<prompt> Serum prolactin levels are highestREM sleep24 hrs after paurition1 hr after runningWhen Estrogens are high  <response>: Normaladult serum PRL levels are about10-25 mgLinwomenand10-20 mgL in men. PRL secretion is pulsatile, with the highest secretory peaks occurring during rapid eye movement sleep. Peak serum PRL levels up to 30 mgL occur between 4:00 and 6:00 a.m. The circulating half-life of PRL is about 50 min. 