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The Journal of Clinical Endocrinology & Metabolism Vol. 83, No. 6 1846-1852
Copyright © 1998 by The Endocrine Society


Original Studies

Glucocorticoid Receptor Polymorphism, Skin Vasoconstriction, and Other Metabolic Intermediate Phenotypes in Normal Human Subjects1

Maurizio Panarelli2, Christine D. Holloway, Robert Fraser, John M. C. Connell, Mary C. Ingram, Niall H. Anderson and Christopher J. Kenyon

Clinical Biochemistry, Royal Infirmary (M.P.), Edinburgh; Medical Research Council Blood Pressure Group, Western Infirmary (C.D.H., R.F., J.M.C.C., M.C.I., N.H.A.), Glasgow; and Molecular Medicine Centre, Western General Hospital (C.J.K.), Edinburgh, Scotland

Address all correspondence and requests for reprints to: Christopher J. Kenyon, Molecular Medicine Center, Western General Hospital, Edinburgh, EH4 2XU, United Kingdom. E-mail: cjk{at}srv0.med.ed.ac.uk


    Abstract
 Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Genetic variation of the glucocorticoid receptor (GR) locus is associated with differences in blood pressure. To define the intermediate phenotypes associated with this variation, we investigated the biochemical and clinical significance of a BclI restriction fragment length polymorphism of the GR locus in 64 normal male volunteers. Blood samples were genotyped as either AA (homozygous large allele; n = 6), Aa (heterozygous; n = 51), or aa (homozygous small allele, n = 7). Four primary glucocorticoid variables were measured including GR binding characteristics and glucocorticoid-sensitive lysozyme release of leukocytes in vitro and the blanching response of forearm skin to budesonide. A large number of secondary variables (urinary and plasma steroid measurements, blood pressure and indices of body fat metabolism, and routine biochemical and hematological measurements) were also considered. In vivo sensitivity to budesonide was greater in AA than aa individuals (mean ± SE EC50 values: 13 ± 5 and 42 ± 10 ng; P < 0.01). In contrast, leukocytes of AA subjects tended to have lower affinity and reduced sensitivity for dexamethasone, although these effects were not statistically significant. Based on urinary steroid measurements, 11ß-hydroxysteroid dehydrogenase activity [ratio of tetrahydrocortisol (THF) to tetrahydrocortisone (THE) metabolites] was not affected by genotype. The relative activities of 5{alpha}- and 5ß-reductase activity (allo-THF/THF + THE) appeared lower in AA than aa subjects (0.22 ± 0.04 cf. 0.33 ± 0.06; P < 0.005) but were not judged to be significantly different when corrected for multiple comparisons. Single and multivariate analyses were carried out to determine which variables influence GR binding characteristics and glucocorticoid responsiveness and to see whether cardiovascular risk factors (blood pressure and body fat) were influenced by glucocorticoid-dependent functions. Only 15–20% of the variations in the dissociation constant (Kd) and maximum binding capacity (Bmax) were influenced by other variables; plasma cholesterol was the most important for affinity and plasma sodium concentration for binding capacity. Multivariate analysis showed that several factors including GR genotype and urinary cortisol account for 10% of the variation of in vivo responses to glucocorticoid hormones; plasma calcium concentration was the only variable that contributed to in vitro sensitivity of leukocytes to dexamethasone. Glucocorticoid-dependent responses were of negligible importance in determining blood pressure or percentage body fat within the narrow physiological ranges of the present study. We conclude that GR genotype affects steroid sensitivity in a tissue-specific manner because of altered GR function or possibly because of linkage to a locus that controls hormone access to the receptor by influencing steroid metabolism.


    Introduction
 Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
IN MAN, mutations of the glucocorticoid receptor (GR) have been identified that affect cardiovascular functions and intermediary metabolism (1, 2). In addition, the DNA restriction enzyme BclI has identified a common polymorphism of the GR locus with two allelic variants (3). Two independent clinical investigations have suggested that this GR polymorphism is linked to altered GR function. Watt et al. (4) screened patients to identify genetic factors that determine blood pressure. The larger GR allele was one of very few factors that appeared to be more common in a group genetically predisposed to develop hypertension. Similarly, the larger allele was more common in obese hyperinsulinemic women than lean controls (5). Hypertension and obesity are recognized cardiovascular risk factors that are often linked (6, 7). Clearly, it is important to establish whether glucocorticoid responsiveness is altered in hypertensive and obese patients in keeping with this polymorphic genotype. However, we are aware that, in both conditions, neuroendocrine adaptations could secondarily affect glucocorticoid hormone secretion and function. To avoid the confounding effects of disease therefore, we assessed GR function in relation to genotype in normotensive subjects.

