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Depression by Relaxin of Neurally Induced Contractile Responses in the Mouse Gastric Fundus¹

Departments of Physiological Sciences³ and Anatomy,⁴ Histology and Forensic Medicine, University of Florence, Florence, Italy Prosperius Institute,⁵ Florence, Italy

The peptide hormone relaxin, which attains high circulating levels during pregnancy, has been shown to depress small-bowel motility through a nitric oxide (NO)-mediated mechanism. In the present study we investigated whether relaxin also influences gastric contractile responses in mice. Female mice in proestrus or estrus were treated for 18 h with relaxin (1 µg s.c.) or vehicle (controls). Mechanical responses of gastric fundal strips were recorded via force-displacement transducers. Evaluation of the expression of nitric oxide synthase (NOS) isoforms was performed by immunohistochemistry and Western blot. In control mice, neurally induced contractile responses elicited by electrical field stimulation (EFS) were reduced in amplitude by addition of relaxin to the organ bath medium. In the presence of the NO synthesis inhibitor L-NNA, relaxin was ineffective. Direct smooth muscle contractile responses were not influenced by relaxin or L-NNA. In strips from relaxin-pretreated mice, the amplitude of neurally induced contractile responses was also reduced in respect to the controls, while that of direct smooth muscle contractions was not. Further addition of relaxin to the bath medium did not influence EFS-induced responses, whereas L-NNA did. An increased expression of NOS I and NOS III was observed in gastric tissues from relaxin-pretreated mice. In conclusion, the peptide hormone relaxin depresses cholinergic contractile responses in the mouse gastric fundus by up-regulating NO biosynthesis at the neural level.

¹ This study was supported by funds from the University of Florence, Florence, Italy. The financial support of Telethon-Italy (grant GGP02152) is also gratefully acknowledged.

² Correspondence: Maria Caterina Baccari, Department of Physiological Sciences, University of Florence, Viale G.B. Morgagni 63, I-50134 Florence, Italy. FAX: 39 055 437 9506; mcaterina.baccari{at}unifi.it

This article has been cited by other articles:

				M. C. Baccari, S. Nistri, M. G. Vannucchi, F. Calamai, and D. Bani Reversal by relaxin of altered ileal spontaneous contractions in dystrophic (mdx) mice through a nitric oxide-mediated mechanism Am J Physiol Regulatory Integrative Comp Physiol, August 1, 2007; 293(2): R662 - R668. [Abstract] [Full Text] [PDF]

				M. C. Baccari, D. Bani, M. Bigazzi, and F. Calamai Influence of Relaxin on the Neurally Induced Relaxant Responses of the Mouse Gastric Fundus Biol Reprod, October 1, 2004; 71(4): 1325 - 1329. [Abstract] [Full Text] [PDF]