Thyroid and Fat Tissue Metabolism

Study Summary

This study will use a technique called microperfusion to examine how thyroid hormones are involved in fat metabolism. The thyroid gland produces two kinds of hormones: T3 and T4. Some of the T4 is changed to T3 in various organs after leaving the thyroid. The T3 stimulates the body to burn fat. People have different rates at which they can change T4 to T3, and this may lead to differences in body fat among different people. Microperfusion is based on the exchange of substances across tiny holes of a small plastic tube called a "probe," which is inserted after numbing the skin over a fat pad. Through these openings, the fat pad is continuously rinsed with small amounts of fluid, and an exchange of substances occurs. The fluid drips from the other opening of the probe and is collected in a vial. Small amounts of study drugs are infused and the amount of substances released by the fat pad in response to them are measured. Healthy normal volunteers 18 years of age and older may be eligible for this study. Candidates are screened with a medical history, physical examination and blood tests. Participants undergo microperfusion. A needle is placed in an arm vein for collecting blood samples before and at the end of the experiment for measuring thyroid hormones and other substances in the blood. The skin over the fat pad next to the umbilicus (navel) is numbed and two microperfusion probes are inserted. A salt water solution is infused into the fat pad for one hour and the substances in the fluid are measured as the fluid leaves the fat pad. After 1 hour isoproterenol, a drug that aids in energy production by fat, is added to help determine the level of fat metabolism. After an additional hour small amounts of thyroid hormone are added to the fluid and samples are collected as they leave the body. Two catheters are inserted during each experiment. Small volumes of sterile fluid are circulated continuously in the tubing and samples are collected at regular intervals.