Effect of aging on vasopressin and aquaporin responses to dehydration in Fischer 344-brown-Norway F1 rats.

The plasma vasopressin (VP) response to 72 h of water deprivation is attenuated in 30-mo-old Fischer 344 (F344) rats relative to 4-mo-old rats. This appears to reflect an inability to increase VP synthesis. In contrast, elevated plasma VP has been reported in the Brown-Norway (BN) strain of rats secondary to reduced renal VP responsivity. The response to dehydration in the F1 cross of these strains (F344BNF1) was evaluated. Male rats, 4 and 30 mo old, were deprived of water for 72 h or allowed water ad libitum. In response to dehydration, plasma sodium and hematocrit were significantly increased in both young and aged rats (P < 0.05), but plasma VP, urine osmolality, and aquaporin 2 expression were only increased in the young rats (P < 0.05). Posterior pituitary content of immunoreactive VP was depleted in the young but not the old rats. Thus the aged F344BNF1 rats demonstrated a deficit in VP release in response to an apparently similar dehydration stimulus. This deficit was different from those previously reported for either the F344 or BN strains. Thus further studies are required to determine the abnormalities underlying this response.