Age-related changes in the secretory pattern of FSH and LH in response to LH-RH in prepubertal female rats

Developmental changes in the pituitary responsiveness and the secretory pattern of FSH and LH in response to a single injection of LH-RH (100 ng/rat, s.c.) as estimated by increases in plasma concentrations of FSH and LH 10, 30 and 60 min after the injection were studied in female rats at 5, 10, 15, 20, 25 and 30 days of age. The pituitary responsiveness to LH-RH for both FSH and LH release increased from 5 to 15 days of age, reached a maximum on 15 days of age and declined thereafter, whereas a marked increase in the amount of these hormones in the pituitary occurred between 15 and 20 days of age. An apparent change in the secretory pattern of both FSH and LH was observed from 20 days of age onward. In groups up to 15 days of age, plasma concentrations of FSH and LH remained elevated 60 min after the injection of LH-RH, though the plasma concentration of these hormones returned to preinjection concentrations in groups at 20 days of age or later. These results indicate that the age-related changes in the secretory pattern of LH and FSH in response to LH-RH as well as changes in the pituitary responsiveness were apparent during the prepubertal period.