The Relationship between Serum Triiodothyronine and Thyrotropin during Systemic Illness*

Abstract

The reported failure of serum TSH to rise in response to the low serum T3 of severe systemic illness may be due to the known stress inhibition of TSH secretion. We therefore measured TSH and total and free thyroid hormones during the course of recovery from severe illness. During recovery, TSH increased at a time when T3 was rising but still below normal (mean TSH during recovery, 6.5 +/- 0.8 SEM microU/ml, n = 41 vs. normal, 2.5 +/- 0.2 SEM microU/ml; n = 31; P less than 0.001), TSH concentrations were negatively correlated with total and free T3 and less strongly correlated with total T4 but not with free T4. Average TSH concentrations were also significantly elevated in severely ill patients with hypothermia that was unrelated to cold exposure (mean TSH, 5.6 +/- 1.3 microU/ml; n = 11; P less than 0.005). The T3 concentrations in these sera were lower than those of other severely ill patients. Thus, during recovery from severe illness and during hypothermia not induced by cold, the relationship between serum T3 and TSH is qualitatively similar to that seen in primary hypothyroidism and may imply a pituitary response to a deficiency of thyroid hormone.

Effect of Perinatal Asphyxia on Thyroid Hormones

“…Características da síndrome têm sido descritas em vári-as situações como desnutrição protéico-calórica 26 , pós-operatório de grandes cirurgias 24 , sepse 15 , aspiração de mecônio 15 e asfixia 13 . Também está associada ao uso de certas drogas, como corticosteróides 25,[27][28][29] , dopamina [27][28][29] , contrastes iodados 25,[27][28][29] , entre outras.…”

Novel insights into the neuroendocrinology of critical illness

“…Together, these ®ndings indicate that production and/or release of thyroid hormones is reduced in the chronic phase of critical illness, due to impaired hypothalamic stimulation of the thyrotropes, in turn leading to reduced functioning of the thyroid gland. In line with this concept is the rise in TSH marking the onset of recovery from severe illness (43). The exact mechanisms underlying the neuroendocrine pathogenesis of the low thyroid hormone levels in prolonged critical illness is unknown.…”

Suppression of Thyrotropin by Morphine in a Severely Stressed Patient

“…If this hypothesis is correct, TSH suppression and central hypothyroidism can be expected to occur frequently in severely stressed patients receiving morphine. Although it is clear that severe nonthyroid illness causes temporary functional central hypothyroidism [29,30], opinions differ as to whether this should be remedied with thyroid hormone replacement, since it may have evolved as an adaptation to illness [36]. However, the latter argument does not seem relevant to the pharmacologically induced central hypothyroidism that seems to have occurred in our patient.…”

“…The combined effects of the stress induced increase in endorphins and an increased synthesis and activation of opiate receptors probably accounts for the early, sustained inhibition of TSH secretion that occurs in response to stress. This is the probable cause of the central hypothyroidism seen in the euthyroid sick syndrome [29][30][31]. The apparent discrepancy between an inhibitory effect of morphine on TSH in the rat [5][6][7][8][9][10] and its stimulatory effect in normal human subjects [11][12][13][14] is likely to depend on the unavoidable presence of stress in experimental animals and its absence in human subjects who volunteer to receive morphine.…”

“…The free T4 was normal at 1 ng/dl (0.71-1.85), total T4 4.6 mg/dl (4.7-11.4), T3 resin uptake (T3RU) 36% (26)(27)(28)(29)(30)(31)(32)(33)(34)(35)(36)(37), triiodothyronine (T3) 30 ng/dl (45-137). On the fourth hospital day she was successfully extubated and returned to the general medical service in stable condition, although still lethargic.…”