In vivo metabolism of [3H]equilin in the pregnant mare.

This research investigates how pregnant mares metabolize equilin, a hormone. The study finds that most of this hormone is excreted within 24 hours and that it doesn’t transform into classical estrogen hormones.

Introduction to the Study

• The researchers conducted an in-depth study on how pregnant mares in their tenth month of gestation metabolize [3H]Equilin, a hormone also known as 3-hydroxy-1,3,5(10), 7-estratetraen-17-one.
• The way a pregnant mare processes this hormone is an important process to understand, as it provides insights into the role of hormones during pregnancy and their impact on both the mother and the fetus.

Methodology

• The researchers administered the [3H]Equilin intravenously into the pregnant mare.
• Post-administration, maternal urine was collected for three days and blood samples were gathered at specific intervals: 35 minutes, and 3, 6, 12, and 24 hours after the injection.
• The half-life of the hormone and she rate of its elimination from the bloodstream were closely tracked.

Findings

• The half-life of [3H]Equilin’s disappearance from the blood was approximately 2.5 hours.
• Over 90% of the administered dose was excreted in the first 24 hours, with most of the radioactive material (75%) present in the phenolic sulfate fraction.
• Several metabolites of equilin were identified in the extracted, hydrolyzed, and fractionated urine. These include equilin, equilenin, 17 alpha-dihydroequilin, 17 beta-dihydroequilin, 17 alpha-dihydroequilenin, and 17 beta-dihydroequilenin.

Conclusions and Significance

• The results showed that B ring unsaturated estrogens, such as equilin, are not metabolized to B ring saturated estrogens (classical estrogens). This ended the assumption that unsaturated estrogens could metabolize into saturated ones.
• All B ring unsaturated estrogens identified from the pregnant mare’s urine were metabolites of equilin, reinforcing the efficiency of equilin metabolism in the body.
• The study also found that the major metabolite of equilin excreted in the urine was equilin sulfate.
• The secretion rate of equilin, calculated from the specific activity of the isolated equilin sulfate and the amount of equilin injected, was found to be 96 mg/24 hours.
• The main reduced metabolites of equilin were the biologically less active 17 alpha-reduced products.