Differential prolactin response to oral metoclopramide in nulliparous versus parous women throughout the menstrual cycle

OBJECTIVE: To analyze if serum prolactin (PRL) changed throughout the menstrual cycle and if parous women have lower PRL than nulliparous women. DESIGN: A prospective study of PRL was performed in basal conditions and during oral metoclopramide stimulation on days 7, 14, and 21 of menstrual cycle. SETTING: Instituto Nacional de Perinatología, third level medical institution. PATIENTS: Four parous (group A) and seven nulliparous (group B) healthy volunteer women entered and finished the study. INTERVENTIONS: Women were studied each day before and every 30 minutes during 2 hours after oral metoclopramide (10 mg). MAIN OUTCOME MEASURE: Duplicate PRL determinations were performed by radioimmunoanalysis. Hypothesis was formulated before data collection. RESULTS: Group A and B had similar basal PRL levels and no within group differences existed in response to metoclopramide, regardless of the day studied. Group A had lower PRL increments than group B from 60 to 120 minutes on days 14 and 21 (P less than 0.05); the peak increments also were lower on days 7, 14, and 21 (P less than 0.05). CONCLUSIONS: Parous women had a diminished PRL response. Although the dopaminergic tone was similar throughout the menstrual cycle within each group, two distinct levels of dopaminergic tone existed in parous and nulliparous women.