Dynamics of Pulsatile Prolactin Release during the Postpartum Lactational Period*

Abstract

To investigate the pulsatile nature of PRL release in the physiologically hyperprolactinemic postpartum period, we sampled blood at 10-min intervals for 24 h in each of 6 healthy lactating women at both 3 weeks and 3 months postpartum. The subsequent immunoactive PRL time series were subjected to episodic peak detection (Cluster analysis) and multiple parameter deconvolution analysis. The 24-h mean serum PRL concentrations were significantly higher at 3 weeks than at 3 months postpartum; viz. 113 +/- 12 vs. 66 +/- 15 micrograms/L (P = 0.003). Assessment of episodic PRL pulsatility revealed significantly higher maximal PRL peak heights (296 +/- 63 vs. 141 +/- 44 micrograms/L), fractional peak heights (863 +/- 150 vs. 374 +/- 58%), incremental peak amplitudes (250 +/- 60 vs. 96 +/- 3 micrograms/L), and peak areas (13 +/- 3 vs. 4 +/- 1 mg/L.min) in the earlier postpartum period. In contrast, PRL peak frequencies and interpulse intervals were not different in the early and late postpartum sessions. Deconvolution analysis revealed that the mean mass of PRL secretory bursts was significantly greater at 3 weeks (182 +/- 4.1 micrograms/L) than 3 months (15 +/- 1.6 micrograms/L). There were no changes in the calculated half-life of endogenous PRL viz. 29 +/- 2.5 min (3 weeks) vs. 26 +/- 3.0 min (3 months). We conclude that physiological postpartum hyperprolactinemia is achieved by selectively altering the endogenous secretory rate in each PRL release episode, with no change in the number of bursts of PRL discharged or the PRL half-life.