SGLT2 inhibition potentiates the cardiovascular, renal and metabolic effects of sGC stimulation in hypertensive rats with prolonged exposure to high fat diet

Prolonged high-fat diet (HFD) accelerates the cardiovascular, renal, and metabolic dysfunction in hypertensive rats with altered renal development (ARDev). Soluble guanylate cyclase (sGC) stimulation or sodium-glucose cotransporter 2 (SGLT2) inhibition may improve cardiovascular, renal, and metabolic function in settings of hypertension and obesity. This study examined whether 6 wk treatment with an SGLT2 inhibitor (empagliflozin, 7 mg/kg/day) enhances the cardiovascular, renal, and metabolic effects of a sGC stimulator (praliciguat, 10 mg/kg/day) in hypertensive rats with ARDev and prolonged exposure to HFD. Arterial pressure (AP), renal vascular resistance (RVR), fat abdominal volume (FAV), insulin resistance, leptin and triglycerides levels, and intrarenal infiltration of inflammatory cells were higher, but cardiac output and creatinine clearance were lower in hypertensive rats (n = 15) than in normotensive rats (n = 7). Praliciguat administration (n = 10) to hypertensive rats reduced (P < 0.05) AP, FAV, plasma concentrations of leptin and triglycerides, and increased (P < 0.05) cardiac output and creatinine clearance. Empagliflozin administration (n = 8) only increased (P < 0.05) glucosuria and creatinine clearance and decreased (P < 0.05) plasma leptin and triglycerides concentrations in hypertensive rats. Simultaneous administration of praliciguat and empagliflozin (n = 10) accelerated the decrease in AP, improved glucose tolerance, reduced (P < 0.05) incremental body weight gain, and decreased (P < 0.05) insulin resistance index, RVR, and the infiltration of T-CD3 lymphocytes in renal cortex and renal medulla. In summary, the combined administration of praliciguat and empagliflozin leads to a greater improvement of the cardiovascular, renal, and metabolic dysfunction secondary to prolonged exposure to HFD in hypertensive rats with ARDev than the treatment with either praliciguat or empagliflozin alone.

NEW & NOTEWORTHY This is the first study, to our knowledge, showing that SGLT2 inhibition potentiates the beneficial cardiovascular, renal, and metabolic effects elicited by sGC stimulation in hypertensive rats with prolonged high-fat diet. The effects of the simultaneous administration of praliciguat and empagliflozin are greater than those elicited by either one alone. The effects of the simultaneous treatment may be related to a greater reduction in the inflammatory status.

Gender differences in the renal changes induced by a prolonged high-fat diet in rats with altered renal development

The mechanisms involved in renal dysfunction induced by high-fat diet (HFD) in subjects with altered renal development (ARDev) are understudied. The objective of this study is to examine whether there are sex-dependent differences in the mechanisms involved in the hypertension and deterioration of renal function in SD rats with prolonged HFD and ARDev. The role of angiotensin II (Ang II) in the arterial pressure (AP) increments, the renal hemodynamic sensitivity to Ang II, glomerular damage and changes in fat abdominal volume, plasma adipokine levels, renal NADPHp67phox expression, and renal infiltration of immune cells were examined. Hypertension and deterioration of renal function were enhanced (P < 0.05) in both sexes of rats with HFD and ARDev. The decrease (P < 0.05) of AP elicited by candesartan in hypertensive rats was similar to that induced by the simultaneous administration of candesartan and apocynin. The greater (P < 0.05) renal vasoconstriction induced by Ang II in both sexes of rats with HFD and ARDev was accompanied by an enhanced (P < 0.05) infiltration of CD-3 cells and macrophages in the renal cortex and renal medulla. The increments (P < 0.05) in the renal expression of NADPHp67phox and glomeruloesclerosis were greater (P < 0.05) in males than in females with HFD and ARDev. Our results suggest that the hypertension and deterioration of renal function induced by HFD in rats with ARDev are Ang II-dependent and mediated by increments in oxidative stress and immune system activation. Sex-dependent increments in oxidative stress and glomerular damage may contribute to the deterioration of renal function in these rats.

Magnetic field homogeneity of a conical coaxial coil pair

An analytical study of the magnetic field created by a double-conical conducting sheet is presented. The analysis is based on the expansion of the magnetic field in terms of Legendre polynomials. It is demonstrated analytically that the angle of the conical surface that produces a nearly homogeneous magnetic field coincides with that of a pair of loops that fulfills the Helmholtz condition. From the results obtained, we propose an electric circuit formed by pairs of isolated conducting loops tightly wound around a pair of conical surfaces, calculating numerically the magnetic field produced by this system and its heterogeneity. An experimental setup of the proposed circuit was constructed and its magnetic field was measured. The results were compared with those obtained by numerical calculation, finding a good agreement. The numerical results demonstrate a significant improvement in homogeneity in the field of the proposed pair of conical coils compared with that achieved with a simple pair of Helmholtz loops or with a double solenoid. Moreover, a new design of a double pair of conical coils based on Braunbek's four loops is also proposed to achieve greater homogeneity. Regarding homogeneity, the rating of the analyzed configurations from best to worst is as follows: (1) double pair of conical coils, (2) pair of conical coils, (3) Braunbek's four loops, (4) Helmholtz pair, and (5) solenoid pair.

Abstract 135: Obesity Accelerates the Deterioration of Renal Function in Developmental Programming of Hypertension. Role of Angiotensin Ii and Oxidative Stress

Numerous studies have shown gender-dependent differences in the deterioration of renal function in models of developmental programming of hypertension (DPH). It is also known that obesity is associated to changes in renal function and that both angiotensin II (Ang II) and oxidative stress are involved in the renal alterations that occur in obesity and in animals with DPH. The main objectives were to examine whether the increment of arterial pressure (AP) and the deterioration of renal function are accelerated as a consequence of obesity in SD rats with DPH; whether these changes are gender-dependent; and to evaluate the role of Ang II and oxidative stress in these AP and renal function changes. A high fat diet (60%) was given during the first 4 months of age and DPH was induced by an AT receptor antagonist during nephrogenic period (ARAnp). Systolic AP (mmHg) was greater (P<0.05) in ARAnp-obese rats (167 ± 3 in ♂; 146 ± 4 in ♀) than in ARAnp (155 ± 3 in ♂; 137 ± 3 in ♀); obese (147 ± 2 in ♂; 137 ± 2 in ♀) or control (127 ± 1 in ♂; 119 ± 2 in ♀) rats. Three days administration of candesartan (7 mg/kg/day) led to a decrease in AP that was greater (P<0.05) in ARAnp-obese rats (55 ± 3 in ♂; 45 ± 4 in ♀) than in ARAnp (40 ± 3 in ♂; 37 ± 4 in ♀); obese (38 ± 4 in ♂; 27 ± 4 in ♀) or control (12 ± 2 in ♂; 14 ± 3 in ♀) rats. The acute Ang II infusion (30 ng/kg/min) induced an increase in renal vascular resistance (mmHg/ml/min/gr kw) that was also greater in ARAnp-obese rats (217 ± 45% in ♂; 145 ± 38% in ♀) than in ARAnp (103 ± 9% in ♂; 97 ± 8% in ♀); obese (106 ± 14% in ♂; 106 ± 17 in ♀) or control (51 ± 7% in ♂; 51 ± 10% in ♀) rats. The response to candesartan or Ang II infusion in ARAnp-obese rats was gender-dependent and may be explained by an enhanced oxidative stress. The expression of P67phox in the renal cortex was greater (P<0.05) in ARAnp-obese rats (3,00 ± 0,05 in ♂; 2,60 ± 0,04 in ♀) than in ARAnp (1,16 ± 0,04 in ♂; 1,66 ± 0,03 in ♀); obese (0,94 ± 0,06 in ♂; 1,02 ± 0,02 in ♀) or control (1,00 ± 0,02 in ♂; 1,02 ± 0,023 in ♀) rats. The results of this study suggest that obesity at an early age enhances the hypertension and accelerates the deterioration of renal function that occurs when cardiovascular disease is programmed during the perinatal period. It is also shown that Ang II and oxidative stress seems to play an important role in these AP and renal function changes.

