Lepidium meyenii Walp. improves sexual behaviour in male rats independently from its action on spontaneous locomotor activity

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Abstract

Lepidium meyenii Walpers (Maca) is traditionally employed in the Andean region for its supposed properties to improve energy and fertility. The aim of this study was to evaluate the effect of acute and chronic Maca pulverised root oral administration on rat sexual behaviour. Sixty male sexually experienced rats (20 group) were daily treated for 15 days with Maca 15 mg kg−1, Maca 75 mg kg−1 or saline 0.5 ml kg−1. The following sexual performance parameters were evaluated at first and last day of treatment: 1st mount (ML), 1st intromission (IL), ejaculation (EL) and postejaculatory (PEL) latencies, intercopulatory interval (ICI) and copulatory efficacy (CE). An activity cage test was carried out to evaluate if Maca-induced locomotion changes could indirectly improve rat sexual performances. It was observed that both lower and higher Maca doses acutely decreased ML, IL and ICI in a significant way (P<0.05), while only the 75 mg kg−1 dose decreased the PEL (T=29, P<0.05). This effect seems to be the only one dose-dependent. After 15 days of treatment, both doses are able to significantly decrease ML, IL, EL and PEL, while the 75 mg kg−1 dose decreased the ICI (T=40, P<0.05) too. IL, EL and PEL variations seem to be dose-related after chronic treatment. Moreover, chronic Maca treatment induced an apparently not dose-related increase in rat locomotion, during the second 10-min period of observation in the activity cage. The late in Maca-induced locomotion modification excludes that improvement of tested sexual performance parameters is related to an increase in rat aspecific activity. Thus, it was concluded that both acute and chronic Maca oral administration significantly improve sexual performance parameters in male rats.

Introduction

The incidence of sexual inadequancy in human males, including sexual impotence, and the concern that it causes in the affected subjects, are indirectly indicated by the great number of available treatments (drugs or combination of drugs for systemic administration, topical application or intracavernous injection) (Montorsi et al., 1995). The increasing number of men seeking help for impotence has expanded basic physiological and pharmacological research on sexual performance.

Many plants extracts are traditionally employed among different cultures in order to improve sexual performances (Gay et al., 1975, Hollister, 1975, Kirkorian, 1984, Nishimoto et al., 1984, Popik et al., 1995, Susset et al., 1989, De Smet, 1997a, Arletti et al., 1999); in spite of this, pharmacologists generally disparage this use, and few experimental studies have been performed in order better to define claims of efficacy (Clark et al., 1984, Taha et al., 1995, De Smet, 1997b).

Lepidium meyenii Walpers, well known in South America as ‘Maca’, is an Andean crop which it is found only in a very restricted area of central Peru in the department of Jinin and Pasco, in the agro-ecological zone above 4000 m where low temperature and strong winds limit other crops, but it can be successfully cultivated outside its current ‘natural’ habitat. Maca is a biennial herbaceous plant, whose subterraneous part (hypocotyl) is edible and highly valued for its nutritional value (especially proteins and minerals). The rural community is firmly convinced that eating Maca enables couples who think they are infertile to have children (Quiros et al., 1996, Toledo et al., 1998). Moreover, recently, athletes are finding Maca to be an excellent alternative to anabolic steroids (but the real efficacy in this field has still to be totally proved) (Grunewald and Bailey, 1993).

The aim of the present study is to determine the effect of acute and chronic oral administration of a purified extract from L. meyenii root on male rats sexual performances and spontaneous locomotion.

Section snippets

Animals

A total of 110 Sprague–Dawley rats of either sex (90 males and 20 females) were obtained from Charles River (Calco, Como, Italy). They were housed in groups of three, males and females separately, in Plexiglas cages (40×25×15 cm), in climatized colony rooms (21±1°C; 60% humidity) on a 12 h light/dark cycle, with lights off at 07:00 h. The rats were 3 months old on arrival, and weighed 240–260 g (males) and 180–200 g (females). Food in pellets (MIL, Morini, S. Polo d'Enza, Reggio nell'Emilia,

Sexual performances

As shown in Table 1, both lower and higher acutely administered Maca doses significantly decreased ML, IL and ICI (P<0.05), while only the 75 mg kg−1 dose decreased the PEL (T=29, P<0.05). This effect was more evident with the higher dose (m vs. M: T=25, P<0.05). After 15 days of treatment, both doses are able to decrease ML, IL, EL and PEL in a statistically significant way (Table 2), while only the 75 mg kg−1 dose reduced ICI (T=40, P<0.05). IL, EL and PEL variations after chronic treatment

Discussion

Clinical plant-based research has made particularly rewarding progress in many important fields like that of anticancer drugs (taxoids and comptothecins). In addition to fluid plant-derived drugs there is an enormous market for crude herbal medicines. Natural product research can often be guided by ethnopharmacological knowledge, and it can give substantial contribution to drug innovation by providing novel chemical structures and/or mechanisms of actions (Harvey, 1999).

Sexual incompetence,

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