Pituitary-thyroid function in patients with Cushing's syndrome--comparative study before and after extirpation of adrenal cortex tumor

Abstract

The pituitary-thyroid function and the metabolism of the thyroid hormones in the blood were investigated in 19 patients with Cushing's syndrome before and after an adrenalectomy, 16 patients had adrenal adenomas and 3 patients had modular adrenal hyperplasias. Serum T4, free T4 (FT4), T3, reverse T3 (rT3), TBG and TSH were measured in all patients by radioimmunoassay, and changes in serum TSH, PRL and HGH following the injection of TRH 500 micrograms in 10 out of 19 patients were observed to evaluate the pituitary functions. Serum T4, FT4 and rT3 were within normal limits and not significantly changed after the surgical treatment. Serum TBG levels in patients before the surgical treatment were also within the normal range. After the treatment, a small but significant increase in TBG levels was observed. Serum TSH levels were suppressed before the surgery and increased after the surgery, but a coefficient of correlation between serum cortisol and TSH levels was not statistically significant. The serum T3 levels were abnormally low in Cushing's syndrome and increased significantly (p less than 0.001), accompanying the normalization of serum cortisol levels, after the surgical treatment. Moreover, there was a negative correlation between serum T3 and cortisol levels before the treatment (r = -0.586), but it was not statistically significant (before the treatment: T3 0.71 +/- 0.04 ng/ml, cortisol 30.2 +/- 2.1 micrograms/dl, after the treatment: T3 1.58 +/- 0.15 ng/ml, cortisol 7.5 +/- 2.0 micrograms/dl). To evaluate further the metabolic changes in circulating thyroid hormones, T3/T4, T3/rT3, TBG/T4 and TBG/T3 were compared before and after the adrenalectomy. Significant decreases in T3/T4 (p less than 0.001) and T3/rT3 (p less than 0.05) and a significant increase in TBG/T3 (p less than 0.05) were observed before the surgery. On the other hand, TBG/T4 was not significantly different before or after the surgery. The TSH response to TRH was significantly higher in postoperative patients than in preoperative patients (p less than 0.05). Before the surgical treatment no responses of serum HGH to TRH were observed in any patients, while after the treatment, abnormal increases from 4.5 +/- 1.4 ng/ml to 10 +/- 1.1 ng/ml at 15 min. after TRH administration were observed. There was no difference between PRL response to TRH before or after the surgery.(ABSTRACT TRUNCATED AT 400 WORDS)