Hypovolemic state: age-related influence of water restriction on cardiac nitric oxide synthase in rats

We have assessed the influence of water restriction stress on the nitric oxide (NO) synthase in heart and aorta tissues in young 2-month-old and middle-aged 12-month-old rats.

Animals were divided into control and 24- and 72-h water-deprived groups. We evaluated systolic blood pressure (SBP), biochemical parameters, nitrate and nitrite urinary excretion (UNOx), NADPH-diaphorase activity, and protein levels of NOS in the right atria, left ventricle, and thoracic aorta tissues.

Water restriction during 72 h increased SBP (16%) in 2-month-old rats but decreased it after 24 and 72 h (9 and 15%, respectively) in 12-month-old rats. Atria, aorta endothelium, and smooth muscle NOS activity increased (32, 63, and 88%, respectively) only after 72 h of water restriction in 2-month-old rats. It also increased not only after 72 h but also after 24 h in atria (27 and 18%, respectively) and in ventricle (39 and 67%, respectively) in 12-month-old rats. Meanwhile, in this group's aorta smooth muscle, the enzyme activity decreased (16 and 7%, respectively). A major difference seen between ages was the changes in UNOx excretion, which decreased in the younger in 24 and 72 h (47 and 81%, respectively) and increased in the middle-aged rats (193 and 389%, respectively). Water restriction did not change cardiovascular endothelial and neuronal NOS protein levels in any group.

NO pathways could contribute to the development of age-related cardiovascular adaptation to volume depletion induced by water restriction.