Nitric oxide, prostaglandins and angiotensin II in the regulation of renal medullary blood flow during volume expansion

Regulation of medullary blood flow (MBF) is essential in maintaining renal function and blood pressure. However, it is unknown whether outer MBF (OMBF) and papillary blood flow (PBF) are regulated independently when extracellular volume (ECV) is enhanced. The aim of this study was to determine whether OMBF and PBF are differently regulated and whether there is an interaction between nitric oxide (NO), prostaglandins (PGs) and angiotensin II (Ang II) in regulating OMBF and PBF when ECV is enhanced. To achieve these goals, OMBF and PBF were measured by laser-Doppler in volume-expanded rats treated with a cyclooxygenase inhibitor (meclofenamate, 3 mg/kg) and/or a NO synthesis inhibitor (L-nitro-arginine methyl ester (L-NAME), 3 μg/kg/min) and/or Ang II (10 ng/kg/min). OMBF was unchanged by NO or PGs synthesis inhibition but decreased by 36 % (P < 0.05) when L-NAME and meclofenamate were infused simultaneously. PBF was similarly reduced by L-NAME (12 %), meclofenamate (17 %) or L-NAME + meclofenamate (19 %). Ang II did not modify OMBF, but it led to a similar decrease (P < 0.05) in OMBF when it was administered to rats with reduced NO (32 %), PGs (36 %) or NO and PGs (37 %) synthesis. In contrast, the fall in PBF induced by Ang II (12 %) was enhanced (P < 0.05) by the simultaneous PGs (30 %) or PGs and NO (31 %) synthesis inhibition but not in L-NAME-treated rats (20 %). This study presents novel findings suggesting that blood flows to the outer medulla and renal papilla are differently regulated and showing that there is a complex interaction between NO, PGs and Ang II in regulating OMBF and PBF when ECV is enhanced.

Sex-dependent hypertension and renal changes in aged rats with altered renal development

Numerous studies have evaluated blood pressure (BP) and renal changes in several models of developmental programming of hypertension. The present study examined to what extent BP, renal hemodynamic, and renal structure are affected at an old age in male and female animals with altered renal development. It also evaluated whether renal damage is associated with changes in cyclooxygenase (COX)-2 and neuronal nitric oxide synthase (NOS1) expression and immunoreactivity. Experiments were carried out in rats at 10–11 and 16–17 mo of age treated with vehicle or an ANG II type 1 receptor antagonist during the nephrogenic period (ARAnp). A progressive increment in BP and a deterioration of renal hemodynamics were found in both sexes of ARAnp-treated rats, with these changes being greater ( P < 0.05) in male rats. The decrease in glomerular filtration rate at the oldest age was greater ( P < 0.05) in male (74%) than female (32%) ARAnp-treated rats. Sex-dependent deterioration of renal structure was demonstrated in optical and electron microscopic experiments. COX-2 and NOS1 immunoreactivity were enhanced in the macula densa of male but not female ARAnp-treated rats. The present study reports novel findings suggesting that stimuli that induce a decrease of ANG II effects during renal development lead to a progressive increment in BP and renal damage at an old age in both sexes, but these BP and renal changes are greater in males than in females. The renal damage is associated with an increase of COX-2 and NOS1 in the macula densa of males but not females with altered renal development.

Renal effects induced by prolonged mPGES1 inhibition

The importance of membrane-bound PGE synthase 1 (mPGES1) in the regulation of renal function has been examined in mPGES1-deficient mice or by evaluating changes in its expression. However, it is unknown whether prolonged mPGES1 inhibition induces significant changes of renal function when Na+ intake is normal or low. This study examined the renal effects elicited by a selective mPGES1 inhibitor (PF-458) during 7 days in conscious chronically instrumented dogs with normal Na+ intake (NSI) or low Na+ intake (LSI). Results obtained in both in vitro and in vivo studies have strongly suggested that PF-458 is a selective mPGES1 inhibitor. The administration of 2.4 mg·kg−1·day−1 PF-458 to dogs with LSI did not induce significant changes in renal blood flow (RBF) and glomerular filtration rate (GFR). A larger dose of PF-458 (9.6 mg·kg−1·day−1) reduced RBF ( P < 0.05) but not GFR in dogs with LSI and did not induce changes of renal hemodynamic in dogs with NSI. Both doses of PF-458 elicited a decrease ( P < 0.05) in PGE2 and an increase ( P < 0.05) in 6-keto-PGF1α. The administration of PF-458 did not induce significant changes in renal excretory function, plasma renin activity, and plasma aldosterone and thromboxane B2 concentrations in dogs with LSI or NSI. The results obtained suggest that mPGES1 is involved in the regulation of RBF when Na+ intake is low and that the renal effects elicited by mPGES1 inhibition are modulated by a compensatory increment in PGI2. These results may have some therapeutical implications since it has been shown that prolonged mPGES1 inhibition has lower renal effects than those elicited by nonsteroidal anti-inflammatory drugs or selective cyclooxygenase-2 inhibitors.

COX2 inhibition during nephrogenic period induces ANG II hypertension and sex-dependent changes in renal function during aging

This study was performed to test the hypothesis that ANG II contributes to the hypertension and renal functional alterations induced by a decrease of COX2 activity during the nephrogenic period. It was also examined whether renal functional reserve and renal response to volume overload and high sodium intake are reduced in 3-4- and 9-11-mo-old male and female rats treated with vehicle or a COX2 inhibitor during nephrogenic period (COX2np). Our data show that this COX2 inhibition induces an ANG II-dependent hypertension that is similar in male and female rats. Renal functional reserve is reduced in COX2np-treated rats since their renal response to an increase in plasma amino acids levels is abolished, and their renal ability to eliminate a sodium load is impaired (P < 0.05). This reduction in renal excretory ability is similar in both sexes during aging but does not induce the development of a sodium-sensitive hypertension. However, the prolonged high-sodium intake at 9-11 mo of age leads to a greater proteinuria in male than in female (114 ± 12 μg/min vs. 72 ± 8 μg/min; P < 0.05) COX2np-treated rats. Renal hemodynamic sensitivity to acute increments in ANG II is unaltered in both sexes and at both ages in COX2np-treated rats. In summary, these results indicate that the reduction of COX2 activity during nephrogenic period programs for the development of an ANG II-dependent hypertension, reduces renal functional reserve to a similar extent in both sexes, and increases proteinuria in males but not in females when there is a prolonged increment in sodium intake.

Wrist skin temperature, motor activity, and body position as determinants of the circadian pattern of blood pressure

Although the circadian blood pressure (BP) pattern has been extensively studied, the determinants of this rhythm are not fully understood. Peripheral vasodilatation is a regulatory mechanism for BP maintenance. However, it remains to be established whether the increase of nocturnal distal skin temperature associated with heat loss could also reflect the dipping status. For the first time, this paper investigates the relationship between BP and skin wrist temperature (WT), to evaluate whether the WT circadian rhythm can serve as screening procedure to detect dipping/non-dipping BP patterns. In addition, the authors compare the relationship between WT and other variables previously described as determinants of the BP pattern, such as physical activity and body position. Measurements of WT, motor activity, and body position for 5 d, plus ambulatory BP for 24-h during that span, were obtained from 28 diurnally active normotensive volunteers. WT was negatively correlated, whereas activity and body position were positively correlated, with systolic and diastolic BPs. However, these relationships were stronger during the rest than activity phase. In addition, a 78.6% concordance was detected between the observed dips in BP and the predicted BP pattern calculated based on the WT rhythm. Thus, these results suggest that the increase in WT produced by heat loss during the rest phase through peripheral skin blood vessels is the result of blood vessel vasodilatation reflexes in response to a shift from a standing to a supine position, together with shift in the circadian sympathetic/parasympathetic balance (nocturnal parasympathetic activation). In conclusion, WT could be considered as a potential new screening procedure to implement the diagnosis of non-dipping BP pattern.

