Urinary kallikrein in Dahl-Iwai salt-sensitive and -resistant rats

This study was designed to evaluate the differences between the renal kallikrein in newly established Dahl-Iwai rats under salt loading and that of Sprague-Dawley rats (SD). Urinary kallikrein quantity and activity was markedly lower in Dahl-Iwai rats than in SD even during the control period. Moreover, kallikrein quantity and activity in Dahl-Iwai salt-sensitive rats (SS) were clearly diminished in comparison with salt-resistant rats (SR). The kallikrein activity/ quantity ratio was also lower in SS and SR than in SD during the control period. After salt loading, systolic blood pressure increased only in SS. Kallikrein activity in SS and SR, and kallikrein quantity in SS were increased, whereas those in SD did not change. Although the kallikrein activity/quantity ratio in SR reached the same level in SD after salt loading, that in SS was lower throughout the experiment. These results suggest that Dahl-Iwai rats are less able hereditarily to produce renal kallikrein and that there may exist structurally abnormal kallikrein that may have a lower activity. Different kinetics of renal kallikrein between SS and SR by salt loading might be explained by kallikrein inhibitors or abnormal kallikrein or nonkallikrein kininogenase. These different kinetics of renal kallikrein may play some role on blood pressure elevation in SS.