Document Detail

Placental progestagens in the sheep and horse and the changes leading to parturition.
MedLine Citation:
PMID:  7995342     Owner:  NLM     Status:  MEDLINE    
Placental progestagen production and metabolism during pregnancy, the changes which precede parturition and the extent of fetal involvement in the latter processes are compared in the sheep and the horse. Neither species requires the presence of a corpus luteum for maintenance of the latter part of pregnancy, but the mechanisms involved in placental progesterone/progestagen production are very different in the two species. In sheep the primary product is progesterone (P4), levels of which are high in the maternal but not the fetal circulations. By contrast, in the mare P4 is not detectable in maternal blood after 200 days gestation although it is present in the placenta and fetal circulation. A range of P4 metabolites (primarily 5 alpha-pregnanes) are produced by the equine placenta, while in the fetus pregnenolone and its metabolites are the predominant progestagens. In sheep the prepartum endocrine cascade in which the rise in fetal cortisol stimulates enzyme changes in the placenta so that P4 declines and estrogens and prostaglandins eventually rise, is fairly well established compared with the events preceding delivery in the mare. In the latter species there is a gradual rise in progestagens for 10-20 days before term, at a time when the fetal adrenal is relatively quiescent and unresponsive to ACTH i.e. fetal cortisol levels are low. In the last 24-48 h before delivery maternal progestagens fall, just after fetal plasma cortisol concentrations begin to escalate. The ways in which maternal and fetal prepartum endocrine changes may be interrelated and the possibility of a fetal trigger to parturition in the mare are discussed.
M Silver
Publication Detail:
Type:  Journal Article; Review    
Journal Detail:
Title:  Experimental and clinical endocrinology     Volume:  102     ISSN:  0232-7384     ISO Abbreviation:  Exp. Clin. Endocrinol.     Publication Date:  1994  
Date Detail:
Created Date:  1995-01-17     Completed Date:  1995-01-17     Revised Date:  2005-11-16    
Medline Journal Info:
Nlm Unique ID:  8302802     Medline TA:  Exp Clin Endocrinol     Country:  GERMANY    
Other Details:
Languages:  eng     Pagination:  203-11     Citation Subset:  IM    
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MeSH Terms
Gestational Age
Horses / metabolism*
Labor Onset / metabolism*
Placenta / metabolism*
Progesterone / metabolism
Progestins / biosynthesis,  metabolism*
Sheep / metabolism*
Reg. No./Substance:
0/Progestins; 57-83-0/Progesterone

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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