The luteotrophic action of decidual tissue: the stimulating effect of decidualization on the serum progesterone level of pseudopregnant rats.

On day 5 (4th diestrous day), pseudopregnant rats were arranged in pairs, one member of which was subjected to hysterectomy (H-ect) and the other to uterine scratching to induce formation of decidual tissue (DT). Blood samples were collected from each pair of rats immediately before and at various intervals after operation until day 13, and with very few exceptions were assayed for progesterone by CPB in the same assay. From 21 such pairs, the following findings emerged: During the period from day 7-day 11 inclusive, a DT-bearing rat's serum progesterone level was higher than that of its H-ect paired control in 79% of the paired comparisons; the mean serum progesterone level of the DT-bearing rats was higher than that of the H-ect rats on each day during this period; and the progesterone level group mean for all the DT-bearing rats during this period was at least 25% (P less than 0.05) higher than that of the H-ect rats. On days 6, 12, and 13, however, no significant differences were found between the 2 groups by any basis of comparison. Ordinary pseudopregnant rats (subjected only to 1aparotomy on day 5) and rats subjected to uterine scratching which failed to form DT had progesterone levels below or similar to, respectively, those of the H-ect members in the pairs. The findings were interpreted as evidence that DT increases the rate of progesteron secretion.