Original Article: Laboratory Investigation Ureteral relaxation through calcitonin gene-related peptide release from sensory nerve terminals by hypotonic solution Serena Materazzi, Daiana Minocci, Gaetano De Siena, Silvia Benemei and Romina Nassini Section of Clinical Pharmacology and Oncology, Department of Health Sciences, University of Florence, Florence, Italy Abbreviations & Acronyms CGRP = calcitonin gene- related peptide CGRP-LI = calcitonin gene- related peptide-like immunoreactivity NKA = neurokinin A TRP = transient receptor potential TRPV1 = transient receptor potential vanilloid 1 TRPV4 = transient receptor potential vanilloid 4 Correspondence: Serena Materazzi Ph.D., Section of Clinical Pharmacology and Oncology, Department of Health Sciences, University of Florence, Viale Pieraccini 6, 50139 Florence, Italy. Email: serena.materazzi@unifi.it Received 18 January 2015; accepted 12 May 2015. Online publication 24 June 2015 Objectives: To evaluate the influence of hypotonic solutions on ureteral relaxation mediated by the release of calcitonin gene-related peptide from intramural sensory nerve endings. Methods: Urine osmolarity of Sprague–Dawley rats drinking water low in salt content (Fiuggi water) or a reference water for 7 days was measured. Release of calcitonin gene- related peptide-like immunoreactivity from slices of rat ureter and urinary bladder by hypotonic solutions was assessed by an immunometric assay. The mechanism through which hypotonic solutions inhibit neurokinin A-induced phasic contractions of isolated rat ureters was evaluated by organ bath studies. Results: A 7-day consumption of Fiuggi water in rats reduced urine osmolarity by ~40%. Exposure to hypotonic solutions released calcitonin gene-related peptide-like immunoreactivity from slices of rat ureter. This response was abated in a calcium-free medium, after capsaicin desensitization, and in the presence of the unselective transient receptor potential channel antagonist, ruthenium red. Exposure of isolated rat ureteral preparations to a hypotonic solution inhibited neurokinin A-evoked phasic contraction. This response was attenuated by capsaicin desensitization and in the presence of the calcitonin gene-related peptide receptor antagonist, calcitonin gene-related peptide 8-37 . Transient receptor potential vanilloid 1 or transient receptor potential vanilloid 4 antagonists did not affect the neurogenic and calcitonin gene-related peptide-dependent relaxation. Conclusion: Present data show that hypotonic solution evokes calcitonin gene-related peptide release from capsaicin-sensitive intramural sensory nerves, thus inhibiting ureteral contractility, through a transient receptor potential-dependent mechanism. However, this mechanism does not involve transient receptor potential vanilloid 1 or transient receptor potential vanilloid 4. Future studies with appropriate in vivo models should investigate the hypothesis that hypostenuric urine diffusing into the ureteral tissue might favor ureteral relaxation through this novel mechanism. Key words: calcitonin gene-related peptide, nephrolithiasis, osmolarity, sensory nerves, ureteral relaxation. Introduction Nephrolithiasis is a highly recurrent clinical condition affecting a significant and increasing proportion of the general population, with a prevalence rate in economically developed countries hovering between 4% and 20%. 1 It often causes disability and hospitalization, rep- resenting a relevant burden for affected patients and healthcare systems. Recent advance- ments in the treatment of kidney stones markedly reduced the clinical complications of this condition. 2 Nevertheless, considering that treatment is not suitable for all patients, and is not devoid of adverse reactions, 3 prevention should be carefully considered. 4 Among the different prevention options, the consumption of a soft oligomineral water, such as Fiuggi water, has been reported to markedly reduce the risk of calculosis. 4 However, the mecha- nisms that, produced by drinking oligomineral water, ameliorate nephrolithiasis are poorly understood. Ureteric peristalsis is a coordinated muscular contraction propagating along the ureter and providing the active mechanism of urine transport, mainly as a result of the activation of latent pacemakers in the ureter. Pacemaker activity fires action potentials, generating 878 © 2015 The Japanese Urological Association International Journal of Urology (2015) 22, 878--883 doi: 10.1111/iju.12837