The Role of Aldosterone on Augmented Exercise Pressor Reflex in Hypertension
The Role of Aldosterone on Augmented Exercise Pressor Reflex in Hypertension
Hypertensive patients often show an exaggerated rise in blood pressure during exercise
 through overactivity of the exercise pressor reflex. An increasing body of evidence suggests
 a role for aldosterone in augmenting the exercise pressor reflex in hypertensive humans. We
 hypothesize that this effect of aldosterone is mediated by its direct action on the central
 nervous system and that administration of mineralocorticoid receptor antagonists constitute
 an effective treatment for EPR overactivity in hypertension, independent of reductions in
 resting BP.
Hypertensive patients are known to display exaggerated rise in blood pressure (BP) during
 exercise but the underlying mechanisms are poorly understood.

 Traditionally, muscle afferents were dichotomized as metaboreceptors, which are activated
 slowly and only during intense or ischemic muscle contraction, or mechanoreceptors, which
 respond quickly to even mild deformation of their receptive fields. The increase in
 sympathetic nerve activity and BP caused by activation of these receptors, known as exercise
 pressor reflex, is normally buffered by activation arterial baroreceptors, which are reset to
 operate at higher BP range but at the same level of sensitivity. Mechanisms responsible for
 overactive exercise pressor reflex in hypertension remain unknown, but an increasing body of
 evidence suggested a role for aldosterone in regulating resting central sympathetic outflow
 in both hypertensive rats and humans.

 Experiments will be performed on 3 groups of subjects 1) stage I (140-159/90-99 mmHg)
 subjects with essential hypertension, 2) stage I hypertensive subjects with Primary
 Aldosteronism (PA), and 3) normotensive controls. All participants will attend a baseline
 study visit, which will include a physical examination, a medical history review, vital sign
 measurements, and blood and urine collection. Small electrodes will be used to measure muscle
 nerve activity while the subjects perform a series of exercises that include passive arm
 cycling, active arm cycling, rhythmic hand grip, sustained hand grip and cold pressor test.
 Muscle blood flow will be measured before and after hand grip exercises.

 A subgroup of subjects with essential hypertension and PA will be assigned to receive
 Eplerenone or Amlodipine on a randomized, double-blinded design. Participants will attend two
 weeks visits over a period of 16 weeks. Study visits include measurement of vital signs and
 blood samples collection. After completing 8 weeks on each medication, muscle nerve activity
 will be measured while performing the same exercises described in the baseline study visit.
Inclusion Criteria:

 -  Experiments will be performed on 3 groups of nondiabetic human subjects:

 -  1) stage I (140-159/90-99 mmHg) subjects with essential hypertension.

 -  2) stage I hypertensive subjects with primary aldosteronism

 -  3) normotensive controls.

 Exclusion Criteria:

 -  1) Any evidence of cardiopulmonary disease, left ventricular hypertrophy or systolic
 dysfunction by echocardiography.

 -  2) Blood pressure averaging ≥160/100 mmHg

 -  3) Estimated glomerular filtration rate (eGFR) < 90 mL/min/1.73m2

 -  4) Diabetes mellitus or other systemic illness

 -  5) Pregnancy

 -  6) Hypersensitivity to nitroprusside, phenylephrine, amlodipine or eplerenone

 -  7) Any history of substance abuse or current cigarette use

 -  8) Any history of psychiatric illness

 -  9) History of malignancy