The distribution and ontogeny of polypeptide YY (PYY)-and pancreatic polypeptide (PP)-immunoreactive cells in the gastrointestinal tract of rat

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Abstract
The distribution and ontogeny of polypeptide YY (PYY)-and pancreatic polypeptide (PP)-immunoreactive cells in the gastrointestinal tract of rat were investigated. PYY-immunoreactive cells were numerous in the pylorus, ileum and colon and only a few cells were observed in the corpus, duodenum, jejunum and rectum. On the other hand, a few PP-immunoreactive cells were seen in the colon only. Both PYY-and PP-immunoreactive cells were of the open type, i.e., they extended from the basal lamina to the gut lumen. PYY-immunoreactive cells were observed first in the lower half of the stomach and in the intestine of 19 day-old embryo. The localization of the cells seemed to move along towards the pylorus and the lower part of the intestine. PP-immunoreactive cells could only be detected for the first time in the colon of 2 day-old rat. These cells appeared temporarily in the pylorus and rectum during the period 7 to 21 days after birth. It was concluded that the difference between PYY-and PP-immunoreactive cells in the distribution, frequency and ontogeny provide further evidence that PYY and PP occur in two independent cell types.