Secretion rates of thyroxine, triiodothyronine, and reverse triiodothyronine in man during surgery

Abstract

The secretion rates of T4, T3, and rT3 were studied in experiments of short duration by a new method based on determinations of the hormone difference across the thyroid combined with simultaneous electromagnetic thyroid blood flowmetry during surgery in 70 euthyroid patients. The secretion rate of T3 was similar in normal thyroid tissue and nodular goitre, but those of T4 and rT3 were lower in nodular goitre and solitary adenoma (P < 0.05). In 61 patients with normal thyroid tissue or nodular goitre the secretion rates during surgery (mean \ m=+-\ sem) were for T4 222 \ m=+-\ 28 nmol/day, for T3 27.4 \m=+-\ 3.1nmol/ day, and for rT3 3.5 \ m=+-\ 0.5 nmol/day. In relation to the individual T4 secretion rate, the secretion rate of T3 was 12.5 \m=+-\3.0% and that of rT3 1.2 \ m=+-\0.9%.In these short-term experiments we found a secretion rate for T4 during operation about 50% greater than in earlier long-term kinetic studies, but which tallied with a recent report using a 4-compartment model. For T3 and rT3 it was 2\p=n-\3times greater than earlier estimates. The secretion was estimated to be 50% of the total production rate for T3 and 6% for rT3. If proportional adjustment were performed to yield a T4 secretion of about 130 nmol/day, T3 and rT3 secretion rates would still be greater than earlier reported.No method as yet exists for measuring directly the rate of thyroid hormone secretion in man (Chopra 1978). Indirect measurement of production rates of thyroid hormones has been achieved with radionucleides using different compartment models (Sterling et al. 1954;DiStefano & Fisher 1979). However, the methods for separation of iodothyronines other than T4 have been criticized (Aickin et al. 1977;Rudolph et al. 1978); and it is difficult by kinetic methods to distinguish secretion from extraglandular conversion of the hormones.In animals the secretion rates of thyroid hor¬ mones have been estimated as the product of the arteriovenous hormone difference and the thyroid blood flow (Mowbray & Peart 1960;Falconer 1967). Application of this method to man should avoid some of the problems in compartment models. Hormone differences across the thyroid may be measured during surgery (Tegler et al. 1976) and a method for thyroid flowmetry has recently been reported (Tegler et al. 1981). Our aim was therefore to study the secretion rates of T4, T3, and rT3 in man by a direct method using hormone differences across the thyroid gland and simultaneous electromagnetic blood flowmetry.Material and Methods PatientsTen men and 21 women, aged 57 (33-78) years (mean and range), with normal thyroid tissue in the lobe studied were admitted for surgery for hyperparathyroidism (n = 25), unilateral adenoma, nodular goitre or follicular carcinoma (n = 6). All lobes studied were macroscopically normal; and 15 randomly chosen were histologically normal. All patients were euthyroid on the basis of clinical findings and serum concentrations of T4, T3, and thyrotrophin (Odell et al. 1965).Thirty euthyroid subjects, 5 men and 25 women aged 56 (26 -...

Basal and Thyrotropin-Stimulated Secretion Rates of Thyroglobulin from the Human Thyroid Gland during Surgery

“…On the other hand even vigorous diagnostic palpation is not associated with any elevation of the peripheral Tg concen¬ tration (22). In this study great care was taken to avoid trauma to the thyroid gland (9,14,15). However, we observed a rise in peripheral Tg concentration already at the beginning of the surgical procedure before any obvious trauma to the thyroid gland.…”

“…The type of anesthesia was chosen to give the least possible variation in the circulation and to avoid increased release of catecholamines. The basal thyroid blood flow and secretion rates of thyroid hormones were independent of the different types of anesthesia used (9,15). …”

“…Corresponding data for T4 were 65-140 nmol/L (mean = 103), 3% (n = 40) and 12%, and for TSH 0.5-5.0 mU/L, 10% and 16%. The secretion rates of Tg were calculated in the same way as those of the thyroid hormones (9,14).…”

“…The surgical procedure aimed at giving the least possible trauma to the thyroid gland (9,14). The type of anesthesia was chosen to give the least possible variation in the circulation and to avoid increased release of catecholamines.…”

Further data supporting episodic degenerative discharge of thyroid hormone from nodular goiters.

“…The thyroid hormone levels in the peripheral vein are known to be the same as those in the artery (Westgren et al, 1977;Hooper et al, 1978;Tegler et al, 1982). Therefore, the hormonal gradients between the thyroid and peripheral veins reflect the secretion of these hormones in the thyroid.…”