Urinary free cortisol: an intermediate phenotype and a potential genetic marker for a salt-resistant subset of essential hypertension.
BACKGROUND
Emerging evidence suggests a role for cortisol in essential hypertension, and preliminary reports indicate that urinary free cortisol (UFC) may be an intermediate phenotype.


OBJECTIVE
The objectives of this study were: 1) confirm bimodality of UFC, 2) assess whether UFC variations aggregate in hypertensive families, and 3) compare low-mode and high-mode UFC groups for distinguishing features.


METHODS
Subjects included 390 hypertensives and 166 normotensives from the general community.


METHODS
Subjects had blood pressure and laboratory measurements on high- and low-salt diets. Familial aggregation was evaluated in 250 hypertensive siblings from 117 families.


RESULTS
Hypertensives had higher UFC than normotensives (P<0.001) and bimodal distribution of UFC (P<0.0001). Analyses were controlled for gender and dietary sodium, which are confounding determinants of UFC. Mean low-mode UFC (33.8+/-10.6 microg per 24 h) was similar to that of normotensives. The high mode, comprising 31.3% of hypertensives, had less change in mean arterial pressure between diets than the low mode (P=0.01) without any other significant differences. Observed proportions of concordance and discordance for UFC mode differed significantly from that expected (P<0.001). Observed concordance for the high mode was twice that expected, whereas for the low mode, it was similar to that expected by chance. Family membership explained a significant proportion of variance in UFC classification (P=0.027). UFC mode of one sibling was a significant predictor of the UFC mode of the other sibling [odds ratio 6.6, 95% confidence interval (2.4-18.0), P<0.001].


CONCLUSIONS
High-mode UFC is an intermediate phenotype of hypertension associated with salt resistance and a strong familial component supporting heritability.
Chamarthi
Bindu
B
Division of Endocrinology, Diabetes, and Hypertension, Brigham and Women's Hospital and Harvard Medical School, 221 Longwood Avenue, Boston, Massachusetts 02115, USA.
Kolatkar
Nikheel S
NS
Hunt
Steven C
SC
Williams
Jonathan S
JS
Seely
Ellen W
EW
Brown
Nancy J
NJ
Murphey
Laine J
LJ
Jeunemaitre
Xavier
X
Williams
Gordon H
GH
D000328:Adult; D001794:Blood Pressure; D002648:Child; D015331:Cohort Studies; D004032:Diet; D004039:Diet, Sodium-Restricted; D005260:Female; D005819:Genetic Markers; D006801:Humans; D006854:Hydrocortisone / Q000652:urine*; D006973:Hypertension / Q000145:classification / Q000503:physiopathology / Q000652:urine*; D008875:Middle Aged; D012982:Sodium, Dietary
D005819:Genetic Markers; D012982:Sodium, Dietary; D006854:Hydrocortisone