Previous data from our laboratory and others suggest that the motivational component of male rat sexual behaviour plays an important role in the sexual satiation phenomenon. The aim of the present study was to establish the effect of a physiological increase in sexual motivation, by means of changing the stimulus female (Coolidge effect), on the sexual exhaustion phenomenon and to assess the impact of lesioning the central noradrenergic (NA) system on the Coolidge effect. Results suggest that: (a) interfering with the putative sexual motivation decline resulting from multiple ejaculation, by changing the stimulus female, interferes with the establishment of an inhibitory process responsible for the sexual inhibition that follows sexual satiation; and (b) the neurotoxic lesion of the NA system does not block the stimulatory effect of such manipulation. It is concluded that different mechanisms modulate sexual behaviour expression in sexually exhausted male rats depending on the type of stimulus challenge to which they are subjected, i.e. pharmacological or physiological.