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. Author manuscript; available in PMC: 2020 Mar 9.
Published in final edited form as: BJOG. 2006 Dec;113(Suppl 3):17–42. doi: 10.1111/j.1471-0528.2006.01120.x

Table 1:

Source of steroids and mechanism for progesterone withdrawal before parturition in several species (Reproduced with permission from reference 377). Modified from Liggins, GC. Endocrinology of parturition. In: Novy, MJ & Resko, JA, editors. Fetal Endocrinology. New York: Academic Press. 1981, p. 211–37.

Species Sources of steroids in late pregnancy Fall in maternal progesterone concentration Mechanisms
Mouse Corpus luteum Yes Luteolysis
Rat Corpus luteum Yes Luteolysis
Rabbit Corpus luteum Yes Luteolysis
Goat Corpus luteum Yes P450 c17/ Luteolysis
Cow Placenta Yes P450 c 17
Sheep Placenta Yes P450 c 17
Guinea pig Placenta No ?
Primates Feto-placental unit No ?

P450 C17 enzymes (17alpha-hydroxylase and C17–20 lyases activities) are induced in the placenta by an increase in fetal cortisol concentration. Luteolysis is provoked by prostaglandin F2α acting on fetal plasma receptor.