Increased Vasopressin Secretion: An Early Manifestation of Aging in the Rat

Vasopressin release and renal water conserving capacity were measured in normal Long-Evans rats ranging in age from 2 to 17 months. Twenty-four hour urine volume rose and urine osmolality fell as the animals aged, with the first differences evident by age 10 months. Assessment of vasopressin release from isolated hypothalamic-neurohypophy-sial units by means of an in vitro perifusion system demonstrated that hormone discharge increased as the animals aged, being evident by age 7 months. The increased vasopressin releasability could not be attributed to the greater vasopressin content present in the posterior pituitary of the older rats. The data suggest that increased vasopressin secretion is an early manifestation of aging in the rat and that the consequent hypervasopressinemia may affect the renal tubule with resultant diminished responsiveness to the hormone. A LTERATION in water regulatory capacity is recognized- t \. as an accompaniment of the aging process in humans and in rats. Many studies have documented an age-associ-ated impairment in kidney concentrating function with cor-responding decline in renal water conserving ability (Beck & Yu, 1982; Bengele et al., 1981; Dicker & Nunn, 1958; Miller, 1985). Even though some studies have claimed that antidiuretic hormone (ADH, vasopressin) secretion may be impaired with advanced age (Rodeck et al., 1960; Sladek et al., 1981;Zbuzek&Wu, 1982;Zbuzeketal., 1983), much data exist that indicate that the decline in water conserving capacity is not a consequence of ADH deficiency. Thus, administration of exogenous ADH does not correct the impaired urine concentration found in aged humans (Mille