Mechanisms underlying sex differences in progressive renal disease

Men with nondiabetic renal disease exhibit a faster rate of decline in renal function compared with women. To investigate this sex difference in renal disease progression, our research group has been studying the renal wrap (RW) model of hypertension in rats. Compared with RW female rats, the glomerulosclerosis index, mean glomerular volume, and proteinuria were greater (3.1-, 1.7-, and 1.8-fold, respectively) in RW males under conditions in which no differences in the degree of hypertension were detected, suggesting that sex differences may exist in the mechanisms underlying renal injury, independent of blood pressure. Gonadal steroids contribute to these sex differences, because orchidectomy attenuated and ovariectomy exacerbated the severity of renal injury, whereas dihydrotestosterone and 17β-estradiol (E₂) replacement prevented these respective effects. Chronic renal disease is associated with impairment in nitric oxide (NO) signaling and elevated levels of superoxide. Sex differences were observed in RW-induced changes in renal nitric oxide synthesis (NOS) protein abundance. Whereas RW had no effect on NOS in the female kidney, endothelial NOS was elevated and neuronal NOS was decreased in the male kidney, suggesting that renal injury may cause dysfunction in NO metabolism in the male. Sex differences in superoxide signaling were also observed. Renal cortical nicotinamide adenine dinucleotide phosphate oxidase activity was 1.3-fold higher in RW males than in RW females, and ovariectomy increased enzyme activity 1.4-fold, whereas E₂ replacement prevented this effect. These changes in enzyme activity were mirrored by changes in protein abundance of the p22^phox regulatory subunit. Our findings suggest that E₂ may protect the female kidney from hypertension-associated renal disease by attenuating injury-induced superoxide production.     

A perinatal nitric oxide donor increases renal vascular resistance and ameliorates hypertension and glomerular injury in adult fawn-hooded hypertensive rats

Enhancing perinatal nitric oxide (NO) availability persistently reduces blood pressure in spontaneously hypertensive rats. We hypothesize that this approach can be generalized to other models of genetic hypertension, for instance those associated with renal injury. Perinatal exposure to the NO donor molsidomine was studied in fawn-hooded hypertensive (FHH) rats, a model of mild hypertension, impaired preglomerular resistance, and progressive renal injury. Perinatal molsidomine increased urinary NO metabolite excretion at 8 wk of age, i.e., 4 wk after treatment was stopped (P < 0.05). Systolic blood pressure was persistently reduced after molsidomine (42-wk females: 118 +/- 3 vs. 141 +/- 5 and 36-wk males: 139 +/- 4 vs. 158 +/- 4 mmHg; both P < 0.001). Perinatal treatment decreased glomerular filtration rate (P < 0.05) and renal blood flow (P < 0.01) and increased renal vascular resistance (P < 0.05), without affecting filtration fraction, suggesting persistently increased preglomerular resistance. At 4 wk of age natriuresis was transiently increased by molsidomine (P < 0.05). Molsidomine decreased glomerulosclerosis (P < 0.05). Renal blood flow correlated positively with glomerulosclerosis in control (P < 0.001) but not in perinatally treated FHH rats. NO dependency of renal vascular resistance was increased by perinatal molsidomine. Perinatal enhancement of NO availability can ameliorate development of hypertension and renal injury in FHH rats. Paradoxically, glomerular protection by perinatal exposure to the NO donor molsidomine may be due to persistently increased preglomerular resistance. The mechanisms by which increased perinatal NO availability can persistently reprogram kidney function and ameliorate hypertension deserve further study.     

Sexual dimorphism in the renin-angiotensin system in aging spontaneously hypertensive rats

In young adult spontaneously hypertensive rats (SHR), mean arterial pressure (MAP) is higher in males than in females and inhibition of the renin-angiotensin system (RAS) eliminates this sex difference. After cessation of estrous cycling in female SHR, MAP is similar to that in male SHR. The purpose of this study was to determine the role of the RAS in maintenance of hypertension in aging male and female SHR. At 16 mo of age, MAP was similar in male and female SHR (183+/-5 vs. 193+/-8 mmHg), and chronic losartan (40 mg.kg-1.day-1 po for 3 wk) reduced MAP by 52% (to 90+/-8 mmHg, P<0.05 vs. control) in males and 37% (to 123+/-11 mmHg, P<0.05 vs. control) in females (P<0.05, females vs. males). The effect of losartan on angiotensin type 1 (AT1) receptor blockade was similar: MAP responses to acute doses of ANG II (62.5-250 ng/kg) were blocked to a similar extent in losartan-treated males and females. F2-isoprostane excretion was reduced with losartan more in males than in females. There were no sex differences in plasma renin activity, plasma angiotensinogen or ANG II, or renal expression of AT1 receptors, angiotensin-converting enzyme, or renin. However, renal angiotensinogen mRNA and protein expression was higher in old males than females, whereas renal ANG II was higher in old females than males. The data show that, in aging SHR, when blood pressures are similar, there remains a sexual dimorphism in the response to AT1 receptor antagonism, and the differences may involve sex differences in mechanisms responsible for oxidative stress with aging.     