Role of angiotensin II in arterial pressure and renal hemodynamics in rats with altered renal development: age- and sex-dependent differences

Numerous studies have demonstrated that angiotensin II (ANG II) is involved in hypertension and renal changes occurring as a consequence of an adverse event during renal development. However, it was unknown whether this involvement is sex and age dependent. This study examines whether the increments in arterial pressure (AP) and in the renal sensitivity to ANG II are sex and age dependent in rats with altered renal development. It also evaluates whether the ANG II effects are accompanied by increments in AT(1) receptors and oxidative stress. Experiments were performed in 3- to 4- and 10- to 11-mo-old rats treated with vehicle or an AT(1) receptor antagonist (ARAnp) during the nephrogenic period. ARAnp-treated rats were hypertensive, but an age-dependent rise in AP was only found in males. Three days of treatment with candesartan (7 mg·kg(-1)·day(-1)) led to a fall of AP that was greater (P < 0.05) in male than in female 10- to 11-mo-old ARAnp-treated rats. Oxidated proteins were elevated (P < 0.05), and the decrease in AP elicited by candesartan was reduced (P < 0.05) when these rats are also treated with tempol (18 mg·kg(-1)·day(-1)). Hypertension was not maintained by an elevation of AT(1) receptors in kidneys and mesenteric arteries. The acute renal hemodynamic response to ANG II (30 ng·kg(-1)·min(-1)) was similarly enhanced (P < 0.05) in both sexes of ARAnp-treated rats at 3-4 but not at 10-11 mo of age. Our results suggest that an adverse event during the nephrogenic period induces an ANG II-dependent increment in AP that is aggravated only in males during aging and that oxidative stress but not an increase in AT(1) receptor contributes to the rise in AP. This study also shows that the renal hemodynamic sensitivity to ANG II is transitorily enhanced in both sexes of rats with altered renal development.

Renal effects of prolonged high protein intake and COX2 inhibition on hypertensive rats with altered renal development

Cyclooxygenase 2 (COX2) is involved in regulating renal hemodynamics after renal ablation. It is also known that high protein intake (HPI) leads to a deterioration of renal function when there is preexisting renal disease and that there are important gender differences in the regulation of renal function. This study tested the hypothesis that the role of COX2 in regulating renal function and the renal hemodynamic effects elicited by HPI are enhanced when nephrogenesis is altered during renal development. It was also expected that the role of COX2 and the effects elicited by HPI are age and sex dependent. Newborn Sprague-Dawley rats were treated with an AT1 ANG II receptor antagonist during the nephrogenic period (ARAnp). Experiments were performed at 3–4 and 10–11 mo of age. Arterial pressure was elevated ( P < 0.05) at both ages and in both sexes of ARAnp-treated rats. Renal COX2 expression was only elevated ( P < 0.05) at 10–11 mo of age in both sexes of ARAnp-treated rats. COX2 inhibition induced greater renal vasoconstriction in male and female hypertensive than in normotensive rats at both ages. HPI did not induce glomerular filtration rate (GFR) in the youngest hypertensive rats and in the oldest female hypertensive rats. However, the GFR decreased during HPI (0.63 ± 0.07 to 0.19 ± 0.05 ml/min) in the oldest male hypertensive rats. The HPI-induced increment in proteinuria was greater ( P < 0.05) in male (99 ± 22 mg/day) than in female (30 ± 8 mg/day) hypertensive rats. These results show that COX2 plays an important role in the regulation of renal function when renal development is altered and that prolonged HPI can lead to a renal insufficiency in males but not in females with reduced nephron endowment.

Hypertension and sex differences in the age-related renal changes when cyclooxygenase-2 activity is reduced during nephrogenesis

Several studies have proposed that cyclooxygenase-2 (COX2) is involved in the regulation of nephrogenesis and that an impaired nephrogenesis may induce the development of hypertension. This study was designed to test the hypothesis that the decrease of COX2 activity leads to a reduction in nephron number, an increase in arterial pressure, and age-dependent renal alterations that are greater in male than in female rats. Arterial pressure was measured from the first to the 16th month of life in rats treated with vehicle or a COX2 inhibitor during the nephrogenic period. Stereological and histological evaluations and renal function studies were performed at different ages. Arterial pressure increased (14%; P<0.05) and nephron number decreased (17%; P<0.05) to similar levels in male and female COX2-treated rats. However, glomerular filtration rate (31%) and renal plasma flow (25%) decreased (P<0.05) in male but not in female COX2-treated rats. A greater (P<0.05) age-dependent elevation in glomerular hypertrophy was also found in male COX2-treated rats compared with their female littermates. Glomerulosclerosis and tubulointerstitial damage in renal cortex and medulla were also significantly enhanced in male but not in female aged COX2-treated rats. Our results demonstrate that the decrease in COX2 activity during renal development leads to a reduction in nephron number and to an elevation in arterial pressure that are similar in males and females. However, the consequent age-dependent deterioration of the renal structure and renal function is only significantly enhanced in male rats.

Age- and sodium-sensitive hypertension and sex-dependent renal changes in rats with a reduced nephron number

We have demonstrated that the reduction of angiotensin II effects during the nephrogenic period reduces the nephron number and induces the development of hypertension. The hypotheses examined are that this reduction of angiotensin effects leads to the development of an age-dependent sodium sensitive hypertension and that the hypertension is angiotensin II dependent. Newborn rats were treated with an angiotensin II type 1 receptor antagonist during the first 2 weeks of age. At 3 to 4 and 11 to 12 months of age, changes in systolic blood pressure, proteinuria, and renal function in response to a prolonged high sodium intake were examined. The basal blood pressure response to the administration of the angiotensin II receptor antagonist was also evaluated at both ages. Basal blood pressure was similarly elevated (P<0.05) in male and female treated rats, and the increment was age dependent. High sodium intake only elicited a blood pressure elevation (136+/-1 to 154+/-3 mm Hg; P<0.05) and a decrease in glomerular filtration rate (28%; P<0.05) at 11 to 12 months in treated rats. Blockade of angiotensin II receptors during renal development induced an increase (P<0.05) in proteinuria that was age and sex dependent, but high sodium intake only induced an elevation in proteinuria in the younger rats (50%; P<0.05). Hypertension was maintained by angiotensin II at both ages because blood pressure decreased to normal levels after treatment with an angiotensin II type 1 receptor antagonist. This study shows that the reduction of angiotensin II effects during the nephrogenic period modifies renal function and induces the development of an angiotensin II-dependent hypertension that becomes sodium sensitive during aging.

Characterization of manures from fish cage farming in Chile

This study aims to characterize salmonid manures and to determine their potential use in agricultural soils. Sampling was carried out below salmon and trout cages in farms located in lakes and in the sea in the South of Chile during 2002-2003. Manure was analyzed for macronutrients, micronutrients and heavy metals. Results showed a high variability between samples and differences between sea and lake manure. Dry matter contents were low averaging c. 12-15%. Manures showed low OM contents with values <c. 15% and a neutral pH (c. 7.0). Both manures had low total N contents with values of <0.9%, more than 75% of which was in the organic form. Lake manure showed high contents of P (1.56%), Ca (3.89%), Fe (27,948 ppm), Mn (446 ppm), Al (31,789 ppm), As (5.13 ppm), Cd (1.04 ppm), Cr (18.8 ppm), Ni (12.3 ppm), Pb (3.5 ppm) and Zn (393 ppm). Sea manure had high contents of Mg (1.65% ppm), K (0.63%), Na (11.8%) and Cu (89 ppm). Salmonid manure had low nutrients and heavy metal contents and a potential use in agricultural soils, which could reduce the risks of water pollution on water from fish farming.

Changes in renal hemodynamics and excretory function induced by a reduction of ANG II effects during renal development

The aim was to evaluate whether blockade of ANG II effects during renal development modifies the renal response to an increment of plasma amino acid concentration. It was also examined in anesthetized rats whether the reduction of the renal ability to eliminate an acute volume expansion (VE), elicited by blockade of ANG II during renal development, is sex and/or age dependent. Newborn Sprague-Dawley rats were treated with vehicle or an AT(1)-receptor antagonist (ARA) during postnatal nephrogenesis. Amino acid infusion induced increments (P < 0.05) of glomerular filtration rate (31 +/- 6%) and renal plasma flow (26 +/- 5%) in male but not in female vehicle-treated rats. Natriuretic and diuretic responses to amino acid infusion were similar in male and female vehicle-treated rats. These renal hemodynamics and excretory responses to amino acid infusion were abolished in ARA-treated rats. Renal responses to VE were evaluated at 3-4 and 9-10 mo of age in vehicle and ARA-treated rats. VE-induced natriuresis and diuresis were reduced by more than 38% (P < 0.05) in 3- to 4-mo-old male and female ARA-treated rats. An age-dependent reduction (P < 0.05) in the renal ability to eliminate VE was found in male but not in female rats treated with ARA. Our results demonstrate that the renal effects induced by an increment in amino acids are abolished when ANG II effects have been reduced during nephrogenesis. In addition, this reduction of ANG II effects elicits an impairment of the renal ability to eliminate an acute VE in males and females, which is aggravated by age only in male rats.

