Pulsatile luteinizing hormone release in postmenopausal women: effect of chronic bromocriptine administration

Pulsatile LH release was studied in 28 healthy postmenopausal women by obtaining blood samples every 5 min for 4 h either basally or after 30 days of bromocriptine (BCT; 3.75 mg/day; n = 14) or placebo (n = 14) administration. Basally, mean plasma LH levels were 46.3 +/- 3.5 (+/- SE) and 53.4 +/- 4.6 mIU/mL in the BCT and placebo groups, respectively. Mean LH pulse frequencies were 4.2 +/- 0.3 and 4.0 +/- 0.4 pulses/4 h, mean pulse amplitudes were 19.2 +/- 1.9 and 20.1 +/- 1.5 mIU/mL, and mean interpulse intervals were 54.3 +/- 3.1 and 54.6 +/- 3.2 min in the two groups, respectively. BCT administration induced no significant changes in mean plasma LH levels, but it significantly (P less than 0.01) decreased LH pulse frequency (1.7 +/- 0.3 pulses/4 h) and amplitude (12.7 +/- 0.8 mIU/mL) and significantly (P less than 0.01) increased mean interpulse interval (126.1 +/- 17.5 min). Placebo administration did not induce any significant changes in pulsatile LH release. These results demonstrate that in postmenopausal women LH secretion is circhoral, and BCT administration can blunt LH pulsatility, suggesting dopaminergic regulation of the GnRH-LH pulse generator.