Biosynthesis of Gastrointestinal Hormones

Leiter, Andrew

Abstract

Pancreatic polypeptide (PP) and Peptide YY (PYY) are members of a brain-gut peptide family. Pancreatic polypeptide, produced in the pancreatic islets, inhibits pancreatic exocrine secretion and biliary tract motility. Peptide YY, which is made in endocrine cells of the colon and ileum, also inhibits pancreatic exocrine secretion. Other effects of PYY include inhibition of intestinal motility, gastric emptying, and gastric secretion of pepsin as well as reduction of intestinal blood flow. The secretion of each peptide appears to be regulated by a number of nutritive and neural stimuli. Increased production of pancreatic polypeptide is frequently associated with pancreatic disease, in particular, with islet cell tumors of the pancreas and diabetes mellitus. Increased secretion of PYY has been observed in chronic diarrheal illnesses associated with malabsorption. Many of the unanswered questions about the biosynthesis and regulation of these two peptides can be addressed by recombinant DNA technology as follows. First, a cDNA encoding a rat PP precursor will be isolated from a rat pancreatic cDNA library using an oligonucleotide primer. The cDNA will be used as a probe to clone and isolate the rat PP gene from a rat genomic library. Secondly, in order to determine whether factors known to regulate the secretion of PP also regulate its biosynthesis, PP mRNA levels will be measured in pancreas from normal rats, diabetic rats, in primary cultures of islets, and in RIN cells using northern blot assays. The precursor of PYY will be identified by the cloning and isolation of its cDNA from a bacteriophage Lambdagt11 expression cDNA library prepared from rat intestine. The library will be screened with a well characterized antibody against PYY. Finally, the tissue localization of PYY and PP and the fetal development of PP will be defined utilizing the technique of in situ hybridization.