Sex and age differences of renal function in rats with reduced ANG II activity during the nephrogenic period

This study was designed to test the hypothesis that blockade of angiotensin II effects during renal development accelerates the aging-related changes in renal hemodynamics and proteinuria, and that these changes are sex dependent. It has also been examined whether the deterioration of urinary concentrating ability elicited by angiotensin II blockade is sex and/or aging dependent. Newborn Sprague-Dawley rats were treated with vehicle or an AT(1) angiotensin II receptor antagonist (ARA) during the first 14 postnatal days. Blood pressure, glomerular filtration rate, proteinuria, and urinary concentrating ability in response to dehydration were examined in conscious rats at 3 and 11 mo of age. ARA treatment elicited a similar increment in blood pressure in males and females that was greater (P < 0.05) at 11 than at 3 mo of age. Glomerular filtration rate only decreased (P < 0.05) in 11-mo-old male ARA-treated rats (0.59 +/- 0.07 vs. 0.80 +/- 0.07 ml.min(-1).g(-1) in control group). At 3 mo of age, proteinuria increased in male (107%) but not in female ARA-treated rats. However, at 11 mo of age, proteinuria increased in both sexes, but the increment was greater (P < 0.05) in male (244%) than in female (138%) ARA-treated rats. Renal ability to concentrate urine in response to prolonged water dehydration was only reduced in ARA-treated males. The reduction of urinary concentrating ability was accentuated by aging. Therefore, we conclude that blockade of angiotensin II effects during renal development elicits an important deterioration of cortical and medullary function that is sex and aging dependent.

Sex differences in the renal changes elicited by angiotensin II blockade during the nephrogenic period

The renin-angiotensin system plays an important role in renal development. However, it is unknown whether reduction in angiotensin II effects during the nephrogenic period leads to different renal alterations in males and females during the adult age. The aim of this study was to evaluate whether the role of angiotensin II on renal development is sex dependent and whether there are sex differences in blood pressure, renal hemodynamics, and severity of renal damage during adult life when nephrogenesis is altered by blocking angiotensin II effects. Newborn Sprague-Dawley rats were treated with an angiotensin II type 1 receptor antagonist (L-158.809; 7 mg/kg per day) during the first 2 weeks of life. At 3 months of age, changes in blood pressure, albuminuria, and renal hemodynamics were assessed, and stereological and histopathologic studies were performed. Blood pressure increased (127+/-0.5 versus 115+/-0.7 mm Hg in control rats; P<0.05) and nephron number decreased (37%; P<0.05) similarly in treated males and females. However, only males had an elevation in albuminuria (5.92+/-1.65 versus 0.33+/-0.09 mg per day in control rats; P<0.05), a fall in glomerular filtration rate (12.6%; P<0.05), and a significant decrease in papillary volume (42%; P<0.05). Mean glomerular volume, glomerulosclerosis, arteriolar hypertrophy, and tubulointerstitial damage in cortex and medulla were also higher (P<0.05) in angiotensin II type 1 receptor antagonist-treated males than in treated females. The results of this study suggest that females seem to be more protected than males to the renal consequences of reducing angiotensin II effects during renal development.

Nitrogen budgets for three cropping systems fertilised with cattle manure

A field plot experiment was set up on a sandy loam soil of SW England in order to determine the efficiency of nitrogen use from different cattle manures. The manure treatments were low and high dry matter cattle slurries and one farmyard manure applied at a target rate of 200 kg total N ha(-1)year(-1), and an untreated control. There were three different cropping systems: ryegrass/clover mixture, maize/rye and maize/bare soil, which were evaluated during 1998/99 and 1999/00. Measurements were made of N losses, N uptake and herbage DM yields. Result showed that manure type had a significant effect on N utilisation only for maize. N balances were negative in maize (approximately -247 to -10 kg N) compared to grass (approximately 5-158 kg N). Agronomic management was more important than manure type in influencing N losses, where soil cultivation appeared to be a key factor when comparing maize and grass systems.

Distribution of nitric oxide synthases and nitrotyrosine in the kidney of spontaneously hypertensive rats

OBJECTIVES

To study the cellular distribution and the expression of the major isoforms of NO synthase (NOS) and of nitrotyrosine in the kidney in spontaneous hypertension.

DESIGN AND METHODS

We have studied by immunohistochemistry the location of the endothelial (eNOS), neuronal (nNOS) and inducible (iNOS) isoforms and nitrotyrosine in kidney slices from normotensive Wistar-Kyoto (WKY) rats and spontaneously hypertensive rats (SHR) using specific antibodies. In order to quantify the expression of these proteins, we have analyzed dissected renal cortical and medullary sections by means of Western blot.

RESULTS

Tubular cells were immunoreactive to nNOS and more numerous in the renal medulla of the SHR compared with that of the WKY, specifically in the outer medulla and the papillary region. Western blot also showed higher expression of nNOS in the renal medulla, but not the renal cortex of the SHR. In contrast, iNOS and eNOS distribution and expression were similar in the kidneys of WKY rats and SHR. Immunohistochemistry showed immunoreactive cells to nitrotyrosine in a variety of renal cells similarly distributed in SHR and WKY kidneys. Western analysis detected three proteins of 14.5, 23.7 and 39 kDa immunoreactive to nitrotyrosine, showing a higher expression in the renal cortex compared to the renal medulla.

CONCLUSIONS

The expression of nNOS is higher in the renal medulla of the SHR, and the distribution of eNOS, iNOS and nitrotyrosine is similar in SHR and WKY rats. It is proposed that the higher expression of the neuronal isoform in the medullary tubular cells is a protective mechanism aimed to improve renal function in spontaneous hypertension.

Role of cyclooxygenase-2 in the control of renal haemodynamics and excretory function

AIM

The available evidence supporting the importance of cyclooxygenase-2 (COX-2) in the regulation of renal haemodynamics and excretory function is summarized. Cyclooxygenase-2-derived metabolites play a very important role in regulating renal haemodynamics when sodium intake is low whereas it plays a minor role in the control of cortical blood flow when sodium intake is normal or elevated. The importance of COX-2 in the regulation of renal haemodynamics seems to be dependent on the endogenous production of other vasoactive products such as nitric oxide (NO) or noradrenaline. The activation of COX-2 in response to a decrease in NO may represent a mechanism aimed at defending the renal vasculature in the face of a decrease in NO levels.

CONCLUSION

Contrary to the important role of COX-2 in the long-term regulation of renal haemodynamics, the metabolites derived from COX-2 seem to be only involved in the acute regulation of renal excretory function.

Role of nitric oxide and cyclooxygenase-2 in regulating the renal hemodynamic response to norepinephrine

We have reported that the renal hemodynamic effects of norepinephrine (NE) are modulated by cyclooxygenase-2 (COX-2)-derived metabolites. Our main objective was to examine whether there is an interaction between nitric oxide (NO) and COX-2 in modulating the renal hemodynamic effects of NE. NE was infused at three doses to anesthetized dogs pretreated with vehicle (n = 8), a selective COX-2 inhibitor (nimesulide) (n = 6), an NO synthesis inhibitor [NG-nitro-l-arginine methyl ester; l-NAME] (n = 8), or with nimesulide and l-NAME (n = 5). During NE infusion, PGE2 excretion increased (125%) in the control group and did not change in the l-NAME-treated dogs. The simultaneous inhibition of NO and COX-2 potentiated to a greater extent the NE-induced renal vasoconstriction than inhibition of either NO or COX-2. The NE-induced renal vasoconstriction during NO and COX-2 inhibition was reduced (P < 0.05) by infusing an AT1 receptor antagonist (n = 6). These results suggest that there is an interaction between NO and COX-2 in protecting the renal vasculature from the NE effects and that angiotensin II partly mediates the NE-induced renal vasoconstriction when NO synthesis and COX-2 activity are reduced.

