Placental protein 12 (PP12) in the human endometrium: tissue concentration in relation to histology and serum levels of PP12, progesterone and oestradiol.

Placental protein 12 (PP12) was measured by radio-immuno-assay in serum and endometrial extracts of 25 women at various phases of the menstrual cycle, and in the decidua from six women undergoing legal abortion in early pregnancy. The results were analysed with respect to endometrial histology and serum oestradiol, progesterone and PP12 concentrations. PP12 was detected in the secretory phase endometrium and decidua, but not in the proliferative phase endometrium. The PP12 concentration in tissue increased from early (1.3-9.4 micrograms/g protein) to late secretory phase (5.3-155 micrograms/g), and considerably higher levels were found in decidua (282-3846 micrograms/g). There was a correlation (P less than 0.001) between endometrial PP12 and serum progesterone levels in non-pregnant women, and there also was a slight correlation (P less than 0.05) between endometrial and serum PP12 concentrations. These results show that PP12 is not pregnancy specific and suggest that the occurrence of PP12 is dependent on progesterone.