Increased Urinary Kallikrein-Like Activity in the Syndrome of Inappropriate Secretion of Antidiuretic Hormone

The renal kallikrein-kinin system: its role as a safety valve for excess sodium intake, and its attenuation as a possible etiologic factor in salt-sensitive hypertension

The distal tubules of the kidney express the full set of the components of the kallikrein-kinin system, which works independently from the plasma kallikrein-kinin system. Studies on the role of the renal kallikrein-kinin system, using congenitally kininogen-deficient Brown-Norway Katholiek rats and also bradykinin B2 receptor knockout mice, revealed that this system starts to function and to induce natriuresis and diuresis when sodium accumulates in the body as a result of excess sodium intake or aldosterone release, for example, by angiotensin II. Thus, it can be hypothesized that the system works as a safety valve for sodium accumulation. The large numbers of studies on hypertensive animal models and on essential hypertensive patients, particularly those with salt sensitivity, indicate a tendency toward the reduced excretion of urinary kallikrein, although this reduction is modified by potassium intake and impaired renal function. We hypothesize that the reduced excretion of the renal kallikrein may be attributable to a genetic defect of factor(s) in renal kallikrein secretion process and may cause salt-sensitive hypertension after salt intake.

Interrelationship between urinary kallikrein and arginine-vasopressin in man

Physiological saline solution was infused in 9 normal subjects and 6 patients with central diabetes insipidus (DI). At 120 min after the start of infusion, arginine vasopressin (AVP) was injected (i.m.). Urine was collected every 30 min fraction. The urinary excretion of kallikrein-like activity (KAL-A) (S-2266 hydrolysis activity) was significantly lower in patients with DI than in normal subjects, without showing the differences of plasma renin activity (PRA), plasma aldosterone concentration (PAC), creatinine clearance (Ccr) and blood pressure between the two groups, except a marked water-diuresis in DI. The urinary excretion of KAL-A correlated positively with the urinary excretion of AVP. AVP administration significantly increased the urinary excretion of KAL-A. After overnight fasting, an acute oral water-loading was carried out for 15 min in 6 normal subjects. Concomitant with a significant suppression of the level of plasma AVP from the first 30 min, a slight, but significant, decrease in urinary excretion of KAL-A was observed in the first 30 min fraction after loading, compared with the control period. Afterwards, the urinary excretion of KAL-A increased prominently with an increase in urine flow. KAL-A in the urine decreased promptly from the first 30 min fraction and then gradually until 120 min after loading. Urine volume and free-water markedly increased except the first 30 min fraction, compared with the control period. Thus it is suggested that AVP is one of factors which actually regulate the secretion of renal kallikrein in man.

Increased urinary kallikrein-like activity during ADH-induced hyponatremia in rats

The urinary kallikrein system was studied during hyponatremia associated with water and vasopressin administration in rats. Two groups of animals were studied. In the experimental group (n = 5), vasopressin (0.4 U/day) was injected intramuscularly for 7 days, and water (15%-20% body weight per day) was given via a stomach tube. The control group (n = 6) received only vasopressin. In the experimental group, plasma sodium concentration (PNa) decreased from 143.2 +/- 0.5 to 130.8 +/- 1.8 (m +/- SEM) mmol/liter (5th day, p less than 0.01) along with plasma osmolality. Urinary kallikrein-like activities (UkaV) increased from 99.1 +/- 7.5 to 172.6 +/- 23.5 mumol X min/day (100 g body weight) (5th day, p less than 0.05; 6th day, p less than 0.05; and 7th day, p less than 0.05) after the administration of vasopressin. Uric acid clearance (Cua) increased from 0.153 +/- 0.014 to 0.275 +/- 0.041 ml/min (5th day, p less than 0.05; 7th day, p less than 0.05). No change was observed in urinary aldosterone excretion (UAldV), creatinine clearance, or blood pressure. UkaV correlated with Cua (r = 0.81, p less than 0.01) and with the degree of change of PNa (r = --0.79, p less than 0.01), respectively. In the control group, no change was observed in the above parameters. A significant relationship between UkaV and fractional Na clearance (r = 0.60, p less than 0.01) was observed. We conclude that the urinary kallikrein system in rats may be stimulated during hyponatremia when induced by water and vasopressin. This increased activity is probably the result of volume expansion associated with water and vasopressin and may have some relationship to fractional Na clearance in the kidney.