Role of cyclooxygenase-2 in the prolonged regulation of renal function

The role of cyclooxygenase-2 (COX-2) in the prolonged regulation of renal function was evaluated during changes in sodium intake and reduction of NO synthesis. It was evaluated in conscious dogs by administering a selective inhibitor (nimesulide) during 8 consecutive days. Nimesulide administration to dogs with normal or high sodium load did not modify glomerular filtration rate but reduced renal blood flow (16%; P<0.05). The vasoconstriction elicited by COX-2 inhibition was greater when NO production was inhibited because glomerular filtration rate decreased by >25% when nimesulide was administered to dogs with a reduced NO synthesis. During low sodium intake, COX-2 inhibition elicited a decrease (P<0.05) of both glomerular filtration rate (34%) and renal blood flow (31%). Sodium excretion only decreased (P<0.05) during the first day of COX-2 inhibition in dogs with normal or high sodium load. The increase in plasma potassium levels elicited by COX-2 inhibition was greater in dogs with low sodium intake and was enhanced when NO production was inhibited. This change in potassium was not secondary to a decrease in plasma aldosterone levels. The results of this study suggest that COX-2-derived metabolites (1) play a more important role in the long-term regulation of renal hemodynamic when sodium intake is low, (2) protect the renal vasculature from the vasoconstriction secondary to a reduction in NO, (3) are only acutely involved in regulating urinary sodium excretion, and (4) play a more important role in regulating plasma potassium concentration when NO synthesis is reduced.

Changes in NOS activity and protein expression during acute and prolonged ANG II administration

The aim of this study was to assess the effects of acute or prolonged increases of ANG II on nitric oxide synthase (NOS) activities and protein expression in mesenteric resistance vessels, left ventricle, renal cortex, and renal medulla. The response of NOS activities to ANG II is compared with that induced by phenylephrine. ANG II or phenylephrine were infused over either 3 h or 3 days to conscious rats. NOS activity was examined by measuring the rate of conversion of L-[14C]arginine to L-[14C]citrulline. Protein levels of endothelial (e) and neuronal (n) NOS were determined by Western blot analysis. Arterial pressure (AP) increased (P < 0.05) during acute and prolonged ANG II infusion. Ca2+-dependent NOS activity values (pmol of citrulline x min(-1) x g wet wt(-1)) for control rats were 21 +/- 9 in mesenteric arteries, 13 +/- 7 in left ventricle, 14 +/- 8 in renal cortex, and 411 +/- 70 in renal medulla. Acute ANG II infusion increased (P < 0.05) Ca2+-dependent NOS activity in renal cortex and renal medulla (81 +/- 18 and 611 +/- 48, respectively), but no differences were found in mesenteric arteries and left ventricle with respect to control rats. In contrast to the renal changes in NOS activity, acute ANG II infusion did not modify eNOS or nNOS expression in any of the tissues examined. Prolonged ANG II infusion increased (P < 0.05) Ca2+-dependent NOS activity in mesenteric arteries (70 +/- 17), renal cortex (104 +/- 31), and left ventricle (49 +/- 8) and did not elicit changes in renal medulla. After a prolonged ANG II infusion, eNOS and nNOS levels increased in all tissues examined with the exception of eNOS in the mesenteric arteries and nNOS in the left ventricle, which were not altered. Acute and prolonged phenylephrine infusion elevated AP to a similar extent as ANG II but only elicited significant increments of Ca2+-dependent NOS activity in renal cortex. These data indicate that acute and prolonged elevations in ANG II upregulate Ca2+-dependent NOS activity and protein expression in different tissues related to the control of blood pressure. However, these ANG II effects are heterogeneous with respect to the tissue implicated, the time course of the stimulation, and the NOS isoform involved. Phenylephrine only induces a significant elevation of Ca2+-dependent NOS activity in renal cortex.

Role of COX-2-derived metabolites in regulation of the renal hemodynamic response to norepinephrine

The objective of this study was to examine the role of cylcooxygenase (COX)-2-derived prostaglandins (PG) in modulating the renal hemodynamic effects of norepinephrine (NE) during low or normal sodium intake. The relative contribution of each COX isoform in producing the PG that attenuate the renal NE effects during normal sodium intake was also evaluated. The renal response to three doses of NE (50, 100, and 250 ng. kg(-1). min(-1)) was evaluated in anesthetized dogs pretreated with vehicle, a selective COX-2 inhibitor (nimesulide), or a nonselective COX inhibitor (meclofenamate). Intrarenal infusion of the two lower doses of NE in vehicle-pretreated dogs with normal sodium intake (n = 8) elicited an increase in renal vascular resistance (RVR; 21 and 34%) without inducing changes in glomerular filtration rate (GFR). The highest dose of NE in this group induced a further increment in RVR (113%) and a decrease in GFR (33%). Pretreatment with nimesulide in dogs with normal sodium intake (n = 7) did not modify the NE-induced increments in RVR but enhanced the decreases in GFR induced by the three NE doses (12, 26, and 64%). The renal hemodynamic response to NE in meclofenamate-pretreated dogs with normal sodium intake (n = 7) was similar to that found in dogs pretreated with nimesulide. Infusion of the lowest dose of NE to vehicle-pretreated dogs with low sodium intake (n = 6) did not modify GFR and elicited an increase in RVR (42%). Infusion of the second and third doses of NE led to a decrease in GFR (35 and 91%) and a rise in RVR (82 and 587%). Infusion of the first two doses of NE in nimesulide-pretreated dogs with low sodium intake (n = 5) induced a fall in GFR (64 and 92%) and an increase in RVR (174 and 2,293%) that were greater (P < 0.05) than those induced by NE in vehicle-pretreated dogs. The elevation in the urinary excretion rates of PGE(2) and 6-keto-PGF(1alpha) elicited by NE was prevented in the nimesulide-pretreated dogs. Our results show that COX-2 inhibition potentiates the renal hemodynamic effects of NE and propose that the PG involved in modulating them are mainly derived from COX-2 activity.

Role of Cyclooxygenase-2-Derived Metabolites and NO in Renal Response to Bradykinin

-It has been reported that bradykinin (BK) can induce or activate both cyclooxygenase (COX) isoforms and that the renal effects of BK seem to be mediated by prostaglandins and NO. The first objective of this study was to evaluate the relative contribution of both COX isoforms in mediating the renal response to BK in anesthetized dogs. The second objective was to examine whether COX-2 inhibition potentiates the renal effects induced by NO reduction during BK administration. Intrarenal BK infusion (8 ng. kg(-1). min(-1), n=6) elicited a significant increment in renal blood flow, sodium excretion, urine volume, and the fractional excretion of lithium. COX-2 inhibition (nimesulide, 5 µg. kg(-1). min(-1), n=6) reduced the renal vasodilatation but did not significantly modify the natriuresis or diuresis secondary to BK. Administration of a nonspecific isozyme COX inhibitor (meclofenamate, 5 µg. kg(-1). min(-1); n=6) did not induce greater effects than those produced by nimesulide. NO synthesis reduction (N:(G)-nitro-L-arginine methyl ester [L-NAME], 3 µg. kg(-1). min(-1)) prevented the renal vasodilatation and the increment in the fractional excretion of lithium induced by BK but did not affect the natriuretic or diuretic response. Simultaneous nimesulide infusion did not modify the renal effects of L-NAME during BK infusion (n=6). Finally, inhibition of both COX isoforms with meclofenamate, in dogs treated with L-NAME (n=6), completely prevented the vasodilator and excretory actions of BK. The results of this study suggest that (1) NO and prostanoids dependent on COX-2 seem to be involved in the renal vasodilatation induced by BK, and (2) there is an interaction between NO and COX-1-derived metabolites in mediating the natriuretic and diuretic response to BK.

