Lysergic acid diethylamide (LSD) and apomorphine both inhibited lordosis behavior in ovariectomized estrogen- and progesterone-treated rats in a dose-dependent manner with similar time courses. Pimozide blocked the apomorphine-induced decrease but only partially reduced the LSD-induced inhibition. Chlorpromazine had a similar effect on LSD inhibition. The predominant action of LSD on female copulatory behavior is not mediated by increased dopamine receptor activity; instead, the LSD effect might be modulated by decreased dopaminergic activity.
In female rats whose ovaries have been removed, sexual receptivity (the lordosis response) can be triggered by estrogen alone or estrogen plus progesterone. Large doses of LSD (≥50 μg/kg) or L-5-HTP (≥2.5 mg/kg) inhibit this behavior, with progesterone enhancing the inhibition. Conversely, small doses of LSD (5–30 μg/kg) increase lordosis when only estrogen is given. This study tested how different hormone treatments affect this stimulatory action. When lordosis was activated by estradiol benzoate alone, a 10 μg/kg dose of LSD increased the response within 10 minutes, but 1 μg/kg had no effect. However, when progesterone was also given, 1 μg/kg of LSD did increase lordosis. Similar results occurred with very small doses of L-5-HTP after certain pretreatments. Progesterone appears to influence serotonin-related mechanisms in this behavior.