Macroprolactinemia, like hyperprolactinemia, may promote platelet activation.

Insulin resistance, which provides a convenient milieu for platelet activation, has been closely associated with atherosclerotic disorders. Although it often accompanies hyperprolactinemia, findings conflict concerning its clinical impact in macroprolactinemia. In order to investigate the relationship between hyperprolactinemia and platelet activation evidenced by ADP-stimulated P-selectin expression on flow cytometry, we studied hyperprolactinemic, macroprolactinemic, and normoprolactinemic subjects. Thirty-four hyperprolactinemic and 44 age- and body mass index-matched euprolactinemic premenopausal women were included. They were matched regarding insulin sensitivity status, waist circumference, blood pressures, and plasma lipids. In order to detect macroprolactinemia among hyperprolactinemic cases, prolactin was measured before and after polyethylene glycol (PEG) precipitation in patients' sera. P-selectin expression was significantly higher in the hyperprolactinemic group (P =0.001), and 41.2% of them exhibited macroprolactinemia. Expression of P-selectin was comparable between the macroprolactin-negative (monomeric hyperprolactinemia; n = 20) and -positive (n = 14) subgroups (P = 0.90). Both subgroups showed greater expression compared with normoprolactinemic controls (P = 0.014 and 0.005, respectively). Platelet activation accompanies the atherosclerotic disorders closely associated with insulin resistance. Among groups matched with regard to insulin-sensitivity markers, both monomeric hyperprolactinemia and macroprolactinemia appeared to promote platelet activation.