Ovariectomy is protective against renal injury in the high-salt-fed older mRen2. Lewis rat

Studies in experimental animals and younger women suggest a protective role for estrogen; however, clinical trials may not substantiate this effect in older females. Therefore, the present study assessed the outcome of ovariectomy in older mRen2. Lewis rats subjected to a high-salt diet for 4 wk. Intact or ovariectomized (OVX, 15 wk of age) mRen2. Lewis rats were aged to 60 wk and then placed on a high-salt (HS, 8% sodium chloride) diet for 4 wk. Systolic blood pressures were similar between groups [OVX 169 +/- 6 vs. Intact 182 +/- 7 mmHg; P = 0.22] after the 4-wk diet; however, proteinuria [OVX 0.8 +/- 0.2 vs. Intact 11.5 +/- 2.6 mg/mg creatinine; P < 0.002, n = 6], renal interstitial fibrosis, glomerular sclerosis, and tubular casts were lower in OVX vs. Intact rats. Kidney injury molecule-1 mRNA, a marker of tubular damage, was 53% lower in the OVX HS group. Independent from blood pressure, OVX HS rats exhibited significantly lower cardiac (24%) and renal (32%) hypertrophy as well as lower C-reactive protein (28%). Circulating insulin-like growth factor-I (IGF-I) levels were not different between the Intact and OVX groups; however, renal cortical IGF-I mRNA and protein were attenuated in OVX rats [P < 0.05, n = 6]. We conclude that ovariectomy in the older female mRen2. Lewis rat conveys protection against salt-dependent increase in renal injury.     

Role of the renal nerves in blood pressure in male and female SHR

Female spontaneously hypertensive rats (SHR) have lower blood pressures than males. The renin-angiotensin system plays an important role in the sexual dimorphism of blood pressure in SHR. The sympathetic nervous system can stimulate renin release, and, therefore, the present study was performed to determine whether the renal sympathetic nerves play a role in the sexual dimorphism of blood pressure in SHR. Male and female SHR underwent bilateral kidney denervation or sham surgery, and, 2 wk later, mean arterial pressure (MAP) and pulse interval were recorded, and baroreflex sensitivity (BRS) was measured by the sequence technique. Left ventricle index (LVI) was also calculated. MAP was higher in sham-operated males than females (182 +/- 5 vs. 169 +/- 4 mmHg; P < 0.01), but, despite the higher MAP in males, LVI was significantly greater in female rats. BRS was not different between sham-operated male and female SHR. Following bilateral renal denervation, MAP was decreased by a similar percentage (8-10%) in males (169 +/- 2 mmHg) and females (152 +/- 3 mmHg), whereas LVI was reduced only in female SHR. BRS was not altered by renal denervation in either sex. These data indicate that renal nerves play a role in the control of blood pressure in SHR independent of sex, but do not play a role in mediating the sex differences in blood pressure.     

