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Alevizaki et al., Athens, Greece, studied vasodilation in
the brachial artery during reactive hyperaemic flow (endothelium dependent)
as well as after sublingual nitroglycerin administration (endothelium independent)
in patients grouped according to serum TSH: group A (n = 7) TSH 0.4-2ľU/ml,
group B (n = 6) TSH 2.01-4 ľU/ml, group C (n = 10) TSH 4.01-10 ľU/ml
and group D (n = 12) TSH > 10 ľU/ml. Nitroglycerin-induced dilatation
was not different in these groups but flow mediated, endothelium- dependent
vasodilatation was significantly higher in group A compared to group B,
group C, and group D. There was an inverse correlation between TSH values
and endothelium-dependent vasodilatation. Other factors that could influence
endothelial function like age, hypertension, and smoking, were similar
in all groups but serum cholesterol tended to increase from group A to
group B, however, the differences were not significant. It is concluded
that endothelium-dependent vasodilatation as a marker of endothelial function,
that is considered to be an early event in the development of atherosclerosis,
is impaired not only in patients with borderline hypothyroidism, but also
in patients with subclinical hypothyroidism.
Diekman et al., Amsterdam and Nijmegen, The Netherlands, tested the hypothesis that in hypothyroidism oxidation rate of LDL particles is increased versus euthyroidism. They tested oxidation kinetics of LDL and serum concentration of LDL in 10 patients with primary hypothyroidism (mean TSH 76 mU/l and mean T4 40 nmol/l) and retested when patients were at least 3 months euthyroid during T4 treatment (mean TSH 2.7 mU/l and mean T4 115 nmol/l). They found during primary hypothoidism that dienes in LDL particles was increased as compared to after T4 treatment (258 vs 187 nmol/mg). Resistance to oxidation of LDL was 43 vs 76 min, and oxidation rate was 15 vs 19 nmol/mg LDL/min respectively. It is concluded that hypothyroidism is associated with increased oxidizability of LDL promoting atherosclerosis. Huber et al., Basel, Switzerland, studied 154 female patients with subclinical hypothyroidism (elevated serum TSH with normal free T4 and total T4 levels) over a mean period of 10 years. They found that after this period 34% of these patients developed overt hypothyroidism, 57% remained in the subclinical stage and 14% normalized their thyroid function. When patients were grouped according to TSH: gr.I TSH <6, gr. II TSH 6-12, and gr. III TSH>12 mU/l, overt hypothyroidism developed in 7.3%, 26% and 78% respectively. TSH reserve after TRH was more predictive in development of overt hypothyroidism than titers of circulating thyroid autoantibodies. |