We characterized phenotype in subjects of known GR genotype by assessing binding of dexamethasone in mononuclear leukocytes and by measuring glucocorticoid responsiveness in the same population of cells. In addition to these in vitro tests, we examined the relationship between genotype and in vivo vascular response to glucocorticoids as the degree of blanching following overnight, direct exposure of discrete areas of skin to hormone (8).

Endogenous glucocorticoids such as cortisol could increase blood pressure via glucocorticoid (type 2) or mineralocorticoid (type 1) receptors (9). Indeed, it is thought that the hypertension and hypokalemia that are associated with mutations of GR are because of excess mineralocorticoid activity (10, 11). In these patients, plasma cortisol, which is raised because of impaired GR, binds to type 1 mineralocorticoid receptor (MR). Accordingly, in the present study, we have assessed separately variables that conventionally are regarded as mineralocorticoid receptor-dependent (plasma renin, plasma aldosterone, hematocrit, and urinary Na/K) or GR-dependent functions (white blood cell number, plasma cortisol, and lipid metabolism).

Finally, we took into account recent hypotheses suggesting that corticosteroid hormone action is modulated by steroid metabolizing enzymes that govern access to receptors (12, 13) and enhance (14, 15) as well as inhibit activity. Urinary steroid metabolite ratios have been measured to give an indication of enzyme activities.


    Subjects and Methods
 Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Subjects

Sixty-four normotensive Caucasian male subjects age 18–40 yr were studied. A careful family history was obtained with particular attention to hypertension, diabetes mellitus, and cardiovascular disease. All subjects provided written informed consent. The study was approved by the Ethical Committee of the Western Infirmary Trust.

Study design

Urine was collected for 24 h before the tests. All subjects arrived at 0830 h. The mean of two blood pressure measurements was recorded after 30 min recumbency and again after 5 min in an upright position, using a Hawksley random zero sphygmomanometer. Body mass index (BMI) was calculated as weight/height2. Measurements of skinfold thickness (16) were used to estimate body density after normalizing for age-dependent variations; these data are presented as percentage body fat. Blood for biochemical tests was withdrawn from an antecubital vein after the subjects had been recumbent for at least 30 min. On a separate occasion, volunteers arrived between 1500 and 1700 h and again at 0830 h on the following day for a skin vasoconstriction test.

Skin blanching

Various amounts (0, 4.9, 19.5, 78.1, 313, 1250, and 5000 ng in 5 µL ethanol) of budesonide (Astra, Kings Langley, UK) were applied in duplicate, in random order, to discrete areas (49 mm2 separated by silicone grease) of the flexor surface of the forearm as described by Teelucksingh et al. (17). After drying, the area was covered with polyester film for 18 h. The degree of blanching was assessed on a scale of 0–3 by a blind independent observer. For each volunteer, a response curve was plotted and an EC50 value for budesonide calculated.

Leukocyte studies

As previously described (18), mononuclear leukocytes prepared from 50 mL citrated blood were used to measure both GR binding characteristics and dexamethasone-sensitive lysozyme release. Dissociation constants (Kd) and binding capacity (sites/cell) for dexamethasone were calculated using the curve-fitting program Ligand (19).

Lysozyme activity in the supernatant was measured photometrically as lysis of Micrococcus lysodeikticus using human recombinant lysozyme as a standard. An IC50 value for dexamethasone was calculated for each individual.

Genotyping of GR

Total genomic DNA was extracted from white blood cells as described (20). Approximately 10 µg was digested using the restriction enzyme BclI (3, 21). Restriction fragments were separated by electrophoresis on 0.8% agarose gel and transferred onto Hybond-N nylon membrane (Amersham, Buckinghamshire, UK) by Southern blotting (4). Fragments were identified as either A [4.5 kilobases (kb)] or a (2.8 kb) by hybridizing the membranes using a 32P-labeled 4.3-kb human GR complementary DNA (22) in 7% SDS/0.5 M phosphate buffer (pH 7.0) at 65 C overnight. Nonspecific binding was washed off in 2x standard saline citrate in 0.1% SDS at 65 C. The membranes were exposed to Hyperfilm MP (Amersham), with intensifying screens, for at least 3 days at 70 C.

