AGING AND ENDOCRINE FUNCTION

The changes which occur in endocrine physiology in the course of normal ageing are rather specific and involve either interesting interplays of endocrine glands and their target organs or changes in hormone degradation rates. Two of the critical 'life-support' endocrine circuits - pituitary-adrenal cortex and pituitary-thyroid - evince changes with age that are secondary to decreased hormone degradation in peripheral tissues; basal circulating hormone levels are maintained and responses to stress are intact. A third critical axis - the β-cell - shows a change in sensitivity. Islet cell perception of hyperglycaemia is depressed ('glucoreceptor defect') and insulin output is appropriately low in the face of modest glucose challenge. Target organ sensitivity to insulin, on the other hand, is probably normal. In contrast, sensitivity of the osmoreceptor is heightened in the aged, and ADH secretion is increased (relative to younger subjects) in response to elevated plasma osmolality. This change is appropriate to decreased renal tubular sensitivity to ADH. Changes with age in the pituitary-ovarian axis are wellknown, and may be paralleled in men, albeit far less dramatically, in terms of circulating androgen and gonadotrophin levels. It is not possible, from these observations, to discern a common denominator which can be regarded as 'characteristic' of endocrine gland ageing. Attempts to describe endocrine gland ageing globally - for example, as a function of altered hormone feedback thresholds in the hypothalamus - have, so far, been unconvincing. On the other hand, studies in animals of peripheral tissue hormone receptors, while incomplete, suggest rather generalized age-related changes. Except for indirect evidence regarding insulin, very little is known in man regarding receptor changes with ageing. © 1979 W. B. Saunders Company Ltd. All rights reserved.