This study will investigate whether growth hormone, administered in a physiological or pulsatile (pulse-like) fashion, can elicit relevant changes in the human immune system while at the same time causing either no change or even an improvement in the metabolic profiles such as insulin sensitivity.

Growth hormone (GH) may enhance the way the human immune system responds. The human body secretes GH in a pulse-like fashion throughout the day. In this study human recombinant GH will be given using a continuous infusion pump to imitate how GH is naturally secreted so that investigators can observe how the human body responds to this method versus daily injections. Specifically, investigators will look at any relevant changes in the human immune system, metabolic profile, and possible side effects.

GH will be administered via subcutaneous (below the skin) infusion pump in a pulsatile fashion compared with once-a-day bolus for 4 weeks. Participants will be wearing this infusion pump continuously for 4 weeks. This study involves two inpatient visits, two 1-day outpatient visits, and about 9-14 short outpatient visits over a 3 month period. Procedures during this study include blood draws, MRI, CT, DEXA scan, insulin clamp procedures, oral glucose tolerance tests, and urine tests

Inclusion Criteria:

• Healthy men only

• Screening laboratory evaluations with no clinically significant abnormal results

  • fasting comprehensive metabolic panel
  • complete blood count with differential and platelets

  • 75-gram oral glucose tolerance test (OGTT)

    • fasting plasma glucose (FPG) less than 100 mg/dL
    • 2-hr OGTT less than 140 mg/dL
  • Insulin-like growth factor-I (IGF-I)
  • thyroid function test (TSH, free T3, free T4)
  • fasting lipid profile
• BMI less than 30
• Have NOT participated in another clinical trial involving any pharmacologic agents within the past 60 days
• Able to complete an informed consent
• Agree to not participate in other clinical trials within the study period

Exclusion Criteria:

• Women
• FPG 100 mg/dL or higher, or 2-hour OGTT 140 mg/dL or higher
• Abnormal Electrocardiogram (EKG)
• Positive stool guaiac
• Evidence of illicit drug use
• History of smoking any tobacco products within one year prior to screening
• Alcohol intake greater than 30 grams (drink more than 2 beers per day OR equivalent amount of alcohol)
• History of Human Immunodeficiency Virus (HIV) infection
• History of active or chronic Hepatitis B and/or C infection
• History of malignancy
• History of coronary disease
• History of seizures or other neurologic diseases
• History of liver or renal diseases
• History of gastrointestinal or endocrine disorders
• History of glucocorticoid use (over one month) or other immunosuppressive agents (any)
• Unable to undergo a magnetic resonance imaging (MRI) procedure
• Any medical history that, in the opinion of the investigator(s), will make participation in the study unsafe