title: Biphasic effects of yohimbine on the ejaculatory response in the dog.
abstract: The effects of various doses (0.01-1.00 mg/kg) of yohimbine, an alpha-2 adrenoceptor antagonist, on the erectile and ejaculatory response elicited by manual penile stimulation were investigated in male dogs. Systemic administration of yohimbine caused a biphasic effect on ejaculatory response; the amount of ejaculate produced by the genital stimulation (for 5 min) was dose-dependently increased by low doses (0.01-0.10 mg/kg) of yohimbine, whereas it was decreased by the highest dose (1.00 mg/kg) of yohimbine. The erectile potency was attenuated only, by the highest dose of yohimbine. The most effective dose (0.10 mg/kg) of yohimbine on ejaculation did not affect the duration of penile erection after removing the genital stimulation. In a stereoisomer's testing, the stimulatory effect on ejaculation was also observed by rauwolscine, an alpha-2 adrenoceptor antagonist (0.03 and 0.10 mg/kg), but not by corynanthine, an alpha-1 adrenoceptor antagonist (0.10 and 0.30 mg/kg). These results suggest that yohimbine at low doses specifically facilitate the ejaculatory response through the blockade of the alpha-2 adrenoceptors. This study also indicates that the effects of yohimbine on male genital responses vary with its dosage used.
authors.affiliation: Center for Laboratory Animal Science, Tohoku College of Pharmacy, Sendai, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Yonezawa
authors.forename: S
authors.initials: S
authors.lastname: Kawamura
authors.forename: R
authors.initials: R
authors.lastname: Ando
authors.forename: T
authors.initials: T
authors.lastname: Tadano
authors.forename: T
authors.initials: T
authors.lastname: Nobunaga
authors.forename: Y
authors.initials: Y
authors.lastname: Kimura
mesh_terms: D000818:Animals; D004285:Dogs; D004305:Dose-Response Relationship, Drug; D004542:Ejaculation / Q000187:drug effects*; D008297:Male; D010410:Penile Erection / Q000187:drug effects; D010812:Physical Stimulation; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects; D015016:Yohimbine / Q000494:pharmacology*
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine