The role of the hypothalamic-pituitary-adrenal (HPA) axis in the regulation of blood pressure

The role of the HPA axis in blood pressure regulation was examined in 6 normal male volunteers by comparing haemodynamic and hormonal effects of placebo, captopril, and dexamethasone given in random order for two days. The average 24-hour systolic and mean arterial pressures on placebo (135+/-6 and 93+/-2mmHg respectively) were significantly higher than on captopril (118+/-1 and 85+/-1mmHg respectively, p < 0.05) but there were no significant changes on dexamethasone compared with placebo (128+/-3 and 89+/-3mmHg respectively). There were no differences in the average 24-hour diastolic blood pressures or heart rates, nor the day-night differences, night:day ratios or percentage changes in blood pressure and heart rate between treatments. Captopril significantly increased active plasma renin concentration, whilst dexamethasone decreased cortisol concentration. These results confirm the role of the renin-angiotensin system in the regulation of blood pressure in normal subjects but suggest that the HPA axis does not play a major role in determining ambulatory blood pressure or day-night variability in the short term.