Bioactive peptides in digesta that regulate gastrointestinal function and intake.

Abstract

Exorphins, a particular class of biologically active peptides that exist within a protein sequence, are released during digestion, absorbed intact, and modulate gastrointestinal motility, secretions, endocrine metabolism, and possibly intake by binding to specific opioid receptors. Casomorphins are a class of exorphin from milk protein that slows gastric motility and emptying in nonruminants. In the mature ruminant, abomasal infusion of casein, 1.25 to 5.0% (wt/vol) for 3 h at 16.7 mL/min, linearly decreased reticular contraction frequency 3.5 to 5.1%, duration 2.0 to 4.0%, and amplitude 5.8 to 15.5% from the control (P < .05). This effect was blocked by intragastric administration of the opioid antagonist naltrexone (.5 mg/kg of BW). Abomasal infusion of an acid hydrolysate of casein exerted more immediate effects on reticular motility that were amplified by administration of the opioid antagonist. Dual excitatory-inhibitory responses are characteristic of opioid regulation. Naltrexone-reversible effects on reticular motility, reticular-omasal orifice opening, and post-prandial insulin rise were also demonstrated when a ruminally undegradable protein supplement containing blood meal, fish meal, corn gluten meal, and meat and bone meal was fed. The effects of opioid peptides on digesta passage and postprandial insulin rise implicate their potential involvement with intake regulation. Saliva is another source of bioactive peptides. Abomasal infusion of saliva (1.5 L/h) linearly increased reticular contraction frequency 2.5 to 7.7% and ruminal dilution rate 33.8% from the control (P < .05). Bioactive peptides may provide new dietary methods for improving productive efficiency of livestock.