Effect of delequamine (RS15385) on female sexual behaviour in the rat

The role of alpha 2-adrenoceptors in mediating the noradrenergic control of female sexual behaviour was investigated employing a selective alpha 2-adrenoceptor antagonist, delequamine (RS15385). The drug was given in graded doses of 0.01-30 mg/kg p.o. to ovariectomised plus adrenalectomised rats primed with either 2 micrograms oestradiol benzoate which yielded mainly non-receptive animals or 5 micrograms oestradiol benzoate followed 48 h later by 0.5 mg progesterone, which stimulated a high level of receptivity. Doses between 0.1 and 30 mg/kg significantly increased lordotic activity (receptivity) with an ED50 of 0.32 mg/kg, but had no effect on ear-wiggling or hopping-and-darting (proceptivity). Delequamine had no inhibitory effect in animals displaying high levels of receptivity. Thus we have shown a selective alpha 2-adrenoceptor antagonist, given orally, can stimulate female receptivity in a dose-dependent manner. Bilateral administration into the ventromedial nucleus, but not medial preoptic area, of delequamine (10 micrograms/side/rat) stimulated receptivity and it is suggested that the alpha 2-adrenoceptor may exert its effect by enhancing endogenous noradrenaline release at its active sites.