Effect of inhibition of nitric oxide synthase on blood pressure and renal sodium handling in renal denervated rats

Prophylactic Treatment with Hydrogen Sulphide Can Prevent Renal Ischemia-Reperfusion Injury in L-NAME Induced Hypertensive Rats with Cisplatin-Induced Acute Renal Failure

(Background and Objectives): Renal ischemia perfusion injury is one of the major issues in kidney transplant. The aim of the study was to investigate the hypothesis that prophylactic treatment-with a hydrogen sulphide donor to an acute renal failure case of hypertensive rats-can minimize the ischemia reperfusion injury of the kidney which is beneficial for kidney transplant. To check this hypothesis, the present study was designed to investigate the effect of chronic administration of a hydrogen sulphide (H2S) donor and sodium hydrosulfide (NaHS) on nuclear factor kappa B (NF-kB) and inter cellular adhesion molecule-1 (ICAM-1) concentration in non-renal failure (NRF) and acute renal failure (ARF) rats in the ischemia-reperfusion injury (IRI) model of the kidney in both normotensive WKY and hypertensive rats (L-nitro arginine methyl ester (L-NAME-induced); (Materials and Methods): A total number of 48 Sprague-Dawley rats were recruited into eight groups each consisting of six animals. Each of these eight groups was used to measure systemic and renal parameters, H2S, antioxidant parameters in plasma, plasma concentration of NF-kB and ICAM-1 and renal cortical blood pressure. ARF was induced by single intraperitoneal (i.p.) cisplatin injection (5 mg/kg). Hypertension was induced by oral administration of L-NAME in drinking water for four weeks at 40 mg/kg/day. NaHS was administered (i.p) at 56 µmol/kg for five weeks while dL-propargylglycine (PAG), a H2S generation inhibitor, was administered as a single intra-peritoneal injection (50 mg/kg). An acute surgical experiment was performed for the induction of renal ischemia for 30 min by renal artery clamping followed by reperfusion for three hours; (Results): Chronic administration of NaHS attenuated the severity of ARF in both normotensive and hypertensive animals (L-NAME) along with lowering the blood pressure in hypertensive groups. NaHS improved the oxidative stress parameters such as total superoxide dismutase (T-SOD), glutathione (GSH) and reduced the malondialdehyde (MDA) concentration along with reduction of NF-kB and ICAM-1 following renal IRI; Conclusions: These findings demonstrate that H2S not only reduced the severity of cisplatin induced ARF but also reduced the severity of renal IRI by upregulating antioxidants along with decreased concentrations of NF-kB and ICAM-1 in normotensive and L-NAME induced hypertensive rats.

Fetal Undernutrition Programming, Sympathetic Nerve Activity, and Arterial Hypertension Development

A wealth of evidence showed that low birth weight is associated with environmental disruption during gestation, triggering embryotic or fetal adaptations and increasing the susceptibility of progeny to non-communicable diseases, including metabolic and cardiovascular diseases, obesity, and arterial hypertension. In addition, dietary disturbance during pregnancy in animal models has highlighted mechanisms that involve the genesis of arterial hypertension, particularly severe maternal low-protein intake (LP). Functional studies demonstrated that maternal low-protein intake leads to the renal decrease of sodium excretion and the dysfunction of the renin-angiotensin-aldosterone system signaling of LP offspring. The antinatriuretic effect is accentuated by a reduced number of nephron units and glomerulosclerosis, which are critical in establishing arterial hypertension phenotype. Also, in this way, studies have shown that the overactivity of the central and peripheral sympathetic nervous system occurs due to reduced sensory (afferent) renal nerve activity. As a result of this reciprocal and abnormal renorenal reflex, there is an enhanced tubule sodium proximal sodium reabsorption, which, at least in part, contributes directly to arterial hypertension development in some of the programmed models. A recent study has observed that significant changes in adrenal medulla secretion could be involved in the pathophysiological process of increasing blood pressure. Thus, this review aims to compile studies that link the central and peripheral sympathetic system activity mechanisms on water and salt handle and blood pressure control in the maternal protein-restricted offspring. Besides, these pathophysiological mechanisms mainly may involve the modulation of neurokinins and catecholamines pathways.

