It has been observed that basal and/or TRH-stimulated serum TSH levels occasionally conflict with the actual values of circulating thyroid hormones in patients with anorexia nervosa. In the present study sixteen female patients with anorexia nervosa during self-induced starvation displayed clinical findings suggesting hypothyroidism, e.g., cold intolerance, constipation, bradycardia, hypothermia and hypercholesterolemia in association with decreased serum total T3 (62.8<5.2ng/dl) and T4 (6.6<0.3μg/dl). Markedly decreased T3 correlated positively with average heart rate (r=0.5655, P<0.025) and negatively with total cholesterol (r=-0.7413, P<0.005). This result may suggest that peripheral metabolic state of the underweight anorexics depends considerably upon the serum T3 concentration.
Despite decreased total thyroid hormones, free T4 assayed by radioimmunoassay was normal in all five cases examined (1.4<0.2ng/dl) and the free T4 index in fifteen cases was normal except in one case. Basal TSH was not increased and TSH response to exogenous TRH was not exaggerated in any. These results may be compatible with a theory that free T4 has a dominant influence on pituitary TSH secretion. Furthermore, glucocorticoids may also have some influence on depressed TSH response, because an inverse correlation between increased plasma cortisol and the sum of net TSH increase after TRH was observed in twelve cases examined.
In conclusion, it is suggested that normal sensitivity of peripheral tissues and pituitary thyrotroph to different circulating thyroid hormones is maintained in anorexia nervosa patients even during severe self-induced starvation, and that the metabolic state in these patients is considerably under the influence of circulating T3.