title: Osmotic hypertonicity of the renal medulla during changes in renal perfusion pressure in the rat.
abstract: 1. The relationship between renal perfusion pressure (RPP) and ion concentration in renal medulla was studied in anaesthetized rats. RPP was changed in steps within the pressure range 130-80 mmHg, while tissue electrical admittance (Y, index of interstitial ion concentration) and medullary and cortical blood flow (MBF and CBF; laser Doppler flowmetry) were measured, along with glomerular filtration rate (C in) and renal excretion. 2. With a RPP reduction from 130 to 120 mmHg, tissue Y remained stable; at 100 and 80 mmHg, Y was 5 and 17 % lower, respectively, than at 120 mmHg. 3. CBF fell less than RPP (partial autoregulation) in the range 130-100 mmHg only. MBF was autoregulated within 120-100 mmHg, but not above or below this range. 4. Each step of RPP reduction was followed by a decrease in sodium and water excretion (UNaV and V). The osmolality of excised inner medulla fragments was similar at 120 and 105 mmHg (586 +/- 45 and 618 +/- 35 mosmol (kg H2O)-1, respectively) but lower at 80 mmHg (434 +/- 31 mosmol (kg H2O)-1, P < 0.01); the ion concentration changed in parallel. 5. The data show that medullary hypertonicity was well preserved during RPP fluctuations within 130-100 mmHg, but not below this range. RPP-dependent changes of UNaV and V were not clearly associated with changes in solute concentration in medullary tissue.
authors.affiliation: Laboratory of Renal and Body Fluid Physiology, Medical Research Centre of the Polish Academy of Sciences, Pawinskiego 5, 02-106 Warsaw, Poland.
authors.forename: L
authors.initials: L
authors.lastname: Dobrowolski
authors.forename: B
authors.initials: B
authors.lastname: Badzyńska
authors.forename: A
authors.initials: A
authors.lastname: Walkowska
authors.forename: J
authors.initials: J
authors.lastname: Sadowski
mesh_terms: D000818:Animals; D004553:Electric Conductivity; D006982:Hypertonic Solutions; D007679:Kidney Medulla / Q000098:blood supply* / Q000000981:diagnostic imaging / Q000502:physiology*; D017078:Laser-Doppler Flowmetry; D008297:Male; D009997:Osmotic Pressure; D011312:Pressure; D051381:Rats; D017208:Rats, Wistar; D012079:Renal Circulation / Q000502:physiology*; D014463:Ultrasonography
chemical_list: D006982:Hypertonic Solutions