Effects of propylthiouracil and bromocryptine on serum concentrations of thyrotrophin and thyroid hormones in normal female horses.

The researchers are exploring the effects of two drugs on the levels of certain hormones in the blood serum of healthy horses, to gain a better understanding of potential diagnostic procedures for thyroid disease in horses. They find that propylthiouracil changes concentrations of these hormones in a way akin to primary hypothyroidism, while bromocryptine does not produce expected changes for secondary hypothyroidism.

Studying the Impact of Propylthiouracil and Bromocryptine

• The study was designed to evaluate the effects of two drugs, propylthiouracil (PTU) and bromocryptine (BROM), on the levels of specific hormones in the blood serum of healthy, mature horses.
• The hormones in question were triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3) and equine thyroid-stimulating hormone (e-TSH, thyrotrophin). PTU and BROM treatments were administered over 28 days.
• The researchers conducted measurements of the aforementioned hormones before the start of treatment and then again at two points – 14 and 28 days into the treatment period. They also examined how these hormone levels responded to the administration of thyrotrophin-release hormone (TRH) at the same points.

Findings of the Study

• The PTU treatment led to a notable decrease in levels of T3, T4, and rT3 by the 28th day of treatment. There was also a measurable increase in e-TSH levels on the same day.
• The BROM treatment, on the other hand, did not significantly alter the levels of any of the hormones under consideration.
• The researchers also observed a decline, following the PTU treatment, in the percentage increase of T4, T3, and e-TSH levels after the administration of TRH. The BROM treatment did not have a similar effect.

Implications of the Research

• Based on their findings, the researchers propose that PTU could be used to simulate primary hypothyroidism in horses for research purposes. However, they do not recommend using BROM to model secondary hypothyroidism, as the expected changes were not observed.
• The study highlighted the potential for further investigation into the use of e-TSH as a diagnostic tool in identifying thyroid dysfunction in horses.
• In conclusion, the research indicates that propylthiouracil can effectively induce primary hypothyroidism. However, there’s a notable variability in horses’ sensitivity to the drug when it’s administered orally.
• The researchers advocate for more studies focused on characterizing equine thyroid disorders. They suggest considering the use of PTU for inducing primary hypothyroidism in experimental settings and e-TSH for diagnosing thyroid disorders in horses.