Table 1_Disruption of the thyroid hormone system and patterns of altered thyroid hormone serum concentrations after chemical exposures in adult rodents – a systematic review.xlsx

The lack of a TSH response may have been due to T4 decreases not being sufficient to change HPT feedback. However, risk of bias analysis also identified deficits in TH/TSH analytical methodology, including the timepoints of TH measurements, possibly explaining discrepancies between studies. We further compared T4/TSH patterns to mechanism-of-action information and other THS-related outcomes and found that THSDCs frequently affected TH synthesis, induced hepatic enzymes involved in TH metabolism, and exhibited other differences in pharmacokinetic properties.

Given the diverse chemical nature of the various THSDCs and variety of molecular targets in the THS, there is likely no single explanation for the different patterns observed.</p>Conclusion<p>Our compilation of T4/TSH patterns observed after different chemical exposures demonstrated that it is important to not solely rely on the canonical serum hormonal patterns to determine adversity of chemical exposures. Chemicals with different responses should be carefully considered, as current regulatory criteria may fail to identify them as being harmful to human health.</p>Systematic review registration<p>zenodo.org/records/5528557, identifier doi.org/10.5281/zenodo.5528557.</p>