Influence of dietary NaCl on L-arginine transport in the renal medulla

Previous work demonstrated that l-arginine, the substrate for nitric oxide (NO) synthase, is carried into inner medullary collecting duct (IMCD) cells via system y+, that the major system y+ gene product in IMCD is the cationic amino acid transporter 1 (CAT1), and that blockade of l-arginine uptake in the renal medulla decreases NO and leads to systemic hypertension. The present study determined the influence of dietary sodium intake on l-arginine uptake in IMCD, on CAT1 immunoreactive protein in the renal medulla, and on the hypertensive response to blockade of l-arginine uptake in the renal medulla. Transport studies in bulk-isolated IMCD demonstrated that l-arginine uptake by IMCD was significantly greater (663 +/- 100 pmol x mg(-1) x min(-1), n = 6) in rats exposed to a low-sodium diet (0.4% NaCl) compared with rats on a normal (1% NaCl, 519 +/- 78 pmol x mg(-1) x min(-1), n = 6) or high-sodium diet (4.0% NaCl, 302 +/- 27 pmol x mg(-1) x min(-1), n = 6). Immunoblotting experiments demonstrated that CAT1 immunoreactive protein was significantly decreased by approximately 30% in rats maintained on a high-NaCl diet (n = 5) compared with rats on a low-NaCl diet (n = 5). In contrast to the l-arginine transport and immunoblotting data, in vivo blockade of l-arginine uptake led to hypertension of equal magnitude in rats maintained on a low- or high-NaCl diet. These results indicate that sodium loading leads to a decrease in immunoreactive CAT1 protein in the rat renal medulla, resulting in decreased l-arginine uptake capacity. The decrease in l-arginine uptake capacity, however, does not alter the blood pressure response to l-arginine uptake inhibition in the renal medulla.     

Sex differences in circulating and renal angiotensins of hypertensive mRen(2). Lewis but not normotensive Lewis rats

Sex differences in blood pressure are evident in experimental models and human subjects, yet the mechanisms underlying this disparity remain equivocal. The current study sought to define the extent of male-female differences in the circulating and tissue renin-angiotensin aldosterone systems (RAASs) of congenic mRen(2). Lewis and control Lewis rats. Male congenics exhibited higher systolic blood pressure than females [200 +/- 4 vs. 146 +/- 7 mmHg, P < 0.01] or Lewis males and females [113 +/- 2 vs. 112 +/- 2 mmHg, P > 0.05]. Plasma ANG II levels were twofold higher in male congenics [47 +/- 3 vs. 19 +/- 3 pM, P < 0.01] and fivefold higher than in male or female Lewis rats [6 +/- 1 vs. 6 +/- 1 pM]. ANG I levels were also highest in the males; however, plasma ANG-(1-7) was higher in female congenics. Male congenics exhibited greater circulating renin and angiotensin-converting enzyme (ACE) activities, as well as angiotensinogen, than female littermates. Renal cortical and medullary ANG II levels were also higher in the male congenics versus all the other groups; ANG I was lower in the males. Cortical ACE2 activity was higher in male congenics, yet neprilysin activity and protein were greater in the females, which may contribute to reduced renal levels of ANG II. These data reveal that sex differences in both the circulating and renal RAAS are apparent primarily in the hypertensive group. The enhanced activity of the RAAS in male congenics may contribute to the higher pressure and tissue injury evident in the strain.     

Sex-related changes in cardiac function following myocardial infarction in mice

Recent awareness of cardiovascular diseases as a number one killer of the middle-aged women has prompted interest in sex differences leading to heart failure (HF). Therefore, we evaluated cardiac function in female and male mice following myocardial infarction (MI) using the Millar pressure-volume (P-V) conductance system in vivo, at time points corresponding to early (2 wk), late compensatory hypertrophy (4 wk), and decompensation (10 wk) to HF. A significant deterioration of the load dependent and independent hemodynamic measurements occurred in both female and male mice during the early phase of hypertrophy. Later, compensatory hypertrophy was marked by a normalization of volumes to control levels in females compared with males. The most notable differences between sexes occurred in the measurements of cardiac contractility during the decompensation to HF. In females, there was a significant improvement in contractility compared with males, which was apparent in the load-independent measurements of preload recruitable stroke work (10 wk post-MI, female=48.7+/-8.0 vs. male=25.2+/-1.8 mmHg, P<0.05) and maximum dP/dt vs. maximum end-diastolic volume (10 wk post-MI, female=359+/-58 vs. male=149+/-28 mmHg.s(-1).microl(-1), P<0.05). Despite these differences, there were no differences in the heart weight to body weight ratio and infarct size between the sexes. These data demonstrate that compensatory hypertrophy is associated with an improvement in contractility and a delayed decompensation to HF in females. However, compensatory hypertrophy in males appears to be undermined by a steady decline in contractility associated with decompensation to HF.     

