Effect of subclinical and clinical hypothyroidism on thyrotropin, prolactin and peripheral tissues

ABSTRACT

Subclinical hypothyroidism appears to be a risky factor for atherosclerosis and for coronary heart diseases and can affect other organs, so its clinical significance is controversial. It was found in about 7.5% of females and 3% of males. Therefore, the metabolic effects of progressive thyroid failure in patients with various degrees of hypothyroidism compared with control subjects were evaluated. This work was carried out on 20 female patients, 10 female patients with subclinical hypothyroidism, 10 patients with overt hypothyroidism and 10 euthyroid women as control. All patients and controls were subjected to medical and endocrine evaluation including measurements of thyrotropin [TSH], prolactin, free thyroxin [FT4], thyroxin [T4], and triiodohyronine [T3], as well as lipid profiles and some tests of peripheral thyroid hormone action. All patients were divided into five groups according to disease severity, grades I to III [subclinical hypothyroidism with normal T4 levels] and grades IV to V [clinical hypothyroidism with diminished T4]. Results, in grade I [basal TSH <6 mu/L] showed significant changes in the clinical index [P <0.05] and apoprotein A-I level [P <0.05]. The findings were similar in grade II [TSH 6-12 mu/L]. More changes were demonstrated in grade III [TSH >12 mu/L] with a definite elevation of ante reflex time [P <0.001] and to a lesser extent creatine kinase. The mean LDL-cholesterol [LDL-C] showed nonsignificant increased level. LDL-C levels were definitely higher in patients with grade III disease compared with the controls [P <0.05] and with patients with grades I and II disease. Total cholesterol, triglyceride and apoprotein B were clearly elevated only in clinical hypothyroidism [grades IV and V] [P < 0.01]. From this study it is concluded that subclinical hypothyroidism has significant effects on some peripheral target organs at an early stage [grades I and II] but affects LDL-C and skeletal muscle only at a later stages. The elevated LDL-C in grade II subclinical hypothyroidism provide a likely pathogenetic explanation for the reported association of coronary heart disease with this syndrome. The effect of increased prolactin secretion observed in subclinical hypothyroidism on gonadal function and infertility needs more researches