Neuropeptides of the cholecystokinin group: effects and mechanisms of action on the gastro-intestinal and gall bladder motility.

The neuropeptides of the cholecystokinin (CCK) group belong to the substances usually referred to as "brain-gut" neuropeptides. They are synthesized in neurons of the central nervous system, in the peripheral and in the autonomous nervous systems, in endocrine cells (types "I", "K" and "A"), as well as in the enteric nervous system of the gastro-intestinal tract and of the pancreas. The CCK-group peptides realize their effects via several different mechanisms (Fig. 1): endocrine or neuroendocrine (classic hormonal mechanism)--the peptide, released by the endocrine cell or by the nerve terminal, is carried by the circulation to the remote target organs; paracrine or neuroparacrine--the peptide, released in the intercellular space, reaches the target effector cells via diffusion. Similarly to the classic neurotransmitters, CCK and its analogues could play a neurotransmitter role, also modulating the release of acetylcholine (ACh) and of other neurotransmitters in enteric and CNS neurons. In the present review article some smooth-muscle and neuromodulatory effects of CCK are described and compared to the results of the authors' studies on the problem.