Episodic Thyrotropin (TSH) and Prolactin (PRL) Secretion During Aging in Postmenopausal Women

Summary

While aging is known to decrease episodic thyrotropin (TSH) secretion in men, no detailed information is available as to age-related alterations in the TSH and prolactin (PRL) release patterns in postmenopausal women (PMW). Accordingly, we compared the TSH and prolactin (PRL) secretory profiles of 6 euthyroid younger PMW (mean age: 53.0 years) with those of 7 euthyroid older PMW (mean age: 80.4 years). In all PMW, blood samples were obtained at 10 minute intervals for 10 hours for serial determinations of TSH and PRL by RIA. While thyroxine (T₄) serum concentrations were not different in younger from older PMW, triiodothyronine (T₃) levels markedly (p < 0.05) decreased in older PMW. In both younger and older PMW, TSH and PRL were secreted episodically (by Cluster pulse algorithm), with considerable inter-individual variabilities in either study group. TSH and PRL pulse attributes (interpulse intervals, frequencies, amplitudes) were comparable in younger and older PMW, although a tendency of mean TSH to increase (p = 0.18) was noted for older PMW. Mean TSH and PRL serum concentrations were positively (r = 0.94, p < 0.01) correlated in older, whereas not in younger PMW. These observations demonstrate that the pulse characteristics of episodic TSH and PRL secretion are preserved in PMW even of old age. However, in view of markedly decreased circulating T₃ concentrations and of no substantial change in the TSH pulsatile secretion in older PMW, the negative feedback on the hypothalamic-pituitary unit may be impaired in elderly women.

Key words

Thyrotropin - Prolactin - Pulsatile - Postmenopausal - Women - Aging