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

Abstract

Ethnopharmacological relevance In the folk medicine Humulus lupulus L. (hops) is mainly recommended as a mild sedative with antispasmodic and digestive properties. It is also reputed to exert an anaphrodisiac effect 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 naïve and sexually potent male rats; thereafter to investigate the role of 8-prenylnarigenin (8-PN) in the effect displayed by the hop extract. Materials and methods Sprague–Dawley male rats both naïve and sexually potent were acutely administered with the hop extract dosed at 5, 10, 25 and 50 mg/kg. In addition the extract was administered daily for 10 consecutive days at the dose of 0.25 mg/kg/day in sexually potent animals. The pure compound 8-PN was acutely administered in naïve rats at the dosages of 5, 12.5 and 25 μg/kg. All the animals were screened 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/kg significantly reduced the percentage of mounting and ejaculating animals, in comparison to vehicle controls. 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 their copulatory 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 their mounting and ejaculating behavior. The presence of 8-PN in the extract could be only partially involved in the observed anaphrodisiac effect.