Biochemical investigations

Routine biochemical and hematological measurements (electrolytes, cholesterol, creatinine, hematocrit, and differential blood cell counts) were carried using autoanalyzers. Aldosterone and cortisol in plasma and urine were measured by standard RIA (Diagnostic Products, Los Angeles, CA). Plasma renin concentration was measured by RIA of generated angiotensin I (AI) (23). Urinary steroid metabolites were analyzed by gas chromatography-mass spectrometry as described previously (24).

Statistical analyses

The summary statistics are presented throughout as means and SE. For each individual variable, mean measurements for each genotype were compared by a one-way ANOVA. The significance level for the four variables of primary interest [receptor Kd and maximum binding capacity (Bmax) for dexamethasone, IC50 of lysozyme release by dexamethasone and skin vasoconstriction by budesonide] was set at P < 0.05, and that for 24 secondary variables at P < 0.0021 (Bonferroni correction for multiple comparisons). Variables with positively skewed distributions were analyzed on a logarithmic scale. Subsequently, pairwise differences were examined by Bonferroni corrected two sample t tests. Simple and multiple linear regression was used to investigate the factors influencing glucocorticoid binding characteristics, glucocorticoid responsiveness, mineralocorticoid-dependent variables, and cardiovascular risk factors with important covariates being selected stepwise for multivariate models.


    Results
 Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
Phenotypes of GR alleles

Restriction fragment length polymorphism analysis identified 6 subjects homozygous for the A allele, 7 homozygous for the a allele, and 51 heterozygotes. There were no significant differences between these genetic groups in terms of age, blood pressure, BMI, and percentage of body fat (Table 1Go). Leukocytes from AA subjects tended to have higher Kd values for dexamethasone (7.7 ± 1.5, 6.0 ± 0.4, 5.9 ± 0.8 for AA, Aa, and aa subjects, respectively) and lower sensitivity for inhibitory effects of dexamethasone (Fig. 1BGo) than those from aa subjects (and intermediate values for the Aa group), but these differences did not achieve statistical significance. The number of dexamethasone binding sites/cell (Bmax) did not differ between genotypes (AA: 6050 ± 750; Aa: 5540 ± 230; aa: 5100 ± 750). AA subjects were significantly more sensitive (P = 0.012, log transformed data) than aa subjects to topical budesonide; the Aa group had an intermediate EC50 value (Fig. 1AGo).


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Table 1. Clinical variables of normal subjects with different glucocorticoid receptors genotype

 


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Figure 1. In vivo and in vitro sensitivity to glucocorticoids. A, Budesonide-induced skin vasoconstriction (EC50 values). B, Dexamethasone-sensitive inhibition of lysozyme release from leukocytes (IC50 values) in subjects with different GR genotypes. Values are means ± SE; n = 6, 51, and 7 for AA, Aa, and aa genotypes, respectively.

 
There were no significant differences between genotypes in plasma and urinary electrolyte levels in glomerular filtration rate and creatinine clearance or in plasma cholesterol and triglyceride concentrations (Table 2Go). Plasma renin concentration was also similar in the three groups (AA: 38.7 ± 11.7; Aa: 29.7 ± 2.3; aa: 34.1 ± 7.1 ng AI/mL-1/h-1). Plasma and urine corticosteroid concentrations are summarized in Table 3Go. There were no significant differences between groups, although plasma and urinary cortisol values tended to be higher in AA subjects than in aa subjects. The ratio of tetrahydrocortisol (THF) + allo-THF to tetrahydrocortisone (THE), an index of 11ß-hydroxysteroid dehydrogenase (11ß-HSD) activity, was not significantly different between groups (Fig. 2AGo). The ratio of allo-THF to THF + THE (Fig. 2BGo) appeared higher in aa subjects than in AA subjects, with an intermediate value for heterozygotes (P = 0.027). This is suggestive of increased 5{alpha}-reductase (or lower 5ß-reductase) activity in the aa group. However, the P value for a comparison between AA and aa groups was 0.005, which did not meet the criteria of significance (P < 0.0021) when corrected for multiple comparisons of secondary variables.


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Table 2. Plasma lipids, plasma and urinary electrolytes, and creatinine clearance in normal volunteers with different glucocorticoid receptor genotype

 

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Table 3. Summary of plasma and urinary steroid values

 


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Figure 2. Ratios of urinary THF and cortisone metabolites in subjects with different GR genotype. A, Ratio of THE/THF metabolites reflects 11ß-HSD. B, Ratio of 3{alpha}5{alpha}/3{alpha}5ß tetrahydro metabolites indicates relative 5{alpha}- and 5ß-reductase activity. Values are means ± SE; n = 6, 51, and 7 for AA, Aa, and aa genotypes, respectively.

