Yumiko Shibouta

Pathophysiological role of endothelin in acute renal failure

In conscious rats, the i.v. injection of endothelin (ET) caused an increase in blood urea nitrogen (BUN), an index of renal dysfunction. In the model of acute renal failure which was induced by occlusion of the bilateral renal arteries of rats followed by reperfusion, ET-monoclonal antibody improved the renal function. In this model, ET-antibody also protected the kidneys from renal proximal tubular necrosis and suppressed Ca++-accumulation in necrotic tissues. Plasma ET level increased 5 min and 5 hr and renal ET content did 5 and 20 hr after reperfusion. BUN level increased 5 and 20 hr after reperfusion. These results strongly suggest that the endogenously increased ET may be one of the important deleterious mediators in the pathogenesis of ischemic acute renal failure.

Protective effects of candesartan cilexetil (TCV-116) against stroke, kidney dysfunction and cardiac hypertrophy in stroke-prone spontaneously hypertensive rats.

The effects of chronic treatment with an angiotensin II receptor antagonist, candesartan cilexetil (TCV-116, 0.1, 1, 10 mg/kg), and an angiotensin converting enzyme inhibitor, enalapril maleate (enalapril, 10 mg/kg), on the development of end-organ damage were examined in stroke-prone spontaneously hypertensive rats (SHRSP). The control SHRSP developed severe hypertension with stroke signs and increased urinary protein excretion. TCV-116 (0.1 mg/kg) reduced the stroke incidence and urinary protein excretion without affecting the blood pressure. TCV-116 (1 and 10 mg/kg) and enalapril reduced blood pressure, the stroke incidence, the urinary indices and left ventricular weight. Circulating renin-angiotensin system (RAS) and renal renin mRNA expression were significantly accelerated or tended to be accelerated in the control SHRSP with end-organ damages. A low dose of TCV-116 tended to reduce the RAS indices in plasma by improving the damages, whereas a high dose (10 mg/kg) increased them by the reflexes with blocking RAS. The present results indicate that chronic All blockade reduces the increase in blood pressure, end-organ damages and RAS related to the damages in SHRSP.

Enhanced thromboxane A2 biosynthesis in the kidney of spontaneously hypertensive rats during development of hypertension.

Arachidonic acid (AA)-induced pressor response and production of thromboxane YXB2, the stable metabolite of TXA2, prostaglandin (PG)-like substance (PLS) and 6-keto-PGF1 alpha the stable metabolite of prostacyclin (PGIs), were studied using isolated, perfused kidneys of 6- and 18-week old spontaneously hypertensive rats (SHR), Wistar-Kyoto rats (WKY), two-kidney, one clip hypertensive rats (RHR) and DOCA/salt hypertensive rats (DOCA/salt HR). The AA-induced pressor response and release of TXB2 were highest in the 6-week old SHR, whereas, the release of PLS and 6-keto-PGF 1 alpha was marked in the 18-wek old SHR and the established hypertensive stages of both RHR and DOCA/salt HR. In the kidneys of SHR and WKy, exogenous TXA2 induced a severe vasoconstriction and there was a positive correlation between the AA-induced pressor response and the release of TXB2 or PLS. Thus, the initiation of hypertension in SHR may follow an accelerated synthesis of TXA2 against PGI2 in response to stimuli which induce a release of AA.

Angiotensin-II-stimulated release of thromboxane a2 and prostacyclin (PGI2 ..) in isolated, perfused kidneys of spontaneously hypertensive rats

Abstract Angiotensin-II(A-II)-stimulated release of rabbit aorta-contracting substance (RCS), prostaglandin-like substance (PLS) and dog coronary-relaxing substance (DRS) was studied in isolated, perfused kidneys of spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). When the perfusion pressure was set at 60–70 mmHg, the dose-related pressor response of the kidney to A-II did not differ significantly between the strains, or between the ages of 6, 12 and 18 weeks. The A-II-induced release of RCS from the kidney was most remarkable in 6-week SHR, slight in 12- and 18-week SHR, but negligible for all ages of WKY. The DRS release was remarkable in 12- and 18-week SHR, but was hardly detectable in 6-week SHR and all ages of WKY. The PLS release was much more remarkable in 18-week SHR than in 6- and 12-week SHR and all ages of WKY. The RCS was confirmed to be thromboxane A2 (TXA2) by: (1) its half-life of 38 sec at 37°, (2) a concomitant release of radio-immunoassayable TXB2: (a stable metabolite of TXA2) into the perfusate and (3) specific inhibition of its release by L-8027 (a TXA2 synthetase inhibitor). The DRS was considered to be prostacyclin (PGI2) by: (1) its half-life of 5.2 min at 37° and (2) its anti-platelet aggregation activity. It is speculated that an enhanced TXA2 synthesis in the 6-week SHR kidney may be involved in increasing the renal vascular resistance and in initiating the process of hypertension.

