The Pattern of Plasma Prolactin Concentration during the First Half of Mouse Gestation1

Mating initiates a pattern of prolactin secretion composed of daily surges which appear with semicircadian rhymicity until Day 8 (Day 0 = Day of plug detection) of mouse gestation. On Day 8, the diurnal (1500-2100 h) prolactin increase diminishes in magnitude in a line selected for high embryo survival (E). By Day 9, the diurnal surge has been terminated. The nocturnal prolactin surge (2400-0900 h) is present in the line E through Day 9 of pregnancy, but on Day 10 it disappears. The temporal pattern of prolactin secretion in a randomly bred control line (C) is similar on Days 2 and 4 of pregnancy to that observed in line E. Collection of head blood and/or trunk blood had no effect on plasma prolactin concentration in either line C or E if no more than 30 seconds elapsed between cage handling and sample collection. In contrast, prolactin levels were dramatically elevated in the blood of animals placed in the same room in which serial exsanguination was performed.