Hypertension induced by a nonpressor dose of angiotensin II in kininogen-deficient rats

Effect of high salt intake in mutant mice lacking bradykinin-B2 receptors

Renal kinins release prostaglandins and nitric oxide via the B2 receptor, promoting diuresis and natriuresis; hence, they may also contribute significantly to blood pressure regulation. We hypothesized that mutant mice lacking the gene encoding for the bradykinin-B2 receptor (B2-KO) become hypertensive when placed on a long-term high-salt diet. To test this, B2-KO and control mice were placed on either a normal (0.2%) or high-Na+ diet (3.15% in food plus 1% saline as drinking water) for 8 weeks. Systolic blood pressure was determined during weeks 6 and 8 by a computerized tail-cuff system. At the end of the 8-week period, mice were anesthetized for determination of mean blood pressure, renal blood flow, and renal vascular resistance. In B2-KO mice maintained on high Na+, systolic blood pressure was 15 mm Hg higher than in knockout animals on normal Na+ (P < .01). In contrast, there was no difference in blood pressure in control mice fed either a normal or a high-Na+ diet. Consistent with the systolic blood pressure data, direct mean arterial pressure revealed that B2-KO mice on high Na+ were hypertensive (115 +/- 6 in B2-KO on high-Na+ diet versus 79 +/- 2.8 in B2-KO on normal Na+, P < .0001); renal blood flow was reduced by 20% (P < .05) and renal vascular resistance was doubled (P < .0001) compared with B2-KO mice on normal Na+. In contrast, control mice on high Na+ were normotensive and tended to have increased renal blood flow and decreased renal vascular resistance compared with control mice on a normal Na+ diet. These findings indicate that kinins play an important role in preventing salt-sensitive hypertension; this may be achieved by maintaining renal blood flow under conditions of high salt intake.

Change in pressor responsiveness to angiotensin II as a determinant of blood pressure after unclipping in two-kidney, one clip hypertensive rats

The hypotensive effect of correction of renal artery stenosis in humans or experimental animals with renovascular hypertension is commonly attributed to decreasing renin secretion from the formerly stenotic kidney. However, plasma renin activity is normal in 50% of individuals with renovascular hypertension. We studied conscious, chronically instrumented two-kidney, one clip (2K1C) rats. The renal artery clip was removed and mean arterial pressure measured for 3 days. The majority of the fall in blood pressure occurred between 2 and 48 hours after unclipping. Measurement of water balance and urinary sodium excretion revealed no effect of unclipping. In another experiment, 2K1C hypertensive rats were chronically treated with enalapril and concomitant infusion of angiotensin II (3.8 pmol/min [4 ng/min] IV) to maintain blood pressure at hypertensive levels and prevent a fall in angiotensin II levels on unclipping. After 5 days, the clip was removed or sham removed, and treatment was continued. Blood pressure was recorded for 7 days. Blood pressure remained elevated in the sham unclipped rats. Unclipped rats exhibited a dichotomous response; blood pressure fell significantly within 48 hours in the majority of rats (responders) but remained elevated in a minority (nonresponders). All treatment was then withdrawn for 2 days. Sham unclipped rats remained hypertensive, and responders exhibited a further small decline in blood pressure. Blood pressure fell to normal in the nonresponders. Blood pressure falls after correction of renal artery stenosis in renovascular hypertension in part because of a decrease in pressor responsiveness to angiotensin II.

Failure of the oxytocin-induced increase in secretion of urinary kallikrein in young spontaneously hypertensive rats

Urinary kallikrein excretion during oxytocin (OT) infusion were studied in anesthetized (sodium pentobarbital, 50 mg/kg, i.p.) young (4-weeks-old) spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). OT-infusion (30 nmol/kg/30 min) to WKY significantly increased urinary excretion of the active kallikrein from the basal levels (25.4 +/- 5.6 10(-2) x AU/15 min, n = 5) to 37.3 +/- 5.0 10(-2) x AU/15 min (P < 0.05, n = 5) and 50.7 +/- 17.1 10(-2) x AU/15 min (P < 0.05, n = 5) 15 and 30 min after the start of OT-infusion, respectively. In SHR, OT-infusion did not increase the urinary excretion of active kallikrein, but did decrease the urine volume and sodium excretion. The concentration of the active kallikrein in the kidney of WKY was not changed by OT-infusion, but that of SHR was slightly increased. The OT-infusion resulted in significantly higher concentrations of the active kallikrein in SHR kidney than in WKY kidney. These results suggest that less excretion of urinary kallikrein in SHR during OT-infusion may be attributable to a lower response in the secretion of kallikrein from the kidney.

Pivotal role of renal kallikrein-kinin system in the development of hypertension and approaches to new drugs based on this relationship

Renal kallikrein is one of the tissue kallikreins, and the distal nephron is fully equipped as an element of the kallikrein-kinin system. Although a low excretion of urinary kallikrein has been reported in essential hypertension, the results from studies on patients with hypertension are not consistent. Congenitally hypertensive animals also excrete lowered levels of urinary kallikrein, but the effects of this are yet unknown. Extensive genetic and environmental studies on large Utah pedigrees suggest that the causes of hypertension are closely related to the combination of low kallikrein excretion and the potassium intake. Mutant kininogen-deficient Brown Norway-Katholiek rats, which cannot generate kinin in the urine, are very sensitive to salt loading and to sodium retention by aldosterone released by a non-pressor dose of angiotensin II, which results in hypertension. The major function of renal kallikrein-kinin system is to excrete sodium and water when excess sodium is present in the body. Failure of this function causes accumulation of sodium in the cerebrospinal fluid and erythrocytes, and probably in the vascular smooth muscle, which become sensitive to vasoconstrictors. We hypothesize that impaired function of the renal kallikrein-kinin system may play a pivotal role in the early development of hypertension. Inhibitors of kinin degradation in renal tubules and agents, which accelerate the secretion of urinary kallikrein from the connecting tubules and increase the generation of urinary kinin, may be novel drugs against hypertension.

The brown Norway rats and the kinin system

In 1979, we found a strain of kininogen-deficient Brown Norway rats. Since then, several studies have used these animals as negative controls of the involvement of the kinin system in physiological and pathophysiological processes. The cause of this deficiency has now been elucidated. This article reviews studies performed with these kininogen-deficient rats. These investigations have mainly focused on the links between the kinin system and the kidneys, hypertension, salivary glands, acute inflammatory reactions, cysteine proteinase inhibition, lymphatic tissues, coagulation, and cardiovascular shock states.

Increase in vascular sensitivity to angiotensin II and norepinephrine after four-day infusion of 0.3 M sodium chloride in conscious kininogen-deficient brown Norway Katholiek rats

Kininogen-deficient Brown Norway Katholiek (deficient BN-Ka) rats excreted a small amount of kinin in their urine, compared with normal BN Kitasato (normal BN-Ki) rats from the same strain. Intraarterial (i.a.) infusion (6 ml/kg/hr) of conscious deficient BN-Ka rats with 0.15 M NaCl did not increase mean arterial blood pressure (MBP) [from 103 +/- 2 (pre) to 93 +/- 6 mmHg (day 4)] and did not cause sodium accumulation in the serum, cerebrospinal fluid or erythrocytes, but 0.3 M NaCl infusion significantly increased MBP from 104 +/- 3 (pre) to 130 +/- 5 mmHg (day 4) with increased sodium levels in the serum, cerebrospinal fluid and erythrocytes. Infusion of 0.3 M NaCl in normal BN-Ki rats neither increased MBP nor accumulated sodium. The dose-response curve of the increase in MBP for angiotensin II injection (i.a., bolus, 1-1000 pmol/kg) in 0.3 M NaCl-infused deficient BN-Ka rats shifted to the left by a factor of 10 compared with that in 0.15 M NaCl-infused deficient BN-Ka rats, and that for norepinephrine injection shifted to the left by a factor of 30. Normal BN-Ki rats did not show any enhancement in MBP elevation with 0.3 M NaCl. These results suggest that the sodium accumulation attributable to a lack of kinin generation may be related to increased vascular reactivity to angiotensin II and norepinephrine.

Ebelactone B, an inhibitor of urinary carboxypeptidase Y-like kininase, prevents the development of deoxycorticosterone acetate-salt hypertension in rats

Kininogen-deficient Brown Norway Katholiek rats (BN-Ka) excrete little urinary kinin, compared with normal rats of the same strain (BN Kitasato rats (BN-Ki)). Deoxycorticosterone acetate-salt treatment increased systolic blood pressure in both rats, but much faster in BN-Ka than in BN-Ki. Daily subcutaneous administration of ebelactone B (15 and 5 mg/kg/day), a rat urinary carboxypeptidase Y-like kininase inhibitor, significantly reduced systolic blood pressure in BN-Ki, but not in BN-Ka. This treatment significantly increased urinary Na+ excretion and reduced Na+ concentration in the erythrocytes in BN-Ki, but not in BN-Ka. An angiotensin-converting enzyme inhibitor, lisinopril (5 mg/kg/day s.c.), did not reduce the systolic blood pressure in either BN-Ki or BN-Ka. These results suggested that ebelactone B has promise as a preventive agent for the development of hypertension acting through the inhibition of urinary kinin degradation.

Approaches to the development of novel antihypertensive drugs: crucial role of the renal kallikrein-kinin system

The renal kallikrein-kinin system has been shown to be important in the development of hypertension, but its precise role remains to be determined. The recent use of mutant rats that are deficient in plasma kininogens and hence incapable of generating kinin in the renal tubules has facilitated elucidation of the involvement of kinin in hypertension. In this article, Masataka Majima and Makoto Katori provide evidence that the renal kallikrein-kinin system plays a crucial role in the development of hypertension and discuss a novel rationale for developing effective new antihypertensive drugs.

Oxytocin-induced natriuresis mediated by the renal kallikrein-kinin system in anesthetized male rats

Intravenous infusion of oxytocin (OT) (10-100 nmol/kg/30 min) to 8-week-old anesthetized male rats resulted in a dose-dependent increase in urine volume, which showed a peak value 30-45 min after the start of OT-infusion. Urinary excretions of sodium, chloride and potassium were also increased by OT, showing peak values at 30-45 min, without any increase in the creatinine level. The natriuresis by OT was accompanied by increased excretion of urinary active kallikrein, which showed a peak value 15 min after the start of OT-infusion. The urinary kinin level was also increased. Intravenous infusion of a kallikrein inhibitor, aprotinin (15 mg/kg/90 min), when started 30 min before the OT-infusion, significantly inhibited the OT-induced increase in urine volume and urinary excretion of sodium, chloride and potassium. Intravenous infusion of a bradykinin B2 antagonist, Hoe 140 (D-Arg[Hyp3,Thi5,D-Tic7,Oic8]BK, 4.5 mg/kg/90 min), when started 30 min before the OT-infusion, significantly inhibited the OT-induced increases in urine volume and urinary excretion of sodium and chloride, but not that of potassium. These results indicate that the OT-infusion induces natriuresis in male rats, and more than half of the natriuresis is mediated by a concomitant increase in excretion of urinary active kallikrein and the kinin generated.

Early blockade of bradykinin B2-receptors alters the adult cardiovascular phenotype in rats

We evaluated whether long-term inhibition of bradykinin B2-receptors by the long-acting antagonist Hoe 140 (D-Arg,[Hyp3,Thi5,D-Tic7,Oic8]-bradykinin) affects the blood pressure of normotensive rats. Neither Hoe 140 (at 75 nmol/d for 8 weeks) nor its vehicle altered systolic pressure of adult rats on a normal or high sodium intake. In further experiments, pairs of Hoe 140-treated rats were mated and their offspring maintained on Hoe 140 and a normal sodium diet. Controls were given vehicle instead of Hoe 140. At 9 weeks of age, rats given Hoe 140 during prenatal and postnatal phases of life showed greater systolic pressures, heart rates, and body weights than controls (122 +/- 1 versus 113 +/- 1 mm Hg, 444 +/- 6 versus 395 +/- 8 beats per minute, 258 +/- 7 versus 213 +/- 3 g, respectively, P < .01), whereas urinary creatinine excretion was reduced (1.13 +/- 0.05 versus 1.36 +/- 0.04 mumol/100 g body wt in controls, P < .05). The difference in blood pressure (confirmed by direct intra-arterial measurement) persisted after 20 days of dietary sodium loading, whereas it was nullified by sodium restriction. In additional experiments, the offspring of untreated rats received Hoe 140 or vehicle from 2 days to 11 weeks of age. At this stage, systolic pressure and body weight were significantly greater in Hoe 140-treated rats compared with controls, and heart rate was similar.(ABSTRACT TRUNCATED AT 250 WORDS)