BACKGROUND
Methoxychlor (MTX) is an insecticide characterized by both estrogenic and antiandrogenic properties that may modify the secretory pattern of prolactin. The objective of the present work was to analyze MTX's effects on changes in the episodic secretion of prolactin induced by thyrotropin-releasing hormone (TRH).
MATERIAL AND METHODS
Adult male Sprague-Dawley rats (400-420 g body weight) were administered 25 or 50 mg/kg/day of MTX s.c. in sesame oil for 30 days. Control animals received the vehicle only.
RESULTS
In animals treated with 50 mg/kg/day of MTX, mean serum prolactin levels and absolute pulse amplitude increased (p< or = 0.05 and p< or = 0.001 respectively). TRH administration (two pulses of 2 Kg) increased both mean serum prolactin levels and the absolute amplitude of the prolactin peaks in all groups studied (p< or = 0.001). The response to TRH was greatly increased in the animals treated with 50 mg/kg/day. TRH reduced the mean life of the hormone in control rats (p< or = 0.01) and in animals treated with 50 mg/kg/day (p< or = 0.001). After TRH administration, the duration of prolactin peaks was increased in the MTX-treated animals (p< or = 0.05 and p< or = 0.001 for 25 and 50 mg/kg/day respectively). TRH reduced the frequency of prolactin pulses in the animals treated with 50 mg/kg/day (p< or = 0.05).
CONCLUSIONS
These data suggest that MTX sensitizes the pituitary to TRH, indicating a direct effect of MTX on the pituitary gland.

Keywords: Activity Cycles, Animals, Insecticides, Male, Methoxychlor, Pituitary Gland, prolactin, Rats, Rats, Sprague-Dawley, Thyrotropin-Releasing Hormone