EFFECT OF AGING ON VASOPRESSIN AND AQUAPORIN RESPONSES TO DEHYDRATIONIN FISCHER-344 BROWN-NORWAY F1 RATS

The plasma vasopressin (VP) response to 72 h of water deprivation is a ttenuated in 30-mo-old Fischer 344 (F344) rats relative to 4-mo-old ra ts. 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 respo nse to dehydration in the F1 cross of these strains (F344BNF1) was eva luated. 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 a nd hematocrit were significantly increased in both young and aged rats (P < 0.05), but plasma VP, urine osmolality, and aquaporin 2 expressi on were only increased in the young rats (P < 0.05). Posterior pituita ry content of immunoreactive VP was depleted in the young but not the old rats. Thus the aged F344BNF1 rats demonstrated a deficit in VP rel ease in response to an apparently similar dehydration stimulus. This d eficit was different from those previously reported for either the F34 4 or BN strains. Thus further studies are required to determine the ab normalities underlying this response.