Youichi Abe

Systemic and Regional Hemodynamic Responses to Tempol in Angiotensin II–Infused Hypertensive Rats

Recent studies have indicated that angiotensin II (Ang II) can stimulate oxidative stress. The present study was conducted to assess the contribution of oxygen radicals to hypertension and regional circulation during Ang II–induced hypertension. With radioactive microspheres, the responses of systemic and regional hemodynamics to the membrane-permeable, metal-independent superoxide dismutase mimetic 4-hydroxy-2,2,6,6-tetramethyl piperidinoxyl (tempol) were assessed in conscious Ang II–infused hypertensive rats. Ang II–infused rats (80 ng/min SC for 12 days: n=25) showed higher mean arterial pressure (MAP: 161±4 mm Hg) and total peripheral resistance (TPR: 1.59±0.08 mm Hg · min−1 · mL−1) than vehicle-infused normotensive rats (116±3 mm Hg and 0.95±0.04 mm Hg · min−1 · mL−1, respectively; n=23). The blood flow rates in the brain, spleen, large intestine, and skin were significantly reduced in Ang II–infused rats compared with vehicle-infused rats, whereas rates in the lung, heart, liver, kidney, stomach, small intestine, mesenterium, skeletal muscle, and testis were similar. Vascular resistance was significantly increased in every organ studied except the lung, in which the resistance was similar. Tempol (216 &mgr;mol/kg IV) significantly reduced MAP by 30±4% from 158±7 to 114±5 mm Hg and TPR by 35±6% from 1.57±0.17 to 0.95±0.04 mm Hg · min−1 · g−1 in Ang II–infused rats (n=9) but had no effect on these parameters in vehicle-infused rats (n=8). In Ang II–infused rats, tempol did not affect regional blood flow but significantly decreased vascular resistance in the brain (29±6%), heart (31±6%), liver (37±7%), kidney (30±7%), small intestine (38±6%), and large intestine (47±7%). Ang II–infused hypertensive rats showed doubled vascular superoxide production (assessed with lucigenin chemiluminescence), which was normalized by treatment with tempol (3 mmol/L, n=7). Further studies showed that the NO synthase inhibitor, N&ohgr;-nitro-l-arginine methyl ester (11 &mgr;mol · kg−1 · min−1 IV, n=11) markedly attenuated the systemic and regional hemodynamic responses of tempol in Ang II–infused rats. These results suggest that in this model of hypertension, oxidative stress may have contributed to the alterations in systemic blood pressure and regional vascular resistance through inactivation of NO.

L-Arginine improves endothelial function in renal artery of hypertensive Dahl rats.

Objectives To clarify whether endothelium-derived contracting factor (EDCF) is developed in renal artery of hypertensive Dahl rats and whether prolonged oral l-arginine treatments prevent development of EDCF and hypertension. Design The effect of prolonged salt treatment with or without l-arginine on the renal artery was examined. Methods and Results Dahl salt-sensitive and -resistant rats were fed a 0.4 or an 8% NaCl diet for 4 weeks. High sodium intake increased arterial pressure in Dahl salt-sensitive rats. The rings of renal arteries were suspended for isometric tension recording. Only in the hypertensive rats, more than 1 μmol/l acetylcholine induced an endothelium-dependent contraction response. The contraction was completely inhibited by indomethacin or ONO-3708 [prostaglandin H2 (PGH2)/thromboxane A2 (TXA2) receptor antagonist], and partially inhibited by OKY-046 (TXA2 synthetase inhibitor). Acetylcholine-induced relaxation was significantly depressed in hypertensive rats, which was partially improved by SQ29548 (PGH2/TXA2 receptor antagonist). Oral l-arginine, but not ONO-8809 (orally active PGH2/TXA2 receptor antagonist) treatment, inhibited the contraction and amended the relaxation. The endothelium-independent contraction to TXA2 receptor agonist U46619 and relaxation to nitroprusside were not altered by l-arginine treatment. The l-Arginine treatment reduced blood pressure and sodium retention with increases in urinary NO−−2/NO−−3 and cGMP excretion. Hydralazine treatment also inhibited development of EDCF. Conclusions The present results suggest that impaired endothelium-dependent relaxation to acetylcholine is caused in part by induction of EDCF synthesis/release in renal arteries of hypertensive Dahl rats. l-arginine can attenuate sodium retention and development of hypertension, which lead to a decrease in EDCF synthesis in renal arteries.