 
Correlations

Single and multiple regression analyses were carried out to determine which variables influenced, first, GR binding characteristics of dexamethasone in leukocytes (Kd and Bmax) and, second, responsiveness to glucocorticoids in vitro (dexamethasone-induced inhibition of lysozyme release) and in vivo (budesonide-induced skin blanching). We also considered whether various indices of glucocorticoid function influenced variables that are regarded as mineralocorticoid-dependent variables (urinary Na/K ratio and plasma renin activity) or cardiovascular risk factors (percent body fat and mean blood pressure).

Single variate analysis showed that loge (Kd) values for dexamethasone and plasma cholesterol values correlated with each other (P < 0.05; Fig. 3AGo). In designing a multivariate model to consider whether other variables might influence Kd and Bmax values in the present study, we selected those which, from a table of correlation values, appeared most probable to have causative effects. By single variate analysis, loge (Kd) values correlated weakly (not significantly) with plasma triglycerides (negative), GR genotype, plasma and urinary cortisol, and urinary cortisol metabolites. When these factors were subjected to multivariate analysis, 20% of loge (Kd) variation was accounted for by a model that included plasma cholesterol, Bmax, and the 5{alpha} ratio of reduced cortisol metabolites (P = 0.002). Similarly, the model that accounted for the biggest proportion of the variation in Bmax (16%) included just two variables, Kd and plasma Na+ (P < 0.01); plasma Na+ correlated with Bmax when considered in single variate analysis (Fig. 3BGo).



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Figure 3. Relationships between Kd values for dexamethasone in leukocytes and plasma cholesterol concentration (n = 62) (A) and plasma sodium concentration and dexamethasone binding capacity in leukocytes (n = 64) (B).

 
By single variate analysis, none of the variables that might be expected to control glucocorticoid hormone activity (Kd, Bmax, plasma or urinary cortisol, and cortisol metabolites) correlated with loge (IC50) values for dexamethasone-induced inhibition of lysozyme release, whereas other variables that were not obviously related to in vitro glucocorticoid responsiveness (plasma calcium, urinary androstenedione, and urinary calcium clearance) were found to contribute 17% of the variation (P = 0.005) in IC50 values.

Budesonide-sensitive skin blanching (in vivo responsiveness to glucocorticoids) correlated with only one variable, urinary cortisol (P < 0.05; single variate analysis). Urinary cortisol and GR genotype accounted for approximately 10% of variation in skin sensitivity in a multivariate model (P = 0.031).

By single variate analysis, GR binding characteristics did not seem important determinants of mineralocorticoid activity. In multivariate analysis, a model that included urinary aldosterone and allo-THF and plasma sodium concentration accounted for 28% of the variation in urinary Na/K ratio (P < 0.0005). Plasma renin levels were bimodally distributed, with a clear subgroup of patients with values >40 ng AI/mL/h. When high and low renin groups were compared, there were no significant differences in any of the glucocorticoid-dependent variables. Separate regression analysis of high (n = 13) and low renin groups (n = 45) showed that white blood cell number correlated significantly with high renin values (P = 0.033).

Two cardiovascular risk factors, blood pressure and body fat, were analyzed in some detail. Using multivariate analysis, a model that included percentage body fat and the ratio of urinary reduced cortisol metabolites accounted for 22% of variation in mean blood pressure (P = 0.001). Three principal factors contributed 29% to variation in percentage body fat: age, sodium excretion, and glomerular filtration rate (P < 0.0005).


    Discussion
 Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
If the BclI polymorphism affects GR phenotype, several physiological consequences might be predicted. Acting through the pituitary-adrenal axis, abnormal steroid binding or overexpression of the GR gene should be reflected in generally higher or lower levels of plasma and urinary cortisol, depending on whether GR function is impaired or enhanced. Acting in concert with other physiological variables, changes in GR function could potentiate or inhibit factors controlling blood pressure or other aspects of intermediary metabolism. GR genotype had limited effects; only skin vasoconstriction was significantly different in subjects homozygous for the larger allele (AA) as compared with those homozygous for the smaller allele (aa), although aspects of urinary cortisol metabolism also tended to be different. Neither plasma cortisol concentration nor urinary free cortisol concentrations were affected by genotype, nor was there strong evidence of a relationship with receptor binding characteristics in leukocytes. These results can be interpreted in three ways: a) GR function may be affected only in selected tissues; b) other factors compensate for altered GR binding; and/or 3) the BclI polymorphism is a marker of dysfunctional gene(s) that influence, but are separate from, the GR gene. Each possibility is discussed in turn.