The influence of nitric oxide synthase 1 on blood flow and interstitial nitric oxide in the kidney

The role of nitric oxide (NO) produced by NO synthase 1 (NOS1) in the renal vasculature remains undetermined. In the present study, we investigated the influence of systemic inhibition of NOS1 by intravenous administration of N(omega)-propyl-L-arginine (L-NPA; 1 mg. kg(-1). h(-1)) and N(5)-(1-imino-3-butenyl)-L-ornithine (v-NIO; 1 mg. kg(-1). h(-1)), highly selective NOS1 inhibitors, on renal cortical and medullary blood flow and interstitial NO concentration in Sprague-Dawley rats. Arterial blood pressure was significantly decreased by administration of both NOS1-selective inhibitors (-11 +/- 1 mmHg with L-NPA and -7 +/- 1 mmHg with v-NIO; n = 9/group). Laser-Doppler flowmetry experiments demonstrated that blood flow in the renal cortex and medulla was not significantly altered following administration of either NOS1-selective inhibitor. In contrast, the renal interstitial level of NO assessed by an in vivo microdialysis oxyhemoglobin-trapping technique was significantly decreased in both the renal cortex (by 36-42%) and medulla (by 32-40%) following administration of L-NPA (n = 8) or v-NIO (n = 8). Subsequent infusion of the nonspecific NOS inhibitor N(omega)-nitro-L-arginine methyl ester (L-NAME; 50 mg. kg(-1). h(-1)) to rats pretreated with either of the NOS1-selective inhibitors significantly increased mean arterial pressure by 38-45 mmHg and significantly decreased cortical (25-29%) and medullary (37-43%) blood flow. In addition, L-NAME further decreased NO in the renal cortex (73-77%) and medulla (62-71%). To determine if a 40% decrease in NO could alter renal blood flow, a lower dose of L-NAME (5 mg. kg(-1). h(-1); n = 8) was administered to a separate group of rats. The low dose of L-NAME reduced interstitial NO (cortex 39%, medulla 38%) and significantly decreased blood flow (cortex 23-24%, medulla 31-33%). These results suggest that NOS1 does not regulate basal blood flow in the renal cortex or medulla, despite the observation that a considerable portion of NO in the renal interstitial space appears to be produced by NOS1.     

The effect of unilateral ureteral obstruction on renal function in pigs measured by diffusion-weighted MRI

The objective of this study was to examine the effect of unilateral ureteral obstruction on the apparent diffusion coefficient (ADC) in pig kidney. Changes in ADC is suggested to reflect changes in the ratio of extracellular to intracellular volume. Thirteen pigs were allocated into three groups: 1) pigs subjected to acute unilateral ureteral obstruction (AUO) (n = 3), 2) pigs subjected to chronic partial unilateral obstruction (CPUO) (n = 3), and 3) control pigs (n = 7). The extra- to intracellular volume ratio was indirectly measured in both the ipsilateral obstructed kidney and contralateral non-obstructed kidney by the ADC of the renal tissue using diffusion-weighted echo-planar magnetic resonance imaging. ADC was 2.07 +/- 0.27 x 10(-3) mm2/s in the cortex and 2.10 +/- 0.24 x 10(-3) mm2/s in the medulla of normal control kidneys. In the obstructed kidney from the AUO group the ADC of the medulla was significantly reduced 24 hours after occlusion of the ureter (1.65 +/- 0.05 x 10(-3) mm2/s vs 2.10 +/- 0.24 x 10(-3) mm2/s; p < 0.05). Similarly ADC decreased slightly in the cortex of the ipsilateral kidney. In contrast, ADC of the ipsilateral kidney of CPUO pigs was increased both in the renal medulla (3.13 +/- 0.21 x 10(-3) mm2/s vs. 2.10 +/- 0.24 x 10(-3) mm2/s; p < 0.05) and cortex (3.09 +/- 0.14 x 10(-3) mm2/s vs. 2.07 x 10(-3) mm2/s, p < 0.05). In conclusion, the results of the present study suggest that diffusion weighted imaging (ADC) may be a useful parameter to incorporate when identifying whether a ureteric obstruction is acute or chronic.     

Tissue distribution of neutrophils in postischemic acute renal failure.