Role of cyclooxygenase-2-derived metabolites and nitric oxide in regulating renal function

The aim of this study was to examine the relative contribution of both cyclooxygenase (COX) isoforms in producing the prostaglandins (PG) involved in the regulation of renal function, when nitric oxide (NO) synthesis is reduced. In anesthetized dogs with reduction of NO synthesis, the renal effects of a nonisozyme-specific COX inhibitor (meclofenamate) were compared with those elicited by a selective COX-2 inhibitor (nimesulide) before and during an extracellular volume expansion (ECVE). Intrarenal N(G)- nitro-L-arginine methyl ester (L-NAME) infusion (1 microg x kg(-1) x min(-1); n = 6) did not elicit renal hemodynamic changes and reduced (P < 0.01) the renal excretory response to ECVE. Intravenous nimesulide (5 microg x kg(-1) x min(-1); n = 6) did not modify renal hemodynamic and reduced (P < 0. 05) sodium excretion before ECVE. Simultaneous L-NAME and nimesulide infusion (n = 7) elicited an increment (37%) in renal vascular resistance (RVR; P < 0.05) before ECVE and no hemodynamic changes during ECVE. The reduced excretory response elicited by L-NAME and nimesulide was similar to that found during L-NAME infusion. Finally, simultaneous L-NAME and meclofenamate infusion (10 microg x kg(-1) x min(-1); n = 7) induced an increase in RVR (91%, P < 0.05), a decrease in glomerular filtration rate (35%, P < 0.05), and a reduction of the renal excretory response to ECVE that was greater (P < 0.05) than that elicited by L-NAME alone. The results obtained support the notion that PG involved in regulating renal hemodynamic and excretory function when NO synthesis is reduced are mainly dependent on COX-1 activity.

Effects of renal perfusion pressure on renal interstitial hydrostatic pressure and Na+ excretion: role of endothelium-derived nitric oxide

The purpose of this study was to examine the role of endothelium-derived nitric oxide in modulating the effect of renal perfusion pressure (RPP) on renal interstitial hydrostatic pressure (RIHP) and urinary Na+ excretion (UNaV). The effects of RPP on renal hemodynamics, RIHP, and Na+ and Li+ excretions were determined in control Sprague-Dawley rats, in Sprague-Dawley rats pretreated with intravenous infusion of NG-nitro-L-arginine methyl ester (L-NAME) at doses of 1, 5, and 50 microg/kg/min, and in rats pretreated with L-NAME (5 microg/kg/min) plus L-arginine (10 mg/kg/min). The RPP was changed from 95 to 135 mm Hg by an electronically servo-controlled aortic occluder above the renal arteries in all groups. Increasing RPP in control rats from 95 to 135 mm Hg increased RIHP (from 4.4 +/- 0.5 to 8.7 +/- 1.2 mm Hg), UNaV (from 2.37 +/- 0.61 to 8.29 +/- 1.59 microEq/min), and fractional excretion of Li+ (from 38.0 +/- 2.5 to 51.4 +/- 6.0%). In rats pretreated with L-NAME (5 microg/kg/min), increases in RPP from 95 to 135 mm Hg had no effect on RIHP (from 1.6 +/- 0.4 to 2.2 +/- 0.6 mm Hg) or fractional excretion of Li+ and markedly attenuated pressure-natriuresis relationship (from 1.84 +/- 0.50 to 2.88 +/- 0.65 microEq/min). Although L-NAME did reduce renal plasma flow and glomerular filtration rate, the autoregulatory responses to RPP were maintained. In rats pretreated with L-NAME plus L-arginine, RIHP, UNaV, and fractional excretion of Li+ responses to RPP were similar to the control rats. The results of this study indicate that endothelium-derived nitric oxide plays an important role in modulating the effect of RPP on Na+ excretion by enhancing the transmission of RPP into the renal interstitium.

Release of nitric oxide after acute hypertension

We have shown that NO production, assessed by measuring changes in plasma nitrate concentration, is down-regulated when blood pressure falls. This study intended to determine first, whether NO-derived plasma nitrate varies in response to increases in blood pressure induced by different mechanical and pharmacologic stimuli, including angiotensin II and catecholamines; and second, specifically to study the interaction between angiotensin II and NO production. An intravenous infusion (4-10 min) of norepinephrine (7.5 microg/kg/min), phenylephrine (30 microg/kg/min), or angiotensin II (0.3 and 3 microg/kg/min) caused hypertension accompanied by an increase in plasma nitrate, as assessed by high-performance capillary electrophoresis. Mechanical hypertension elicited by aortic occlusion also was accompanied by an increase in plasma nitrate. Angiotensin II (0.03, 0.3, and 3 microg/kg/min, 10 min) dose-dependently increased blood pressure. The intermediate and high dose, but not the low dose, of angiotensin II increased plasma nitrate concentration. N(G)-nitro-L-arginine methyl ester (L-NAME) lowered the basal concentration of plasma nitrate, abolished the increase in plasma nitrate elicited by angiotensin II and norepinephrine, and potentiated the pressor effect of the low dose of angiotensin II, although this dose did not increase NO production. L-NAME also potentiated the pressor effects of the intermediate dose of angiotensin II. This study demonstrates that an augmented systemic production of NO, measured as an increase in plasma nitrate, takes place after acute hypertension. The results of this study suggest that an increase in NO generation occurs when angiotensin II hypertension exceeds a certain limit, below which the basal production of NO is sufficient to compensate the vasoconstriction.

Renal effects of prolonged cyclooxygenase inhibition when angiotensin II levels are elevated

We examined the renal functional and hemodynamic changes induced by prolonged cyclooxygenase (COX) inhibition when angiotensin II levels are elevated during several consecutive days. The effects induced by the infusion of either initially subpressor or pressor angiotensin II doses (1 and 5 ng/kg/min) were examined in dogs with or without the simultaneous infusion of meclofenamate (5 microg/kg/min). Experiments were performed in conscious permanently instrumented dogs. Infusion of the lower angiotensin II dose alone (n = 6) caused a late 12+/-2% increase in arterial pressure, a 25+/-6% decrease in renal blood flow (RBF), and a transitory decrease in urinary sodium excretion. COX inhibition reduced the hypertension and renal vasoconstriction, but enhanced the sodium retention, induced by the lower dose angiotensin II infusion (n = 6). The higher angiotensin II dose (n = 6) caused a 25+/-4% increase in arterial pressure, a 24+/-5% decrease in RBF, and a transitory decrease in urinary sodium excretion. Finally, COX inhibition did not modify the renal effects elicited by the higher angiotensin II dose (n = 6). The results of this study suggest that endogenous prostaglandins play an important role in the regulation of the renal and systemic changes induced by prolonged administration of initially subpressor angiotensin II doses. It has also been demonstrated that prolonged COX inhibition does not modify the renal functional and hemodynamic changes elicited by the long-term infusion of a pressor angiotensin II dose.

Renal changes induced by a cyclooxygenase-2 inhibitor during normal and low sodium intake

Cyclooxygenase-2 (COX-2) has been identified in renal tissues under normal conditions, with its expression enhanced during sodium restriction. To evaluate the role of COX-2-derived metabolites in the regulation of renal function, we infused a selective inhibitor (nimesulide) in anesthetized dogs with normal or low sodium intake. The renal effects elicited by nimesulide and a non-isozyme-specific inhibitor (meclofenamate) were compared during normal sodium intake. In ex vivo assays, meclofenamate, but not nimesulide, prevented the platelet aggregation elicited by arachidonic acid. During normal sodium intake, nimesulide infusion (n=6) had no effects on arterial pressure or renal hemodynamics but did reduce urinary sodium excretion, urine flow rate, and fractional lithium excretion. In contrast, nimesulide administration increased arterial pressure and decreased renal blood flow, urine flow rate, and fractional lithium excretion during low sodium intake (n=6). COX-2 inhibition reduced urinary prostaglandin E(2) excretion in both groups but did not modify plasma renin activity in dogs with low (8.1+/-1.1 ng angiotensin I. mL(-1). h(-1)) or normal (1.8+/-0.4 ng angiotensin I. mL(-1). h(-1)) sodium intake. Meclofenamate infusion in dogs with normal sodium intake (n=8) induced a greater renal hemodynamic effect than nimesulide infusion. These results suggest that COX-2-derived metabolites (1) are involved in the regulation of sodium excretion in dogs with normal sodium intake, (2) play an important role in the regulation of renal hemodynamic and excretory function in dogs with low sodium intake, and (3) are not involved in the maintenance of the high renin levels during a long-term decrease in sodium intake.