The restriction site for BclI that gives rise to the GR polymorphism lies out with the exonic region of the gene and conceivably might affect the GR gene promoter. Differences in the GR promoter could give rise to differences in receptor expression levels. By selectively affecting either repressor or enhancer sites within the promoter, glucocorticoid sensitivity will be increased or decreased, respectively, possibly in a tissue-specific manner. Differential usage of the promoter would explain why the skin sensitivity to budesonide of our AA subjects was enhanced compared with aa subjects, whereas white blood cell lysozyme release tended to be less sensitive to dexamethasone, and circulating cortisol concentrations were unaffected. However, mechanisms controlling the human GR promoter usage are yet to be elucidated (25).

An alternative explanation, again based on differential expression, could result from the two isoforms of GR that have recently been described (26, 27). The ß-isoform does not bind ligand itself but can competitively inhibit ligand effects mediated through the {alpha}-isoform. Because it has been suggested that {alpha} and ß are present in varying amounts in different tissues, this represents an alternative way of controlling tissue sensitivity that potentially could be influenced by GR polymorphism.

The molecular basis of glucocorticoid resistance is underinvestigated (for reviews see Ref.28). The idea of differential tissue sensitivity is to be anticipated from earlier studies (29, 30, 31). These earlier studies also described sexual dimorphism in the phenotype of glucocorticoid resistance which is why the present study was restricted to one sex. In part phenotypic, differences can be explained by an imbalance of steroid hormones leading to inappropriate activation of transcription factors (see below). More recently the importance and complexity of interactions of GR with other proteins has been appreciated (32). In the case of some patients with steroid-resistant asthma, for example, it is suggested that GR interaction with inappropriately high levels of the activating protein-1 transcription factor in peripheral mononuclear cells prevent GR from reacting with response elements on DNA (33). Glucocorticoid treatment of patients with tissue-specific resistance causes excess glucocorticoid activity at those other sites that respond normally.

GR interaction with proteins, whether other transcription factors or secondary corepressors and coactivators, often involves GR regions separate from the ligand binding domain (32, 34, 35, 36). As was recently shown (37), mutations at sites on the GR molecule that are important for protein-protein interactions may affect transactivation properties of GR in a tissue-specific manner depending on which gene pathway is involved. If such a mechanism were to be implicated in the present study, one would have to argue that the GR polymorphism marked a mutation of an additional site on an expressed region of the GR gene or of a non-GR protein that interfered with the process of GR-mediated transactivation.

Specificity of steroid hormone action can also be determined by steroid-metabolizing enzymes, which modulate hormone access to receptors. The principal enzymes involved, 11ß-HSD and 5{alpha}- and 5ß-reductases (12, 13, 38, 39, 40, 41), are expressed in a tissue-specific manner. Skin contains several steroid-metabolizing enzymes, and glucocorticoid effects are potentiated by enzyme inhibitors such as carbenoxolone (17). In contrast, leukocytes do not metabolize cortisol, and cortisol binding is unaffected by enzyme inhibitors. In the present study, budesonide and dexamethasone (poor substrates for metabolism) were tested, which makes it unlikely that steroid metabolism could directly account for variations of in vivo and in vitro sensitivity to glucocorticoids. However, if metabolism governs hormone action, this might, secondarily, modulate GR action, which would then be revealed by tests with synthetic steroids. The effect of altered metabolism and secondary changes of gene expression may be of little net importance for endogenous hormone action. Nevertheless, this analysis agrees with our observations that 5{alpha}- and 5ß-reduced cortisol metabolites tend to differ between genotypes, and supports previous observations of a relationship between the reduced metabolites of cortisol and blood pressure (24). Against this hypothesis is evidence that 11ß-HSD rather than 5{alpha}- and 5ß-reductases regulates skin sensitivity to cortisol. Moreover, urinary steroid metabolites may not necessarily reflect metabolism in skin or any other target tissue. GR genotype could be in close linkage dysequilibrium with a separate marker of cardiovascular disease. This is compatible with our findings that some but not all GR-dependent variables are affected. Thus, altered skin sensitivity could be an intrinsic property of vascular smooth muscle and altered steroid metabolism may not be correlated with skin vasoconstriction (42). However, if GR polymorphism is a function of some fundamental aspect of vascular function, one must question why other variables, more commonly associated with vascular reactivity (renin and blood pressure) were unaffected. On balance, therefore, considering that the polymorphism has been positively identified with a GR locus and because, of the many variables tested, the two that were most markedly affected by the polymorphism were associated with glucocorticoid action or metabolism, we suggest that GR function is affected by genotype.

