Autonomic control of the heart is altered in Sprague-Dawley rats with spontaneous hydronephrosis

Assessment of General Toxicity of the Glycyrrhiza New Variety Extract in Rats

The Glycyrrhiza radix (Licorice) is one of the most commonly used medicinal plants in Asian countries, such as China, India, and Korea. It has been traditionally used to treat many diseases, including cough, cold, asthma, fatigue, gastritis, and respiratory tract infections. A Glycyrrhiza new variety, Wongam (WG), has been developed by the Korea Rural Development Administration and revealed pharmacological effects. However, the potential adverse effects of WG have not been revealed yet. This study evaluates the general toxicity of the WG extract through a single and repeated oral dose toxicity study in Sprague-Dawley rats. After single oral dose administration, no significant toxicological changes or mortality was observed up to 5000 mg/kg. Over a 4-week repeated oral dose toxicity study, no adverse effects and target organs were observed up to 5000 mg/kg/day. Over a 13-week repeated oral dose toxicity study, no mortality or toxicological changes involving ophthalmology, water consumption, or hematology were observed up to 5000 mg/kg/day. Although other parameters were changed, the alterations in question were not considered toxicologically significant, since responses remained within normal ranges and were not dose-dependent. In conclusion, the no-observed-adverse-effect level (NOAEL) of WG was higher than 5000 mg/kg/day, and no target organs were identified in rats.

Rats with congenital hydronephrosis show increased susceptibility to renal ischemia-reperfusion injury

Many drug candidates have shown significant renoprotective effects in preclinical models; however, there is no clinically used effective pharmacotherapy for acute kidney injury. The failure to translate from bench to bedside could be due to misleading results from experimental animals with undetected congenital kidney defects. This study was performed to assess the effects of congenital hydronephrosis on the functional capacity of tubular renal transporters as well as kidney sensitivity to ischemia-reperfusion (I-R)-induced injury in male Wistar rats. Ultrasonography was used to distinguish healthy control rats from rats with hydronephrosis. L-carnitine or furosemide was administered, and serial blood samples were collected and analyzed to assess the effects of hydronephrosis on the pharmacokinetic parameters. Renal injury was induced by clamping the renal pedicles of both kidneys for 30 min with subsequent 24 hr reperfusion. The prevalence of hydronephrosis reached ~30%. The plasma concentrations after administration of L-carnitine or furosemide were similar in both groups. I-R induced more pronounced renal injury in the hydronephrotic rats than the control rats, which was evident by a significantly higher kidney injury molecule-1 concentration and lower creatinine concentration in the urine of the hydronephrotic rats than the control rats. After I-R, the gene expression levels of renal injury markers were significantly higher in the hydronephrotic kidneys than in the kidneys of control group animals. In conclusion, our results demonstrate that hydronephrotic kidneys are more susceptible to I-R-induced damage than healthy kidneys. Unilateral hydronephrosis does not affect the pharmacokinetics of substances secreted or absorbed in the renal tubules.

Hydronephrosis and risk of later development of hypertension

AIM

Congenital ureteral obstruction is a fairly common condition in infants, and its clinical management has been long debated during the last decade. The long-term physiological consequences of today's conservative non-surgical management in many asymptomatic hydronephrotic children are unclear.

METHODS

Experimental studies in rats and mice, retrospective studies in children and adults, as well as prospective studies in children are included in this mini review.

RESULTS

Experimental models of hydronephrosis in rats and mice have demonstrated that partial ureteropelvic junction obstruction (UPJO) is casually linked with development of hypertension and renal injuries in later life. The mechanisms are multifactorial and involve increased activity of the renin-angiotensin-aldosterone system and renal sympathetic nerve activity. Furthermore, oxidative stress and nitric oxide deficiency in the affected kidney appear to play important roles in the development and maintenance of hypertension. Clinical case reports in adults and recent prospective studies in children have associated hydronephrosis with elevated blood pressure, which could be reduced by surgical management of the obstruction.

CONCLUSION

Based on current experimental and clinical knowledge regarding the link between partial UPJO and changes in blood pressure, it is proposed that today's non-operative management of hydronephrosis should be reconsidered to reduce the risk of developing elevated blood pressure or hypertension in later life.