Polymorphonuclear neutrophil granulocytes (PMNs) seem to participate in the pathogenesis of renal ischemic reperfusion injury. The kidneys from male Sprague Dawley rats were immersion-fixed after 45 min of renal artery clamping followed by reperfusion for 0, 5, 20, and 120 min, respectively. The tissue distribution of PMNs in the kidneys was studied histochemically using naphthol AS-D chloroacetate esterase as a specific marker for these cells. Neutrophil counts per unit sectional area were obtained for renal cortex, outer and inner medulla. In the cortex separate intraglomerular and peritubular counts, and in the outer medulla separate outer and inner stripe counts were made. After 120 min of reperfusion the total renal PMN counts were 488 +/- 62 (n = 4) compared with 54 +/- 4 (n = 4) per cm2 in nonischemic controls. Within 120 min of reperfusion PMN counts increased by a factor of 8 in the cortex, of 12 in the outer medulla and of 14 in the inner medulla, compared with controls. The ratio of intraglomerular against peritubular PMN counts was approximately 2 in controls, but 0.5 after a 120-min reperfusion interval. The outer stripe of the outer medulla contained only a small number of PMNs whereas PMN counts of 923 +/- 197 (n = 4) per cm2 were found in the inner stripe after 120 min reperfusion. Interestingly, there was a marked increase in PMNs in the inner stripe during the first 5 min of reperfusion but no extravasation of PMNs was observed.(ABSTRACT TRUNCATED AT 250 WORDS)     

Female protection in progressive renal disease is associated with estradiol attenuation of superoxide production

Background: Several types of renal disease progress at a faster rate in men compared with women, but the reasons for this sex difference are not well understood. Chronic renal disease is associated with elevated levels of toxic reactive oxygen species (ROS). Superoxide, the major ROS in the kidney, is generated by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.Objective: To determine if female protection from renal disease progression is consistent with 17β-estradiol (E₂) attenuation of superoxide production, this study was conducted to assess superoxide production in the renal cortex of male and female control and renal wrap (RW) rats, as well as in ovariectomized rats treated with vehicle or E₂.Methods: Sprague-Dawley rats were divided into 2 sham operation male (Sham-M) and female (Sham-F) control groups, and 4 RW hypertensive groups: RW-M; RW-F; RW ovariectomized females treated with vehicle (RW-OVX); and RW ovariectomized females treated with E₂, supplied as a 0.24 mg/60-day release pellet (RW-OVX+E₂). All groups were maintained on a high-sodium (4% NaCl) diet for 6 weeks.Results: Mean (SEM) markers of renal injury and oxidative stress, including urinary protein (mg/24 h: RW-M, 298 [31] vs RW-F, 169 [22]; P < 0.001), microalbuminuria (RW/Sham arbitrary units [AU]/24 h: M, 8.78 [0.58] vs F, 4.31 [1.0]; P < 0.005), and malondialdehyde (nmol/24 h: RW-M, 167 [23] vs RW-F, 117 [8.5]; P < 0.05) levels, as well as mean glomerular volume (μm³ × 10⁶: RW-M, 2.25 [0.16] vs RW-F, 1.25 [0.04]; P < 0.001) and the glomerulosclerotic index (AU: RW-M, 2.64 [0.19] vs RW-F, 1.10 [0.09]; P < 0.001) were greater in both control and RW males compared with females in the same treatment groups. Though RW surgery increased mean arterial pressure in both male and female rats, no sex difference was observed. Under these conditions, mean (SEM) renal cortical NADPH oxidase activity was 1.3-fold higher in RW males compared with RW females (relative light units [RLU]/180 sec: RW-M, 4080 [240] vs RW-F, 3200 [260]; P < 0.05). Ovariectomy increased NADPH oxidase activity by 1.4-fold (RLU/180 sec: RW-OVX, 4520 [184]; P < 0.01) under conditions in which the mean glomerular volume and glomerulosclerotic index were both increased by 1.5-fold, whereas E₂ replacement (RLU/180 sec: RW-OVX+E₂, 2745 [440]) prevented these effects. Furthermore, the effects on NADPH oxidase activity were mirrored by changes in the protein abundance of NADPH oxidase subunit p22P^phox.Conclusion: These results suggest that E₂ protects the female kidney in part by attenuating injury-induced increases in renal superoxide production.     

Prenatal androgens and the timing of seasonal reproductive transitions in sheep.

