The production of progesterone by the follicle begins prior to ovulation at the end of proestrus and reaches the levels of about 5 ng/ml in peripheral blood plasma at the time of ovulation. During the formation of the corpus luteum (until day 15 - 20 post ovulation) progesterone rise markedly and start to decrease gradually until approximately day 60 of pregnancy when a steep prepartal progesterone decline is observed in pregnant animals (prepartal luteolysis) as a prerequisite for parturition. This rapid drop in progesterone coincides with an increase in PGF2α levels due to increased cyclooxygenase 2 production in the fetal trophoblast and strongly implies a role of PGF2α in the onset of parturition.
In non-pregnant dogs, progesterone levels progressively decrease during the extended luteal regression (up to 1 - 3 months), dropping to < 1 ng/ml at anoestrus.
Aglepristone, a synthetic progestagen is used for control of aggression in dogs, to assist maintenance of pregnancy in low-progesterone bitches. caution must be exercised with long-term administration of progesterone due to the greater risk of mammary tumor development.
Abnormal fluctuations of progesterone are associated with a number of conditions including:
- Ovarian remnant syndrome
- Diabetes mellitus
- Cystic endometrial hyperplasia
- Mammary tumors
- Sebaceous carcinoma
- Granulosa cell tumor
- Alopecia X
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