Preimplantation endocrinology in the Djungarian hamster (Phodopus campbelli): progesterone, estrogen, corpora lutea, and embryonic development. G.

This study reports the results of a detailed investigation of pregnancy in the Djungarian hamster, Phodopus campbelli, with a 2-h time resolution from 2000 h on proestrus (Day 0) through 0600 h on Day 5. Comparisons of the serum levels of progesterone (P4) and estradiol-17 beta (E2), along with the extractable content of each in the corpora lutea and the nonluteal portion of the right ovary, were used to assess the sources and circulating levels of these steroids throughout preimplantation pregnancy. Simultaneous investigation of embryonic development and location within the reproductive tract permitted accurate staging of development. The time course for development and implantation was similar to that in other short-cycle rodents, with transit into the uterus on the evening of Day 3 and implantation beginning early on Day 5 of pregnancy. In three different circumstances, tissue accumulations of steroids were not associated with concurrent increases in serum levels. The first, late on proestrus to early Day 1 of pregnancy, was a significant accumulation of P4 in the nonluteal ovary while serum levels remained basal. The second, throughout Day 2 of pregnancy, was an accumulation of P4 in the corpora lutea that paralleled the pattern of serum P4 during a normal estrous cycle, but which, in these pregnant females, was not seen as elevated serum P4 levels. This response is likely to be coitally induced and thus advances the first maternal steroid response to pregnancy by 24 h relative to other short-cycle rodents studied.(ABSTRACT TRUNCATED AT 250 WORDS)