What is the Origin of Thyroid Hormone T3 Deceleration?

This is a clinical descriptor rooted in endocrinology, specifically referring to the phenomenon observed in non-thyroidal illness syndrome (NTIS) and in response to chronic caloric restriction. "Deceleration" precisely describes the reduction in the hormone responsible for setting the pace of metabolism.

What is the Mechanism of Thyroid Hormone T3 Deceleration?

Deceleration is primarily mediated by the downregulation of the deiodinase enzyme type 1 (D1) and type 2 (D2), which are responsible for converting the prohormone T4 into the active T3. Simultaneously, there is often an increase in the production of reverse T3 (rT3), which is metabolically inactive and blocks T3 receptors. This coordinated enzymatic shift effectively signals energy scarcity to the peripheral tissues, resulting in reduced cellular oxygen consumption and a lower resting metabolic rate.

Thyroid Hormone T3 Deceleration ∞ Area

Thyroid Hormone T3 Deceleration

Meaning

Thyroid Hormone T3 Deceleration is the adaptive, often pathological, reduction in the circulating levels and/or peripheral tissue activity of triiodothyronine (T3), the metabolically active form of thyroid hormone. This physiological shift is a core component of the body’s metabolic survival mechanism, resulting in a systemic slowdown of basal energy expenditure and metabolic rate. Clinically, it often presents as unexplained fatigue and difficulty with weight management.