1. We have investigated the potential contribution of medullary interstitial oncotic pressure to the net balance of forces influencing fluid movement through the walls of the ascending vasa recta (AVR) in the exposed papillae of 2-week-old @entity35 . 2. Using a capillary zone electrophoresis (CZE) assay, hyaluronan (HA) concentrations were measured in fresh tissue slices from the @entity8 . HA content per wet weight of tissue decreased from @entity3455 , but as a function of cell-free @entity1986 ( @entity1986 ) HA concentration was relatively constant at 1.6 micrograms HA per mg @entity1986 up to 1600-1800 microns from the tip. Thereafter the concentration fell rapidly to near zero levels. 3. The volume of the @entity1986 was determined using a transmission electron micrographic study of the papilla in age-matched @entity35 . Total interstitial volume (i.e. @entity1986 + @entity2337 , the interstitial cell volume), as a function of total tissue volume, decreased only slightly between 0 and 1800 microns (i.e. from about 40 to 35%). @entity1986 and @entity2337 were found to be reciprocally related with @entity1986 decreasing from 21.8 to 10.2%, while @entity2337 increased from 18.3 to 25.2% over the 1800 microns. 4. Total interstitial oncotic pressures were estimated as the sum of the oncotic pressure due to HA alone plus the oncotic pressure of albumin (A) in an HA matrix. Taking into account reflection coefficients to HA and A, there was an effective oncotic pressure (E pi) of between 3.46 and 6.0 cm @entity2507 on the interstitial side of the AVR. Under free flow conditions an E pi in this range is sufficient to result in a net inward driving force of between 5.4 and 9.3 cm @entity2507 , sufficient to account for current estimates of water reabsorption by the AVR. 5. HA concentrations in the papilla increased over the first 3 weeks of life from 0.313 +/- 0.09 microgram (mg wet weight of slice)-1 (mean +/- S.E.M.) at 1 week to 0.563 +/- 0.06 at 3 weeks of age (P > 0.01)1 in parallel with an age-dependent increase in mean urine osmolarity. It is suggested that the increasing interstitial concentrations of HA may contribute to the development of urinary concentrating ability, which occurs concurrently.

Estimating XXXX renal medullary interstitial oncotic pressures and the driving force for fluid uptake into ascending vasa recta.

@entity8 :: ('MESH:D007674', 'Disease') :: ['renal papilla'] @entity2337 :: ('MESH:C537984', 'Disease') :: ['IC'] @entity2507 :: ('CHEBI:33813', 'Chemical') :: ['H2O'] @entity3455 :: ('MESH:D060725', 'Disease') :: ['tip to base of the papilla'] @entity1986 :: ('MESH:D009395', 'Disease') :: ['IS', 'interstitial space'] @entity35 :: ('10116', 'Species') :: ['Sprague-Dawley rats', 'rats']
@entity35 :: (10116,Species) :: ['rat']
