Formation of estrogens by the pregnant mare. II. Metabolism of 14C-acetate and 3H-cholesterol injected into the fetal circulation.

This research article discusses an experiment where a pregnant mare was injected with 14C-sodium acetate and 3H-cholesterol to investigate the formation of estrogens and the metabolism processes involved. The study offers a new understanding on the biochemical formation of estrogens, indicating a distinct path for ring-B unsaturated estrogens that doesn’t necessitate cholesterol as an obligatory intermediate.

Experiment and Procedure

• A mixture of 14C-sodium acetate and 3H-cholesterol was injected into the fetus of a pregnant mare via the umbilical circulation on day 300 of gestation.
• After the injection, the mare’s abdomen was closed, and its urine was collected for three and a half days.
• The pregnant mare gave birth to a healthy live foal 23 days following the procedure.

Analysis and Findings

• Steroid conjugates found in the mare’s urine were hydrolyzed (broken down with reaction to water) and separated into neutral and phenolic (relating to phenol, a compound distinguished by a hydroxyl group) fractions.
• From the phenolic “sulfate” fraction, various biochemical compounds namely estrone, 17α-estradiol, equilin, equilenin, and 17α-dihydroequilenin were isolated.
• The research observed that only estrone and 17α-estradiol contained both 3H and 14C—the radioactive isotopes of hydrogen and carbon, respectively used in the experiment. However, for the ring-B unsaturated estrogens, they contained only 14C.

Conclusion and Significance

• The findings showcase a split or bifurcation in the conventional path of steroid formation and suggest that ring-B unsaturated estrogens are formed by reactions different from those that lead to the formation of ring-B saturated estrogens. It also demonstrates that it uses intermediates before the formation of cholesterol.
• This research serves as the first example of a biosynthetic pathway leading to the formation of steroids where cholesterol isn’t a compulsory intermediate. This could potentially pose a significant impact on the field’s understanding of steroid biosynthesis.