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In order to investigate the role of the renal kallikrein-kinin (K-K) system in normal (NRH) and low renin (LRH) subgroups of essential hypertension (EHT), daily urinary excretions of renal K-K system components including kallikrein (KAL), total KAL, pre-KAL, kinin (KIN) and kininase (total, I and II), were measured in 21 normotensives (NT) and 45 patients with EHT (NRH: 29, LRH: 16). Urinary KAL and KIN quantities, KAL activity, total and pre-KAL, and kininase (total, I and II) were measured by direct RIA, kininogenase assay, direct RIA of KAL after trypsin treatment, and KIN destroying capacity, respectively. The daily excretions of KAL quantity and activity, total and pre-KAL, and KIN were significantly lower in EHT than in NT. That of total kininase and kininase I were significantly higher in EHT than in NT while no significant difference was found in kininase I between EHT and NT. In comparing NRH and LRH, the urinary KAL activity and KIN were lower in LRH than in NRH, and kininase I was higher in LRH than in NRH. No significant difference, however, was found in total and pre-KAL, KAL quantity and kininase II between NRH and LRH. The ratio of KAL quantity/total KAL which reflects the conversion rate from pre-KAL in the kidney, did not show any significant difference among NT, NRH and LRH.(ABSTRACT TRUNCATED AT 250 WORDS)

Human plasma low molecular weight kininogen was purified with ammonium sulfate fractionation, DEAE-cellulose, CM-Sephadex C-50 and aprotinin-agarose affinity column chromatography, after which this was further purified with Sephadex G-150 and DEAE-Sephadex A-50 column chromatographies. Kallikrein activity was measured as the kininogenase activity reflecting the kinin-producing capacity from kininogen. The purification factor from crude plasma to purified substrate was 44-fold, and the recovery was 18%. The purified human substrate did not contain kinin-generating or destroying enzymes which would interfere with kininogenase activity, and showed a cross-reactivity of less than 0.1% against kinin antiserum. In the kininogenase assay, all kininogen was removed by adding ethanol to terminate the enzyme reaction. Because of the high sensitivity of kinin radioimmunoassay, the kinin levels in urine could be determined in very small amounts of samples (0.5 to 2.0 nl of the original urine). These findings indicated that kinin levels in incubation solution could be measured directly, and the control tubes are unnecessary in this assay procedure. In a comparison among human, dog and bovine low molecular weight kininogen as the substrate for human urinary kallikrein, the enzyme activity was 5 and 80 fold higher in the human low molecular weight kininogen, respectively, suggesting that a human substrate is the best for human enzymes. This simple, specific, sensitive and homologous kininogenase assay system seems to be very useful investigating the physiological or pathophysiological role of the renal kallikrein-kinin system in hypertensive and renal diseases.

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.