Renal kallikrein-kinin system, but not renal dopamine system, mediates thenatriuretic response to intravenous saline infusion in healthy Chinese subjects

1 To assess the role of renal dopamine (DA), sympathetic nervous system (SN S) activity and the renal kallikrein-kinin system in sodium excretion in Ch inese subjects, we studied the effects of intravenous saline infusion on th e urinary excretions of sodium, free DA, free noradrenaline (NA) and kallik rein in eight healthy males aged 23-25 years. 2 After a baseline period of 1 h (hour 0), these subjects received 1 l of 0 .9% saline over 2 h (hours 1 and 2), followed by a 4-h recovery period (hou rs 3-6). From hours 0-4, subjects remained in the supine position, except t o void urine. Distilled water was given orally throughout the study to ensu re an adequate diuresis. 3 A 31-39% increase in sodium excretion (P < 0.05) was seen during hours 2 and 3. Urinary DA did not change throughout the study period. Urinary free NA showed no changes while the subjects remained supine, but an increase of 91-105% (P < 0.02) was seen after the subjects became ambulatory. However, there was a 103-140% increase in urinary kallikrein excretion (P < 0.05) d uring the saline infusion. Urinary kallikrein was still much higher (by 74% ) than the basal level 1 h after the completion of the saline infusion. 4 There is no evidence from the present study that renal DA or SNS play any role in the natriuretic response to saline infusion in Chinese subjects. T he brisk urinary kallikrein response, despite a relatively small salt load, suggests that the renal kallikrein-kinin system may play an important role in extracellular fluid volume and sodium homeostasis in Chinese subjects.