Hydrogen Sulphide Treatment Prevents Renal Ischemia-Reperfusion Injury by Inhibiting the Expression of ICAM-1 and NF-kB Concentration in Normotensive and Hypertensive Rats

Our main objective was to investigate the effect of chronic administration of hydrogen sulphide donor (sodium hydrosulphide) on the expression of intercellular adhesion molecule-1 (ICAM-1) and concentration of nuclear factor-kappa B (NF-kB) in a renal ischemia-reperfusion injury (IRI) model of WKY and L-nitro-arginine-methyl-ester (L-NAME)-induced hypertensive rats. Sodium hydrosulphide (NaHS) was administered intraperitoneally (i.p.) for 35 days while cystathionine gamma lyase (CSE) inhibitor dL-propargylglycine (PAG) was administered at a single dose of 50 mg/kg. Animals were anesthetised using sodium pentobarbitone (60 mg/kg) and then prepared to induce renal ischemia by clamping the left renal artery for 30 min followed by 3 h of reperfusion. Pre-treatment with NaHS improved the renal functional parameters in both WKY and L-NAME-induced hypertensive rats along with reduction of blood pressure in hypertensive groups. Oxidative stress markers like malondialdehyde (MDA), total superoxide dismutase (T-SOD) and glutathione (GSH) were also improved by NaHS treatment following renal IRI. Levels of ICAM-1 and NF-kB concentration were reduced by chronic treatment with NaHS and increased by PAG administration after renal IRI in plasma and kidney. Treatment with NaHS improved tubular morphology and glomerulus hypertrophy. Pre-treatment with NaHS reduced the degree of renal IRI by potentiating its antioxidant and anti-inflammatory mechanism, as evidenced by decreased NF-kB concentration and downregulation of ICAM-1 expression.

Inhibition of L-NAME-induced hypertension by combined treatment with apocynin and catalase: the role of Nox 4 expression

Reactive oxygen species (ROS) such as superoxide (O2-) generated by NAD(P)H oxidases have emerged as important molecules in blood pressure regulation. This study investigated the effect of apocynin and catalase on blood pressure and renal haemodynamic and excretory function in an L-NAME induced hypertension model. Forty Male Wistar-Kyoto (WKY) rats (n=8 per group) were treated with either: vehicle (WKY-C); L-NAME (WKY-L, 15 mg/kg/day in drinking fluid); WKY-L given apocynin to block NAD(P)H oxidase (WKY-LApo, 73 mg/kg/day in drinking water.); WKY-L given catalase to enhance ROS scavenging (WKY-LCat, 10000 U/kg/day i.p.); and WKY-L receiving apocynin plus catalase (WKY-LApoCat) daily for 14 days. L-NAME elevated systolic blood pressure (SBP), 116+/-1 to 181±4 mmHg, reduced creatinine clearance, 1.69+/-0.26 to 0.97+/-0.05 ml/min/kg and fractional sodium excretion, 0.84+/-0.09 to 0.55+/-0.09 % at day 14. Concomitantly, plasma malondialdehyde (MDA) increased six fold, while plasma total superoxide dismutase (T-SOD), plasma nitric oxide (NO) and plasma total antioxidant capacity (T-AOC) were decreased by 60-70 % and Nox 4 mRNA expression was increased 2-fold. Treatment with apocynin and catalase attenuated the increase in SBP and improved renal function, enhanced antioxidative stress capacity and reduced the magnitude of Nox4 mRNAs expression in the L-NAME treated rats. This study demonstrated that apocynin and catalase offset the development of L-NAME induced hypertension, renal dysfunction and reduced oxidative stress status, possibly contributed by a reduction in Nox4 expression during NOS inhibition. These findings would suggest that antioxidant compounds such as apocynin and catalase have potential in treating cardiovascular diseases.

