Experimental evidence of the anaphrodisiac activity of Humulus lupulus L. in naïve male rats

Ethnopharmacological relevance: In the folk medicine Humulus lupulus L. (hops) is mainly recommendedas a mild sedative with antispasmodic and digestive properties. It is also reputed to exert an anaphrodisiaceffect but it is still lacking the experimental evidence of this activity.Aim of the study: To evaluate the influence of Humulus lupulus extract on sexual behavior of both naïveand sexually potent male rats; thereafter to investigate the role of 8-prenylnarigenin (8-PN) in the effectdisplayed by the hop extract.Materials and methods: Sprague–Dawley male rats both naïve and sexually potent were acutely administeredwith the hop extract dosed at 5, 10, 25 and 50 mg/kg. In addition the extractwas administered dailyfor 10 consecutive days at the dose of 0.25 mg/kg/day in sexually potent animals. The pure compound8-PN was acutely administered in naïve rats at the dosages of 5, 12.5 and 25g/kg. All the animals werescreened for their sexual behavior manifestation during the mating test.Results: In naïve rats the acute administration of Humulus lupulus extract at the doses of 25 and 50 mg/kgsignificantly reduced the percentage of mounting and ejaculating animals, in comparison to vehiclecontrols. The other parameters recorded during the mating test were not affected by the hop extract.In sexually potent rats nor the acute neither the repeated administration of the extract modified theircopulatory behavior.The pure compound 8-PN failed to influence male sexual behavior of naïve rats.Conclusion: Humulus lupulus extract exerted an anaphrodisiac effect only in naïve rats by inhibiting theirmounting and ejaculating behavior. The presence of 8-PN in the extract could be only partially involvedin the observed anaphrodisiac effect.