title: Oxytocin receptor is expressed in the penis and mediates an estrogen-dependent smooth muscle contractility.
abstract: Oxytocin (OT) is released by the posterior pituitary during male orgasm and is supposed to participate in the ejaculatory process. We now report evidence demonstrating the presence of an OT receptor gene (real-time RT-PCR and Northern blot) and protein (immunohistochemistry, Western blot, and binding studies) expression in the rabbit and human corpus cavernosum (CC) and its possible involvement in postorgasmic penile detumescence. OT receptor is expressed in the penis at a concentration similar to that present in other portions of the male genital tract and mediates CC contractility. OT-induced CC contractility is clearly regulated by the changing sex steroid milieu. In fact, we found that in a rabbit model of hypogonadotropic hypogonadism (induced by a single administration of the long-acting GnRH agonist triptorelin pamoate, 2.9 mg/kg), OT responsiveness was strongly reduced and was completely restored by estradiol valerate (3.3 mg/kg weekly), but not by testosterone enanthate (30 mg/kg weekly). As we found that CC expresses both subtypes of estrogen receptors and P450 aromatase, we hypothesized a physiological role for endogenous estrogens in regulating OT responsiveness. We therefore treated adult rabbits with an aromatase inhibitor (letrozole, 2.5 mg/kg) or an antiestrogen (tamoxifen, 0.25 mg/kg) for 3 wk. Both treatments significantly reduced CC responsiveness to OT stimulation. In conclusion, these findings indicate that OT might participate in inducing postorgasmic penile flaccidity and suggest a new role for estrogens in the male: regulation of CC responsiveness to OT.
authors.affiliation: Department of Clinical Physiopathology, University of Florence, Italy.
authors.forename: Linda
authors.initials: L
authors.lastname: Vignozzi
authors.forename: Sandra
authors.initials: S
authors.lastname: Filippi
authors.forename: Michaela
authors.initials: M
authors.lastname: Luconi
authors.forename: Annamaria
authors.initials: A
authors.lastname: Morelli
authors.forename: Rosa
authors.initials: R
authors.lastname: Mancina
authors.forename: Mirca
authors.initials: M
authors.lastname: Marini
authors.forename: Gabriella Barbara
authors.initials: GB
authors.lastname: Vannelli
authors.forename: Simone
authors.initials: S
authors.lastname: Granchi
authors.forename: Claudio
authors.initials: C
authors.lastname: Orlando
authors.forename: Stefania
authors.initials: S
authors.lastname: Gelmini
authors.forename: Fabrizio
authors.initials: F
authors.lastname: Ledda
authors.forename: Gianni
authors.initials: G
authors.lastname: Forti
authors.forename: Mario
authors.initials: M
authors.lastname: Maggi
mesh_terms: D000818:Animals; D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D004967:Estrogens / Q000502:physiology*; D007987:Gonadotropin-Releasing Hormone / Q000819:agonists; D006801:Humans; D007006:Hypogonadism / Q000139:chemically induced / Q000503:physiopathology; D066298:In Vitro Techniques; D000077289:Letrozole; D008297:Male; D009119:Muscle Contraction / Q000502:physiology*; D009130:Muscle, Smooth / Q000502:physiology*; D009570:Nitriles / Q000494:pharmacology; D009994:Osmolar Concentration; D010121:Oxytocin / Q000494:pharmacology; D010413:Penis / Q000378:metabolism / Q000502:physiology*; D011817:Rabbits; D018045:Receptors, Oxytocin / Q000378:metabolism*; D013629:Tamoxifen / Q000494:pharmacology; D014230:Triazoles / Q000494:pharmacology; D017329:Triptorelin Pamoate / Q000031:analogs & derivatives*
chemical_list: D047072:Aromatase Inhibitors; D004791:Enzyme Inhibitors; D004965:Estrogen Antagonists; D004967:Estrogens; D009570:Nitriles; D018045:Receptors, Oxytocin; D014230:Triazoles; D017329:Triptorelin Pamoate; D013629:Tamoxifen; D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; D010121:Oxytocin; D000077289:Letrozole