Delay of the initiation of hypertension in spontaneously hypertensive rats by CV-4151, a specific thromboxane A2 synthetase inhibitor

When CV-4151, a specific thromboxane (TX) A2 synthetase inhibitor, was given orally to 4 week old (4w) spontaneously hypertensive rats (SHR) daily for 3 weeks, the initiation of hypertension was delayed by about one week. The agent increased urinary excretion of water, sodium and creatinine, reduced that of TXA2 (as TXB2), increased that of PGI2 (as 6-keto-PGF1 alpha) and enhanced urinary PGI2/TXA2. In 4w Wistar-Kyoto rats (WKY) and 18w SHR was established hypertension, the agent had little effect on blood pressure and renal function. In isolated, perfused kidneys of 6w SHR, CV-4151 markedly inhibited both arachidonic acid-induced pressor action and production of TXA2. TXA2 synthetase activity in renal cortical microsomes of 5w SHR was approximately 1.5 times higher than that in age-matched WKY. CV-4151 inhibited TXA2 synthetase activity of medullary and cortical microsomes more effectively in 5w SHR than in age-matched WKY. Thus, in young SHR, the TXA2 synthetase inhibitor seemed to improve renal function by altering the balance of renal TXA2 and PGI2 biosynthesis and subsequently caused a delay in the initiation of hypertension. The present findings lend support to the idea that an imbalance in the renal TXA2-PGI2 biosynthesis may be involved in the initiation of hypertension in SHR.

Effect of an angiotensin II receptor antagonist, CV-11974, and its prodrug, TCV-116, on production of aldosterone

In dispersed rabbit adrenocortical glomerulosa cells, a non-peptide angiotensin II (AT1) receptor antagonist, CV-11974 (10(-10)-10(-5) M), competitively inhibited angiotensin II- or angiotensin III-stimulated aldosterone production, whereas PD123177, an angiotensin AT2 receptor antagonist, did not. CV-11974 inhibited aldosterone production induced by 4 mM K+ but not by 12 mM K+. CV-11974 had no effect on adrenocorticotropic hormone-stimulated aldosterone or corticosterone production, but inhibited angiotensin II-stimulated corticosterone production. In the rat, TCV-116, the prodrug of CV-11974, (0.1 and 1 mg/kg, p.o.) markedly reduced the elevation of both plasma aldosterone concentration and blood pressure induced by i.v. infusion of angiotensin II. In spontaneously hypertensive rats, TCV-116 at daily p.o. doses of 0.1, 1 and 10 mg/kg for 2 weeks caused a dose-dependent reduction of blood pressure and plasma aldosterone concentration without affecting plasma corticosterone. Thus, TCV-116 inhibited the induction of aldosterone production by not only exogenous but also endogenous angiotensin II.

Endothelin-induced sudden death and the possible involvement of platelet activating factor (PAF)

Endothelin (5 nmol/kg, i.v.) caused a transient hypotension followed by a lasting hypertension in rats. However, an abrupt fall in the blood pressure was observed in most rats 6 to 30 min after the injection of endothelin and sudden death followed with lethality noted over 60 min. An abnormal electrocardiogram (ECG) (ventricular arrhythmias) was observed in rats injected with endothelin. Endothelin (i.v.) also caused sudden death in mice. Pretreatment (5 or 60 min) with specific PAF antagonists, CV-6209 (0.1-3 mg/kg, i.v.) and WEB 2086 (30 mg/kg, p.o.), and a calcium channel blocker, diltiazem (60 mg/kg, p.o.) prevented death and attenuated the ECG changes induced by endothelin, but CV-6209 did not prevent the blood pressure changes induced by endothelin. CV-6209 (0.5-3 mg/kg, i.v.), WEB 2086, diltiazem and dexamethasone (5 mg/kg, i.v.) protected mice against the death induced by endothelin. On the other hand, aspirin (cyclooxygenase inhibitor, 100 mg/kg, p.o.) did not protect mice from the death. Thus, endothelin is a highly toxic peptide with cardiotoxic effects, and PAF may be involved in the pathogenesis of the sudden death.

