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

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Abstract
Mating initiated a pattern of prolactin secretion composed of daily surges which appeared with semicircadian rhythmicity until day 8 (day 0 = day of plug detection) of mouse gestation. On day 8, the diurnal (1500-2100 h) prolactin increase diminished in magnitude in a line selected for high embryo survival (E). By day 9, the diurnal surge terminated. The nocturnal prolactin surge (2400-0900 h) was present in the line E through day 9 of pregnancy, but on day 10 it disappeared. The temporal pattern of prolactin secretion in a randomly bred control line (C) was 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 s elapsed between cage handling and sample collection. Prolactin levels were dramatically elevated in the blood of animals placed in the same room in which serial exsanguination was performed.