Renal sodium handling and blood pressure changes in gestational protein-restricted offspring: Role of renal nerves and ganglia neurokinin expression

Background

Considering long-term changes in renal sodium handling and blood pressure in maternal protein-restricted (LP) offspring, we assumed that the development of LP hypertension results from abnormal dorsal root ganglia (DRG) neurokinin expression associated with impaired responsiveness of renal sensory receptors, promoting a reduced urinary excretion of sodium. The present study investigates whether increased blood pressure in protein-restricted offspring would be associated with changes in the DRG cells and in renal pelvic wall expression of NK1R, SP and CGRP when compared to NP offspring. In addition, we assessed the tubular sodium handling, estimated by creatinine and lithium clearances before and after bilateral renal denervation in conscious LP offspring relative to age-matched NP counterparts.

Methods

Dams received a normal (NP) or low-protein diet (LP) during their entire pregnancy period. Male NP or LP offspring underwent bilateral surgical renal denervation before the 8-week renal functional test and blood pressure measurements. Immunofluorescence staining in DRG cells was assessed in optical sections by confocal laser scanning microscope.

Results

The current data demonstrated a sustained rise in blood pressure associated with a decrease in fractional excretion of sodium (FENa) by reducing post-proximal tubule sodium rejection in 16-wk old LP rats relative to age-matched NP counterparts. According to this study, bilateral renal denervation attenuated blood pressure and increased FENa in LP offspring. Furthermore, an immunohistochemical analysis showed a reduced expression of SP and CGRP in DRGs of LP when compared with NP rats. Renal pelvis of LP rats did not show a strong CGRP expression related to NP rats, whereas there was no change in SP immunostaining.

Conclusions

These observations raise the possibility that impaired DRG and pelvic neurokinin expression associated with responsiveness of renal sensory receptors in 16-wk old LP offspring are conducive to excess renal reabsorption of sodium and development of hypertension in this programmed model.

Animal Models in Cardiovascular Research: Hypertension and Atherosclerosis

Hypertension and atherosclerosis are among the most common causes of mortality in both developed and developing countries. Experimental animal models of hypertension and atherosclerosis have become a valuable tool for providing information on etiology, pathophysiology, and complications of the disease and on the efficacy and mechanism of action of various drugs and compounds used in treatment. An animal model has been developed to study hypertension and atherosclerosis for several reasons. Compared to human models, an animal model is easily manageable, as compounding effects of dietary and environmental factors can be controlled. Blood vessels and cardiac tissue samples can be taken for detailed experimental and biomolecular examination. Choice of animal model is often determined by the research aim, as well as financial and technical factors. A thorough understanding of the animal models used and complete analysis must be validated so that the data can be extrapolated to humans. In conclusion, animal models for hypertension and atherosclerosis are invaluable in improving our understanding of cardiovascular disease and developing new pharmacological therapies.

Early detection of metabolic and energy disorders by thermal time series stochastic complexity analysis

Maintenance of thermal homeostasis in rats fed a high-fat diet (HFD) is associated with changes in their thermal balance. The thermodynamic relationship between heat dissipation and energy storage is altered by the ingestion of high-energy diet content. Observation of thermal registers of core temperature behavior, in humans and rodents, permits identification of some characteristics of time series, such as autoreference and stationarity that fit adequately to a stochastic analysis. To identify this change, we used, for the first time, a stochastic autoregressive model, the concepts of which match those associated with physiological systems involved and applied in male HFD rats compared with their appropriate standard food intake age-matched male controls (n=7 per group). By analyzing a recorded temperature time series, we were able to identify when thermal homeostasis would be affected by a new diet. The autoregressive time series model (AR model) was used to predict the occurrence of thermal homeostasis, and this model proved to be very effective in distinguishing such a physiological disorder. Thus, we infer from the results of our study that maximum entropy distribution as a means for stochastic characterization of temperature time series registers may be established as an important and early tool to aid in the diagnosis and prevention of metabolic diseases due to their ability to detect small variations in thermal profile.

Impact of taurine supplementation on blood pressure in gestational protein-restricted offspring: Effect on the medial solitary tract nucleus cell numbers, angiotensin receptors, and renal sodium handling

OBJECTIVE

The current study considers changes of the postnatal brainstem cell number and angiotensin receptors by maternal protein restriction (LP) and LP taurine supplementation (LPT), and its impact on arterial hypertension development in adult life.

