Micronized oral progesterone increases the circulating level of endometrial secretory PP14/beta-lactoglobulin homologue.

The effect of luteal phase supplementation of micronized oral progesterone, 200 mg daily, on the serum levels of endometrial secretory placental protein 14 (PP14)/beta-lactoglobulin homologue was studied in a double blind/cross-over fashion on five infertile women with apparently normal ovulatory cycles. Blood samples were taken on cycle days 10-12, 20-22 and 24-27, and the serum progesterone and PP14 concentrations were measured by specific radioimmunoassays. In each progesterone cycle the serum progesterone levels were higher than in the corresponding placebo cycle. In each case, the serum concentration of endometrial PP14 was also higher during progesterone than placebo treatment, but this was seen in the late luteal phase only. In view of the previous demonstration of endometrial synthesis of PP14 and the immunological identity between PP14 and progestogen-dependent endometrial protein, these results indicate that endometrial protein secretion can be increased by micronized oral progesterone in infertile ovulatory women whose serum progesterone level is within the normal range.