Mechanisms that subserve estradiol's induction of increased prolactin concentrations: Evidence of amplitude modulation of spontaneous prolactin secretory bursts

Estradiol stimulates hyperprolactinemia in human beings and in experimental animals by mechanism(s) that remain largely undefined. We have tested the hypothesis that estrogen modulates episodic and rhythmic prolactin release. To this end we studied six postmenopausal women by repetitive venous sampling basally and on days 1, 5, 10, and 30 after intravaginal placement of an estradiol-impregnated polymeric silicone (Silastic) ring. Computerized analysis of episodic prolactin pulsatility revealed that estrogen amplified prolactin pulse amplitude threefold without changing prolactin pulse frequency. Fourier analysis disclosed heightened amplitudes of specific ultradian rhythms, and deconvolution analysis demonstrated a sevenfold increase in the mass of prolactin secreted per pulse with no change in its half-life. We conclude that estradiol selectively augments the amplitude of episodic prolactin puisatility, amplifies ultradian rhythms, and increases the mass of prolactin released per secretory burst.