Growth Hormone Administration and the Human Immune System

Overview

Background: \- In elderly individuals, an age-associated decline in the immune system s ability to function is believed to contribute to increased incidence of infection, autoimmune disorders, and cancer. This decline in immune system function may be related to the decline in the body s production of growth hormone, which helps regulate human development and may contribute to the health of the immune system. Researchers are interested in studying whether growth hormone, given as an infusion over time, can improve the function of the immune system and other body systems associated with good health. Objectives: \- To study the effects of growth hormone administration on the immune systems of healthy men. Eligibility: \- Healthy men between 25 and 50 years of age. Design: * This protocol will involve three separate studies: Study I, Study IB, and Study II. Participants in Study I and Study IB may participate in Study II as directed by the researchers. * Participants will be screened with a full medical history and physical examination, and will provide blood, urine, and stool samples; have a glucose tolerance test; and have other tests as required by the researchers. * Participants will have an infusion pump with a small catheter inserted beneath the skin to administer the study chemicals (either growth hormone or placebo). * Study I and Study IB participants will receive pulses of growth hormone through the infusion pump at regular intervals to monitor the body s response to the hormone. Study IB participants will receive a higher dose of growth hormone than Study I participants. * Throughout the study period, all participants will have frequent blood and urine tests, as well as tests of glucose tolerance and metabolism, imaging studies, and other tests as required by the researchers. * Study II participants will be divided into two groups. The first group will receive pulses of either growth hormone or placebo infusion at intervals throughout the day for 4 weeks, followed by an 8-week period without infusions. The second group will receive conventional once-a-day infusion of growth hormone or placebo for 4 weeks, followed by an 8-week period without infusions. * Throughout the study period, all participants will have frequent blood and urine tests, as well as tests of glucose tolerance and metabolism, imaging studies, and other tests as required by the researchers.

Objectives and Specific Aims: We plan to investigate whether growth hormone, administered in a physiological or pulsatile fashion, can elicit relevant changes in the human immune system while at the same time associated with no change or even an improvement in the metabolic profiles such as insulin sensitivity. Experimental Design and Methods: Thirty-eight healthy men, age 25-50, will be recruited for this study. There are three parts to this study: Study I, Study IB and Study II. Study I and IB each involve six subjects and are designed to test the hypothesis that pulsatile subcutaneous infusion of GH via a subcutaneous infusion pump yields a reasonable pulsatile GH pattern. The dose of GH used in Study IB is three-fold higher than in Study I. Study I and IB are done first before proceeding to Study II. Study II is a randomized, double-blinded, placebo-controlled 12-week study involving 26 subjects divided into 2 groups: Group A and Group B. Group A involves 13 subjects receiving pulsatile GH or placebo infusion for 4 weeks with 8-week washout after intervention. Group B involves 13 subjects receiving conventional once a day subcutaneous infusion of GH or placebo for 4 weeks with 8-week washout after intervention. Medical Relevance and Expected Outcome: This study ascertains the significance of the effect of pulsatile growth hormone administration on the human immune system and metabolic profile.