Neural Mechanism of Aldosterone-induced Insulin Resistance

Patients with high aldosterone hormone have higher blood glucose than normal people. This study is being done to understand how aldosterone hormone affects the nerve activity that controls blood flow in the muscles and blood glucose. The information may be helpful in selecting blood pressure medications which can improve not only blood pressure but also improve blood sugar.

Patients with primary aldosteronism are known to have impaired insulin sensitivity, which is improved after removal of aldosterone-producing adenoma. In patients with essential hypertension, plasma aldosterone levels have been also shown to positively correlate with indices of insulin resistance. Mechanism underlying aldosterone-induced insulin resistance is unknown. Aldosterone has been shown to interfere with insulin signaling the vascular cells by increasing production of reactive oxygen species via activation of NADPH oxidase, resulting in decreased availability of nitric oxide (NO), the key mediator for insulin-mediated vasodilation. Treatment with mineralocorticoid receptor antagonists has been shown to improve insulin sensitivity in mice with obesity and metabolic syndrome. Aldosterone has also been shown to increase resting sympathetic vasoconstrictor activity to the peripheral circulation. However, effects of aldosterone and mineralocorticoid receptor antagonists on insulin-mediated skeletal muscle vasodilation, sympathetic activation, and vascular oxidative stress have not been assessed in humans. The investigators will collect venous endothelial cells, and measure skeletal muscle microvascular perfusion using Octafluoropropane microbubble contrast agents, and measure sympathetic nerve activity in normotensive controls (NT), stage 1 essential hypertensive subjects (ET), and patients with primary aldosteronism (PA) during hyperinsulinemic euglycemic clamp.

hypertension, blood pressure, sympathetic nerve activity, vascular oxidative stress, nitric oxide, nitric oxide synthase (eNOS), endothelium, endothelial dysfunction, endothelial cell protein expression, microvascular blood flow, flow mediated dilation, endothelial cell collection, microbubbles, Definity

We will perform following procedures: DEFINITY® infusion Flow mediated vasodilation Endothelial cell collection Microvascular perfusion assessment using Definity Microneurography

We will perform the following procedures: DEFINITY® infusion Human Recombinant Regular Insulin infusion Dextrose infusion Flow mediated vasodilation Endothelial cell collection Microvascular perfusion assessment using Definity Microneurography

The DEFINITY® vial contains components that upon activation yield perflutren lipid microspheres, a diagnostic drug that is intended to be used for contrast enhancement during echocardiographic procedures. The vial contains a clear, colorless, sterile, non-pyrogenic, hypertonic liquid, which upon activation with agitation, provides a homogeneous, opaque, milky white injectable suspension of perflutren lipid microspheres. The suspension of activated DEFINITY® will be infused intravenously at a rate of 0.20 to 0.27 ml/min, not to exceed a maximum dose of 2 vials per study subject per day or visit.

The plasma insulin concentration will be acutely raised and maintained at at a steady state by a prime-continuous insulin infusion.

The plasma glucose concentration will be held constant at 90 mg/dl by a variable glucose infusion during euglycemic hyperinsulinemic clamp

Flow mediated vasodilation (FMD), which is a non-invasive assessment of endothelial function, will be performed on the brachial artery using ultrasound. After a clear picture of the artery has been obtained, the cuff on the same arm will be inflated until it is tight for five minutes. During and following this, the subject's arm will continue to be imaged to monitor maximal increase in the brachial artery diameter.

We will collect endothelial cells from a superficial vein, usually in the arm. Following insertion of a peripheral intravenous (IV) catheter, we will collect cells from the inner lining of the vein using a thin, flexible J-tipped wire. The wire will be inserted through the IV into the vein and then removed, along with a sampling of endothelial cells. The cells collected will be processed and stained for several proteins involved in endothelial cell function, using immunofluorescent technique.

Using high-resolution ultrasound, we will measure skeletal muscle blood flow during infusion of a solution containing the octafluoropropane microbubble contrast agent, Definity. The solution will be a dilution of 1 vial of Definity to 30 cc of normal saline. The ultrasound probe will be placed over the forearm to obtain images while octafluoropropane microbubbles (Definity) are infused intravenously at the rate of 0.20 to 0.27 ml/min, not to exceed a maximum dose of 2 vials per study subject per day or visit. The microvascular perfusion assessment using Definity be performed at rest as well as during slow and fast handgrip exercises.

Sympathetic nerve activity from the peroneal nerve measured by inserting a tiny needle directly into the nerve in the leg. Investigators will localize the nerve by electrical stimulation over the skin using a blunt probe. .The recording needle will remain in position throughout the study.

Inclusion Criteria: Normotensive controls Stage I (140-159/90-99 mmHg) untreated subjects with essential hypertension Patients with PA and stage I (140-159/90-99 mmHg) hypertension Exclusion Criteria: Congestive heart failure or coronary artery disease Blood pressure averaging > 159/99 mmHg Serum creatinine > 1.5 mg/dL Diabetes mellitus or other systemic illness Left ventricular hypertrophy by echocardiography or ECG Pregnancy Hypersensitivity to spironolactone, chlorthalidone, amlodipine, human recombinant insulin or Definity Any history of substance abuse (other than tobacco) History of gouty arthritis Patients with right-to-left, bi-directional, or transient right-to-left cardiac shunts Hypersensitivity to perflutren, blood, blood products or albumin

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