Angiotensin-(1-7) reduces renal angiotensin II receptors through a cyclooxygenase-dependent mechanism.
In the kidney, angiotensin-(1-7) [Ang-(1-7)] exhibits diuretic and natriuretic properties associated with an increase in prostaglandin production. The prohypertensive effects of Ang II are attenuated in rats infused with Ang-(1-7), consistent with recent work showing that Ang-(1-7) downregulates AT1 receptors in Chinese hamster ovary-AT1A or vascular smooth muscle cells. To determine whether exposure to Ang-(1-7) reduces AT1 receptors in the kidney through an increase in prostaglandin production, kidney slices from Sprague-Dawley rats were incubated with 10 n -1 microM Ang-(1-7) in the presence or absence of 5 microM meclofenamate, a cyclooxygenase inhibitor. Following these treatments, the kidney slices were retrieved, frozen, and sectioned for determination of [125I]-Ang II binding using in vitro receptor autoradiography. Greater than 90% of the specific binding was competed for by losartan, indicating that the majority of binding was to the AT1 receptor. Incubation of kidney slices with 1 microM Ang-(1-7) caused a 20% reduction in [125I]-Ang II binding (n = 8) in the cortical tubulointerstitium, which was prevented when Ang-(1-7)-treated slices were incubated in the presence of 5 microM meclofenamate (1 +/- 2% increase, n = 8; p < 0.05). Incubation with 5 microM meclofenamate alone had no effect on [125I]-Ang II binding (-3 +/- 3%). The decrease in [125I]-Ang II binding with Ang-(1-7) was also blocked by the Ang-(1-7) antagonist [d-Ala7]-Ang-(1-7). Treatment with 1 microM [d-Ala7]-Ang-(1-7) alone had no effect on [125I]-Ang II binding (-3 +/- 6% of control). Pretreatment with 1 microM Ang II caused a similar reduction in [125I]-Ang II binding in the cortical tubulointerstitium. Neither Ang-(1-7) nor Ang II had any effect on [125I]-Ang II binding in the glomeruli and the area of the vasa recta of the kidney. These original findings suggest that prior exposure to Ang-(1-7) or Ang II causes a modest decrease in the number of AT1 receptors in the cortical tubulointerstitial area of the kidney. The reduction in Ang II binding by Ang-(1-7) was blocked by meclofenamate and [d-Ala7]-Ang-(1-7), suggesting that cyclooxygenase products released through activation of a novel receptor participate in this effect.
Clark
Michelle A
MA
The Hypertension and Vascular Disease Center, Wake Forest University School of Medicine, Winston-Salem, North Carolina 27157, U.S.A.
Tallant
E Ann
EA
Tommasi
Ellen
E
Bosch
Susan
S
Diz
Debra I
DI
D000803:Angiotensin I / Q000494:pharmacology*; D057911:Angiotensin Receptor Antagonists; D000818:Animals; D004305:Dose-Response Relationship, Drug; D007668:Kidney / Q000737:chemistry / Q000187:drug effects* / Q000378:metabolism*; D008297:Male; D010446:Peptide Fragments / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011945:Receptors, Angiotensin / Q000032:analysis / Q000378:metabolism*
D057911:Angiotensin Receptor Antagonists; D010446:Peptide Fragments; D011945:Receptors, Angiotensin; D000803:Angiotensin I; D011451:Prostaglandin-Endoperoxide Synthases; C118790:angiotensin I (1-7)