METHODS AND RESULTS

The brain tissue studies were performed by immunoblotting, immunohistochemistry, and isotropic fractionator analysis. The current study shows that elevated blood pressure associated with decreased fractional urinary sodium excretion (FENa) in adult LP offspring was reverted by diet taurine supplementation. Also, that 12-day-old LP pups present a reduction of 21% of brainstem neuron counts, and, immunohistochemistry demonstrates a decreased expression of type 1 angiotensin II receptors (AT1R) in the entire medial solitary tract nuclei (nTS) of 16-week-old LP rats compared to age-matched NP and LPT offspring. Conversely, the immunostained type 2 AngII (AT2R) receptors in 16-week-old LP nTS were unchanged.

CONCLUSION

The present investigation shows a decreased FENa that occurs despite unchanged creatinine clearance. It is plausible to hypothesize an association of decreased postnatal nTS cell number, AT1R/AT2R ratio and FENa with the higher blood pressure levels found in taurine-deficient progeny (LP) compared with age-matched NP and LPT offspring.

Impaired dipsogenic and renal response to repetitive intracerebroventricular angiotensin II (AngII) injections in rats

The role of the central nervous system (CNS) in the control of blood pressure and hydrosaline homeostasis has been demonstrated by several studies. While circulating angiotensin II (AngII) tends to retain sodium by a direct renal action as well as through aldosterone release, stimulation of brain AngII receptors has been reported to induce natriuresis. Repetitive intracerebroventricular AngII injection was recently demonstrated to be capable of leading to desensitisation of the dipsogenic effect of AngII stimuli. The aim of the current study was to investigate a possible central desensitisation to AngII stimuli by observing the effects of a low-concentration solution of AngII on the dipsogenic and natriuretic mechanisms in conscious rats, compared with appropriate age-matched 0.15 M NaCl-injected subjects, as evaluated by lithium clearance. The present report confirmed earlier reports on the potent natriuretic and dipsogenic effects of central AngII receptor stimulation. Natriuresis is mediated by a decrease in sodium reabsorption in the proximal and post-proximal tubule segments of the nephron. The current findings lend further support to the idea that AngII, in the CNS, is instrumental in the regulation of body fluid homeostasis. The magnitude of the dipsogenic and renal response to AngII was significantly decreased by repetitive stimulus.

CHRONIC SALT LOADING AND CARDIOVASCULAR-ASSOCIATED CHANGES IN EXPERIMENTAL DIABETES IN RATS

1. High-sodium intake may increase blood pressure and diabetes is a salt-sensitive condition. In the present study, we evaluated cardiovascular changes and their neurohumoral mechanisms in streptozotocin (STZ)-diabetic rats that underwent chronic salt loading. 2. We studied male Wistar rats (150-280 g) 14 days after the injection of either STZ (50 mg/kg, i.v.; D; n = 18) or citrate buffer (C; n = 16). After the induction of diabetes, animals were maintained for 14 days with free access to standard rat chow and tap water (C and D groups) or 1% NaCl solution (C-S and D-S groups). We conducted two experiments. Experiment 1 consisted of basal arterial pressure (AP) measurement (30 min) followed by the evaluation of AP responsiveness to phenylephrine and sodium nitroprusside. One day later, with the rats anaesthetized, a blood sample was collected to test for glycaemia, plasma angiotensin-converting enzyme (ACE) activity and renin. Kidneys were removed for the determination of tissue ACE activity. Experiment 2 comprised 24 h urine collection followed by 3 days of cardiovascular records, which consisted of a 30 min basal AP measurement, followed by injection of blockers of the vasopressin system, the renin-angiotensin system (RAS) and the sympathetic system. Basal haemodynamic data, baroreflex evaluation and AP responses to blockade of the vasopressin system with vasopressin V(1) receptor antagonist (aAVP; 10 mg/kg, i.v.), the RAS by losartan (10 mg/kg, i.v.) and the sympathetic system by hexamethonium (20 mg/kg, i.v.) were determined. 3. Glycaemia was similar between C and C-S (P = 0.612) and between D and D-S (P = 0.552), but higher in diabetic compared with non-diabetic rats (P < 0.0001). The D-S rats had an increment of 24% in mean AP compared with D (120 +/- 4 vs 97 +/- 2 mmHg, respectively; P = 0.0001), which was not seen in C-S compared with C rats. A positive association was noted between urinary sodium and mean AP (r = 0.37; P = 0.04). Plasma renin was undetectable in D-S rats. The response to acute drug blockade of vasopressin and the RAS was similar among groups, but hexamethonium elicited a more pronounced decrease in AP in D-S compared with D rats (P = 0.001). 4. The main neurohumoral mechanisms of salt-induced cardiovascular changes in STZ-diabetes are increased sodium and vascular sensitivity to adrenergic stimuli, which act in combination to produce a final result of higher AP levels, a finding not observed in control rats. Baroreflex derangements induced by diabetes were not affected by salt overload.

