Primary Outcome Measures:
- Growth hormone nadir, defined as the lowest measured growth hormone after administration of a suppressive agent (oral glucose or rhIGF-I)
Secondary Outcome Measures:
- Changes in IGFBP-1, insulin, glucose, bioactive IGF-I after administration of placebo, OGTT and rhIGF-I
Other: oral glucose tolerance test
Participants will have their blood drawn for a baseline value and then will be asked to drink a beverage with 75 grams of sugar. Blood will then be drawn every 30 minutes for 2 hours.
Other: Subcutaneous administration of recombinant human IGF-1
Participants will receive a subcutaneous injection of recombinant human IGF-1 followed by a series of blood draws.