HETEROGENEITY OF HUMAN PROLACTIN LEVELS IN SERUM DURING THE EARLY POSTPARTUM PERIOD

The distribution of molecular forms of prolactin in serum Of women dur ing the 1st postpartum week was studied using column chromatography. S erum was analyzed 1,4 and 7 days postpartum. Using this technique, thr ee molecular forms of prolactin were detected with approximate molecul ar weights of less-than-or-equal-to 100, 48 and 22 kDa; these were ter med 'big-big', 'big' and 'little' prolactin, respectively. The relativ e amount of each form was measured in relation to the total amount of immunoreactive prolactin eluted from the column. Throughout the first postpartum week big-big prolactin represented a minor fraction of the total immunoreactive prolactin in the serum of lactating women: 4.9%, 5.2% and 4.6% on days 1,4 and 7, respectively. There was a gradual dec rease in the higher molecular weight forms of prolactin (big-big plus big prolactin) from the 1st to the 7th postpartum day. This was associ ated with a significant increase of the little prolactin from 62.8 +/- 7.2% at the 1st postpartum day to 72.6 +/- 6.5% at the 7th day (p < 0 .05).