Role of renal sympathetic nerve activity in hypertension induced by chronic nitric oxide inhibition

Nitric oxide levels are diminished in hypertensive patients, suggesting nitric oxide might have an important role to play in the development of hypertension. Chronic blockade of nitric oxide leads to hypertension that is sustained throughout the period of the blockade in baroreceptor-intact animals. It has been suggested that the sympathetic nervous system is involved in the chronic increase in blood pressure; however, the evidence is inconclusive. We measured renal sympathetic nerve activity and blood pressure via telemetry in rabbits over 7 days of nitric oxide blockade. Nitric oxide blockade via Nω-nitro-l-arginine methyl ester (l-NAME) in the drinking water (50 mg·kg−1·day−1) for 7 days caused a significant increase in arterial pressure (7 ± 1 mmHg above control levels; P < 0.05). While the increase in blood pressure was associated with a decrease in heart rate (from 233 ± 6 beats/min before the l-NAME to 202 ± 6 beats/min on day 7), there was no change in renal sympathetic nerve activity (94 ± 4 %baseline levels on day 2 and 96 ± 5 %baseline levels on day 7 of l-NAME; baseline nerve activity levels were normalized to the maximum 2 s of nerve activity evoked by nasopharyngeal stimulation). The lack of change in renal sympathetic nerve activity during the l-NAME-induced hypertension indicates that the renal nerves do not mediate the increase in blood pressure in conscious rabbits.

Development of hypertension in a pyelonephritis-induced model: the effect of salt intake and inability of renal sodium handling

The role of the kidney in the control of blood pressure has been convincingly demonstrated by several studies. Recent evidence has suggested that subtle acquired tubulointerstitial injury may cause a defect in sodium excretion function, thus leading to salt-sensitive hypertension. There are no reports, however, examining the effect of experimental chronic pyelonephritis on renal sodium handling and arterial pressure. Thus, to examine the influence of salt intake and unilateral nephrectomy, unanesthetized, unrestrained rats were randomly assigned to one of two separate groups: sham-operated rats (CO) or chronic unilateral pyelonephritic rats (CP). After twenty one days, the pyelonephritic group was subdivided in two: one subgroup continued with water intake (CPw), while the other was changed to 0.9% NaCl intake (CPs), like the control group (COs). After seven days, all rats were submitted to unilateral nephrectomy of the left normal kidney. Data presented herein show that chronic pyelonephritis produced an increase in mean arterial pressure (CO: 121.4 +/- 1.0 mmHg to CP: 127.0 +/- 0.9 mmHg, p = 0.000) that was enhanced by saline ingestion (COs: 121.6 +/- 1.4 mmHg; CPw: 127.0 +/- 1.8 mmHg; CPs: 132.1 +/- 1.2 mmHg, p = 0.000) and further aggravated by unilateral nephrectomy (CO: 125.2 +/- 2.6 mmHg; CPw: 127.5 +/- 0.9 mmHg; CPs: 139.2 +/- 1.1 mmHg, p = 0.000). Unchanged blood pressure measurements (120.2 +/- 2.3 mmHg) were observed beyond 21 days in control rats maintained on water regimen when compared with saline-drinking groups. These changes in mean arterial pressure were observed despite an increased fractional sodium excretion in the CPs group compared to the other groups before uninephrectomy (COs: 0.125 +/- 0.025%; CPw: 0.045 +/- 0.013%; CPs: 0.292 +/- 0.046%; p = 0.000), as compared to CPw after uninephrectomy (COs: 0.249 +/- 0.077%; CPw: 0.062 +/- 0.011%; CPs: 0.363 +/- 0.195%, p = 0.019). In addition, it was shown that daily liquid intake was higher in CPs than in CPw but similar to COs, both before uninephrectomy (COs: 42.8 +/- 2.6 ml/d; CPw: 34.3 +/- 3.5 ml/d; CPs: 51.8 +/- 3.7 ml/d, p = 0.006) and after uninephrectomy (COs: 40.9 +/- 5.5 ml/d; CPw: 33.8 +/- 1.4 ml/d; CPs: 53.0 +/- 3.5 ml/d, p = 0.004). The current data suggest that chronic pyelonephritis promotes an inability of renal tubules to handle sodium excretion when exposed to sodium overload and aggravated by uninephrectomy, thus constituting a model for salt-sensitive hypertension.

