Aim: 

The peptide hormone relaxin (RLX) has been shown to depress gastric and ileal contractile responses through a nitric oxide (NO)-mediated mechanism. Aim of this study was to investigate whether RLX also influences spontaneous motility and nitric oxide synthase (NOS) expression in ex vivo colonic preparations.

Methods: 

Circular strips of proximal colon from female mice were mounted in organ baths for isometric recording of the mechanical activity. Immunohistochemistry and Western-Blot analysis were performed to evaluate NOS expression.

Results: 

Colonic preparations exhibited spontaneous contractile activity consisting of rhythmic changes in isometric tension. RLX caused a decay of the basal tension followed by a stable increase in amplitude of the spontaneous contractions. Both these effects were abolished by the guanylate cyclase inhibitor, ODQ. RLX, added to the bath medium in the presence of either tetrodotoxin or the NO synthesis inhibitor L-NNA, no longer decreased the basal tension but still increased the amplitude of the spontaneous contractions. The NO donor NaNO₂ closely mimicked the response elicited by RLX. Colonic segments treated with RLX showed an increase of the neurogenic nNOS immunoreactivity and a decrease of the myogenic one.

Conclusions: 

These results indicate that RLX exerts a dual effect in the mouse colon by regulating, in opposite manner, the expression of the neurogenic and the myogenic nNOS.