This study is designed to test the hypothesis that pulsatile (pulse-like) subcutaneous (under the skin) infusion of growth hormone (GH) via a pump will yield a reasonable pulsatile GH pattern.

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.

This study, Study I, involves six subjects and is designed to test the hypothesis that pulsatile subcutaneous infusion of GH via a pump will yield a reasonable pulsatile GH pattern. Study I involves one inpatient visit. Procedures during this study include blood draws, MRI, and insulin clamp procedures.

Study I will be followed by Study Ib, with the same six participants. Study Ib will test the hypothesis that pulsatile subcutaneous infusion of GH via a pump will yield a reasonable pulsatile GH pattern. GH will be administered at three times the dose that was used in Study I. Study Ib involves one screening visit and one inpatient overnight visit. No MRI or insulin clamp procedure will be performed.

This study will be followed by Study II, which is the main study and will examine the effects of GH via subcutaneous infusion pump in a pulsatile fashion compared with once-a-day bolus for 4 weeks.

• Aging
• Immune System

• Steinmann GG, Klaus B, Müller-Hermelink HK. The involution of the ageing human thymic epithelium is independent of puberty. A morphometric study. Scand J Immunol. 1985 Nov;22(5):563-75.
• Steinmann GG. Changes in the human thymus during aging. Curr Top Pathol. 1986;75:43-88. Review. No abstract available.
• Murphy WJ, Durum SK, Longo DL. Role of neuroendocrine hormones in murine T cell development. Growth hormone exerts thymopoietic effects in vivo. J Immunol. 1992 Dec 15;149(12):3851-7.
• Murphy WJ, Durum SK, Longo DL. Differential effects of growth hormone and prolactin on murine T cell development and function. J Exp Med. 1993 Jul 1;178(1):231-6.

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