Perspective: Research Activity of Enteropancreatic and Brain/Central Nervous System Hormones Across Invertebrates and Vertebrates(1).

INTRODUCTION

Insulin, glucagon, cholecystokinin, insulin-like growth factor, neuropeptide Y and somatostatin

The aim here is not to describe the sources, mechanisms of action, gene regulation or function of gastroenteropancreatic (GEP) hormones, but rather to describe the trends in research activity on these peptides in invertebrates and vertebrates, and to suggest further areas of needed research. In this study computer searches were used to access the pertinent comprehensive databases and to elucidate the progress of research in specific scientific areas. The trends in research activity are judged by the number of publications in any one search (explained in a later section). We do not cite individual papers, but rather we refer to the total number of citations or reviews written for each of the peptides within a given time period. It should also be noted at the outset that our knowledge is restricted and it may appear, from our database search, that certain peptides are not found in a particular organism or phylum. This probably reflects not that these peptides are absent, but rather that there is a lack of research dedicated to identifying these peptides in these organisms.

The present review was limited to six representative peptides from the so-called hormonal molecular families and superfamilies, which are listed in Table 1, that are produced in the GEP system and/or brain/ central nervous system/nerve cells (see below) in invertebrates and vertebrates. The peptides that were selected for this study are insulin and insulin-like growth factors-I and -II (IGF-I and -II) of the insulin/insulin-like growth hormone family, glucagon of the secretin family, somatostatin of the somatostatin family, cholecystokinin (CCK) of the gastrin family and neuropeptide Y (NPY) of the pancreatic polypeptide family. Table 1 lists the hormones and proteins secreted by the mammalian pancreas and illustrates the many peptides that are produced in the gastroenteropancreatic (GEP) system (Norman and Litwack, 1997).

TABLE 1. Hormones and proteins secreted by the pancreas and gastrointestinal system.(*)

 
Hormone/protein                  Number of amino acid residues 
 
Hormones and proteins secreted 
  by the mammalian pancreas: 
   Glucagon                                       29 
   Insulin                                        51 
   Islet amyloid polypeptide 
    (IAPP) or "amylin"                            37 
   Chromogranin A                                 49 
   Parathyroid-related protein                   141 
   Somatostatin                                   14 
   Pancratic polypeptide                          36 
      Peptide Family                            Hormones 
 
The families of the related 
mammalian gastrointestinal 
peptide hormones: 
 
Secretin                      Enteroglucagon 
                              Glicentin 
                              Glucagon 
                              GIPSecretin 
                              VIP 
                              Growth hormone-releasing factor 
Gastrin                       CCK 
                              Gastrin 
Pancreatic polypeptide        PP 
                              NPY 
                              PYY 
Tachykinin-bombesin           Neurokinins 
                              Neuormedins 
                              Substance K 
                              Substance P 
                              Gastrin-releasing peptide 
Opioids                       Enkephalin 
                              [Beta]-endorphin 
                              ACTH 
                              [Alpha]-melanocyte-stimulating 
                              hormone 
                              dynorphins 

(*) Modified from Norman and Litwack (Norman and Litwack, 1997).