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Decreased Basal and Stimulated Thyrotropin Secretion in Healthy Elderly Men^*

A. VAN COEVORDEN, E. LAURENT, C. DECOSTER, M. KERKHOFS, P. NEVE, E. VAN CAUTER and J. MOCKEL

Department of Endocrinology Brussels, Belgium
Department of Internal Medicine Brussels, Belgium
Department of Psychiatry Brussels, Belgium
Department of Clinical Chemistry Brussels, Belgium
Department of Institute of Interdisciplinary Research Brussels, Belgium
School of Medicine, Free University of Brussels Brussels, Belgium
Department of Medicine, University of Chicago Chicago, Illinois 60637

Address all correspondence and requests for reprints to: Eve Van Cauter, Ph.D., Department of Medicine, Box 138, University of Chicago, 5841 South Maryland Avenue, Chicago, Illinois 60637.

To delineate the effects of aging on basal and stimulated TSH secretion, we studied the 24-h profile of plasma TSH levels and the TSH response to TRH stimulation (200 µg TRH, iv) in eight healthy elderly men, aged 67–84 yr, and eight normal young men, aged 20–27 yr. Subjects with thyroid antibodies against microsomal or thyroglobulin antigens were excluded. During the 24-h study, blood was sampled at 15-min intervals. TSH levels were measured by an ultrasensitive immunoradiometric assay. Sleep was polygraphically monitored, and circadian and pulsatile TSH variations were quantified using specifically designed computer algorithms.

In older men, the 24-h mean TSH concentration was approximately 50% lower than that in young men (0.78 ± 0.37 vs. 1.43 ± 0.41 µU/mL; P < 0.01), but basal T₃ levels were only slightly lower (93 ± 12 vs. 115 ± 16 ng/dL; P < 0.02), while basal T₄ levels were normal. The normal diurnal variation of TSH levels, with a nocturnal acrophase and an afternoon nadir, as well as the pulsatile nature of TSH release were preserved in elderly men. When expressed in microunits per mL, the amplitude of these temporal variations was reduced in elderly men compared to that in younger subjects. However, when expressed in relation to the mean TSH levels, the amplitudes of diurnal and pulsatile variations were similar in both groups of subjects. TRH-induced TSH secretion was lower in old than in young men (area under the curve, 15.9 ± 6.3 µU/mL. 10 min in elderly men vs. 42.0 ± 16.6 µU/mL. 10 min in young men; P < 0.002). However, the TRH-induced elevations of T₃ and T₄ were of similar magnitude in both groups.

These results indicate that in healthy elderly men, the overall 24-h TSH secretion is decreased, and the pituitary is less responsive to stimulation by TRH. However, the chronobiological modulation is preserved. These alterations could reflect an adaptative mechanism to the reduced need for thyroid hormones in old age. The thyroid keeps an intact capacity to respond to acute increases in TSH concentrations.

^* This work was supported by a grant from the Ministère de la Politique Scientifique (Actions Concertées) and Grant FRSM 3.4539.84 from the Fonds National de la Recherche Scientifique Médicale.

Research Fellow of the Fonds National de la Recherche Scientifique.

Received November 28, 1988.

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