@article{3098900,
    title = "Human duodenal enteroendocrine cells: source of both incretin peptides,
GLP-1 and GIP",
    author = "Theodorakis, MJ and Carlson, O and Michopoulos, S and Doyle, ME and and Juhaszova, M and Petraki, K and Egan, JM",
    journal = "American Journal of Physiology - Endocrinology and Metabolism",
    year = "2006",
    volume = "290",
    number = "3",
    pages = "E550-E559",
    publisher = "AMER PHYSIOLOGICAL SOC",
    issn = "0193-1849, 1522-1555",
    doi = "10.1152/ajpendo.00326.2004",
    keywords = "duodenum; euglycemia; type 2 diabetes; glucagon-like peptide-1; gastric
inhibitory polypeptide",
    abstract = "Among the products of enteroendocrine cells are the incretins
glucagon-like peptide-1 (GLP-1, secreted by L cells) and
glucose-dependent insulinotropic peptide (GIP, secreted by K cells).
These are key modulators of insulin secretion, glucose homeostasis, and
gastric emptying. Because of the rapid early rise of GLP-1 in plasma
after oral glucose, we wished to definitively establish the absence or
presence of L cells, as well as the relative distribution of the
incretin cell types in human duodenum. We confirmed the presence of
proglucagon and pro-GIP genes, their products, and glucosensory
molecules by tissue immunohistochemistry and RT-PCR of laser-captured,
single duodenal cells. We also assayed plasma glucose, incretin, and
insulin levels in subjects with normal glucose tolerance and type 2
diabetes for 120 min after they ingested 75 g of glucose. Subjects with
normal glucose tolerance (n = 14) had as many L cells (15 +/- 1),
expressed per 1,000 gut epithelial cells, as K cells (13 +/- 1), with
some containing both hormones (L/K cells, 5 +/- 1). In type 2 diabetes,
the number of L and L/K cells was increased (26 +/- 2; P < 0.001 and 9
+/- 1; P < 0.001, respectively). Both L and K cells contained
glucokinase and glucose transporter-1, -2, and -3. Newly diagnosed type
2 diabetic subjects had increased plasma GLP-1 levels between 20 and 80
min, concurrently with rising plasma insulin levels. Significant
coexpression of the main incretin peptides occurs in human duodenum. L
and K cells are present in equal numbers. New onset type 2 diabetes is
associated with a shift to the L phenotype."
}