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Background: On the basis that (1) multiple interactions exist between the hormonal and immune systems, and (2) aging is accompanied by changes in thyroid hormone metabolism and responsiveness, we postulate that thyroid hormones may be involved in the observed decrease in natural killer (NK) activity in a population of apparently healthy elderly subjects. The purpose of the study is to compare NK cytotoxic activity and serum concentrations of TSH and thyroid hormones in healthy old and young people, and to assess in vitro the effects of triiodothyronine (T[sub 3] ) on NK activity. Materials and Methods: Sixteen of the 47 healthy old people (mean age 64 ± 5.2) were classified as optimally healthy, and the remainder as ‘almost healthy’ (according to the criteria of the Senieur protocol) [Ligthart et al., Mech Ageing Dev 1984;28:47–55]; the mean age of the healthy young people was 23.3 ± 2.3 years. NK cytotoxic activity of peripheral blood mononuclear cells was assessed using [sup 51] Cr release from K562 target cells. The cutoff level for defining low and high NK responses was set at a value of 20%. Serum concentrations of TSH, total thyroxine (T[sub 4] ) and total triiodothyronine (T[sub 3] ) were measured by radioimmunoassay. Results: NK activity in the ‘optimally healthy’ elderly was high (mean 41 ± 12%, SE), whereas ‘almost healthy’ subjects showed low NK activity (mean 6 ± 5%). Serum T[sub 4] and TSH levels, but not T[sub 3] concentrations were similar in both the young and old. We observed a significant correlation (r = 0.53, n = 21, p < 0.05) between the serum total T[sub 3] level and the NK activity in the elderly individuals. Under in vitro conditions exogenous T[sub 3] significantly increased NK activity in the elderly subjects who had serum T[sub 3] values at the lower end of the reference range. However, no effect of T[sub 3] on NK activity was observed in peripheral blood mononuclear cells obtained from either old or young individuals who had serum T[sub 3] levels at the midpoint of the range. Conclusion: Decreased serum concentrations of total T[sub 3] may contribute to low NK activity in the ‘almost healthy’ subgroup of the elderly.Copyright © 2001 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

In order to explore the morphological basis of the altered feeding behaviour of old rats, an ultrastructural investigation of the magnocellular neurons of the hypothalamic paraventricular nucleus (PVN) was performed. Young and old male Wistar rats, 5 and 24 months old, respectively, and with each age group comprising 12 animals, were divided into 3 groups. The rats in Group I were used as controls (normally fed), the rats of Group II were fasted for 48 hours and in Group III the rats were fasted for 48 hours and then refed for 24 hours. The brains were fixed by perfusion and histological and ultrathin sections were obtained by routine methods. Common features of the magnocellular PVN neurons of young and old rats were abundant Golgi complexes and short fragments of RER localised at the cell periphery. In contrast to young rats, the PVN neurons of old animals showed deep indentations of the nuclear envelope and age-related residual bodies. In both age groups fasting for 48 hours led to the expansion of the Golgi complexes and dilatation of RER cisternae. In contrast to those in fed rats, RER cisternae in the neurons of old fasted animals were situated between the nuclear envelope and the Golgi zone. Prolonged RER cisternae were distributed in the peripheral cytoplasm of refed old rats. Our observations suggest that at the ultrastructural level the process of ageing does not change the responsiveness of magnocellular PVN neurons to fasting-refeeding.

Many hypothalamic nuclei are involved in the regulation of food intake and energy homeostasis. An ultrastructural investigation of the hypothalamic ventromedial nucleus (VMN), a hypothetical "satiety centre" was performed to explore the morphological basis of altered feeding behaviour of old rats in an experimental model of fasting/refeeding. Young (5 months old, n=12) and old (24 months old, n=12) male Wistar rats were fasted for 48 hours, then refed for 24 hours and sampled thereafter. Brain tissue was fixed by perfusion, histological and ultrathin sections were obtained by routine methods. Although food intake was similar in control young and old rats, during refeeding old animals consumed less chow than young ones. The EM analysis of VMN neurones of old control rats revealed, besides typical age-related residual bodies, deep indentations of the nuclear envelope and the presence of long, undulating rough endoplasmic reticulum cisternae in the cell periphery. In both young and old rats fasting for 48 hours led to the expansion of Golgi complexes and increased folds of the nuclear envelope, which is suggestive of enhanced cellular activity of the VMN neurones. These fasting-induced alterations were sustained in the VMN neurones of refed rats in both age groups. The results showed that the VMN neurones of old control rats differ at the ultrastructural level from young ones. However, starvation and subsequent refeeding cause similar alterations in the hypothalamic neurones of "satiety centre" of both young and old rats.