MGU was assessed with GLP-1 or saline infusion during pituitary-pancreatic normo - ( plasma glucose ( PG ) : 4.5 mM , n = 10 ) and hypoglycemic clamps ( PG : 3.0 mM , n = 8 ) by positron emission tomography with ( 18 ) fluoro-deoxy-glucose ( ( 18 ) F-FDG ) as tracer .