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

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

reversal of cholesterol transport in hyperlipoproteinemia

High levels of high density lipoprotein cholesterol [HDL-C] can reverse cholesterol accumulation in the arterial wall by reversing cholesterol transport. To determine this fact by getting high levels of HDL-C fraction of serum nicotinic acid was given in a 3 g daily dose for 6 weeks to 20 patients of mean age 52 +/- 9 years, with type IIa, type IIb and type IV hyperlipoproteinemia [HLP]. The cholesterol levels of serum very low density [VLDL] and low density [LDL] lipoprotein decreased during treatment [P <0.05]. Serum HDL cholesterol levels increased by 37%. Changes in the concentrations of HDL-C after 6 weeks of drug treatment were not related to the type of HLP, neither were these effects of nicotinic acid correlated with changes in VLDL or LDL lipid levels. From this study it was concluded that HDL-C could be increased by prolonged nicotinic acid therapy and, therefore, could reverse cholesterol transport. High levels of HDL-C is an important determinant of the antiatherogenic effects of the drug