To assess the effect of short-term low-dose growth hormone therapy on the mobilization of endothelial progenitor cells from the bone marrow within a group of healthy adults.

We are proposing a pilot study to assess the effect of the administration of recombinant human growth hormone on the number of endothelial progenitor cells (EPC's) in the peripheral circulation. An increase in the number of EPC's is viewed as beneficial, as it has been postulated that they provide an endogenous repair mechanism to counteract endothelial injury. Additionally, a reduced number of EPC's has been found to independently predict atherosclerotic disease progression. Mechanisms proposed for enhancing the number of circulating EPC's and their function include an increase in proliferation, mobilization from the bone marrow, or prevention of EPC apoptosis. Thus, a pharmacologic manipulation of the number of EPC's in the peripheral circulation could potentially serve as a mechanism by which endothelial function, and thus vascular health, may be improved.

Inclusion Criteria:

• Adults age 18 thru 65
• Serum IGF-1 in the lower half of the age and gender-specific normal range at the time of screening visit

Exclusion Criteria:

• Systemic hypertension, as defined as current BP >140/90 on screening visit, or taking anti-hypertensive therapy.
• Diabetes mellitus, as defined by known diagnosis or Fasting Blood Glucose >126 at the time of screening visit.
• Women who are pregnant or nursing, as confirmed by history or seum beta-hCG at the time of screening visit.
• Women who are taking exogenous oral estrogens of any kind.
• Personal history of active cancer or recurrence within the past 10 years, with the exception of non-melanoma skin cancer.
• Personal history of an untreated benign intracranial neoplasm.
• Initiation of statin therapy during the course of the study.
• A serum IGF-1 level below the age and gender-specific normal range at the time of screening visit.
• Renal insufficiency, as defined by a GFR <60 mls/min/1.73 m2 upon Renal Function panel at the time of screening visit.
• Hepatic insufficiency, as defined by an AST and/or ALT >twice the upper limit of normal at the time of screening visit.