Is the renin-angiotensin system involved in urinary concentration mechanisms?

Renin release elicited by i.v. injection of loop-diuretics was used to study the effects of angiotensin II (AII) on intrarenal hemodynamics. The vasoconstrictive action of intrarenally synthesized AII predominates in the efferent glomerular arteriole. Such a vasoconstrictive effect could affect blood flow in the vasa recta which stem from efferent arterioles of juxtamedullary glomeruli. Renin secretion and renal inner medullary blood flow (tissue clearance of 133Xe) were simultaneously measured before and after frusemide-induced renin release. The relationship between renin secretion and renal inner medullary blood flow was inverse. Changes in renal medullary blood flow may be physiological determinants of medullary osmolality and renal concentration ability. The intrarenal role of AII in urinary concentration recovery after frusemide was examined. Inhibition of renin release by propranolol or AII-blockade (by saralasin or Hoe 409) delayed recovery of urinary osmolality. In the conscious rat, propranolol slowed down recovery of the cortico-papillary gradient for sodium. Its vasoconstrictive action on the efferent glomerular arteriole might enable the renin-angiotensin system to participate in the control of renal excretion of salt and water.