Decrease in blood and ovarian 3 alpha- and 3 beta-androstanediol levels in rats induced to ovulate with pregnant mare...

Area of Science:

• Reproductive Endocrinology
• Steroid Metabolism
• Hormonal Regulation of Ovulation

Background:

• Progesterone metabolism in rat ovaries shifts before ovulation.
• 5 alpha-androstane-3 alpha, 17 beta-diol (3 alpha-diol) is a major metabolite.
• Shift occurs towards 4-ene-3-oxosteroids production.

Purpose of the Study:

• Investigate changes in 3 alpha-diol and its 3 beta-epimer levels in blood and ovaries.
• Examine testosterone concentrations around the first ovulation.
• Determine the role of the LH surge in these metabolic changes.

Main Methods:

• Studied immature PMSG-treated rats.
• Measured hormone levels (androstanediols, testosterone) in blood and ovaries at specific time points post-PMSG.
• Blocked the LH surge using pentobarbitone to assess its influence.

Main Results:

• Testosterone levels increased significantly in blood and ovaries 48 hours after PMSG.
• Androstanediol concentrations in blood decreased sharply.
• Ovarian 3 beta-diol and 3 alpha-diol levels significantly decreased before ovulation.
• LH surge blockade delayed but did not prevent the decrease in blood diols.

Conclusions:

• The decrease in androstanediol production precedes the first ovulation in intact rats.
• This decrease is dependent on the LH surge.
• Reduced androstanediol levels are essential for initiating ovulation by removing inhibition on uterine/ovarian growth and LH release.