also showed elevated systolic and diastolic blood pressure values during the recovery phase. PS rats demonstrated a greater increase in blood pressure variability compared with control animals during exposure to restraint stress, and showed more prolonged heart rate responses to acute stress and delayed recovery than controls. There was no effect of prenatal stress on baroreflex regulation of heart rate. PS females showed a greater increase in systolic arterial pressure and blood pressure variability and delayed heart rate recovery following return to the home cage then did PS males. These findings demonstrate for the first time that prenatal stress can induce long-term, sex-related changes in the sensitivity of the cardiovascular system to subsequent stress.

Glucocorticoids decrease GTP cyclohydrolase and tetrahydrobiopterin-dependent vasorelaxation through glucocorticoid receptors

Excess glucocorticoids result in decreased aortic dilation and expression of guanosine triphosphate (GTP) cyclohydrolase 1 (GTPCH1) messenger RNA (mRNA), the rate-limiting enzyme in the production of the nitric oxide synthase (NOS) cofactor tetrahydrobiopterin (BH4). It was hypothesized that this response is a genomic effect mediated through the glucocorticoid receptor (GR). Endothelium-intact rat aortas were incubated with dexamethasone (DEX; 1.3 x 10(-6) M) or vehicle for 2 or 6 hours and isometric force generation was measured. Maximum acetylcholine-induced relaxation in DEX-2hr aortas was not different compared with control values; however, acetylcholine-induced relaxations in DEX-6hr aortas were significantly decreased. Coincubation with sepiapterin (10(-4) M), which produces BH4 via a salvage pathway, restored relaxation in DEX-6hr aortas to that of controls. Coincubation with the GR antagonist mifepristone (10(-6) M) completely blocked the DEX-induced decrease in relaxation. Spironolactone (10(-5) M), a mineralocorticoid receptor antagonist, had no effect. GTPCH1 mRNA expression was significantly decreased in DEX-6hr aortas compared with control values. This was blocked by mifepristone; however, spironolactone and cycloheximide did not prevent the decrease of GTPCH1 by DEX. These results support the hypothesis that GTPCH1 downregulation by glucocorticoids is mediated through the GR and contributes to reduced endothelium-dependent relaxation.

Effect of cortisol on norepinephrine-mediated contractions in ovine uterine arteries

Cortisol potentiated norepinephrine (NE)-mediated contractions in ovine uterine arteries (UA). We tested the hypothesis that cortisol regulated alpha(1)-adrenoceptor-mediated pharmacomechanical coupling differentially in nonpregnant UA (NUA) and pregnant UA (PUA). Cortisol (10 ng/ml for 24 h) significantly increased contractile coupling efficiency of alpha(1)-adrenoceptors in NUA, but increased alpha(1)-adrenoceptor density in PUA. Cortisol potentiated NE-induced inositol 1,4,5-trisphosphate [Ins(1,4,5)P(3)] synthesis in both NUA and PUA, but increased coupling efficiency of alpha(1)-adrenoceptors to Ins(1,4,5)P(3) synthesis only in NUA. Carbenoxolone alone did not affect NE-mediated Ins(1,4,5)P(3) production, but significantly enhanced cortisol-mediated potentiation of NE-stimulated Ins(1,4,5)P(3) synthesis in PUA. In addition, cortisol potentiated the NE-induced increase in Ca(2+) concentration in PUA, but increased NE-mediated contraction for a given amount of Ca(2+) concentration in NUA. Collectively, the results indicate that cortisol potentiates NE-mediated contractions differentially in NUA and PUA, i.e., by upregulating alpha(1)-adrenoceptor density leading to increased Ca(2+) mobilization in PUA while increasing alpha(1)-adrenoceptor coupling efficiency and myofilament Ca(2+) sensitivity in NUA. In addition, the results suggest that pregnancy increases type 2 11 beta-hydroxysteroid dehydrogenase activity in the UA.

