title: Experimental selective elevation of renal medullary blood flow in hypertensive rats: evidence against short-term hypotensive effect.
abstract: OBJECTIVE
  Renal medullary blood flow (MBF) can be selectively increased by intrarenal or systemic infusion of bradykinin (Bk) in anaesthetized normotensive rats. We reproduced this effect in a number of rat models of arterial hypertension and examined whether increased perfusion of the renal medulla can cause a short-term decrease in blood pressure (BP) that is not mediated by increased renal excretion and depletion of body fluids.
  
  
  METHODS
  In uninephrectomized Sprague-Dawley rats, BP was elevated to approx. 145 mmHg by acute i.v. infusion of noradrenaline (NA) or angiotensin II (Ang II) (groups 1, 2), 2-week exposure to high-salt diet (3), high-salt diet + chronic low-dose infusion of Ang II using osmotic minipumps (4) or chronic high-dose Ang II infusion on normal diet (5). Uninephrectomized spontaneous hypertensive rats (SHR) were also examined (6,7). To selectively increase medullary perfusion, in anaesthetized rats, bradykinin was infused during 30-75 min into the renal medullary interstitium or intravenously.
  
  
  CONCLUSIONS
  Bradykinin increased outer- and inner-medullary blood flow (laser-Doppler fluxes) by 10-20% in groups (1, 2), by 30-50% in groups (3, 4, 5) and approx. 20% in SHR (6, 7). The concurrent increase in total renal blood flow (Transonic probe) was < 3%. A minor (<3%) decrease in BP was seen only in rats acutely rendered hypertensive by NA or Ang II infusions; however, the decreases in BP and increases in medullary perfusion were not correlated. Thus, there was no evidence that in hypertensive rats, substantial selective increases in medullary perfusion can cause a short-term decrease in BP.
authors.affiliation: Laboratory of Renal and Body Fluid Physiology, M. Mossakowski Medical Research Centre of the Polish Academy of Sciences, Warsaw, Poland.
authors.forename: B
authors.initials: B
authors.lastname: Bądzyńska
authors.forename: J
authors.initials: J
authors.lastname: Sadowski
mesh_terms: D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D001794:Blood Pressure; D001920:Bradykinin / Q000494:pharmacology; D006973:Hypertension / Q000378:metabolism*; D007668:Kidney / Q000098:blood supply / Q000187:drug effects / Q000502:physiology*; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D012079:Renal Circulation / Q000502:physiology*; D012965:Sodium Chloride / Q000494:pharmacology*
chemical_list: D000804:Angiotensin II; D012965:Sodium Chloride; D001920:Bradykinin