A large amount of evidence showing that monocarboxylic fatty acids are regulators of exocrine and endocrine functions has accumulated in ruminant and non-ruminant animals. In this review we focus on recent findings concerning the actions of fatty acids on the pancreas and pituitary GH secreting cells (somatotrophs) of the ruminant with their other actions on a variety of organs.
In general, short-chain fatty acids control cell proliferation, intestinal motility and secretion of saliva and digestive fluid although they are widely established as an energy source. All fatty acids studied so far, both short-chain fatty acids or long-chain fatty acids, are stimulators of the acinar cells of the exocrine pancreas, however these fatty acids are also inhibitors of acetylcholine-induced exocrine secretion. The action of fatty acids is dependent on the body mass of the animal, and shows a concentration (or dose)-dependency. The action is also dependent on chemical structure of short-chain fatty acids. The fatty acids seem to be recognized by trypsin-sensitive protein(s) in the cell membrane. The stimulatory action of fatty acids is attributed to an increase in the intracellular calcium ion concentration. However, fatty acids are inhibitors for pituitary somatotrophs because they suppress the basal and GHRH (or GHRP)-induced GH release. The inhibitory actions of fatty acids are spread over many cellular signaling processes, such as cytosolic concentrations of calcium ions and cyclic AMP, calcium channel activity and GHmRNA abundance.
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