Cortisol-mediated potentiation of uterine artery contractility: effect of pregnancy

During pregnancy, maternal plasma cortisol concentrations approximately double. Given that cortisol plays an important role in the regulation of vascular reactivity, the present study investigated the potential role of cortisol in potentiation of uterine artery (UA) contractility and tested the hypothesis that pregnancy downregulated the cortisol-mediated potentiation. In vitro cortisol treatment (3, 10, or 30 ng/ml for 24 h) produced a dose-dependent increase in norepinephrine (NE)-induced contractions in both nonpregnant and pregnant (138-143 days gestation) sheep UA. However, this cortisol-mediated response was significantly attenuated by approximately 50% in pregnant UA. The 11 beta-hydroxysteroid dehydrogenase (11-beta HSD) inhibitor carbenoxolone did not change the effect of cortisol in nonpregnant UA but abolished its effect in pregnant UA by increasing the NE pD(2) in control tissues from 6.20 +/- 0.05 to 6.59 +/- 0.11. The apparent dissociation constant value of NE alpha(1)-adrenoceptors was not changed by cortisol in pregnant UA but was decreased in nonpregnant UA. There was no difference in glucocorticoid receptor density between nonpregnant and pregnant UA. Cortisol significantly decreased endothelial nitric oxide (NO) synthase protein levels and NO release in both nonpregnant and pregnant UA, but the effect of cortisol was attenuated in pregnant UA by approximately 50%. Carbenoxolone alone had no effects on NO release in nonpregnant UA but was decreased in pregnant UA. These results suggest that cortisol potentiates NE-mediated contractions by decreasing NO release and increasing NE-binding affinity to alpha(1)-adrenoceptors in nonpregnant UA. Pregnancy attenuates UA sensitivity to cortisol, which may be mediated by increasing type-2 11-beta HSD activity in UA.

Effects of high sodium intake on cardiovascular aldosterone synthesis in stroke-prone spontaneously hypertensive rats

OBJECTIVES

Aldosterone is synthesized in extra-adrenal tissues such as the vasculature, heart and brain. The mechanisms underlying the effect of high salt intake on the development and acceleration of vascular injury and cardiac hypertrophy in the stroke-prone spontaneously hypertensive rats (SHRSP) are still not clear. The goal of this study was to determine whether high salt intake increases cardiovascular aldosterone synthesis in SHRSP.

METHODS

Four-week-old SHRSP were given tap water or 0.9% NaCl solution for hydration for 4 weeks in addition to a normal salt diet. Isolated rat mesenteric arteries and hearts were perfused for 2 h, and the perfusate was analysed by high-performance liquid chromatography. The concentrations of aldosterone synthase gene (CYP11B2) mRNA and angiotensin II receptor (AT1R) mRNA were determined by competitive polymerase chain reaction.

RESULTS

Salt-loaded SHRSP had higher blood pressures than SHRSP with normal salt intake. Plasma aldosterone concentrations and plasma renin activity were decreased by high salt intake. Aldosterone production, the expression of CYP11B2 mRNA and AT1R mRNA in mesenteric arteries and hearts were significantly increased by high salt intake.

CONCLUSIONS

These results suggest that high salt intake increases aldosterone production and expression of the AT1R mRNA in the cardiovascular tissue in SHRSP, which may contribute to the development of malignant hypertension in salt-loaded SHRSP.

Disorders of mineralocorticoid synthesis

Abnormalities of mineralocorticoid synthesis and/or metabolism profoundly affect the regulation of electrolyte and water balance and of blood pressure. Characteristic changes in extracellular potassium, sodium and hydrogen ion concentrations are usually diagnostic. Serious deficiency may be acquired, for example in Addison's disease, or inherited. In most of the inherited syndromes, the precise molecular changes in specific steroidogenic enzymes have been identified. Mineralocorticoid excess may be caused by aldosterone or 11-deoxycorticosterone by inadequate conversion of cortisol to cortisone by 11beta-hydroxysteroid dehydrogenase type 2 in target tissues (see Chapter 4), by glucocorticoid receptor deficiency or by constitutive activation of renal sodium channels. Changes in electrolyte balance and renin as well as the abnormal pattern of corticosteroid metabolism are usually diagnostic. Where these abnormalities are inherited (e.g. 11beta- or l7alpha-hydroxylase deficiencies, glucocorticoid remediable hyperaldosteronism (GRA), receptor defects, Liddle's syndrome), the molecular basis is again usually known and, in some cases, may provide the simplest diagnostic tests. Primary aldosteronism, although readily identifiable, presents problems of differential diagnosis, important because optimal treatment is different for each variant. Moreover, the mechanisms by which the variants develop are poorly understood. Finally, a significant proportion of patients with essential hypertension show characteristics of mild mineralocorticoid excess, for example low renin levels. Is this relevant to pathophysiology and, if so, is the effect induced via classic mechanisms of action or through newly discovered direct actions on the brain, heart and blood vessels? These questions are the subject of current research.

