Role of progesterone in mediating stress-related litter deficits in the golden hamster (Mesocricetus auratus).

Primiparous females were mated to proven breeders and half received a subcutaneous implantation of a progesterone-filled silastic capsule on Day 3 which was removed on Day 14. The other half of the group received no treatment. Blood samples were taken from all individuals on Days 3, 7, 11 and 14. The females were paired for brief periods on Days 4, 5 and 6 with a conspecific matched for treatment group, age, weight and stage of pregnancy. Controls were exposed to a novel area instead of a conspecific. Within each of the pairs, one female was consistently dominant to the other. At parturition, all pups were counted, sexed and weighed. Among the untreated group, there were no significant differences between litter sizes or sex ratios (defined as percentage male) produced by control and dominant females. Subordinate females produced significantly smaller litters than control or dominant dams and significantly lower sex ratios than dominant dams. Subordinates produced fewer males than control or dominant dams, but there were no differences in the number of females produced. Among animals given progesterone implants, there were no significant reductions in litter size or sex ratio produced by subordinate dams compared with control or dominant dams. This study showed that female golden hamsters exposed to social subordination early in pregnancy produced smaller and more female-biased litters, and that these effects were accompanied by a significant reduction in circulating progesterone concentrations. When subordinate females were given supplementary doses of progesterone before exposure to stress, they did not show significant litter deficits.(ABSTRACT TRUNCATED AT 250 WORDS)