Effect of Tri-Iodothyronine Replacement on the Metabolic and Pituitary Responses to Starvation

Abstract

To determine the implication of decreased T3 production during fasting, seven normal men were fasted for 80 hours on two occasions; they received 5 microgram of T3 every three hours durnig the second fast. The mean serum T3 concentration declined during the control fast from 120 to 73 ng per deciliter (P less than 0.01), but remained slightly above base-line values during the T3 fast. Mean serum T4 concentrations did not change, and mean serum rT3 concentrations increased, during both fasts. The peak serum TSH increment after TRH was 11.1 micromicron per milliliter before fasting, 8.9 (not significant) after the control fast and 2.2 (P less than 0.01) after the T3 fast. Urea excretion was 9.1 per cent higher during the T3 fast; there were no differences in the changes in blood glucose, plasma fatty acids or other substrates during the two fasts. Pretreatment with potassium iodide lowered serum T4 concentrations and increased the serum TSH response to TRH after fasting. We conclude that the decrease in serum T3 concentrations during fasting spares muscle protein. Fasting is accompanied by a lower set point of TSH secretion, which remains sensitive to changes in serum thyroid hormone concentrations.

Plasma prolactin response to thyrotropin releasing hormone in children with newly diagnosed insulin dependent diabetes.

“…It may be of interest to note that the basal and TRH-induced TSH secretions were within normal ranges in children with newly diagnosed IDD and none of them did exhibit the high TSH response to TRH, despite the decreases of circulating thyroid hormone levels. This finding is in accord with previous results (LeRoith et al 1980) that the basal TSH secretion and the response to TRH were normal in diabetic patients with IDD, and may be compatible with the view (Gardner et al 1979) that the reduction in the extrathyroidal conversion of T4 to T3 in fasting and nonthyroidal conditions is accompanied by a lower set-point of pituitary TSH secretony activity.…”

Hormones and metabolites of arctic foxes (Alopex lagopus) in response to season, starvation and re-feeding

“…Ketone bodies partially replace glucose as the brain's main source of energy, and enable the adaptive conservation of body protein (Owen et al, 1967;Goodman et al, 1980;Groscolas, 1986). Decreased levels of fT 3 are also reported to limit the breakdown of muscle protein (Gardner et al, 1979). Thus, levels of FFA, b-OHB and fT 3 found in this study indicate increased lipolysis, suggesting that muscle protein conservation occurs during starvation in the arctic fox.…”

Novel insights into the neuroendocrinology of critical illness

“…Low concentrations of binding proteins and inhibition of hormone binding, transport and metabolism by elevated levels of free fatty acids and bilirubin have been proposed as factors contributing to the low-T3 syndrome at tissue level (36). The acute changes in the thyroid axis have been interpreted teleologically as an attempt to reduce energy expenditure, at least when they occur during starvation (37), and thus as an appropriate response that does not warrant intervention. Whether this is also applicable to other acute stress conditions, such as surgery, infection or the initial phase of critical illness, is still a matter of controversy (38).…”

“…In the chronic phase of critical illness, serum PRL levels are no longer as high as in the acute phase and the secretory pattern is characterized by a reduced pulsatile fraction (24,37). A role for endogenous dopamine has been suggested (63).…”