Formation of steroids by the pregnant mare. VI. Metabolism of [14C]farnesyl pyrophosphate and [3H]dehydroepiandrosterone injected into the fetus.

The research article discusses an experiment conducted on a pregnant horse to study the metabolism of certain steroids. The researchers injected a combination of [4,8,12-14C]farnesyl pyrophosphate and [3H]dehydroepiandrosterone into the fetus during surgery and collected maternal urine for analysis over six days. The results contribute to the understanding of the biosynthesis pathway of estrogens.

Experiment and Research Methodology

• The experiment was initiated by injecting a mixture of [4,8,12-14C]farnesyl pyrophosphate and [3H]dehydroepiandrosterone into a horse fetus during a surgical procedure known as laparotomy.
• Maternal urine was collected over the span of six days following the operation.
• Steroid conjugates present in the urine were extracted with Amberlite XAD-2 resin. Then these were hydrolyzed and divided into neutral and phenolic fractions for further analysis.

Research Findings

• From the phenolic fraction, several substances were isolated: Estrone, 17 alpha-estradiol, equilin [3-hydroxy-1,3,5(10),7-estratetraen-17-one], and 17 alpha-dihydroequilin [1,3,4(10),7-estratetraene-3,17 alpha-diol]. The radiochemical purity of these isolated substances was also determined.
• It was found that only estrone and 17 alpha-estradiol contained both 3H and 14C. The B ring unsaturated estrogens, equilin and 17 alpha-dihydroequilin, contained only 14C.
• From the neutral fraction, the researchers isolated 14C-labeled 3 beta-hydroxy-5 alpha-pregnan-20-one, 5 alpha-pregnane-3 beta-20 beta-diol, and 5 alpha-pregnane-3 beta, 20 alpha-diol.

Conclusions Drawn from the Research

• Based on the experimental outcomes and prior research findings, the researchers deduced that the biosynthesis process of both ring B saturated and unsaturated estrogens follows the same pathway until the stage of farnesyl pyrophosphate.
• According to the suggested biosynthesis pathway, the divergence in the classical pathway of steroid biosynthesis occurs at a point after the creation of farnesyl pyrophosphate but prior to the formation of squalene and cholesterol.