| Abstract: | Five healthy women who had previously undergone spontaneous menopause and had not received exogenous estrogens were studied with infusions of synthetic GnRH and dopamine to ascertain the site of dopaminergic modulation of pituitary gonadotropin secretion. Infusion of dopamine at 4 micrograms/kg . min for 5 h induced a significant decrease in circulating LH concentrations, but not those of FSH. LH levels returned to baseline concentrations during the postinfusion period. Infusion with synthetic GnRH at 10 micrograms/h for 5 h induced a biphasic change in circulating gonadotropin levels. When dopamine and GnRH were simultaneously infused for 5 h, FSH and LH responses were not statistically different from those observed when GnRH was infused alone. We conclude that in normal postmenopausal women, dopamine modulates pituitary gonadotropin secretion by affecting GnRH-secreting neurons in the median eminence and possibly at other hypothalamic sites. |
