The rôle of oestrogens and progesterone in the onset of parturition in various species

Bedford, C.A.; Challis, J.R.; Harrison, F.A.; Heap, R.B.

Journal of Reproduction and Fertility. Suppl 16 Suppl 16: 1-23

1972


ISSN/ISBN: 0449-3087
PMID: 4566886
Document Number: 5897
The onset of parturition is regulated by the complex interactions of endocrine, neural and mechanical factors. Striking variations between species exist which, hitherto, have precluded any universal explanation of the regulation of parturition; rather, they have pointed to the earlier existence of some common mechanism that is now remote in the history of mammalian development. Despite the basic variations of the regulation of parturition, there are certain features of gestation that are common to many mammals. The length of gestation is remarkably constant within species, yet remarkably different between them. Gestation may be short, as in the hamster (14 days), or long, as in the elephant (22 months), though within a given species the variation in gestation length is small. A notable feature encountered in most mammals, if not all, concerns the essential role of progesterone in the maintenance of the pregnant state. When progesterone secretion is interrupted, either experimentally or accidentally, gestation is rapidly terminated, and it has been proposed that progesterone withdrawal may constitute an important stimulus to the onset of parturition, though whether this is true in all species is more debatable.

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The rôle of oestrogens and progesterone in the onset of parturition in various species