Insights Into Glucocorticoid-Associated Hypertension

The association between excess glucocorticoids and hypertension has been much discussed but poorly understood. From both clinical observations and laboratory studies, it is clear that glucocorticoids exert their effects at many different sites responsible for blood pressure regulation. Isoforms of the enzyme 11ss-hydroxysteroid dehydrogenase (11ss-HSD), located in steroid-responsive tissues, metabolize endogenously produced glucocorticoids. These enzymes limit steroid access to mineralocorticoid and/or glucocorticoid receptors. In the kidney, synthetic and endogenous glucocorticoids are capable of enhancing transepithelial sodium transport in the presence of 11ss-HSD inhibition. Proximal tubule reabsorption of sodium can be indirectly augmented after chronic exposure to glucocorticoids. In this segment, steroids have a permissive effect, increasing the expression of both Na(+), K(+) adenosine triphosphatase along the basolateral membrane and Na(+)-H(+) exchanger along the apical membrane of epithelial cells. Although glucocorticoids themselves produce no increase in sodium reabsorption in this segment, angiotensin II-stimulated sodium transport is significantly greater in proximal tubular cells pretreated with glucocorticoids. The increased transport in distal renal segments is more direct and stems in part from glucocorticoid cross-over binding to mineralocorticoid receptors. In vascular tissue, synthetic and endogenous glucocorticoids, after inhibition of the dehydrogenase reaction, magnify the response to circulating vasoconstrictors. The effects of glucocorticoids in vascular tissue is indirect, upregulating the expression of receptors to many vasoconstrictors and downregulating the effects of potential vasodilators. Thus, glucocorticoids have the potential to alter both circulating volume and vascular resistance.

Perinatal development and adult blood pressure

A growing body of evidence supports the concept of fetal programming in cardiovascular disease in man, which asserts that an insult experienced in utero exerts a long-term influence on cardiovascular function, leading to disease in adulthood. However, this hypothesis is not universally accepted, hence animal models may be of value in determining potential physiological mechanisms which could explain how fetal undernutrition results in cardiovascular disease in later life. This review describes two major animal models of cardiovascular programming, the in utero protein-restricted rat and the cross-fostered spontaneously hypertensive rat. In the former model, moderate maternal protein restriction during pregnancy induces an increase in offspring blood pressure of 20-30 mmHg. This hypertensive effect is mediated, in part, by fetal exposure to excess maternal glucocorticoids as a result of a deficiency in placental 11-ss hydroxysteroid dehydrogenase type 2. Furthermore, nephrogenesis is impaired in this model which, coupled with increased activity of the renin-angiotensin system, could also contribute to the greater blood pressure displayed by these animals. The second model discussed is the cross-fostered spontaneously hypertensive rat. Spontaneously hypertensive rats develop severe hypertension without external intervention; however, their adult blood pressure may be lowered by 20-30 mmHg by cross-fostering pups to a normotensive dam within the first two weeks of lactation. The mechanisms responsible for this antihypertensive effect are less clear, but may also involve altered renal function and down-regulation of the renin-angiotensin system. These two models clearly show that adult blood pressure is influenced by exposure to one of a number of stimuli during critical stages of perinatal development.

