Abstract

BACKGROUND Peptide YY (PYY) is involved in the regulation of several gut functions, including secretion and motility. It exerts its effects through a family of six receptors, commonly named the Y receptor family.

AIMS To characterise the effects of PYY on strips of rat proximal colon in vitro, and to determine the pathways and receptors involved.

METHODS Contractions of strips removed from the muscle layer of rat proximal colon were recorded under isometric conditions, using PYY, Y receptor agonists and antagonists, and nerve blockers. Reverse transcription-polymerase chain reaction was also performed to detect the presence of mRNA coding for Y receptors. Finally, smooth muscle cells were isolated to estimate the cell length and intracellular Ca²⁺ concentration in the presence and absence of PYY.

RESULTS PYY, neuropeptide Y (NPY), pancreatic polypeptide (PP) and [Leu31,Pro34]NPY induced a dose dependent contraction of strips from proximal colon. Tetrodotoxin partially inhibited the PYY and NPY induced contractions, and strongly inhibited the PP induced contraction. Specific antagonists showed the involvement of cholinergic nicotinic receptors and NK1 receptor. BIBP 3226, a specific Y1 antagonist, did not modify the colonic smooth muscle response to PYY, whereas blocking L-type Ca²⁺ channels with D-600 abolished its effects. Moreover, PYY induced an increase in intracellular Ca²⁺ concentration, associated with a reduction in cell length. mRNA encoding Y1 and Y4 receptors were detected in the muscle strips.

CONCLUSIONS These findings suggest that PYY stimulates colonic contractile activity in vitro through (a) a nervous Y4 dependent pathway and (b) a pathway involving a potential new receptor on myocytes.