Hyaluronan content in the kidney in different states of body hydration.

Growing evidence suggests that the interstitial hyaluronan (HA) content is a determinant of the fluid exchange barrier in tissues through its high resistance to water flow. This study addressed the possible involvement of renal papillary HA in water balance regulation. In anesthetized rats during different states of renal water handling (euvolemia, water diuresis, antidiuresis), in desert rodents, and in Brattleboro rats (diabetes insipidus) with a hereditary difference in water handling, regional renal HA and water contents were measured. The intrarenal HA distribution is heterogeneous, with 100 times larger amounts in the papilla than in the cortex. Compared with control rats, two hours of water diuresis increased the papillary HA content by 48% and that in the outer medulla by 52%, leaving the cortex unaffected. After 24 hours of water deprivation, papillary HA was decreased by 17%, while outer medullary HA remained unchanged. In gerbils, papillary and outer medullary HA contents were only 25 and 13%, respectively, of those in normal rats, while the cortical content was similar. In Brattleboro rats, the outer medullary HA content was significantly higher (285%) than in the normal rat, while the papillary content was similar. Generally, papillary HA was positively correlated to water content but was inversely related to urine osmolality. The amount of renal papillary HA changes in response to water balance of the organism. When excess water needs to be excreted, increased papillary interstitial HA could antagonize water reabsorption. The opposite occurs during water conservation. HA may play a role in renal water handling by affecting physicochemical characteristics of the papillary interstitial matrix and influencing the interstitial hydrostatic pressure, thereby determining interstitial water diffusion.