Alterations in Basal and TRH-Stimulated Serum Levels of Thyrotropin, Prolactin, and Thyroid Hormones in Starved Obese Men

Abstract

To investigate further the alterations in pituitary-thyroid function seen during starvation, we have measured basal and TRH-stimulated serum levels of thyrotropin (TSH), prolactin (PRL), growth hormone, thyroxine (T₄), triiodothyronine (T₃), free (T₄), free T₃, and reverse T₃ during prolonged fasting in seven obese men. Fasting was associated with a significant decrease in serum T₄, T₃, and free T₃, while there was an increase in serum reverse T₃; these values tended to return toward pre-fast levels as the fast continued beyond 3 weeks. No significant changes were seen in basal serum TSH, PRL, growth hormone, or free T₄. Although the TSH response to TRH was diminished during fasting, PRL, T₄, and T₃ responses were unchanged. In addition to transient alterations in the peripheral metabolism of T₄, these findings suggest that alterations in the thyroid hormone binding capacity of serum carrier proteins may occur during fasting. The blunted TSH response to TRH despite reduction of serum T₃ concentration suggests that subtle alterations in hypothalamic-pituitary function may also occur.