Role of nitric oxide and prostaglandins in the long-term control of renal function

Previous studies have reported evidence of an important interaction between nitric oxide (NO) and prostaglandins in the acute regulation of renal function. The objective of this study was to determine in conscious dogs whether the renal effects of the prolonged administration of a cyclooxygenase inhibitor are enhanced when NO synthesis is reduced. Meclofenamate infusion (5 microg x kg(-1) x min(-1)) during 4 consecutive days (n=8) elicited a continuous decrease (P<0.05) in renal blood flow and plasma renin activity and a transitory decrease in sodium excretion. NG-Nitro-L-arginine methyl ester (L-NAME) infusion (5 microg x kg(-1) x min(-1)) during 6 days (n=8) produced a significant increase in arterial pressure and a transitory decrease (P<0.05) in both renal blood flow and plasma renin activity. The simultaneous inhibition of NO and prostaglandin synthesis (n=7) led to an increase in arterial pressure and a decrease in renal blood flow similar to those observed during the administration of either L-NAME or meclofenamate. In contrast, this simultaneous inhibition produced a decrease in glomerular filtration rate, which was not observed in the previous groups, and also induced an increase in renal vascular resistance and a decrease in sodium excretion greater (P<0.05) than those found during the inhibition of either NO or prostaglandins. Only a transitory decrease in plasma renin activity was found during meclofenamate infusion in this group. The results of this study present new evidence that the renal vasoconstrictor and antinatriuretic effects induced by the prolonged infusion of a cyclooxygenase inhibitor are significantly enhanced when NO synthesis is reduced. These results suggest that renal function may be more sensitive to the prolonged administration of a cyclooxygenase inhibitor in situations where NO production is reduced.

Renal changes induced by nitric oxide and prostaglandin synthesis reduction: effects of trandolapril and verapamil

The benefits of the simultaneous administration of low doses of a calcium antagonist and a converting enzyme inhibitor in the treatment of hypertension and renal vasoconstriction are well established. The objective of this study was to evaluate whether the administration of low doses of a calcium antagonist and a converting-enzyme inhibitor have beneficial effects in treating the renal alterations induced by the acute administration of a cyclooxygenase inhibitor when nitric oxide synthesis is reduced. These effects were examined in anesthetized dogs before and during an acute sodium load. It was found that the intrarenal infusion of meclofenamate (5 microg x kg[-1] x min[-1]), simultaneously with a low dose of NG-nitro-L-arginine methyl ester (1 microg x kg[-1] x min[-1]), produced a 40% decrease of renal blood flow and glomerular filtration rate and a reduction in the renal excretory response to the sodium load. In a second group of dogs, intrarenal verapamil (0.5 microg x kg[-1] x min[-1]) was effective in blocking the effects of nitric oxide and prostaglandin synthesis inhibition on sodium excretion and glomerular filtration rate but did not modify the effects on renal blood flow. An intrarenal infusion of trandolapril (0.3 microg x kg[-1] x min[-1]) was effective in a third group of dogs in reducing the renal hemodynamic effects but not in preventing the antinatriuretic effect observed in the first group. Finally, in a fourth group, the simultaneous administration of verapamil and trandolapril was effective in treating all the renal changes induced by the cyclooxygenase inhibitor when nitric oxide synthesis was reduced. These results suggest that the combination of low doses of trandolapril and verapamil has additive effects in treating the renal vasoconstriction and antinatriuresis induced by the acute administration of a cyclooxygenase inhibitor, when nitric oxide synthesis is reduced.

Comparative effects of nitric oxide synthesis inhibition and catecholamine treatment in a rat model of endotoxin shock

Catecholamines and volume repletion are currently used for the treatment of septic shock. However, the prognosis of patients suffering from this condition is very poor. An overproduction of nitric oxide (NO) seems to be related to the hypotension and tissue damage of endotoxin shock. Thus, treatment with NO synthase inhibitors has been proposed. Using a rat model of septic shock we have studied the effects of noradrenaline or the NO synthase inhibitor, NG-nitro-L-arginine methylester (L-NMMA) on arterial pressure, tissue damage and NO production. Anaesthetized rats treated with Salmonella typhosa showed a decrease in blood pressure accompanied by an increase in the plasma concentration of cytosolic enzymes (transaminases and lactate dehydrogenase, markers of cell disruption) and nitrite plus nitrate (NO2-/NO3-, markers of NO production). A large proportion of these animals (40%) died before the end of the experiment. Co-treatment with noradrenaline resulted in temporary maintenance of arterial pressure followed by a decline, despite the dose being increased progressively. No differences were observed in plasma cytosolic enzymes, NO2-/NO3- or mortality compared with animals treated with lipopolysaccharide (LPS) alone. In contrast, administration of L-NMMA (10 mg kg-1) to septic animals prevented the fall in blood pressure and death caused by endotoxin. This treatment markedly diminished cell disruption, as measured by the plasma levels of necrosis enzymes, and partially, but significantly, reduced the production of NO as assessed by plasma NO2-/NO3-. We conclude that tissue damage in septic shock is related to the overproduction of NO and not exclusively to the hypotension that follows this increased production. Thus, maintenance of blood pressure with catecholamines fails to improve cellular damage. Instead, partial inhibition of NO generation is sufficient to ameliorate the haemodynamic and tissue-damaging effects of septic shock and improves survival in this model of endotoxaemia.

Role of angiotensin II in the renal effects induced by nitric oxide and prostaglandin synthesis inhibition

The objective of this study was to examine the renal effects of changes in intrarenal angiotensin II levels during the administration of a cyclooxygenase inhibitor, when nitric oxide synthesis is reduced. In the first group of dogs, the administration of meclofenamate and a subpressor dose of L-NAME induced an increase (P < 0.05) in arterial pressure (14 +/- 2 mm Hg), a decrease (P < 0.05) in RBF (180 +/- 13 to 111 +/- 10 mL/min) and GFR (37 +/- 3 to 24 +/- 5 mL/min), and a reduction in the renal excretory response to a sodium load. In the second group, the administration of a converting enzyme inhibitor prevented the increase in arterial pressure, the renal vasoconstriction, and the increase in the proximal but not the distal tubular sodium reabsorption induced by the inhibition of prostaglandins and nitric oxide synthesis. In the third group, it was found that a small increase in the intrarenal angiotensin II levels, which does not produce changes in renal function in control conditions, induced a significant decrease in RBF (183 +/- 14 to 71 +/- 12 mL/min) and GFR (36 +/- 3 to 13 +/- 4 mL/min) when meclofenamate was administered and nitric oxide synthesis was slightly reduced. The results of this study suggest that renal vasoconstriction and increased proximal sodium reabsorption during the reduction of nitric oxide and prostaglandin synthesis are produced by endogenous angiotensin II levels. These results also suggest that endogenous intrarenal nitric oxide and prostaglandins may serve as homeostatic mediators of angiotensin II effects when the intrarenal levels are inappropriately elevated, as occurs in salt-sensitive hypertension.

Nitric oxide synthase activity in renal cortex and medulla of normotensive and spontaneously hypertensive rats

The medullary portion of the kidney plays a crucial role in the control of sodium and water excretion and arterial pressure. This control is anomalous in hypertension and may be related to an impaired renal nitric oxide (NO) production. We have measured the activity of NO synthase (NOS) in the renal medulla, renal cortex, heart, and aorta from normotensive Wistar Kyoto rats (WKY) and spontaneously hypertensive rats (SHR). Enzyme activity was determined by measuring the conversion of 14C-L-arginine to 14C-L-citrulline. Ca2+-dependent NOS activity was considerably higher in the renal medulla than in the other tissues studied, both in WKY and SHR. The medulla and heart of the SHR displayed a higher Ca2+-dependent NOS activity compared to that of WKY. No differences were found in the Ca2+-independent NOS activity, except for the renal cortex of the SHR, which was higher than in the rest of the tissues. These observations indicate that the renal medulla has a high relative capacity to synthesize NO and suggest that the impaired renal medullary control of arterial pressure of genetic hypertension is not due to a reduced NO production by the kidney.

