Influence of sex steroids and prolactin on haloperidol-induced catalepsy.

The effects of sex steroids and prolactin on haloperidol-induced catalepsy were investigated in male rats. Repeated administration with estradiol benzoate (5 micrograms/rat, twice daily for 10 days) significantly potentiated catalepsy induced by 0.25 or 0.5 mg/kg haloperidol, but no effect was observed 10 min or 1 h after a single injection of estradiol benzoate (5 or 50 micrograms/rat). Conversely, a single administration with the catecholestrogen 2-hydroxyestradiol (50 micrograms/rat) significantly increased haloperidol-induced catalepsy, suggesting that catecholestrogens may directly interfere with nigrostriatal dopaminergic transmission. Haloperidol-induced catalepsy has been found to be attenuated in conditions of hyperprolactinaemia resulting from anterior pituitary isograft underneath the kidney capsule. This is consistent with the hypothesis that prolactin may stimulate nigro-striatal dopaminergic function. Results obtained also indicate that medroxy-acetate progesterone, a progesterone derivative, may influence haloperidol-induced catalepsy. Specifically, a single administration with medroxy-acetate progesterone (5 mg/kg, i.p.) enhanced catalepsy but opposite effects were observed after repeated administration of medroxy-acetate progesterone (5 mg/kg, i.p., once a day for 7 days).