Both the onset of puberty in the lamb and the annual resumption of reproductive activity in adult male and female sheep are characterized by increased secretion of LH due to reduced responsiveness to steroid inhibition. However, the timing of puberty is sexually differentiated, for males undergo a reduction in sensitivity to steroid feedback at 10 wk of age, whereas females remain highly responsive to steroid inhibition until 30 wk. This sex difference is determined by androgens in utero. The present study was conducted to determine whether a sex difference exists in the timing of seasonal transitions in adult males and females. We compared serum LH in gonadectomized, estradiol-treated males (n = 7), females (n = 6), and androgenized females (n = 5) from blood samples collected twice weekly for one year. As determined by changes in the pattern of LH secretion, the onset and termination of the autumn breeding season were not different between males, females, and androgenized females (termination: 1 February +/- 4 days, mean +/- SE all groups; onset: males, 22 August +/- 4 days; females, 5 September +/- 18 days; androgenized females, 16 September +/- 10.5 days). However, there was a transient increase in LH (20 May to 23 June) in males, but not in females or androgenized females. Although no effects of prenatal testosterone were evident in the control of LH secretion in adult androgenized females, LH secretion in androgenized males was elevated throughout the nonbreeding season in 3 of 5 animals, indicating that exogenous testosterone may reduce seasonal increases in responsiveness to steroid inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)     

Large BP-dependent and -independent differences in susceptibility to nephropathy after nitric oxide inhibition in Sprague-Dawley rats from two major suppliers

The N(ω)-nitro-l-arginine methyl ester (l-NAME) model is widely employed to investigate the role of nitric oxide (NO) in renal injury. The present studies show that Sprague-Dawley rats from Harlan (H) and Charles River (CR) exhibit strikingly large differences in susceptibility to l-NAME nephropathy. After 4 wk of l-NAME (～50 mg·kg(-1)·day(-1) in drinking water), H rats (n = 13) exhibited the expected hypertension [average radiotelemetric systolic blood pressure (BP), 180 ± 3 mmHg], proteinuria (136 ± 17 mg/24 h), and glomerular injury (GI) (12 ± 2%). By contrast, CR rats developed less hypertension (142 ± 4), but surprisingly no proteinuria or GI, indicating a lack of glomerular hypertension. Additional studies showed that conscious H, but not CR, rats exhibit dose-dependent renal vasoconstriction after l-NAME. To further investigate these susceptibility differences, l-NAME was given 2 wk after 3/4 normotensive nephrectomy (NX) and comparably impaired renal autoregulation in CR-NX and H-NX rats. CR-NX rats, nevertheless, still failed to develop proteinuria and GI despite moderate hypertension (144 ± 2 mmHg, n = 29). By contrast, despite an 80-90% l-NAME dose reduction and lesser BP increases (169 ± 4 mmHg), H-NX rats (n = 20) developed greater GI (26 ± 3%) compared with intact H rats. Linear regression analysis showed significant (P < 0.01) differences in the slope of the relationship between BP and GI between H-NX (slope 0.56 ± 0.14; r = 0.69; P < 0.008) and CR-NX (slope 0.09 ± 0.06; r = 0.29; P = 0.12) rats. These data indicate that blunted BP responses to l-NAME in the CR rats are associated with BP-independent resistance to nephropathy, possibly mediated by a resistance to the renal (efferent arteriolar) vasoconstrictive effects of NO inhibition.     

Renal tissue NO and intrarenal haemodynamics during experimental variations of NO content in anaesthetised rats.

Direct renal nitric oxide (NO) measurements were infrequent and no simultaneous measurements of renal cortical and medullary NO and local perfusion. Large-surface NO electrodes were placed in renal cortex and medulla of anaesthetised rats; simultaneously, renal blood flow (RBF, index of cortical perfusion) and medullary laser-Doppler flux (MBF) were determined. NO synthase inhibitors: nonselective (L-NAME) or selective for neuronal NOS (nNOS) (S-methyl-thiocitrulline, SMTC), and NO donor (SNAP), were used to manipulate tissue NO. Baseline tissue NO was significantly higher in medulla (703+/-49 NM) than in cortex (231+/-17 nM). Minimal cortical and medullary NO current measured after maximal L-NAME dose (2.4 mg kg(-1) i.v.) was taken as tissue NO zero kevel. This dose decreased RBF and MBF significantly (-43%). SMTC, 1.2 mg kg(-1) h(-1) i.v., significantly decreased tissue NO by 105+/-32 nM in cortex and 546+/-64 nM in medulla, RBF and MBF decreased 30% and 20%, respectively. Renal artery infusion of SNAP, 0.24 mg kg(-1) min(-1) significantly increased tissue NO by 139+/-18 nM in cortex and 948+/-110 nM in medulla. Since inhibition of nNOS decreased medullary NO by 80% and MBF by 20% only, this isoform has probably minor role in the maintenance of medullary perfusion.     