Aldosterone and vascular damage

Although the aldosterone escape mechanism is well known, aldosterone has often been neglected in the pathophysiologic consequences of the activated renin-angiotensin-aldosterone system in arterial hypertension and chronic heart failure. There is now evidence for vascular synthesis of aldosterone aside from its secretion by the adrenal cortex. Moreover, aldosterone is involved in vascular smooth muscle cell hypertrophy and hyperplasia, as well as in vascular matrix impairment and endothelial dysfunction. The mechanisms of action of aldosterone may be either delayed (genomic) or rapid (nongenomic). Deleterious effects of aldosterone leading to vascular target-organ damage include (besides salt and water retention) decreased arterial and venous compliance, increased peripheral vascular resistance, and impaired autonomic vascular control due to baroreflex dysfunction.

Maintenance of maternal diet-induced hypertension in the rat is dependent on glucocorticoids

Recent epidemiological evidence suggests that adult cardiovascular risk is determined by birth weight and factors that influence birth weight, such as maternal nutrition. Data from animal models suggest that an interaction between nutrition and glucocorticoid hormones "programs" increased risk of adult hypertension. Increased fetal exposure to maternal glucocorticoids that is proposed to occur from a reduction in the placental barrier to maternal glucocorticoid, 11beta-hydroxysteroid dehydrogenase, is suggested to program hypertension in the resultant offspring from both glucocorticoid-treated and maternally protein-restricted rats. The extent to which postnatal glucocorticoid stimulation may influence the progression of hypertension in the offspring from protein-restricted rat dams was assessed in 6-week-old male Wistar rats, prenatally exposed to either an 18% casein (control) or 9% casein (low protein) diet. Rats from each dietary group were sham operated, adrenalectomized or adrenalectomized, and treated with 20 mg corticosterone/kg body weight per day. Before surgery, systolic blood pressure was significantly higher in the low protein-exposed rats compared with controls (165+/-3.8 versus 142+/-3.3 mm Hg, P<.0001). Adrenalectomy of the low protein-exposed animals significantly reduced the blood pressure to control levels, while corticosterone replacement restored the hypertensive state. No effect of adrenalectomy on blood pressure was observed in 18% casein controls. In both dietary groups adrenalectomy decreased brain, but not hepatic, glucocorticoid-sensitive enzyme activities and corticosterone treatment elevated activities of all enzymes. The data suggest that maternal diet-induced hypertension is dependent on an intact adrenal gland postnatally and that glucocorticoids are key trophic agents in maintaining the high blood pressure.

A comparative study of cardiovascular, endocrine and behavioural effects of betamethasone and dexamethasone administration to fetal sheep

1. Chronically instrumented, late-gestation fetal sheep were prepared to: (1) characterize cardiovascular, endocrine and behavioural effects of fetal treatment with clinical doses of betamethasone and dexamethasone; (2) define specific differences, if any, in the actions of betamethasone and dexamethasone of measured fetal responses; and (3) assess the contribution of changes in peripheral vascular resistance to the glucocorticoid-induced hypertension. 2. Following baseline, either saline (n = 9), betamethasone (n = 9), or dexamethasone (n = 6) was infused for 48 h in fetal sheep commencing at 125 days of gestation. A pronounced increase in fetal blood pressure occurred following both betamethasone and dexamethasone treatment. The nature and magnitude of this increase was similar following treatment with either glucocorticoid. 3. To address possible mechanisms contributing to the glucocorticoid-induced fetal hypertension, fetal plasma catecholamine levels and changes in fetal femoral haemodynamics were assessed following fetal glucocorticoid treatment. A fall in fetal plasma noradrenaline and adrenaline concentrations occurred during betamethasone and dexamethasone treatment. In contrast, a progressive femoral vasoconstriction occurred during betamethasone treatment. 4. A modest fall in the incidence of fetal breathing movements occurred during fetal treatment with either betamethasone or dexamethasone. The magnitude of this reduction was similar with treatment of either glucocorticoid. The fall in fetal breathing during betamethasone and dexamethasone treatment was not associated with a fall in the incidence of fetal low voltage electrocortical activity. 5. Our results indicate that prenatal betamethasone and dexamethasone treatment of late-gestation fetal sheep, in doses similar to those employed clinically, is associated with fetal cardiovascular, endocrine and behavioural effects. Both betamethasone and dexamethasone induce similar increases in fetal blood pressure and similar falls in the incidence of fetal breathing movements. The pronounced betamethasone-induced fetal hypertension is associated with an increase in fetal femoral vascular resistance.

