Assessing thyroid function in dogs is complex due to various factors affecting hormone levels. Age, breed, physical activity, and medications can influence thyroid hormone concentrations. Additionally, sex hormones, particularly in the estrous cycle, may impact thyroid activity. This study aimed to explore these interactions, focusing on female German Shepherds.
Key Findings:
The study monitored thyroid hormone levels and sex hormone concentrations across different stages of the estrous cycle in healthy female German Shepherds. Notably, higher levels of total thyroxine (TT4) were found during estrus and diestrus compared to proestrus and anestrus. This aligns with previous findings suggesting progesterone dominance during these phases may elevate TT4. However, no significant differences were observed in total triiodothyronine (TT3) concentrations among estrous phases.
There was a positive correlation between progesterone and TT4 levels, indicating a potential influence of progesterone on thyroid activity. Similarly, a negative correlation was found between 17-β-estradiol and TT4, suggesting estrogen dominance during proestrus may lower TT4 levels. However, thyroid-stimulating hormone (TSH) concentrations did not correlate with sex hormones.
Some dogs exhibited TT4 and free thyroxine (fT4) levels below reference ranges during proestrus, but this didn't indicate hypothyroidism, as TSH levels remained normal. These fluctuations during the estrous cycle may not significantly impact thyroid diagnosis but warrant further investigation.
Conclusion:
The study suggests that the stage of the estrous cycle may influence thyroid hormone levels in female German Shepherds. While fluctuations occur, they may not alter diagnostic outcomes significantly. However, more extensive studies are needed to confirm these findings and their clinical implications. Understanding these interactions enhances our knowledge of thyroid function in dogs and aids in accurate diagnosis and treatment.
Authors: Paola Scarpa, Filippo Tagliasacchi, Francesca Iavazzo, Michela Beccaglia, Adriano Monino, Paolo Dri, Gianpaolo Milite
Published: December 13th, 2023.
