McPhail index

Progesterone induces characteristic morphological changes of the endometrium after estrogen-induced proliferation of this tissue. This effect is the basis of the endometrium transformation assay, in which immature rabbits are primed with estradiol for several days and are subsequently treated with a progestin, either by oral application or by subcutaneous injection. The proliferating response of the uterus is examined by histological analysis and quantitated with the McPhail index on a scale from 1 to 4, with 4 as maximal effect. The assay is very sensitive and specific, even if the rabbit expresses only the B isoform of PR. 

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