The Physiological Responses and Adaptation of Brown Adipose Tissue to Chronic Treatment With Beta3-Adrenergic Receptor Agonists

Background:

Brown adipose tissue (BAT) is a type of fat in the body. It may prevent weight gain, improve insulin sensitivity, and reduce fatty liver. Researchers want to see if BAT helps the body burn energy.

Objective:

To learn more about how BAT works to burn energy.

Eligibility:

People ages 18-40 with a body mass index between 18 and 40

Design:

Participants will be screened with:

Medical history

Physical exam

Blood, urine, and heart tests

Dietitian interview

Participants will have an overnight baseline visit. This includes:

Repeats of screening tests

Exercise test

Scans. For one scan, a radioactive substance is injected into the arm.

FSIVGIT: An IV is inserted into veins in the right and left arms. Glucose and insulin are injected in one arm. Blood glucose and insulin levels are measured from the other.

Metabolic suite: Participants stay 18-19 hours in a room that measures their metabolic rate. Monitors on the body measure heart rate, movement, and temperature.

Optional fat biopsy: A small piece of tissue is removed with a needle.

Participants will take 2-4 pills daily for 4 weeks. All women will take the drug mirabegron. Men will be randomly get either the drug or a placebo.

All participants will have a visit after 2 weeks of the pills. They will repeat the screening tests.

Participants will have an overnight visit 2 weeks later. They will repeat the baseline tests.

Participants will keep food and medication diaries.

Participants will have a follow-up visit 2 weeks after stopping the pills. This includes heart tests.