Does prolonged dopaminergic blockade alter the LH pulsatile secretion in normal cycling and postmenopausal women?

To investigate effects of prolonged dopaminergic antagonism on LH pulsatile secretion, 22 normal cycling women (10 in the early follicular phase (days 3 and 4), 6 in the late follicular phase (days 10 to 13), 6 in the midluteal phase (days 6 to 8 after ovulations) and 8 postmenopausal women were studied before and during 8-h dopamine receptor blockade imposed by metoclopramide. Sequential 8-h infusions of either saline (50 ml/h) or metoclopramide (30 micrograms . kg-1 . h-1) were conducted on two consecutive days. LH pulsatile activity was assessed in blood samples obtained at 15 min intervals during these 8-h infusion periods. Based estradiol and progesterone concentrations were lowest (p. less than 0.001) in postmenopausal and highest (p less than 0.001) in the midluteal phase women, 8-h metoclopramide infusions evoked prompt (within 90 min, p less than 0.001) and sustained (greater than 70 micrograms/l, p less than 0.001) increases of PRL, similar (p = 0.78) in magnitude for normal cycling and postmenopausal women. Metoclopramide infusions failed to significantly modify the LH pulsatile activity during the menstrual cycles and in hypogonadal women. These observations suggest that even in the presence of high circulating estradiol and progesterone concentrations the dopaminergic inhibition may not be operating. However, any possible stimulatory effect on LH secretion by dopamine receptor blockade may be confounded by the concomitant metoclopramide-induced hyperprolactinemia.