Altered renal sodium handling in spontaneously hypertensive rats (SHR) after hypertonic saline intracerebroventricular injection: role of renal nerves

The mechanism by which blood pressure rises in the SHR strain remains to be elucidated. Also, there is a surprising lack of experimental data on the natriuretic mechanisms induced by intracerebroventricular (ICV) injection of hyperosmotic saline (HoS) in SHR. In normotensive animals ICV injection of HoS causes coordinated responses including natriuresis and inhibition of renal sympathetic nerve activity. In the present study, we hypothesized that presumable blunting of the sympathoinhibitory response to centrally injected HoS may contribute to a lack of suppression of efferent renal nerve outflow in SHR. To test this hypothesis, the present study evaluates the influence of renal denervation after central HoS injection at increasing concentration on urinary sodium handling in SHR compared with age-matched normotensive WKy rats. The study confirmed previous data showing pronounced natriuretic response to centrally HoS stimuli but also demonstrated that the creatinine clearance (C(Cr)) and fractional sodium excretion responses diminished as graded NaCl concentrations were increased in WKy rats but not in SHR. In SHR, increased FE(Na) obtained by central administration of 0.90 M NaCl was produced by increases in proximal (FEP(Na)) and post-proximal fractional urinary sodium rejection without changes in C(Cr), indicating a direct tubular effect. Renal denervation caused significant antinatriuresis by decreased C(Cr) and increased FEP(Na) reabsorption in WKy but not in SHR. This study suggests that natriuresis observed only after higher centrally HoS stimuli with a rightward shift of dose-response curve provides evidence of a down-regulation of target organ responsiveness of periventricular areas of genetic hypertensive rats.

Early altered renal sodium handling determined by lithium clearance in spontaneously hypertensive rats (SHR): Role of renal nerves

The mechanism by which blood pressure rises in the SHR strain remains to be elucidated. Since the long-term changes in renal sodium tubule handling associated with genetic hypertension have not been examined in detail, we hypothesized that SHR hypertension development may result from sustained renal sympathetic nerve overactivity and consequently decreased urinary sodium excretion. To test this hypothesis, we assessed renal sodium handling and cumulative sodium balance for 10 consecutive weeks in unanesthetized renal-denervated SHR, performed prior to the start of the entire 10-week metabolic studies, and their age-matched normotensive and hypertensive controls. The present investigation shows that SHR excreted less sodium than Wistar-Kyoto (WKy) rats during the initial 3-week observation period (p <0.05). This tendency was reversed when SHR were 10-wk old. Fractional urinary sodium excretion (FENa+) was significantly lower in 3 and 6-wk-old SHR when compared with the WKy age-matched group, as follows: SHR3-wk-old: 0.33 +/- 0.09% and WKy3-wk-old: 0.75 +/- 0.1% (P <0.05); SHR(6-wk-old): 0.52 +/- 0.12% and WKy6-wk-old: 0.83 +/- 0.11%. The decreased FENa+ in young SHR was accompanied by a significant increase in proximal sodium reabsorption (FEPNa+) compared with the normotensive age-matched control group (P <0.01). This increase occurred despite unchanged creatinine clearance (CCr) and fractional post-proximal sodium excretion (FEPPNa+)in all groups studied. The decreased urinary sodium excretion response in SHR up to the age of 6 weeks was significantly eradicated by bilateral renal denervation of SHR3-wk-old: 0.33 +/- 0.09% and SHR6-wk-old: 0.52 +/- 0.12% to DxSHR 3-wk-old: 1.02 +/- 0.2% and DxSHR 6-wk-old: 0.94 +/- 0.2% (P <0.01), in renal denervated rats. The current data suggest that neural pathways may play an instrumental role on renal sodium reabsorption as result of sustained sympathetic nervous system overexcitability.