Dietary troglitazone decreases oxidative stress in early stage type II diabetic rats.

Oxidative stress is involved in the initiation and development of atherosclerosis in diabetes. We tested the hypothesis that oxidative stress is already increased in early stage type II diabetes, and that troglitazone may prevent the increase. Three groups of 20 week old rats were studied: untreated Otsuka Long-Evans Tokushima Fatty (OLETF) rats, as an animal model of type II diabetes, OLETF rats treated with troglitazone, and control Long-Evans Tokushima Otsuka (LETO) rats. Plasma lipid hydroperoxides (LOOH) concentration, as an indication of lipid peroxidation, and superoxide dismutase (SOD) activity in the thoracic aorta were measured. Plasma LOOH concentration was significantly higher in non-treated OLETF rats compared to LETO rats and treatment with troglitazone completely prevented this increase. SOD activity was significantly decreased in non-treated OLETF rats compared to LETO rats and troglitazone attenuated the diminution of it. These observations demonstrate oxidative stress is already increased in the early stage of type II diabetes and we confirmed troglitazone has the effect of an antioxidant in vivo.

Renal interstitial concentration of adenosine during endotoxin shock.

The present experiments were designed to measure the renal interstitial concentration of adenosine in an attempt to determine whether adenosine participates in the regulation of renal hemodynamics during endotoxin shock. The renal concentration of adenosine in response to lipopolysaccharide (LPS) administration was measured in anesthetized dogs using a microdialysis method. Renal hemodynamic responses to LPS were also determined with and without the adenosine A(1) receptor antagonist, (E)-(R)-1-[3-(2-phenylpyrazolo[1, 5-a]pyridin-3-yl)acryloyl]pyperidin-2-ylacetic acid (FK352). Intravenous administration of LPS (0.5 mg/kg) significantly decreased renal blood flow and mean arterial pressure. These parameters reached the minimum level at 5-10 min after the LPS administration and then returned to their respective preinjection levels. The renal interstitial concentration of adenosine increased from 118+/-18 to 381+/-46 nM. During treatment with FK352, LPS decreased renal blood flow and mean arterial pressure, however, these reductions were significantly attenuated. LPS also increased adenosine concentration, but its rise was reduced along with the attenuation of LPS-induced renal blood flow reduction. These results suggest that adenosine was involved in LPS-induced renal hemodynamic changes and that FK352 has a protective effect against renal dysfunction during endotoxin shock. Since the adenosine concentration was inversely proportional to renal blood flow levels, it can be assumed that adenosine plays an important role as a mediator, but not as an initiator of renal hemodynamic changes during endotoxin shock.

Possible role of uncoupling protein in regulation of myocardial energy metabolism in aortic regurgitation model rats

SPECIFIC AIMSMyocardial mitochondrial energy metabolism in heart failure is still controversial. We focused on serial changes in the cardiac performance and adenosine triphosphate (ATP) biosynthesi...