The thromboxane A2/prostaglandin endoperoxide receptor antagonist activity of CV-4151, a thromboxane A2 synthetase inhibitor.

The thromboxane A2/prostaglandin endoperoxide (TXA2/PGH2) receptor antagonist activity of CV-4151, a potent TXA2 synthetase inhibitor, was examined. CV-4151 inhibited guinea pig and human platelet aggregation induced by U-44069 with IC50 values of 1.2 +/- 0.3 X 10(-5) and 1.9 +/- 0.4 X 10(-5) M, respectively, and inhibited the specific binding of [3H]U-46619 to washed guinea pig and human platelets with IC50 values of 1.2 +/- 0.3 X 10(-6) and 5.1 +/- 1.0 X 10(-6) M, respectively. CV-4151 competitively inhibited the contraction of rabbit aortic strips induced by U-44069 with a pA2 value of 5.90. In experiments in mice in vivo, CV-4151 (1 and 10 mg/kg i.v.) significantly inhibited the thrombocytopenia induced by U-44069 in a dose-dependent manner. These results show that CV-4151 has a distinct TXA2/PGH2 receptor antagonist effect, and that this effect together with its inhibition of TXA2 synthetase could be important for the pharmacological action of this compound.

Renal effects of pinane-thromboxane A2 and indomethacin in saline volume-expanded spontaneously hypertensive rats

In 6-week old spontaneously hypertensive rats (SHR), indomethacin (5 mg/kg i.v.) and pinane-thromboxane A2 (PTA2) (50 micrograms/kg per h i.v.) a thromboxane A2 (TXA2) antagonist as well as a TXA2 synthetase inhibitor, resulted in natriuresis accompanied by an increase in p-aminohippuric acid and inulin clearances. Indomethacin acted as an antidiuretic in 6 week Wistar-Kyoto rats (WKY). PTA2 did not alter renal functions in either 6 week WKY and 18 week SHR. Basal urinary excretion of TXB2 (UTXB2V) was greater in 6 week SHR than in 6 week WKY and 18 week SHR, and that of 6-keto-PGF1 alpha (U6-keto-PGF1 alpha V) did not differ among these strains. Thus, U6-keto-PGF1 alpha V/UTXB2V was lower in the 6 week SHR. Basal urinary excretion of PGE (UPGEV) was much greater in 18 week SHR than in the 2 other groups. In the 6 week SHR, PTA2 decreased UTXB2V and increased U6-keto-PGF1 alpha V without affecting UPGEV, and indomethacin reduced UTXB2V more markedly than did U6-keto-PGF1 alpha V and UPGEV. Thus, both PTA2 and indomethacin increased U6-keto-PGF1 alpha V/UTXB2V in the 6 week SHR. These findings indicate that a disequilibrium in the biosynthesis of vasoconstrictive TXA2 and of vasodilator PGI2 may be involved in water and sodium retention in SHR during the developmental phase of hypertension.

Antidiuresis induced by β1- and β2-adrenergic agonists in ethanol-anesthetized rats

Abstract The β1- and β2-adrenergic in antidiuresis and sodium retention induced by β-adrenergic agonists were analysed in ethanol-anesthetized, water-diuretic rats. Intravenous infusions of isoprenaline, salbutamol and carbuterol did not affect inulin clearance but all increased plasma renin concentration to the same extent. Propranolol completely blocked the decreases in urine volume (V) and urinary sodium excretion (UNaV) induced by isoprenaline; practolol (β1-blocker) inhibited only the decrease in UNaV and butaxamine (β2-blocker) inhibited only the decrease in V. The ratios of doses of β-agonists which decreased UNaV and V by 50% %ED50 UNaV decrease/ED50 V decrease) were 0.34, 0.68, 1.56 and 2.36 for isoprenaline, tretoquinol, salbutamol and carbuterol, respectively. This increasing order of the ratios coincided with the order reported for the preponderance of the β2- over β1-component of these agonists. These results indicate that the decrease in UNaV induced by β-antagonists is related to β1, while the decrease in V is related to β2 stimulation.