The conversion of thyroxine to triiodothyronine in the lung: comparison of activity of type I iodothyronine 5' deiodinase in lung cancer with peripheral lung tissues.

UNLABELLED: Triiodothyronine (T3) is the main active hormone, which is derived 20% from the thyroid gland and 80% from peripheral tissues. Thyroxin--5' deiodinases play a leading role in maintaining appropriate T3 concentrations in the different cells and organs: including the lung. The deiodinases present in pneumocytes were found to be localised in endoplasmatic reticulum. Aims of this study were: 1. To estimate activities of Type I and Type II iodothyronine 5' deiodinases (DI, DII) in two histological types of lung cancer. 2. To investigate possible differences in DI and DII activities between tumour tissue and peripheral lung tissue. 3. To study whether DI and DII activities are related to the extent of the disease process and grade of differentiation of lung cancer. MATERIAL: We studied 44 patients undergoing thoracotomy due to lung cancer. Histologically: 23 pts--squamous cell cancer, 21 pts adenocarcinoma. In all patients both tumour and peripheral lung tissue were studied. DI activity was measured in pmol 1251- released from 125 IrT3/min/mg of proteins, DII activity--in fmol 125I- released from 125IT4/hour/mg of protein.
RESULTS: In most specimens DI and DII activities were observed. DI activity in specimens from lung peripheral tissue was: 3.3-58.3 pmol/min/mg of protein (mean 22.20) and in lung cancer tissue was: 2.0-44.7 pmol/min/mg of proteins (mean 13.3). DII activity in lung peripheral tissue ranged from 19 to 242 fmol/h/mg protein (mean 94.4) and in lung cancer ranged from 21 to 253 fmol/h/mg protein (mean 107.9).
CONCLUSIONS: 1. Conversion of T4 to T3 occurs also in the lung. 2. The activity of DI is statistically significantly lower, in lung cancer than in peripheral lung tissue (13.3 +/- 9.5 vs 22.20 +/- 13.4 pmol/min/mg protein) respectively, p < 0.001. 3. DII activity in lung is present and similar in peripheral lung and lung cancer tissue. 4. There is a non-significant trend for correlation of DI activity and grade of differentiation (G1-G3) of tumour tissue and stage of lung cancer. Abbreviations' list: T3--triiodothyronine, T4--thyroxine, FT4--free thyroxine, rT3--revers triiodothyronine TSII--Thyroid Stimulating Hormone Type I lodothyronine 5'deiodinase = type I 5'deiodinase = 5'DI = DI Type II Iodothyronine 5'deiodinase = typeII 5'deiodinase = 5'DII = DII E.S.S.--Euthyroid Sick Syndrome, hDII = human type II iodothyronine deiodinase HDII-b, hDII-c = two novel splice variants SCC--Squamous Cell Cancer, A--adenocarcinoma, BMI--Body Mass Index BSA--Bovine Standard Albumin, DTT-1,4 Dithio-L-treitol, PTU--Propylothiouracil TCA--Tricholoroacetic Acid, TNM--Tumour Nodule Metastases (class.) G1-G3-grade of differentiation, COPD--Chronic Obstructive Pulmonary Disease.