TNF-alpha inhibition reduces renal injury in DOCA-salt hypertensive rats

Studies suggest that the inflammatory cytokine TNF-alpha plays a role in the prognosis of end-stage renal diseases. We previously showed that TNF-alpha inhibition slowed the progression of hypertension and renal damage in angiotensin II salt-sensitive hypertension. Thus, we hypothesize that TNF-alpha contributes to renal inflammation in a model of mineralocorticoid-induced hypertension. Four groups of rats (n = 5 or 6) were studied for 3 wk with the following treatments: 1) placebo, 2) placebo + TNF-alpha inhibitor etanercept (1.25 mg.kg(-1).day(-1) sc), 3) deoxycorticosterone acetate + 0.9% NaCl to drink (DOCA-salt), or 4) DOCA-salt + etanercept. Mean arterial blood pressure (MAP) measured by telemetry increased in DOCA-salt rats compared with baseline (177 +/- 4 vs. 107 +/- 3 mmHg; P < 0.05), and TNF-alpha inhibition had no effect in the elevation of MAP in these rats (177 +/- 8 mmHg). Urinary protein excretion significantly increased in DOCA-salt rats compared with placebo (703 +/- 76 vs. 198 +/- 5 mg/day); etanercept lowered the proteinuria (514 +/- 64 mg/day; P < 0.05 vs. DOCA-salt alone). Urinary albumin excretion followed a similar pattern in each group. Urinary monocyte chemoattractant protein (MCP)-1 and endothelin (ET)-1 excretion were also increased in DOCA-salt rats compared with placebo (MCP-1: 939 +/- 104 vs. 43 +/- 7 ng/day, ET-1: 3.30 +/- 0.29 vs. 1.07 +/- 0.03 fmol/day; both P < 0.05); TNF-alpha inhibition significantly decreased both MCP-1 and ET-1 excretion (409 +/- 138 ng/day and 2.42 +/- 0.22 fmol/day, respectively; both P < 0.05 vs. DOCA-salt alone). Renal cortical NF-kappaB activity also increased in DOCA-salt hypertensive rats, and etanercept treatment significantly reduced this effect. These data support the hypothesis that TNF-alpha contributes to the increase in renal inflammation in DOCA-salt rats.     

Enhanced renal expression of preproendothelin mRNA during chronic angiotensin II hypertension

The purpose of this study was to determine the role of endothelin in mediating the renal hemodynamic and arterial pressure changes observed during chronic ANG II-induced hypertension. ANG II (50 ng x kg(-1) x min(-1)) was chronically infused into the jugular vein by miniosmotic pump for 2 wk in male Sprague-Dawley rats with and without endothelin type A (ET(A))-receptor antagonist ABT-627 (5 mg x kg(-1) x day(-1)) pretreatment. Arterial pressure increased in ANG II rats compared with control rats (149 +/- 5 vs. 121 +/- 6 mmHg, P < 0.05, respectively). Renal expression of preproendothelin mRNA was increased by approximately 50% in both the medulla and cortex of ANG II rats. The hypertensive effect of ANG II was completely abolished in rats pretreated with the ET(A)-receptor antagonist (114 +/- 5 mmHg, P < 0.05). Glomerular filtration rate was decreased by 33% in ANG II rats, and this response was attenuated in rats pretreated with ET(A)-receptor antagonist. These data indicate that activation of the renal endothelin system by ANG II may play an important role in mediating chronic renal and hypertensive actions of ANG II.     

Effect of renal medullary H2O2 on salt-induced hypertension and renal injury

Dahl salt-sensitive (SS) and consomic, salt-resistant SS-13(BN) rats possess substantial differences in blood pressure salt-sensitivity even with highly similar genetic backgrounds. The present study examined whether increased oxidative stress, particularly H2O2, in the renal medulla of SS rats contributes to these differences. Blood pressure was measured using femoral arterial catheters in three groups of rats: 1) 12-wk-old SS and consomic SS-13(BN) rats fed a 0.4% NaCl diet, 2) SS rats fed a 4% NaCl diet and chronically infused with saline or catalase (6.9 microg x kg(-1) x min(-1)) directly into the renal medulla, and 3) SS-13(BN) fed high salt (4%) and infused with saline or H2O2 (347 nmol x kg(-1) x min(-1)) into the renal medullary interstitium. After chronic blood pressure measurements, renal medullary interstitial H2O2 concentration ([H2O2]) was collected by microdialysis and analyzed with Amplex red. Blood pressure and [H2O2] were both significantly higher in SS (126 +/- 3 mmHg and 145 +/- 17 nM, respectively) vs. SS-13(BN) rats (116 +/- 2 mmHg and 56 +/- 14 nM) fed a 0.4% diet. Renal interstitial catalase infusion significantly decreased [H2O2] (96 +/- 41 vs. 297 +/- 52 nM) and attenuated the hypertension (146 +/- 2 mmHg catalase vs. 163 +/- 4 mmHg saline) in SS rats after 5 days of high salt (4%). H2O2 infused into the renal medulla of consomic SS-13(BN) fed high salt (4%) for 7 days accentuated the salt sensitivity (145 +/- 2 mmHg H2O2 vs. 134 +/- 1 mmHg saline). [H2O2] was also increased in the treated group (83 +/- 1 nM H2O2 vs. 44 +/- 9 nM saline). These data show that medullary production of H2O2 may contribute to salt-induced hypertension in SS rats and that chromosome 13 of the Brown Norway contains gene(s) that protect against renal medullary oxidant stress.     

