Endocrine Abstracts (2007) 13 OC24

Acute aldosterone responses to ACTH predict both cortisol responses and blood pressure

Rebecca Reynolds1, Brian Walker1, David Phillips2, Holly Syddall2, Eleanor Davies3, Robert Fraser3 & John Connell3

1Endocrinology Unit, Queen’s Medical Research Institute, University of Edinburgh, Edinburgh, United Kingdom; 2MRC Epidemiology Resource Centre, Southampton, United Kingdom; 3Glasgow Cardiovascular Research Centre, University of Glasgow, Glasgow, United Kingdom.

Background: Aldosterone levels in plasma are reported to be associated with risk of hypertension. Aldosterone secretion from the zona glomerulosa is regulated acutely by the renin/angiotensin system and plasma potassium. The role of ACTH in regulation of aldosterone secretion is disputed.

Aim: We have utilised a large population study of middle aged adults to test the extent to which acute aldosterone responses to ACTH are associated with cortisol responses and predict blood pressure.

Methods: We used stored serum samples from 205 men and 106 women aged 67–78 y, from Hertfordshire UK. None had pituitary or adrenal disease or were receiving steroid therapy. Participants had undergone an overnight low dose (0.25 mg) dexamethasone (dex) suppression test and a low dose (1 μg) ACTH stimulation test.

Results: Aldosterone concentrations were skewed and were log-transformed for analysis; median aldosterone was 6.22 ng/dl (range 0.15–38.74), and was higher in men than women (6.95 vs 4.89, P<0.0001). There were significant correlations between aldosterone and blood pressure measurements in men (systolic r=0.21, P=0.004; diastolic r=0.17, P=0.02) with a similar trend in women (systolic r=0.17, P=0.08). There were significant correlations between post-dex aldosterone concentrations and cortisol (r=0.36, P<0.0001 for men and r=0.29, P=0.003 for women) and similar associations for ACTH stimulated values. Aldosterone levels were significantly correlated with fasting plasma cortisol measured 6 years previously in men (r=0.31, P<0.001).

Discussion: Our findings add support for the notion that aldosterone is an important regulator of blood pressure. These data identify a common component in regulation of aldosterone and cortisol; the correlation of the stimulated levels suggest that ACTH influences baseline aldosterone synthesis. Our findings suggest that ACTH interacts with factors such as angiotensin II and potassium to determine the set point of aldosterone secretion and identify a mechanism whereby the pituitary may contribute to chronic blood pressure regulation.

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