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This version published online on April 28, 2005
Endocrinology, doi:10.1210/en.2004-1628
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Submitted on December 16, 2004
Accepted on April 22, 2005

OXYTOCIN MEDIATES THE ESTROGEN-DEPENDENT CONTRACTILE ACTIVITY OF ENDOTHELIN-1 IN HUMAN AND RABBIT EPIDIDYMIS

Sandra Filippi, Annamaria Morelli, Linda Vignozzi, Gabriella Barbara Vannelli, Mirca Marini, Pietro Ferruzzi, Rosa Mancina, Clara Crescioli, Nicola Mondaini, Gianni Forti, Fabrizio Ledda, and Mario Maggi*

Andrology Unit and Endocrinology Unit, Department of Physiopathology, Interdepartmental Laboratory of Functional and Cellular Pharmacology of Reproduction, Departments of Pharmacology and Clinical Physiopathology, Department of Anatomy, Histology and Forensic Medicine, Department of Urology, Department of Pharmacology, University of Florence, Florence, 50139, Italy

* To whom correspondence should be addressed. E-mail: m.maggi{at}dfc.unifi.it.

Epididymis is a sex steroid (androgen + estrogen)-sensitive duct provided with spontaneous motility, allowing sperm transport. We previously reported that the oxytocin receptor (OTR) mediates an estrogen-dependent increase in epididymal contractility. Since endothelin-1 (ET-1) also regulates epididymal motility, we tested its sex steroid dependence in a rabbit model. We demonstrated that estrogens up-regulate responsiveness to ET-1, which is reduced by blocking aromatase activity (letrozole, 2.5 mg/Kg) or by triptorelin (2.9 mg/Kg)-induced hypogonadism, while it is fully restored by estradiol valerate (E2v, 3.3 mg/Kg weekly) but not by testosterone enanthate (T, 30 mg/Kg weekly). However, changing sex steroid milieu did not affect either ET-1, its receptor gene or protein expression. Two structurally distinct OTR-antagonists (OTA and atosiban) almost completely abolished ET-1 contractility, without competing for [125I]ET-1 binding, suggesting that oxytocin (OT)/OTR partially mediate ET-1 action. Immunohistochemical studies in human and rabbit epididymis demonstrated that both OT and its synthesis-associated protein, neurophysin I (NpI), are expressed in the epithelial cells facing the muscular layer, suggesting local OT production. Quantitative RT-PCR demonstrated a high abundance of OT transcripts in human epididymis. OT transcript was also originally detected and partially sequenced, in rabbit epididymis. To verify whether ET-1 regulates OT release, we used rabbit epididymal epithelial cell cultures. These cells expressed a high density of [125I]ET-1 binding sites and responded to ET-1 with a dose-dependent OT release. Hence, we propose that an ET-1-induced OT/OTR system activation underlies the estrogen-dependent hyper-responsiveness to ET-1. These local sources might promote the spontaneous motility necessary for sperm transport.
Key words: oxytocin • endothelin • epididymis • estrogens • hypogonadism




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