Immunoreactive prolactin in breast milk and plasma of women with hyperprolactinemia, galactorrhea and menstrual dysfunction.

Prolactin levels were measured by radioimmunoassay in paired breast milk and plasma samples of 11 hyperprolactinemic women with galactorrhea and various menstrual disorders (amenorrhea, n = 8; oligomenorrhea, n = 2; luteal phase defect, n = 1) before and during treatment with bromocriptine (Parlodel, Sandoz). Pretreatment levels of prolactin in the milk and plasma were 80 +/- 13 ng/mL (mean +/- SEM) and 47 +/- 7 ng/mL (P less than 0.05), respectively. While on treatment, the concentration gradient for prolactin remained in favour of the milk, with values for milk and plasma 59 +/- 11 and 29 +/- 3 ng/mL (P less than 0.01), respectively. Thus, bromocriptine lowered the prolactin concentrations in both breast milk and plasma. Since prolactin in milk is biologically active, these findings may be relevant to the initiation and maintenance of lactation in women with abnormal lactogenesis.