Evaluation of progesterone deficiency as a cause of fetal death in mares with experimentally induced endotoxemia.

The study investigates whether low progesterone, a key hormone in pregnancy, causes fetal death in horses where a systemic inflammatory response (endotoxemia) has been experimentally induced. Researchers administered a substitute for progesterone (altrenogest) daily to pregnant horses, to compensate for the decrease caused by a toxin-induced inflammatory reaction. They evaluated foetal survival rates and hormone levels at different points during gestation.

Study Methodology

• The researchers experimented with mares (female horses) that were 21 to 35 days pregnant. These mares (numbered 14 in total) were going through endotoxemia, an inflammation process induced for the purpose of the experiment.
• The mares were treated daily with a prescribed amount of altrenogest, a synthetic hormone that acts like progesterone. This was done to compensate for the loss of natural progesterone caused by inflammation.
• The mares were divided into three groups based on the duration of the altrenogest treatment: until day 40 (group 1), day 70 (group 2), and day 50 (group 3).

Main Findings

• The study observed that all mares went through a two-phase change in PGF2 alpha secretion (a substance involved in inflammation and uterine contraction) after the endotoxin injection, with peaks at 30 minutes and 105 minutes.
• All mares experienced a prodigious drop in plasma progesterone levels within 24 hours of the endotoxin injection.
• In Group 1, progesterone levels dropped drastically for all mares, causing fetal death in 6 out of 7 mares within 4 days after stopping the altrenogest treatment.
• In contrast, in one mare from Group 1, where the progesterone level increased after the treatment, the foetus survived.
• In Group 2, all mares remained pregnant, even though their plasma progesterone levels were extremely low from the day after endotoxin injection until the end of the altrenogest treatment.

Implications

• This study offers solid evidence that a severe reduction in the concentration of endogenous progesterone due to endotoxemia can potentially lead to fetal death.
• The survival of fetuses despite low progesterone levels during endotoxemia suggests that other factors may also play a key role in maintaining pregnancy. This could be of significant importance for further studies in veterinary obstetrics.