The pharmacology of nitric oxide in the peripheral nervous system of blood vessels

Unanticipated, novel hypothesis on nitric oxide (NO) radical, an inorganic, labile, gaseous molecule, as a neurotransmitter first appeared in late 1989 and into the early 1990s, and solid evidences supporting this idea have been accumulated during the last decade of the 20th century. The discovery of nitrergic innervation of vascular smooth muscle has led to a new understanding of the neurogenic control of vascular function. Physiological roles of the nitrergic nerve in vascular smooth muscle include the dominant vasodilator control of cerebral and ocular arteries, the reciprocal regulation with the adrenergic vasoconstrictor nerve in other arteries and veins, and in the initiation and maintenance of penile erection in association with smooth muscle relaxation of the corpus cavernosum. The discovery of autonomic efferent nerves in which NO plays key roles as a neurotransmitter in blood vessels, the physiological roles of this nerve in the control of smooth muscle tone of the artery, vein, and corpus cavernosum, and pharmacological and pathological implications of neurogenic NO have been reviewed. This nerve is a postganglionic parasympathetic nerve. Mechanical responses to stimulation of the nerve, mainly mediated by NO, clearly differ from those to cholinergic nerve stimulation. The naming "nitrergic or nitroxidergic" is therefore proposed to avoid confusion of the term "cholinergic nerve", from which acetylcholine is released as a major neurotransmitter. By establishing functional roles of nitrergic, cholinergic, adrenergic, and other autonomic efferent nerves in the regulation of vascular tone and the interactions of these nerves in vivo, especially in humans, progress in the understanding of cardiovascular dysfunctions and the development of pharmacotherapeutic strategies would be expected in the future.

Acute intracerebroventricular insulin microinjection after nitric oxide synthase inhibition of renal sodium handling in rats

The role of the central nervous system (CNS) in the control of hydrosaline homeostasis has been strikingly demonstrated by several studies. Recent and growing evidence suggests that insulin or a nonapeptide-derived from the C-terminus of the insulin beta-chain may influence many brain functions. However, there is little information on the insulin-activated neural pathways regulating urinary sodium excretion. Also, we examined the influence of nitric oxide synthase activity by chronic oral administration of N(omega)-nitro-l-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthesis, after previous i.c.v. administration of insulin to unanesthetized, unrestrained rats that were randomly assigned to one of seven separated groups: (a) i.c.v. 0.15 M NaCl-injected (n = 11) and i.c.v. 126 ng (n = 11) insulin-injected rats; (b) i.c.v. insulin-injected in systemic L-NAME-treated (n = 10) and vehicle-treated insulin-injected rats (n = 10); and (c) subcutaneously (SC) insulin-injected rats (n = 5). We showed that centrally administered insulin produced increase in the urinary output of sodium (from 0.15 M NaCl: 855.6 +/- 85.1 Delta%.min(-1) to 126 ng insulin: 2055 +/- 310.6 Delta%.min(-1)) and potassium (126 ng: from 0.15 M NaCl: 460.4 +/- 100 Delta%.min(-1) to 126 ng insulin: 669 +/- 60.8 Delta%.min(-1)). The urinary sodium excretion response to i.c.v. 126 ng insulin microinjection was significantly abolished by previous systemic treatment of animals with 15 mg/kg/day L-NAME (from vehicle + 126 ng insulin: 1935 +/- 258.3 Delta%. min(-1) to L-NAME + 126 ng insulin: 582.3 +/- 69.6 Delta%. min(-1)). In addition, we showed that insulin-induced natriuresis occurred by increasing post-proximal tubule sodium rejection (FEPP(Na)), despite an unchanged glomerular filtration rate (C(Cr)). The current data suggests the novel concept that CNS NO-dependent neural pathways may play an instrumental role on efferent insulin-sensitive nerve activity from periventricular region. Speculatively, it seems interesting to suggest that perhaps one of the efferent signals triggered by insulin in the CNS may be nitrergic in nature, and that defects in this efferent signal could result in insulin central resistance, inability of renal tubules to handle the hydro electrolyte balance and hypertension.

