Glucocorticoid receptor polymorphism, skin vasoconstriction, and other metabolic intermediate phenotypes in normal human subjects

Abstract

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, 11 beta-hydroxysteroid dehydrogenase activity [ratio of tetrahydrocortisol (THF) to tetrahydrocortisone (THE) metabolites] was not affected by genotype. The relative activities of 5 alpha- and 5 beta-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.