Differences in the metoclopramide-induced prolactin release related to age at first full-term pregnancy or nulliparity

To investigate if an association exists in parous women between metoclopramide-induced prolactin (PRL) release and chronological age at first full-term pregnancy and to compare their response to a group of non-parous women, we studied 139 healthy, non-lactating women, aged 15.8-48.2 years, on days 18-22 of their menstrual cycle (except two post-menopausal women). There were 61 parous women divided according to chronological age at first full-term pregnancy: 22 were aged less than or equal to 20.0 years, 25 were aged 20.1-29.9 years and 14 were aged >30 years. There were also 50 nulliparous women and 28 women who had experienced only first trimester abortions. Three basal blood samples were obtained before oral metoclopramide (10 mg) was administered; subsequently samples were taken at 60, 90 and 120 min. Duplicate serum PRL determinations were performed by radioimmunoanalysis and the area under the curve (AUC) calculated. In parous women, the PRL AUC was positively correlated with chronological age at first full-term pregnancy (P < 0.0001), and it was lower than in nulliparous women or in women with abortions. These data suggest that in parous women a greater dopaminergic tone may exist compared with non-parous women, which seems to decrease gradually as chronological age at first full-term pregnancy increases.