Sex and sex hormones influence the development of albuminuria and renal macrophage infiltration in spontaneously hypertensive rats

There is a sex difference in hypertensive renal injury, with men experiencing greater severity and a more rapid progression of renal disease than women; however, the molecular mechanisms protecting against renal injury in women are unknown. The goal of this study was to determine whether sex hormones modulate blood pressure and the progression of albuminuria during the developmental phase of hypertension in male and female spontaneously hypertensive rats (SHR). Studies were also performed to examine how sex and sex hormones influence two major risk factors for albuminuria, overactivation of the renin-angiotensin system and oxidative stress. Blood pressure was measured by telemetry in gonad-intact and gonadectomized male and female SHR. Microalbumin excretion, measured over time, and macrophage infiltration were used to assess renal health. Male SHR had significantly higher blood pressures than female SHR, and gonadectomy decreased blood pressures in males with no effect in females. Male SHR displayed a gonad-sensitive increase in albuminuria over time, and female SHR had a gonad-sensitive suppression in macrophage infiltration. Female SHR had greater plasma ANG II levels and similar levels of renal cortical ANG II vs. levels shown in males but less AT(1)-receptor protein expression in the renal cortex. Female SHR also had a gonad-sensitive decrease in renal oxidative stress. Therefore, the renal protection afforded to female SHR is associated with lower blood pressure, decreased macrophage infiltration, and decreased levels of oxidative stress.     

Inhibition by calcium antagonism of circulating and renal endothelin in experimental congestive heart failure

Endothelin (ET) is a potent vasoconstrictor and sodium-regulating peptide whose tissue and plasma concentrations are increased in congestive heart failure (CHF). ET may mediate its vasoconstrictor and sodium-regulatory actions secondary to an increase in intracellular calcium. Calcium influx may augment ET synthesis. Although felodipine, a dihydropyridine calcium-channel antagonist, is effective in reducing vascular resistance in generalized vasoconstriction, its actions in CHF on circulating and local tissue ET remain undefined. The current studies were designed to determine the modulating actions of felodipine (oral, 40 mg/day for 7 days; n = 6) in an experimental canine model of CHF produced by chronic thoracic inferior vena caval constriction (TIVCC) compared with normal (n = 7) and TIVCC-alone (n = 7) dogs. We hypothesized that felodipine would decrease circulating and renal ET. Plasma ET was significantly increased in TIVCC compared with normal dogs (26 +/- 0. 5 vs. 12 +/- 0.7 pg/ml, P < 0.05) and was markedly decreased by felodipine compared with TIVCC alone (14 +/- 3 vs. 26 +/- 0.5 pg/ml, P < 0.05). Renal ET immunohistochemical staining demonstrated the presence of ET in normal kidney, which was markedly increased in renal cortex and medulla in TIVCC dogs. Renal cortical and medullary ET staining densities were markedly decreased with felodipine compared with those with TIVCC alone. In the TIVCC + felodipine group, cardiovascular hemodynamics also was markedly improved compared with the TIVCC-alone group [systemic vascular resistance: 27 +/- 2 vs. 44 +/- 3 resistance units (RU), P < 0.05; pulmonary vascular resistance: 3.3 +/- 0.1 vs. 5.7 +/- 0.4 RU, P < 0.05; cardiac output: 2.9 +/- 0.2 vs. 1.7 +/- 0.1 l/min, P < 0.05]. This study demonstrates important modulating inhibitory actions of felodipine on renal and plasma ET in an experimental model of CHF.