The human 11 beta-hydroxysteroid dehydrogenase type II enzyme: comparisons with other species and localization to the distal nephron

Effective glucocorticoid inactivation is currently thought to be an indispensable feature of mineralocorticoid target cells. The enzyme 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) inactivates glucocorticoids and prevents them from binding to the non-selective mineralocorticoid receptor. In the kidney it is the NAD dependent high affinity isoform (11 beta-HSD2) which is thought to endow specificity on the receptor. The recent cloning of the human, sheep and rabbit 11 beta-HSD2 enzymes permits a comparison of the enzyme from the three species. Human and rabbit enzymes are 87% identical and of similar length, while the human and sheep enzymes have only 75% identity. The last 12 residues in all three species were found to be highly divergent, but most of the ovine dishomology can be accounted for by the deletion of a single nucleotide toward the C-terminus of the protein resulting in a shift in reading frame generating a protein 27 residues longer than the human isoform. Numerous other deletions were also observed in this region of the sheep cDNA sequence. Furthermore, the rabbit cDNA also displayed a large degree of dishomology with the human sequence a short distance downstream from the termination codon. Conserved overlapping cytoplasmic translocation signals were observed in all three species, suggesting a topology whereby the enzyme is anchored into the endoplasmic reticulum by multiple hydrophobic regions in the N-terminus and the bulk of the 11 beta-HSD2 peptide is sited in the cytoplasm. A polyclonal antibody generated against the C-terminus of human 11 beta-HSD2 was used to localize the enzyme within the kidney. A high level of immunoreactive was observed in distal tubules and collecting ducts, localizing the enzyme to the same part of the nephron as the mineralocorticoid receptor. Moderate levels of staining were also seen in vascular smooth muscle cells. These results support the notion that 11 beta-HSD2 is an autocrine protector of the mineralocorticoid receptor and that it plays an important role in cardiovascular homeostatic mechanisms.

Comparison of 11 beta-hydroxysteroid dehydrogenase in spontaneously hypertensive and Wistar-Kyoto rats

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) modulates glucocorticoid interactions with mineralocorticoid and glucocorticoid receptors in vivo, by converting 11 beta-hydroxyglucocorticoids to their inactive 11-ketone derivatives. Defective 11 beta-oxidation of glucocorticoids has been associated with hypertension. The objective of this study was to investigate whether 11 beta-HSD contributes to the occurrence of hypertension in spontaneously hypertensive rats (SHRs). The liver and kidney microsomal oxidations of corticosterone (the physiological glucocorticoid in rats) in organs from juvenile (3 weeks old) and adult (3 months old) SHR and Wistar-Kyoto (WKY) rats, with NAD and NADP, show no differences between rat strains. For cortisol, with NADP, adult SHRs show (1.3-3 times; P < 0.05) lower kidney microsomal oxidation rates. The liver microsomal reduction of cortisone shows remarkable interstrain differences; with NADH, reduction is conducted only by adult WKY rats, whereas with NADPH, juvenile animals show similar reduction rates, but at adulthood, only WKYs reduce cortisone. Using Western blot analysis with antibodies against 11 beta-HSD1, positive signals are obtained only for liver microsomes, appearing somewhat lower in SHRs for juvenile but not adult animals. Urinary corticosterone/11-dehydrocorticosterone ratios (measured in adult animals) are not different between rat strains, but are elevated after administration of corticosterone in both strains (although significant only in SHRs). The data provide no indications for exaggerated stimulation of renal corticosteroid receptors, due to modified 11 beta-HSD, in SHRs. However, the experiments suggest the existence of multiple 11 beta-HSDs, in addition to 11 beta-HSD1 and 11 beta-HSD2, some of which may be modified in SHR, but the nature and physiological role of these 11 beta-HSDs is unclear.

