• INCLUSION CRITERIA:

  1. Subjects will be healthy male and female adult volunteers, between the ages of 18 and 65, able to provide informed consent. Patients younger than 18 are excluded as this is a purely physiologic study and we are unable to justify any potential risk. However, should our preliminary findings show potential clinically relevant benefits for children, the protocol could be modified to include them. Patients older than 65 are excluded due to intrinsic differences in thyroid hormone dynamics, compared with younger subjects, which could confound study interpretation .

EXCLUSION CRITERIA:

1. BMI less than or equal to 19 or greater than or equal to 35 Kg/m(2)
2. Hypothyroidism, or TSH levels above the normal limits (current replacement therapy or TSH greater than 4.0 mcIU/mL)
3. Hyperthyroidism, or TSH levels below the normal limits (current or previous therapy or TSH less than 0.4 mcIU/mL)
4. Autoimmune thyroid disease (as defined by a positive anti-TPO, anti-TG, or anti-TSH receptor antibody titer)
5. Hypertension (Blood pressure greater than 140/90 or use of antihypertensive medication)
6. Liver disease or ALT serum concentrations greater than 1.5 times the upper laboratory reference limit.
7. Renal insufficiency or estimated creatinine clearance less than or equal to 50 mL/min (MDRD equation).
8. History of, and/or current Diabetes Mellitus (fasting glucose greater than 126 mg/dL)
9. Iodine deficiency (spot urine iodine concentration less than 42 mcg/L)
10. History of, and/or current coronary artery disease
11. History of, and/or current asthma
12. History of, and/or current seizures or chronic headache
13. History of, and/or current depression
14. History of pituitary tumor
15. Pregnancy (women of child-bearing potential must have a negative pregnancy test prior to inclusion and at the time of TRH testing)
16. Known allergy to TRH
17. Current use of prescription medication or certain non-prescription medications and dietary supplements which could affect thyroid function and/or metabolism.