Endocrine Abstracts

Background: Cholesterol is a major component of the cell membrane. It plays an important role in its physiology affecting vital properties, such as membrane fluidity, cation transport, cell receptors, osmotic resistance etc. Abnormal conditions that change serum cholesterol concentration (SC) can also alter erythrocyte membrane cholesterol concentration (EMCC) possibly resulting in differentiation of several membrane functions.

Aim: To investigate whether changes in SC, usually observed in hyperthyroidism, affect EMCC.

Patients and methods: About 35 healthy controls (24 male, 11 female, age: 39.46±10.86) and 23 patients with hyperthyroidism (3 men, 20 women, age: 36.00±8.19) were studied. SC, EMCC, triiodothyronine (T₃), thyroxine (T₄) and thyroid stimulating hormone (TSH) were measured in all.

Results: Serum T₃ did not differ between the two groups (1.22±0.30 versus 1.10±0.24). In the patients as compared to the controls T4 was significantly (P<0.001) higher (11.51±0.59 versus 8.22±1.70) and TSH significantly (P<0.001) lower (0.12±0.06 versus 2.59±1.14). SC was significantly lower (P<0.001) in the patients (151.21±29.27) than in the controls (216.49±21.28). EMCC was also significantly lower (P<0.001) in the patients (36.08±9.95) than in the controls (145.37±17.06). The ratio of SC/EMCC was significantly (P<0.001) higher in the patients (4.68±2.23 versus 1.51±0.23). In the patients with hyperthyroidism there was a significant negative correlation of SC to T₄ (P=0.023) and a positive one of EMCC to TSH (P=0.031).

Conclusions: Hyperthyroidism seems to decrease both SC and EMCC in a degree related to its severity. However the decrease of EMCC is much greater, thus resulting in a considerable depletion of erythrocyte membrane from its structural component. The possible consequences of this depletion to cell physiology have to be investigated.