Acta med. scand. Vol. 197, pp. 15-17, 1975

THE ADHESIVENESS OF HUMAN BLOOD PLATELETS AND THYROID FUNCTION Arvid J. Hellem;Erik Segaard and Jan H. Solem From the Department of Internal Medicine, Akershus Central Hospital, University of Oslo, Oslo, Norway

Abstract. Hypothyroidism is associated with severe coronary atherosclerosis.In spite of this the reported incidence

of angina pectoris and myocardial infarction in untreated hypothyroidism is small. Since many authors consider the formation of a thrombus in coronary arteries to be the final event of the process which leads to myocardial infarction, changes in the platelet function may explain the paradoxical rarity of myocardial infarction in untreated hypothyroidism. To evaluate this hypothesis, platelet adhesiveness has been estimated before and after treatment in 9 hypothyroid and 16 thyrotoxic patients. In thyrotoxicosis the platelet adhesiveness was significantly increased, but decreased to normal after treatment. In hypothyroidism platelet adhesiveness was abnormally low but increased to normal value after thyroid hormone replacement. This may be an important factor in precipitating myocardial infarction in patients with hypothyroidism and coronary artery atherosclerosis. Patients with thyrotoxicosis and hypothyroidism are in an exceptional position with regard to coronary heart disease. Extensive clinical and necropsy studies have shown that severe coronary atherosclerosis occurs twice as frequently in patients with myxoedema as in controls matched for age, sex, BP and associated extra thyroideal disorders (18). Despite hypercholesterolaemia and increased atherosclerosis, the incidence of myocardial infarction in untreated myxoedema is not increased. When thyroxin is given to such patients the incidence of angina pectoris and the risk of precipitating myocardial infarction increases ( 19). In hyperthyroidism the plasma cholesterol level is low, but the incidence of atherosclerosis is unknown. However, an incidence of angina pectoris from 10 to 12 % has been reported (3). Consequently it should be expected that a coincidental occurrence of myocardial infarction and thyrotoxicosis would

not be a rarity. In an unselected series of 384 patients suffering from thyrotoxicosis, 7 developed myocardial infarction during an active stage of thyrotoxicosis, and in a further 8 there appeared signs of acute coronary disease suggestive of mild myocardial infarction (4). Thus thegeneral impression of the infrequency of myocardial infarction in active thyrotoxicosis seems not to be valid. The profound influence of thyroid dysfunction on metabolic processes is well recognized, but its relation to platelet adhesiveness has been sparingly investigated (16, 17). The first stage in thrombus formation is the adhesion of platelets to the injured vessel wall and to each other, leading to the formation of the white thrombus. As thromboembolic disorders have been reported to be associated with increased platelet adhesiveness (7, 14), it seemed important to determine whether alterations in thyroid function were associated with changes in platelet adhesiveness. PATIENTS AND METHODS Nine hypothyroid and 16 thyrotoxic patients have been examined with regard to the adhesivenessof blood platelets by the glass bead filter method of Hellem (9)before, during and after treatment. The main principle of the method is to expose native blood to a standardized glass bead column. By an electrically driven mechanical device the blood from a graduated syringe is forced through the glass bead column at a constant rate. The difference of the platelet count before and after passage through the column gives the number of adhesive platelets. This is expressed as percentage of the initial count. The normal value by this method is 75% with a S.D. of 13. In addition the primary bleeding time has been estimated in 6 hypothyroid patients and in all the thyrotoxic patients by a modification of Ivy’s method (2). Normal value < 12 min. Acia mcd. scand. 197

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A . J . Hellem et al.

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Fig. 1 . Percent adhesive platelets and PBJ before and after treatment in 9 hypothyroid patients.

Fig. 2. Percent adhesive platelets and PBJ before and after treatment in 16 thyrotoxic patients.

RESULTS

The mean platelet number was 231 000 before and 250000 after treatment. This difference is not significant. The mean bleeding time remained unchanged after treatment (6 1 min).

Hypothyroidism

Fig. 1 shows platelet adhesiveness and PBJ before and after treatment in the 9 hypothyroid patients. The mean platelet adhesiveness was 43 %before and 73% after treatment. This difference is highly significant @

The adhesiveness of human blood platelets and thyroid function.

Hypothyroidism is associated with severe coronary atherosclerosis. In spite of this the reported incidence of angina pectoris and myocardial infarctio...
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