Spontaneous termination of an induced pseudopregnancy in the Djungarian hamster, Phodopus campbelli.

The mechanisms which underlie the termination of a functional pseudopregnancy and the return to a behavioral estrus in the Djungarian hamster, Phodopus campbelli, were investigated through changes in (1) serum prolactin concentrations; (2) progesterone and estradiol concentrations in the serum and extracted corpus luteum, ovulatory follicle, and non-luteal portion of the ovary; and (3) corpus luteum and non-luteal ovary weight. Females were asynchronous in the timing of resumption of behavioral estrus, ranging between Days 9 and 11 postcoitus with the mode on Day 10. Unlike proestrus of a cycle, mating following a pseudopregnancy was associated with a large surge of progesterone in serum. Early pseudopregnancy was characterized by high pulsatile changes in serum prolactin, stable serum and corpus luteum progesterone, low concentrations of serum and ovarian estradiol, and high, stable corpus luteum weight. Although the day of return to behavioral estrus varied across females, there was synchrony between females in the timing of regression of corpus luteum function and structure. Serum prolactin and progesterone levels significantly decreased by Day 7 but were not followed by a decrease in corpus luteum progesterone content until Day 8. Changes in luteal function were also uncoupled from changes in weight since luteal weight remained high through Day 8 before disappearing from the ovary by Day 9. The pattern and level of prolactin surges during pseudopregnancy is the same as that seen during pregnancy, suggesting that the termination of coitally induced pituitary prolactin surges is spontaneous.