Effect of the crude extract of Vernonia polyanthes Less. on blood pressure and renal sodium excretion in unanesthetized rats

This study evaluated the effect of oral crude Vernonia polyanthes Less. hydroalcoholic extract administration (CHE, 0.5 and 1.0 g/kg body wt., daily for 7 days) on arterial blood pressure and renal sodium excretion in conscious rats. CHE administration decreased arterial blood pressure dose-dependently followed by a significant rise in creatinine clearance and a fall in fractional post-proximal sodium excretion was compared to the control group. These results suggest that blood pressure decrease induced by the oral crude Vernonia hydroalcoholic extract may be blunted by reduction of the post-proximal renal sodium excretion. Thus, the present study shows that Vernonia extract is a potential vasodilatation agent in normotensive rats without any effects on renal tubule autoregulation mechanisms.

Hypertension in L-NAME-treated diabetic rats depends on an intact sympathetic nervous system

We demonstrated previously that induction of diabetes in rats that were treated chronically with the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) causes a severe, progressive increase in mean arterial pressure. This study tested the role of the sympathetic nervous system in that response. Rats were instrumented with chronic artery and vein catheters and assigned randomly to four diabetic groups pretreated with vehicle (D), L-NAME (D+L), the alpha(1)- and beta-adrenergic receptor antagonists terazosin and propranolol (D+B), or L-NAME, terazosin, and propranolol (D+LB). After baseline measurements were taken, rats were pretreated; 6 days later, streptozotocin was administered and 3 wk of diabetes ensued. D+L rats had a marked, progressive increase in arterial pressure that by day 20 was approximately 60 mmHg greater than in D rats. The pressor response to L-NAME was significantly attenuated in diabetic rats cotreated with adrenergic blockers. During week 1 of diabetes, plasma renin activity (PRA) increased and then returned to control levels in D rats. PRA increased progressively in D+L rats, and chronic adrenergic receptor blockade restored the biphasic renin response in D+LB rats. These results suggest that the sympathetic nervous system may be involved in the hypertensive response to onset of diabetes in L-NAME-treated rats, possibly through control of renin secretion.

Renal denervation abolishes the protective effects of ischaemic preconditioning on function and haemodynamics in ischaemia-reperfused rat kidneys

Studies were conducted to investigate the role of renal sympathetic nerves in the process of acquiring ischaemic tolerance in ischaemic preconditioned ischaemia-reperfused rat kidneys. Two periods of 3-min occlusion of bilateral renal arteries was performed prior to 30-min bilateral ischaemia and 90-min reperfusion in acute renal denervated or innervated kidneys. The glomerular filtration rate (GFR), fractional excretion of sodium (FENa) and lithium (FELi), and renal blood flow (RBF) were assessed in reperfused kidneys. Ischaemic preconditioning significantly improved values for all these parameters as compared with no treated ischaemia-reperfused kidneys. Denervation caused slight increase in GFR, diuresis and natriuresis without improving RBF after reperfusion. However, protecting effects of ischaemic preconditioning on renal function were disappeared in denervated kidneys, while in innervated kidneys the effects of ischaemic preconditioning were maintained. These results clearly showed that ischaemic preconditioning pre-treatment protects kidneys against ischaemia-reperfusion injury, and the effects are, at least in part, mediated by sympathetic nerves, as the protective effects were abolished by denervation.