Changes in nitric oxide release in vivo in response to vasoactive substances

1. Changes in the release of nitric oxide (NO) in vivo were studied in rats following the administration of endothelium-dependent and -independent vasodilators as well as the NO synthesis inhibitor, NG-nitro-L-arginine methyl ester (L-NAME). NO production was assessed by measuring variations of nitrate in plasma by capillary ion analysis. 2. Intravenous administration of the endothelium-dependent vasodilators, bradykinin (2 and 10 micrograms kg-1 min-1) or substance P (0.3-3 micrograms kg-1 min-1) caused a transient dose-dependent hypotension followed by an increase in plasma nitrate concentration (maximal increments: 33 +/- 5% and 38 +/- 6%, for bradykinin and substance P, respectively). Prior administration of L-NAME (10 mg kg-1 min-1) inhibited the hypotension and increase in plasma nitrate caused by these substances. Intravenous administration of sodium nitrate (200 micrograms kg-1) also produced a transitory elevation in plasma nitrate which was similar in magnitude as that caused by the vasodilators. A rapid and transitory increment in plasma nitrate was observed after i.v. administration of authentic NO (400 micrograms kg-1). 3. Rats receiving the endothelium-dependent vasodilators, prostacyclin (0.6 micrograms kg-1 min-1) or adenosine (3 mg kg-1 min-1) intravenously showed a drop in blood pressure paralleled by a decrease in plasma nitrate (maximal decreases: 34 +/- 5% and 24 +/- 4%, for prostacyclin and adenosine, respectively). A similar effect on the plasmatic concentration of nitrate was observed when L-NAME (10 mg kg-1 min-1, i.v.) was administered to the animals. 4. This study demonstrates that (i) changes in plasma nitrate can be detected in vivo after stimulation or inhibition of NO synthase, (ii) an increased production of NO, measured as plasma nitrate, is related to the hypotension caused by bradykinin and substance P and (iii) a diminished concentration of plasmatic nitrate is associated to the hypotension induced by adenosine or prostacyclin (endothelium-independent vasodilators), suggesting that the L-arginine: NO pathway is capable of rapid down-regulation in response to a fall in blood pressure.

Effects of verapamil on the renal actions induced by nitric oxide and prostaglandin synthesis inhibition

This study was designed to determine the effects of a calcium antagonist (verapamil) on the renal actions induced by nitric oxide synthesis inhibition, with and without simultaneous prostaglandin synthesis inhibition. The renal effects of verapamil (2 micrograms/kg/min) were examined in anesthetized dogs before and after an increase of extracellular volume and during the reduction of nitric oxide synthesis (1 microgram/kg/min NG-nitro-L-arginine methyl ester [L-NAME]), with and without the administration of a cyclooxygenase inhibitor (5 micrograms/kg/min meclofenamate). Nitric oxide synthesis inhibition produced an increase in proximal sodium reabsorption (lithium clearance technique) and a decrease in the excretory response to volume expansion that was prevented by the administration of verapamil. The administration of a cyclooxygenase inhibitor, during nitric oxide synthesis inhibition, elicited an increase in arterial pressure, an important renal vasoconstriction, and reduced the renal excretory response to volume expansion. The antinatriuretic effect produced by the simultaneous reduction of nitric oxide and prostaglandin synthesis, before and after the volume expansion, was abolished with the verapamil infusion. However, the increase of arterial pressure and renal vasoconstriction were only partly affected by verapamil. We found that the antinatriuretic effect secondary to the reduction of nitric oxide synthesis, during an increase in extracellular volume, is prevented by the administration of verapamil. Additionally, the administration of verapamil completely prevents the antinatriuretic, but not the vasoconstrictor, effects induced by the administration of a cyclooxygenase inhibitor when nitric oxide is slightly reduced.

Role of Nitric Oxide in the Control of Sodium Excretion

Recent findings suggest that nitric oxide plays a pivotal role in maintaining homeostasis of the extracellular volume. This short review provides evidence supporting the important role of nitric oxide in the regulation of sodium excretion during increments of arterial pressure and in response to acute and prolonged increments of extracellular volume.

Interactions between angiotensin and nitric oxide in the renal response to volume expansion

This study examined, in anesthetized dogs, the possible interactions between nitric oxide (NO) and angiotensin II (ANG II) in mediating the renal response to an extracellular volume expansion (ECVE). It was found that the intrarenal maintenance of ANG II levels (group 1) or the intrarenal NO synthesis inhibition (group 2) did not induce changes in renal hemodynamics but reduced (P < 0.05) the ECVE-induced increments in sodium excretion and fractional lithium excretion (FeLi). In the third group, ANG II synthesis was inhibited during NO synthesis blockade. It was found in this group that the NO synthesis inhibition reduced the ECVE-induced increment in sodium excretion (P < 0.05) but did not modify the ECVE-induced increment in FeLi. These results suggest that the increase of proximal sodium reabsorption induced by the No synthesis inhibition is mediated by endogenous ANG II levels. In the fourth group, it was observed that NO synthesis inhibition, during the intrarenal maintenance of ANG II levels, induced a decrease of renal blood flow (P < 0.05) and reduced the natriuretic response to ECVE to a lower level (P < 0.05) than that observed in groups 1 and 2. The results of this group suggest that endogenous NO modulates the vasoconstrictor and antinatriuretic effects of ANG II during an ECVE. In summary, the results of this study suggest that there is an important interaction between NO and ANG II in mediating the renal response to an ECVE.

Role of prostaglandins and nitric oxide in mediating renal response to volume expansion

The objective of the present study was to examine, in anesthetized dogs, the possible interaction between prostaglandins (PG) and nitric oxide (NO) in mediating the renal response to an extracellular volume expansion (ECVE). The renal response to ECVE was examined during 1) intrarenal infusion of a PG synthesis inhibitor, 2) intrarenal administration of a NO synthesis inhibitor, and 3) simultaneous inhibition of PG and NO synthesis in the right kidney. Compared with the control group, the ECVE-induced increments in sodium excretion and fractional excretion of lithium were not affected by the PG synthesis inhibition. The NO synthesis inhibition did not induce changes in renal hemodynamics but reduced (P < 0.05) the ECVE-induced increments in sodium excretion and fractional excretion of lithium. When PG and NO synthesis were simultaneously inhibited in the right kidney during ECVE, there were no significant differences between the renal hemodynamics of both kidneys. However, compared with the left kidney, the ECVE-induced changes in sodium excretion and fractional excretion of lithium were reduced in the right kidney. The reduction of the natriuretic response to ECVE was greater (P < 0.05) than in the dogs where only NO synthesis was inhibited. Our results suggest a major interaction between NO and PG in mediating the renal hemodynamic and excretory responses to an increase in extracellular volume.

Interaction between angiotensin II and nitric oxide in control of renal hemodynamics in conscious dogs

Recent in vitro studies have provided evidence that the vasoconstrictor actions of angiotensin II on afferent arterioles are enhanced by nitric oxide synthesis inhibition. Although these studies suggest that nitric oxide may play a role in protecting the afferent arterioles from angiotensin II-induced vasoconstriction, the importance of this interaction in the regulation of glomerular filtration rate and renal blood flow in the intact, conscious animal is not known. The objective of the present study was to determine the role of nitric oxide in modulating the renal hemodynamic and excretory effects of angiotensin II. Angiotensin II was infused at rates of 0.5, 1.0, and 2.0 micrograms.kg-1.min-1 intrarenally in conscious, chronically instrumented dogs in both the presence and absence of nitric oxide synthesis inhibition by continuous intrarenal infusion of NG-nitro-L-arginine methyl ester (3 micrograms.kg-1.min-1). At a dose of 0.5 micrograms.kg-1.min-1, angiotensin II decreased renal plasma flow by 19%, while having no effect on glomerular filtration rate in control dogs. In contrast, angiotensin II decreased renal plasma flow by 54%, glomerular filtration rate by 40%, and increased renal vascular resistance by 125% in the presence of intrarenal nitric oxide synthesis blockade. At doses of 1.0 and 2.0 micrograms.kg-1.min-1, angiotensin II reduced renal plasma flow by 36 and 45%, glomerular filtration rate by 17 and 23%, and increased renal vascular resistance by 80 and 120%, respectively, in control dogs.(ABSTRACT TRUNCATED AT 250 WORDS)