Study on the mechanisms of glucocorticoid-induced hypertension: glucocorticoids increase transmembrane Ca2+ influx in vascular smooth muscle in vivo

Blood pressure (BP) and ex vivo influx rate of Ca2+ in excised aortae were measured in rabbits implanted with silastic rubber strips impregnated with glucocorticoids (GC) [dexamethasone (DEX) or cortisol (FK)], or carbenoxolone (CX) [inhibitor of 11 beta-hydroxysteroid dehydrogenase (11-HSD), in a large (lg) or a small (sm) (10 times smaller) concentration], or FK plus CX (sm), or DEX plus RU 38486 (a specific GC-receptor blocker). After 4-6 weeks rabbits implanted with DEX, CX (lg), and FK+CK (sm) developed hypertension. Those implanted with FK alone (yielding physiological serum concentration of FK), CX (sm), and DEX+RU 38486 did not develop hypertension. Rates of unidirectional influx of Ca2+ measured in rings of excised aortae were in all hypertensive rabbits more than twice those in the control rabbits (implanted with silastic strips not containing any steroids). In all normotensive rabbits, Ca2+ influx rates remained normal. We conclude that, in analogy with the in vitro findings in cultured vascular smooth muscle (VSM) cells treated with GC, also in vivo, the elevation of tissue levels of GC causes an increase in the influx rate of Ca2+ in VSM. We propose that this may be the main pathogenic mechanism of GC-induced hypertension.

Effects of prolonged (48 h) infusion of cortisol on blood pressure, renal function and fetal fluids in the immature ovine foetus

1. This study describes the effects of prolonged (48 h) infusion of cortisol into ovine foetuses (100-110 days of gestation: term is 150 days) at a time when endogenous plasma cortisol concentrations are < 5 nmol/L. 2. In four chronically cannulated foetuses (107 +/- 0.9 day) the infusion of saline (0.9% NaCl; w:v 0.19 mL/h, 48 h) had no effect on blood pressure, renal function, or composition of amniotic and allantoic fluids. 3. In six foetuses (107 +/- 1 day) the infusion of cortisol (250 micrograms/h) increased plasma cortisol concentrations from 4.1 +/- 0.7 to 118 +/- 9 nmol/L (P < 0.001), increased mean arterial pressure from 34 +/- 1 to 40 +/- 1 mmHg (P < 0.001), increased glomerular filtration rate (P < 0.05), urine flow rate, and free water clearance (P < 0.01). 4. There was a significant increase in excretion rates of potassium and creatinine as a result of cortisol infusion, but no natriuresis, indicating some functional maturation of the fetal kidney. 5. Cortisol infusion had no effect on the volumes of amniotic and allantoic fluids; allantoic fluid composition was unchanged; significant decreases occurred in amniotic fluid osmolality, sodium and chloride concentrations, and in lung liquid osmolality, potassium, creatinine, magnesium, glucose and fructose concentrations. 6. Thus prolonged exposure of the immature ovine foetus to elevated cortisol concentrations produced significant alterations in the water and electrolyte balance of the foetus.

Nitric oxide- and hydrogen peroxide-mediated gene expression by glucocorticoids and FK506 in histamine paw edema of mice

An immunosuppressant FK506 binds with a component (hsp 56) of glucocorticoid receptor (GR) complex. Dexamethasone (Dex) never suppressed histamine paw edema of mice before 1 hr after its dosing as new protein(s) synthesis is required. However, FK506 (0.01-10 mg/kg, oral) 1.5 hr before 0.1 mg/kg Dex (s.c.), suppressed edema at 30 min. This suppression and that at 3 hr, were abolished by nitric oxide (NO) synthesis inhibitors (1-300 mg/kg). Nitroprusside (NO donor), catalase and molybdate (GR complex stabilizing protease inhibitor) enhanced the suppression. FK506, not cyclosporin A, was demonstrated for the first time in vivo to enhance GR and a hypothesis is proposed that FK506 might enhance GR and AP-1 signalings in a system reciprocally controlled by NO and H2O2.