Fig. 13. Progesterone and prolactin pulsatile secretion. Blood samples taken every 20 minutes over 24 hours from a normal woman were assayed for progesterone and prolactin. The simultaneous progesterone (A) and prolactin (B) secretory patterns are depicted. Secretory events (pulses) are marked by arrows. There was no relationship between the prolactin and progesterone secretory events. There were increases in serum prolactin with meals and onset of sleep, but environmental factors such as food and sleep did not affect the progesterone secretion pattern.