[The APUD concept and its clinical significance. 2. Effect of gastrointestinal hormones, polypeptides and neurotransmitters on the physiological course and disease processes of the intestinal tract and the nervous system].

The neurally programmed APUD-cells from ectodermal origin are of peculiar significance in two respects: 1. They represent the largest endocrine gland of the whole organism and the peptides, which are secreted by the different APUD-cells, exercise a great influence on most of the motoric and secretory processes within the whole gastrointestinal tract just as on many metabolic processes as demonstrated on the so-called "enteropancreatic axis". Neoplasias of these APUD-cells, the "Apudomes", give rise to peculiar clinical syndromes. Early diagnosis of an apudome can be reached today by radioimmunologic detection of high concentrations of the responsible peptide in the blood enabling us to initiate an effective therapy at least for some of the known apudomes. 2. Beyond that the APUD-cells and their corresponding peptides are representing the so-called "peptidergic" division of the nervous system which acts as third-line effector to modulate not only the actions of the autonomic division but also of each other. The given example of the modulating effect of substance P or of the endorphines on the perception of pain is only one single aspect of the broad functional spectrum of these neuropeptides. The discovery, that the very same peptide can be detected in endocrine cells as well as in neurones, has opened one of the most fascinating and provocative developments in biology of the present time and some surprising new details can be expected in the next future.