Eligible subjects will receive a measurement of endogenous glucose production (EGP) with a prime-continuous infusion of 3-3H-glucose. The EGP measurement will be performed in the morning after a 10-12 hour overnight fast and will last 8 hours (from 6 AM to 2 PM). After a 3-hour tracer equilibration period, subjects (20 per group) will receive one of the following medications: (i) placebo; (ii) exenatide 5 ug subcutaneously; (iii) dapagliflozin (10 mg); and (iv) dapagliflozin 10 mg plus exenatide 5 ug. Following the test medication at 9 AM, blood samples will be drawn every 15 minutes for an additional 5 hours and plasma glucose, insulin, C-peptide, glucagon, cortisol, growth hormone, and catecholamine concentrations and glucose specific activity will be measured.
Visit 1: Screening. Medical history \& physical exam will be performed. Blood will be drawn for fasting plasma glucose \[FPG\], routine blood chemistries, complete blood count \[CBC\], lipid profile, HbA1c, and thyroid function \[TSH\], Urinalysis, electrocardiogram \[EKG\], albumin/creatinine ratio and pregnancy test will be performed.
Visit 2: EGP Measurement: The rate of endogenous glucose production will be measured with 3-3H-glucose infusion. \[3-3H\]-glucose infusion will be started at 6 in the morning \[AM\] and continued until 2:30 afternoon \[PM\](5 hours after drug administration). At 6 AM a catheter will be placed into an anticubital vein and a prime (40 uCi x FPG/100)- continuous (0.4 uCi) infusion of \[3-3H\]- glucose will be started and continued until 2:30 PM. (5 hours after drug administration). Participant's hand will be placed in a box heated to 50-60°C (122-140°F). Baseline blood samples will be obtained at-210, -60, -50, -45, -40, -35, -30, -20, -10, and 0 . After 3.5 hours of tracer equilibration blood samples will be obtained every 10-20 minutes from 9 AM to 2 PM. Plasma glucose, insulin, C-peptide, glucagon, cortisol, growth hormone, and catecholamine concentrations, and \[3-3H\]-glucose specific activity will be measured. Urine will be collected from 6 to 9 AM and from 9 AM to 2 PM. Urinary volume and glucose concentration will be measured and urinary glucose excretion rate calculated. The study will end at 2:30 PM.
Visit 3: Double Tracer Oral Glucose Tolerance Test \[OGTT\]: Within the week after the measurement of EGP, all subjects will have a 5-hour OGTT with measurement of plasma glucose, insulin (I), C-peptide (CP), and glucagon concentrations at -180, -6-, -5-, -45, -40, -35, -30, -20, -10, 0 and every 15-30 minutes thereafter to obtain a measure of overall glucose tolerance, insulin secretion (CP0-120/G0-120), insulin sensitivity (\[Matsuda Index=MI\]), beta cell function, (CP0-120/G0-120 x MI), and suppression of plasma glucagon concentration (64). At 7 AM a catheter will be placed into an antecubital vein and a prime (25 uCi x FPG/100)- continuous (0.25 uCi) infusion of \[3-3H\]- glucose will be started and continued until 3 PM. Urinary volume and glucose concentration will be measured and urinary glucose excretion rate calculated.
HbA1c will be measured 2x, 1 on the day of the OGTT \& 1 on the day of the EGP measurement.