Effects of furosemide on the tubular reabsorption of nitrates in anesthetized dogs

The present study was performed to determine the tubular sites of nitrite and nitrate (NO) reabsorption and the effects of furosemide on the renal handling of NOx in anesthetized dogs, using renal clearance and stop-flow methods. Furosemide (2 mg/kg, i.v.) increased the urinary excretion rates of Na+ (U(Na+)V) and NOx (U(NOx)V) with a reduction of tubular reabsorption rates of Na+ and NOx. During inhibition of renal nitric oxide (NO) synthesis by an intrarenal infusion of L-nitro arginine (30 microg/kg-min), furosemide also increased U(NOx)V and decreased tubular reabsorption rate of NOx from 96.5+/-0.8% to 86.6+/-1.7%. An intravenous infusion of 10% mannitol (0.5 ml/kg-min) also increased both U(Na+)V and U(NOx)V. In addition, after furosemide administration or mannitol infusion. U(NOx)V was correlated with U(Na+)V. In stop-flow experiments, the distal dip in NOx curve was observed and the site of the dip in NOx curve was identical to that of Na+ curve. Furosemide shifted upward the U/P(Na+)/U/P(Cr) and U/P(NOx)/U/P(Cr) at the distal dip, indicating inhibition of Na+ and NOx reabsorption at distal tubules. These results indicate that more than 96% of the filtered NOx is reabsorbed in the renal tubules, and that the tubular handling of NOx is very close to that of Na+. In addition, the stop-flow experiments demonstrate that furosemide inhibited the reabsorption of NOx as well as Na+ at the distal tubule.

Effects of glucagon on the renal hemodynamics of dogs

An intrarenal infusion of glucagon resulted in an increase of glomerular filtration rate (GFR) with the same order of magnitude of renal blood flow (RBF) but did not affect the intrarenal distribution of blood flow. A superimposition of acetylcholine and glucagon decreased GFR even though RBF increased significantly. These findings indicate that the effect of glucagon on GFR depended on the selective dilation of afferent arterioles without any change in permeability of glomerular capillaries and redistribution of filtration.

Role of nitric oxide in regulation of renal sympathetic nerve activity during hemorrhage in conscious rats

The effect of inhibition of nitric oxide (NO) synthesis on the responses of blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) during hemorrhaging was examined with the use of an NO synthase inhibitor, N G-nitro-l-arginine methyl ester (l-NAME), in conscious rats. In the 0.9% saline group, hemorrhage (10 ml/kg body wt) did not alter BP but significantly increased HR and RSNA by 88 ± 12 beats/min and 67 ± 12%, respectively. Intravenous infusion of l-NAME (50 μg ⋅ kg-1 ⋅ min-1) significantly attenuated these tachycardic and sympathoexcitatory responses to hemorrhage (14 ± 7 beats/min and 26 ± 12%, respectively). Pretreatment ofl-arginine (87 mg/kg) recovered the attenuation of HR and RSNA responses induced byl-NAME (92 ± 6 beats/min and 64 ± 10%, respectively).l-NAME by itself did not alter the baroreceptor reflex control of HR and RSNA. Hemorrhage increased the plasma vasopressin concentration, and its increment in thel-NAME-treated group was significantly higher than that in the 0.9% saline group. Pretreatment with the vascular arginine vasopressin V1-receptor antagonist OPC-21268 (5 mg/kg) recovered the attenuation of RSNA response induced byl-NAME (54 ± 7%). These results indicate that NO modulated HR and RSNA responses to hemorrhage but did not directly affect the baroreceptor reflex arch. It can be assumed that NO modulated the baroreflex function by altering the secretion of vasopressin induced by hemorrhage.The effect of inhibition of nitric oxide (NO) synthesis on the responses of blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) during hemorrhaging was examined with the use of an NO synthase inhibitor, N(G)-nitro-L-arginine methyl ester (L-NAME), in conscious rats. In the 0.9% saline group, hemorrhage (10 ml/kg body wt) did not alter BP but significantly increased HR and RSNA by 88 +/- 12 beats/min and 67 +/- 12%, respectively. Intravenous infusion of L-NAME (50 microg. kg(-1). min(-1)) significantly attenuated these tachycardic and sympathoexcitatory responses to hemorrhage (14 +/- 7 beats/min and 26 +/- 12%, respectively). Pretreatment of L-arginine (87 mg/kg) recovered the attenuation of HR and RSNA responses induced by L-NAME (92 +/- 6 beats/min and 64 +/- 10%, respectively). L-NAME by itself did not alter the baroreceptor reflex control of HR and RSNA. Hemorrhage increased the plasma vasopressin concentration, and its increment in the L-NAME-treated group was significantly higher than that in the 0.9% saline group. Pretreatment with the vascular arginine vasopressin V(1)-receptor antagonist OPC-21268 (5 mg/kg) recovered the attenuation of RSNA response induced by L-NAME (54 +/- 7%). These results indicate that NO modulated HR and RSNA responses to hemorrhage but did not directly affect the baroreceptor reflex arch. It can be assumed that NO modulated the baroreflex function by altering the secretion of vasopressin induced by hemorrhage.

