Neural mechanisms of aldosterone-induced insulin resistance.
Aim 1: We will collect venous endothelial cells, and measure skeletal muscle microvascular perfusion using Octafluoropropane microbubble contrast agents (Definity), and measure SNA in normotensive controls (NT), stage 1 essential hypertensive subjects (ET), and patients with primary aldosteronism (PA) during hyperinsulinemic euglycemic clamp. Two IV lines will be placed on opposite arms. One will be in the antegrade position and the other will be in the retrograde position in the forearm, wrist, or hand. To collect endothelial cells a thin wire will be inserted in the i.v. line placed antegradely to collect cells from the inner lining of the vein. The cells collected will be processed and stained for several proteins involved in vascular oxidative stress and endothelial cell function (eNOS, nitrotyrosine, NADPH oxidase), using immunofluorescent technique. To assess the microvascular perfusion in the skeletal muscle, Definity (IND # 104,397) will be administered at the rate of 0.20 to 0.27 ml/min at baseline for 15 minutes. Then, subjects will be randomized to a 2-h euglycemic hyperinsulinemic clamp or saline infusion using a crossover design. A 2-h euglycemic hyperinsulinemic clamp will take place after 12 h fast. The antegrade line will be used to infuse insulin, 20% dextrose and 0.9 Normal Saline Solution (NSS) with 20 mEq potassium chloride per liter. The retrograde line will be placed in a hot box at 60°C and used to draw blood. The plasma insulin concentration will be acutely raised and maintained at approximately 100 mU/L by a prime-continuous insulin infusion. The insulin delivery rate will be 40 mU/m2/min. The plasma glucose concentration will be held constant at 90 mg/dl by a variable glucose infusion using the negative feedback principle described by DeFronzo, et al 7. Infusion of microbubble contrast will be repeated every 30 min during the clamp at the same rate as above. Administration of microbubble contrast agents during ultrasonography have been shown to be more reliable than the traditional Doppler ultrasonography and other noninvasive technique in assessing skeletal muscle perfusion in humans during glucose clamp and exercise 8, 9. The total dose of Definity use will not exceed 2 vials per study subject per day or visit. Then the subjects will be asked to return to the lab in 2 weeks to finish studying in the remaining arm. Study will be repeated in patients with aldosterone-producing adenoma one month after adrenalectomy to remove aldosterone producing adenoma.
Aim 2: In 25 subjects with essential HTN, we will collect venous endothelial cells, and measure skeletal muscle microvascular perfusion using Octafluoropropane microbubble contrast agents (Definity), and measure SNA during hyperinsulinemic euglycemic clamp as above. These procedures will be done at baseline and after 12 weeks of spironolactone, chlorthalidone, and amlodipine, using randomized crossover design. There will be period of 2 week washout between each treatment. The dose of amlodipine (5-10 mg/day), chlorthalidone (12.5-25 mg/day) and spironolactone (25-50 mg/day) will be titrated to keep SBP < 140 and DBP <90 mmHg. BP, serum Na, K, glucose, and Cr will be monitored after 4 weeks and 12 weeks of drug administration in each group.
Experiments will be performed in a) normotensive controls, b) stage I (140-159/90-99 mmHg) untreated subjects with essential hypertension, and c) patients with PA and stage I (140-159/90-99 mmHg) hypertension.
All subjects are between 18-75 years old without target organ disease.
Hypertensive patients and PA patients who are currently on pharmacologic treatment of hypertension will be required to stop their antihypertensive medications for 3 weeks before the study and will be eligible to participate if their resting BP are below 160/100 mmHg after antihypertensive medications are withheld for 3 weeks. During period of washout from antihypertensive medications, our research nurse will provide counseling to all subjects to maintain healthy lifestyle intervention as recommended by the current JNC standard guidelines including: 1. Maintain normal body weight (body mass index 18.5–24.9 kg/m2), 2. Adopt DASH eating plan (a diet rich in fruits, vegetables, and low-fat dairy products), 3. Dietary sodium reduction (reduce dietary sodium intake to no more than 100 mmol per day or 2.4 g sodium or 6 g sodium chloride), 4. Engage in regular aerobic physical activity such as brisk walking (at least 30 minutes per day, most days of the week), 5. Moderation in amount of alcohol consumption. Because lifestyle modification alone is the recommended treatment for stage I hypertension up to 2 months according to current guidelines of the Seventh Report of the JNC 7 and the studies will be performed only in subjects with uncomplicated hypertension and with no co morbidities, we believe that this duration of washout period will not expose subjects to excessive cardiovascular risks.