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Introduction Several surveys of elderly people in different countries during the last decade [1-11] have found a high prevalence of increased thyroid-stimulating hormone (TSH) levels, but results vary with the [...]

The aim of this study was to assess the prevalence of increased thyroid-stimulating hormone (TSH) levels (subclinical or undiagnosed hypothyroidism) in a representative sample of a community-living elderly population and to examine the relationships with cognitive functions and depressive symptoms. An epidemiological study was made of a cohort of 2792 subjects over 65 years of age. A blood sample was obtained from 425 volunteers of this cohort and assayed for TSH. Every subject participating in the study was interviewed and given a battery of neuropsychological tests by a psychologist. Three hundred and eighty-one subjects (89.7%) had normal TSH levels; 18 subjects (4.2%) had TSH lower than 0.4 microU/ml, associated in two of them with hyperthyroxinaemia. Twenty-six subjects (6.1%) had increased TSH levels, associated in 18 of them with a normal free thyroxine level and in eight with a low free thyroxine level. Increased TSH levels were significantly linked with female sex and with the presence of symptoms of depression on the CES-D scale but not with impairment of cognitive function.

We studied the electrophysiological properties of individually characterized TSH-secreting cells cultured from pituitary fragments surgically removed from three patients, two who had primary TSH-secreting adenomas and one who had chronic TSH hypersecretion (hyperplasia) secondary to primary hypothyroidism. The TSH-secreting cells were excitable and had calcium-dependent action potentials. More than 80% of the cells cultured from the two patients with TSH-secreting adenomas were spontaneously active, whereas fewer cells (20%) cultured from the hypothyroid patient were spontaneously active. TRH (50 nmol/L) induced a complex pattern of electrical changes. The initial response was transient hyperpolarization (activation of potassium conductance), followed by increased low amplitude voltage fluctuations occasionally leading to action potentials. These TRH-induced electrophysiological changes were similar to those reported in rat and human PRL-secreting adenoma cells. These results suggest that TRH may have an identical mode of action in tumoral PRL and TSH cells. In the cells from the hypothyroid patient, the initial response to TRH cells was similar, but the second phase response was greater. The findings that the cells cultured from these patients behaved differently with regard to their electrophysiological characteristics (action potentials) and responses to TRH may reflect the different clinical conditions from which they were derived.