Effect of age and testosterone on the vasopressin and aquaporin responses to dehydration in Fischer 344/Brown-Norway F1 rats

To determine if the aging-associated decline in testosterone results in att enuated vasopressin (VP) responses to dehydration, testosterone implants we re given to aged male Fischer 344/Brown-Norway F1 (F344BNF1) rats. Water de privation caused comparable dehydration, increased plasma VP (pVP), and dec reased posterior pituitary (PP) VP content in 4-, 15-, and 28-month-old rat s. Dehydration increased VP mRNA content of supraoptic nuclei only at 4 mon ths, whereas VP mRNA length was increased at both 4 and 15 months of age. T he elevated pVP in the water-deprived aged rats indicates that even without an increase in VP mRNA content, PP VP storage was adequate to maintain ele vated pVP Dehydration increased aquaporin-2 content at 4, but not at 15 or 28 months of age, suggesting decreased renal responsiveness to VP. Testoste rone replacement did not produce dehydration-induced increases in VP mRNA o r aquaporin-2. Therefore, testosterone deficiency does not result in altere d VP responses to dehydration in aged F344BNF1 rats.