Formation of steroids by the pregnant mare. V. Metabolism of 14C-isopentenylpyrophosphate and 3H-dehydroisoandrosterone injected into the fetus.

This study reveals how, in pregnant horses, metabolites of the chemical compound isopentenylpyrophosphate and the hormone dehydroisoandrosterone are processed in the fetus and subsequently detected in the mother’s urine. This has shed light on the processes of steroid biosynthesis in equine pregnancy.

Research Methodology

• The experiment involved the injection of a mixture of two compounds – 1-14C-isopentenylpyrophosphate and 3H-dehydroisoandrosterone – directly into the muscle of a horse fetus during a surgical procedure known as laparotomy.
• The urine of the pregnant mare was then collected for a period of four days following the procedure.
• The researchers focused on extracting steroid conjugates, or compounds formed by the combination of two molecules, from the urine. This extraction was carried out using Amberlite XAD-2 resin.
• These conjugates were then broken down in a process known as hydrolysis and separated into two categories: phenolic and neutral fractions.

Findings

• From the phenolic fraction, the scientists isolated estrone, 17alpha-estradiol, equilin and equilenin – all compounds related to estrogen.
• It was observed that only estrone and 17alpha-estradiol contained both injected compounds, while estrogens with unsaturated ring B only contained 14C-labelled isopentenylpyrophosphate.
• From the neutral fraction, the researchers isolated 3 compounds: 3beta-hydroxy-5alpha-pregnan-20-one, 5alpha-pregnane-3beta,20beta-diol and 5alpha-pregnan-3beta, 20alpha-diol, all containing 14C-labelled isopentenylpyrophosphate.

Conclusion

• The results show that the biosynthesis pathways of both the saturated and unsaturated ring B estrogens are alike until the stage where isopentenylpyrophosphate is involved.
• This points towards a divergence from the previously assumed classical pathway of steroid biosynthesis at a point after the formation of isopentenylpyrophosphate and before the creation of squalene, a cholesterol precursor. This new understanding of the biosynthesis pathway gives a more detailed understanding of how horse bodies process steroids during pregnancy.