Twelve healthy young ( six males , six females ; age 22.22.3 yr ) and 12 older ( six males , six females ; age 68.71.0 yr ) subjects had measurements of blood glucose , serum insulin and plasma incretin hormones [ glucagon-like peptide-1 ( GLP-1 ) and glucose-dependent insulinotropic polypeptide ( GIP ) ] and calculations of insulin resistance ( homeostatic model assessment ) and - cell function corrected for insulin sensitivity , before and during intraduodenal infusions of glucose at 1 , 2 , or 3 kcal/min or saline for 60 minutes .