Effects of troglitazone on collagen accumulation and distensibility of aortic wall in prestage of non-insulin-dependent diabetes mellitus of Otsuka Long-Evans Tokushima Fatty rats.

We investigated the effect of troglitazone (TG) on aortic distensibility and histopathology at the preclinical stage in the non-insulin-dependent diabetes mellitus (NIDDM) model. Twenty male diabetic and 20 male nondiabetic rats were each divided into two groups: treated-DM, untreated-DM, treated-nonDM, and untreated-nonDM. TG (0.2%) was mixed in chow in the treated groups. From age 5 to 15 weeks, fast blood glucose and insulin were monitored. At 15 weeks, oral glucose tolerance test results, aortic wall histopathology, and collagen content were studied, and intravascular ultrasound images and aortic pressure were recorded. Aortic diameter was measured during the cardiac cycle, and the stiffness parameter beta was calculated. Blood glucose (mg/dl) 2 h after loading in treated-DM (139+/-20) was normalized (untreated-DM, 188+/-27; p<0.05). Insulin concentration (ng/ml) in treated-DM (3.2+/-0.4) was lower than that in untreated-DM (8.1+/-1.5; p<0.01). At 15 weeks, beta in untreated-DM (2.4+/-0.8) was larger than those in untreated-nonDM (1.5+/-0.4; p<0.0001) and in treated-DM (1.9+/-0.4, p = 0.0081). Aortic wall collagen (mg/g dry weight) increased in untreated-DM (32.8+/-3.3) as compared with treated-DM (28.1+/-3.8; p = 0.048). Histomorphometry showed decreased medial area (mm2) in treated-DM (0.55+/-0.05) compared with untreated-DM (0.78+/-0.12; p<0.0001). This study suggests that TG may prevent metabolic abnormalities and the deterioration of aortic distensibility at an early prediabetic stage.

Effects of Dibutyryl Cyclic AMP and Propranolol on Renin Secretion in Dogs

Summary The effect of cAMP and DbcAMP on renin secretion and renal he-modynamics was studied in anesthetized dogs. The infusion of cAMP into a renal artery failed to increase renin secretion significantly, but DbcAMP caused a significant increase in renin secretion. Both cAMP and DbcAMP had a vasodilator effect on renal vessels, without any change in renal blood pressure. These two compounds, however, differed in their effects on GFR and urine flow. cAMP infusion transiently decreased GFR, without significant effects on urinary flow and urinary sodium excretion, but DbcAMP increased GFR, urinary flow, and urinary sodium excretion. Time course studies, however, indicated that there was no direct relationship between renin secretion and RBF or urinary sodium excretion during DbcAMP infusion. The β-adrenergic blocking agents, propranolol and sotalol, decreased both arterial and renal venous PRA, but failed to affect the DbcAMP-induced renin secretion. These findings suggest that the effect of DbcAMP on renin secretion is associated with its action on JGC and not with electrolyte or renal hemodynamic changes. The authors express thanks to Ms. Sharon Hallabrin for her clerical assistance.