Augmentation of endogenous intrarenal angiotensin II levels in Val5-ANG II-infused rats

Abstract

In angiotensin II (ANG II)-induced hypertension, intrarenal ANG II levels are increased by AT1 receptor-mediated ANG II internalization and endogenous ANG II generation. The objective of the present study was to determine the relative contribution of de novo formation of endogenous ANG II. Male Sprague-Dawley rats were divided into three groups: sham operated ( n = 6), Val5-ANG II infused ( n = 16), and Ile5-ANG II infused ( n = 6). Val5-ANG II and Ile5-ANG II were infused at 80 ng/min via subcutaneous osmotic minipump for 13 days, followed by harvesting of blood and kidney samples. In six Val5-ANG II-infused rats, urine was collected on the day before infusion and on day 12 of infusion. Extracted samples were subjected to HPLC to separate Val5-ANG II from Ile5-ANG II followed by RIA. Systolic blood pressure increased significantly from 121 ± 2 to 206 ± 4 mmHg in the Val5-ANG II-infused rats and from 124 ± 3 to 215 ± 5 mmHg in the Ile5-ANG II-infused rats. In the Val5-ANG II-infused rats, the plasma Ile5-ANG II levels increased 196.2 ± 70.1% compared with sham plasma Ile5-ANG II concentration. Val5-ANG II levels were 150.0 ± 28.2 fmol/ml which accounted for 53.5 ± 10.1% of the total ANG II in plasma. The kidney Ile5-ANG II levels in the Val5-ANG II-infused rats increased 69.9 ± 30.7% compared with sham kidney Ile5-ANG II concentrations. Intrarenal accumulation of Val5-ANG II accounted for 52.5 ± 5.3% of the total kidney ANG II during Val5-ANG II infusion while endogenous Ile5-ANG II accounted for 47.5 ± 8.6%. The urinary Ile5-ANG II excretion rate on day 12 increased 93.2 ± 32.1% compared with preinfusion level indicating increased formation of endogenous ANG II. Thus, the increases in intrarenal ANG II levels during chronic ANG II infusions involve substantial stimulation of endogenous ANG II formation which contributes to overall augmentation of intrarenal ANG II.