A monoclonal antibody raised to gastric inhibitory polypeptide (GIP) has been compared with conventional rabbit and guinea-pig antisera to GIP. Four staining methods were tested and of these the peroxidase antiperoxidase (PAP) method proved to give the best results with both the mouse and rabbit antibodies. The monoclonal antibody, when used to stain pancreatic tissue, gave negative results whereas a distinct population of gut endocrine cells was readily demonstrable, suggesting that GIP is not a constituent of the mammalian pancreas. The monoclonal antibody was found to be the most sensitive for immunocytochemistry achieving the titre of 1:10(6) in rat gut. A C-terminal specific antibody, with a high affinity and avidity to GIP, it was clearly the preferred antibody for immunocytochemical studies.
The gastric lining is usually divided into two regions, an anterior portion lined by fundic glands, and a posterior with pyloric glands. Cardiac glands are unique to mammals , and even then are absent in a number of species. The distributions of these glands vary between species, and do not always correspond with the same regions as in humans. Furthermore, in many non-human mammals, a portion of the stomach anterior to the cardiac glands is lined with epithelium essentially identical to that of the oesophagus. Ruminants , in particular, have a complex stomach, the first three chambers of which are all lined with oesophageal mucosa. 
Glucose-dependent insulinotropic polypeptide (GIP; gastric inhibitory polypeptide) is a 42 amino acid hormone that is produced by enteroendocrine K-cells and released into the circulation in response to nutrient stimulation. Both GIP and glucagon-like peptide-1 (GLP-1) stimulate insulin secretion in a glucose-dependent manner and are thus classified as incretins. The structure of mammalian GIP is well conserved and both the N-terminus and central region of the molecule are important for biological activity. Following secretion, GIP is metabolized by the endoprotease dipeptidyl peptidase IV (DPP-IV). In addition to its insulinotropic activity, GIP exerts a number of additional actions including promotion of growth and survival of the pancreatic beta-cell and stimulation of adipogenesis. The brain, bone, cardiovascular system, and gastrointestinal tract are additional targets of GIP. The GIP receptor is a member of the B-family of G protein-coupled receptors and activation results in the stimulation of adenylyl cyclase and Ca(2+)-independent phospholipase A(2) and activation of protein kinase (PK) A and PKB. The Mek1/2-Erk1/2 and p38 MAP kinase signaling pathways are among the downstream pathways involved in the regulation of beta-cell function. GIP also increases expression of the anti-apoptotic Bcl-2 and decreases expression of the pro-apoptotic Bax, resulting in reduced beta-cell death. In adipose tissue, GIP interacts with insulin to increase lipoprotein lipase activity and lipogenesis. There is significant interest in potential clinical applications for GIP analogs and both agonists and antagonists have been developed for preclinical studies.