Identification and measurement of testosterone in plasma and follicular fluid of the mare, using gas chromatography-mass spectrometry associated with isotope dilution.

The research focuses on the identification and quantification of testosterone levels in the plasma and follicular fluid of horses using gas chromatography-mass spectrometry in association with isotope dilution. The study also points out that the radioimmunoassay method typically overestimates testosterone concentrations due to high levels of epitestosterone in the follicular fluid.

Testosterone Identification by Mass Spectrometry

• The article reports that testosterone, a vital hormone, was identified in the blood and follicular fluid obtained from mature Graafian follicles of mares. Follicular fluid is the liquid surrounding a mature follicle in the ovary of the mare, while Graafian follicles are ovarian follicles that contain an immature egg.
• This identification was achieved using mass spectrometry, a technique used to analyze and identify chemical compounds by separating ions based on their mass-to-charge ratio. In this case, it was used to detect the presence of testosterone in the sampled fluids.

Validation of Testosterone Quantification

• The research confirms that the quantification of testosterone in plasma was validated using gas chromatography-mass spectrometry. Gas chromatography-mass spectrometry is a method that combines the features of gas-liquid chromatography and mass spectrometry to identify different substances within a test sample. This method allowed the researchers to validate plasma testosterone levels originally determined by radioimmunoassay.

Overestimation of Testosterone by Radioimmunoassay

• Additionally, the article indicates that radioimmunoassay, a method used to measure the concentration of hormones in the body, often overestimates true concentrations of testosterone. This is due to the presence of high levels of epitestosterone in the follicular fluid. Epitestosterone is a biologically inactive epimer of testosterone and can potentially interfere with the accurate measurement of testosterone levels, thus leading to an overestimation.

Higher Testosterone Concentration in Follicular Fluid

• The study suggests that testosterone occurs in mare follicular fluid at a concentration significantly higher than that in peripheral plasma. This implies that the follicle could contribute to the production of circulating testosterone.
• As a result, a biosynthetic pathway involving testosterone for the production of oestradiol-17 beta is likely to occur in the mare’s ovary. Oestradiol-17 beta is a type of estrogen, a hormone critical to the reproductive health and function of many mammalian species. This hormonal route parallels those observed in many other mammalian species.