Our primary aim was to define the phenotype of a GR polymorphism, but we also observed variations in GR binding characteristics that were greater than anticipated from our previous estimates of the interassay variation (18). This observation raised two questions. First, are Kd and Bmax values influenced by any of the other measured variables? Second, do variations in binding characteristics affect responsiveness to glucocorticoids and/or indices of mineralocorticoid activity? Single and multivariate regression analyses were used to try to answer these questions.

For Kd and Bmax values, small percentages of variation could be accounted for by other variables. Plasma cholesterol, Bmax, and GR genotype were implicated in a multivariate model of Kd variation, but only plasma cholesterol was significant when analyzed alone. Plasma cholesterol could affect steroid uptake by cells but, because glucocorticoids are known to increase plasma cholesterol, it is more likely that variations of Kd cause differences in plasma cholesterol and the other variables.

Variations of Bmax, even by single variate analysis, are associated with differences in plasma sodium. It is difficult to imagine how sodium might affect Bmax, and again it is more likely that Bmax, by influencing glucocorticoid activity, alters membrane cation transport and hence electrolyte homeostasis. In a multivariate model, Kd was the only other variable that influenced Bmax but, because the derivation of Kd and Bmax are interdependent, this may not be of significance. Neither dexamethasone-induced lysozyme release from leukocytes nor budesonide-induced skin vasoconstriction were strongly influenced by glucocorticoid receptor characteristics. Bmax, Kd, GR genotype, and plasma cortisol concentration were contributory factors in a model that accounted for 17% of leukocyte sensitivity

Renal mineralocorticoid receptors are normally protected from endogenous glucocorticoid hormones by 11ß-HSD (12, 13), but hypertension can arise if plasma cortisol overwhelms this protective mechanism (11, 43, 44). For example, mutations in GR causing glucocorticoid resistance and impaired feedback control lead to increased plasma cortisol and symptoms of mineralocorticoid excess. Despite marked variation in GR binding characteristics, neither Kd nor Bmax appeared to primarily affect either of two classical indexes of mineralocorticoid activity, suppression of plasma renin activity and decreased urinary Na/K ratios. Plasma cortisol concentrations did correlate with urinary Na/K ratios, but because plasma aldosterone concentration did too, this may reflect dual control of aldosterone and cortisol secretion.

Finally, although urinary cortisol metabolites, GR genotype, Kd, and plasma cortisol concentrations did feature as minor factors in blood pressure and percent body fat determination, we have not established that glucocorticoid hormones are involved in the development of obesity or hypertension (4, 5). Our subjects were normal volunteers without the extremes of blood pressure or BMI that were the criteria used to select patients in previous clinical studies (45, 46).

In summary, glucocorticoid-dependent vasoconstriction is affected by GR polymorphism. These data are compatible with the observation that individuals with the AA genotype are predisposed to develop hypertension or obesity. We suggest that the polymorphism does not affect the receptor affinity but may lead to tissue-specific differences in GR expression by affecting the GR promoter region. Steroid metabolism by 5{alpha}- and 5ß-reductase enzymes may also be secondarily affected. Regression analysis showed that plasma cholesterol correlated with systolic blood pressure and with leukocyte affinity for dexamethasone. Correlations of GR binding characteristics with other variables may indicate a role for glucocorticoid hormones in electrolyte homeostasis. Glucocorticoid activity was not a major determinant of blood pressure or body fat distribution within the narrow physiological limits of our volunteers, but may be one of several genetic determinants in the pathogenesis of cardiovascular disease.


    Footnotes
 
1 This work was funded by the Medical Research Council and, in part, by the Scottish Hospital Endowments Research Trust. Back

2 Awarded fellowships by the Society for Endocrinology (U.K.) and the British Hypertension Society. Back

Received October 20, 1997.

Revised February 2, 1998.

Accepted February 11, 1998.


    References
 Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

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