Effects of gonadotropin-releasing hormone agonist and clomiphene citrate on estrogen/progesterone-induced hyperprolactinemia in monkeys

The effects of follicular phase clomiphene citrate (CC) and two regimens of leuprolide acetate on estrogen-progesterone-induced hyperprolactinemia in nonhuman primates were studied. All groups received estradiol (E₂) benzoate (12.5 μg intramuscularly on cycle days 2 to 33) and progesterone (P) (silastic implant for cycle days 14 to 33). A gonadotropin-releasing hormone agonist (GnRH-a) (Lupron 0.5 mg daily, TAP Pharmaceuticals, Chicago, IL) was administered from cycle day 2 to 14 in group II and from day 20 of the previous cycle until cycle day 14 in group III. Oral CC was given on cycle days 3 through 7 in group IV. No significant differences of mean E₂ and P concentrations were noted between groups. Neither GnRH-a nor CC had an overall effect on E₂/P-induced hyperprolactinemia. However, for the 5-day interval at the onset of the P treatment there was a significant increase in prolactin (PRL) secretion for group II (130.4 ± 30.6) versus group I (53.9 ± 3.3), group III (64.4 ± 11.1), and group IV (68.8 ± 14.3). This suggests that leuprolide may exert a delayed stimulatory effect on PRL secretion, or that complete suppression of the putative paracrine regulation of PRL stimulation may require more than 13 days of GnRH-a administration.