β-Casomorphins are a family of opioid peptides originally isolated from β-casein. In view of a possible physiological significance of these milk-derived compounds, the effects of bovine β-casomorphin-5 (β-CM-5), β-casomorphin-4 (β-CM-4) and D-Ala2-β-casomorphin-4-NH2 (D-Ala2-β-CM-4-NH2) have been investigated on the peristaltic reflex in the guinea-pig isolated colon and compared with morphine. β-CM-5 and D-Ala2-β-CM-4-NH2 each dose-dependently inhibited the velocity of propulsion of an intraluminal bolus; β-CM-4 was ineffective. IC50 values were 0.30, 5.21 and 0.29 μM for morphine, β-CM-5 and D-Ala2-β-CM-NH2, respectively. The potency ratios vs morphine were 0.06 and 0.96 for β-CM-5 and D-Ala2-β-CM-4-NH2, respectively. Blockade of the peristaltic reflex by β-CM-5 or D-Ala2-β-CM-4-NH2 was reversed by the opioid antagonist naloxone. D-Ala2-β-CM-4-NH2 also dose-dependently inhibited resting acetylcholine output (IC50 = 5.69 μM; potency ratio vs morphine: 0.63). In conclusion, certain β-casomorphins inhibit intestinal propulsion and cholinergic neurotransmission in the guinea-pig colon, probably by acting at opioid receptors.
|Number of pages||4|
|Journal||Journal of Pharmacy and Pharmacology|
|Publication status||Published - 1989|
ASJC Scopus subject areas
- Pharmaceutical Science