Complex sentence: A 2004 study reported that L-carnitine acts as a peripheral antagonist of thyroid hormone action; in particular, L-carnitine inhibited both triiodothyronine (T3) and thyroxine (T4) entry into the cell nuclei.
Split into simpler sentences: A 2004 study found that L-carnitine acts as a peripheral antagonist of thyroid hormone action. In particular, L-carnitine inhibits both triiodothyronine (T3) and thyroxine (T4) entry into the cell nuclei.