Interrelation between the Renin-Angiotensin System and Kallikrein-Kinin System in Patients with Essential Hypertension

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Abstract
In order to investigate the relationship between the kallikrein-kinin (K-K) system and renin-angiotensin (R-A) system, plasma kinin (pKIN), plasma angiotensin II (pAII), plasma renin activity (PRA) and angiotensin converting enzyme activity (ACEA) were determined in 19 essential hypertensives (EHT). pKIN and pATII measurements were performed by highly sensitive radioimmunoassay (RIA), both of which were established in our laboratory. The assay sensitivity of pKIN and pAII were 0.5 pg/tube and 0.1 pg/tube, respectively. In pKIN RIA, pKIN was extracted by ethanol from 0.8 ml of plasma obtained with a syringe containing kinin generating and destroying enzyme inhibitors. In pAII RIA, pAII was measured directly in small amounts of 50-100 microliter, unextracted plasma samples. The level in pAII was significantly higher (p less than 0.05) in the normal renin group (NRH: n = 13) as compared with low renin group of EHT (LRH: n = 6). However, no significant difference was found in pKIN and ACEA between these two groups. Although a significantly positive correlation was observed between pAII and PRA (p less than 0.001) in EHT, the ratio of pAII/PRA tended to be higher in LHR than in NRH. ACEA correlated positively with pAII (p less than 0.01) or PRA (p less than 0.02), respectively. On the other hand, a significant negative correlation was also found between pKIN and pAII (p less than 0.05). From these findings, it was assumed that there was a closed relationship between R-A and K-K systems, and that angiotensin converting enzyme (kininase II) might play some role in the interrelation between both systems.