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

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Abstract
Placental protein 12 (12) was measured by radio-immunoassay 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 12 concentrations. 12 was detected in the secretory phase endometrium and decidua, but not in the proliferative phase endometrium. The 12 concentration in tissue increased from early (1.3–9.4 μg/g protein) to late secretory phase (5.3-155 μg/g), and considerably higher levels were found in decidua (282-3846 μg/g). There was a correlation (P<0.001) between endometrial 12 and serum progesterone levels in non-pregnant women, and there also was a slight correlation (P<0.05) between endometrial and serum 12 concentrations. These results show that 12 is not pregnancy specific and suggest that the occurrence of 12 is dependent on progesterone.