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Problem:  Stress in early pregnancy has been linked to increased abortion rates. Immune stress in early pregnancy inhibits progesterone secretion in mice. As prolactin both mediates implantation and drives progesterone secretion, we hypothesised that stress would decrease prolactin secretion in early pregnancy.

Material and Methods:  Lipopolysaccharide (LPS; 12.5μg intraperitoneally) as an immune stress or vehicle were administered to day 5.5 early pregnant and virgin c57/Bl6J mice. They were killed by decapitation 60, 120 or 240 min later and trunk blood was collected and analysed for prolactin concentration (ELISA); corticosterone was also analysed (RIA).

Results:  LPS significantly decreased prolactin concentration in early pregnancy (P<0.001, 2-way ANOVA); however, there was no significant difference in the virgin groups. In contrast, LPS significantly elevated corticosterone concentration in all groups (P<0.001, 2-way ANOVA), confirming activation of the hypothalamo-pituitary-adrenal stress axis.

Conclusions:  Stress decreased prolactin secretion during early pregnancy, and might explain stress-disrupted implantation and progesterone secretion.