The Role of Mas Receptor on Renal Hemodynamic Responses to Angiotensin 1-7 in Both Irreversible and Reversible Unilateral Ureteral Obstruction Rats

Background:

Unilateral ureteral obstruction (UUO) alters the expression of renin-angiotensin system (RAS) components and angiotensin 1-7 (Ang 1-7) as a main arm of RAS is affected by UUO. The role of Mas receptor antagonist (A779) was examined in renal hemodynamic responses to Ang 1-7 in 3-day UUO and UUO removal (RUUO) in rats.

Materials and Methods:

Forty-five male Wistar rats were randomly divided into three groups of sham operated, UUO, and RUUO, while each group was divided into two subgroups treated with vehicle or A779. Renal blood flow (RBF) and renal vascular resistance (RVR) responses to graded Ang 1-7 infusion were measured at controlled renal perfusion pressure.

Results:

Mean arterial pressure response to Ang 1-7 was increased in vehicle-treated subgroup significantly (P < 0.05) when compared with A779-treated subgroup. However, such observation was not seen in UUO and RUUO rats. The graded Ang 1-7 infusion increased RBF and decreased RVR significantly in vehicle-treated rats (P < 0.005). Furthermore, a significant difference was found between vehicle and A779-treated subgroups in sham, UUO, and RUUO groups (P < 0.005).

Conclusion:

Ang 1-7 could alter the kidney hemodynamics responses in ureteral obstruction models.

Hydronephrosis alters cardiac ACE2 and Mas receptor expression in mice

INTRODUCTION

Hydronephrosis is characterized by substantial loss of tubules and affects renin secretion in the kidney. However, whether alterations of angiotensin-converting enzyme (ACE), ACE2 and Mas receptor in the heart are observed in hydronephrosis is unknown. Thus, we assessed these components in hydronephrotic mice treated with AT1 receptor blockade and ACE inhibitor.

MATERIALS AND METHODS

Hydronephrosis was induced by left ureteral ligation in Balb/C mice except sham-operated animals. The levels of cardiac ACE, ACE2 and Mas receptor were measured after treatment of losartan or enalapril.

RESULTS

Hydronephrosis led to an increase of ACE level and a decrease of ACE2 and Mas receptor in the heart. Losartan decreased cardiac ACE level, but ACE2 and Mas receptor levels significantly increased in hydronephrotic mice (p < 0.01). Enalapril increased ACE2 levels (p < 0.01), but did not affect Mas receptor in the heart. Plasma renin activity (PRA) and Ang II decreased in hydronephrotic mice, but significantly increased after treatment with losartan or enalapril.

CONCLUSIONS

Hydronephrosis increased cardiac ACE and suppressed ACE2 and Mas receptor levels. AT1 blockade caused sustained activation of cardiac ACE2 and Mas receptor, but ACE inhibitor had the limitation of such activation of Mas receptor in hydronephrotic animals.

Evidence for an angiotensin-(1-7) neuropeptidase expressed in the brain medulla and CSF of sheep

Angiotensin-(1-7) [Ang-(1-7)] is an alternative product of the brain renin-angiotensin system that exhibits central actions to lower blood pressure and improve baroreflex sensitivity. We previously identified a peptidase that metabolizes Ang-(1-7) to the inactive metabolite product Ang-(1-4) in CSF of adult sheep. This study purified the peptidase 1445-fold from sheep brain medulla and characterized this activity. The peptidase was sensitive to the chelating agents o-phenanthroline and EDTA, as well as the mercury compound p-chloromercuribenzoic acid (PCMB). Selective inhibitors to angiotensin-converting enzyme, neprilysin, neurolysin, and thimet oligopeptidase did not attenuate activity; however, the metallopeptidase agent JMV-390 was a potent inhibitor of Ang-(1-7) hydrolysis (Ki = 0.8 nM). Kinetic studies using (125) I-labeled Ang-(1-7), Ang II, and Ang I revealed comparable apparent Km values (2.6, 2.8, and 4.3 μM, respectively), but a higher apparent Vmax for Ang-(1-7) (72 vs. 30 and 6 nmol/min/mg, respectively; p < 0.01). HPLC analysis of the activity confirmed the processing of unlabeled Ang-(1-7) to Ang-(1-4) by the peptidase, but revealed < 5% hydrolysis of Ang II or Ang I, and no hydrolysis of neurotensin, bradykinin or apelin-13. The unique characteristics of the purified neuropeptidase may portend a novel pathway to influence actions of Ang-(1-7) within the brain. Angiotensin-(1-7) actions are mediated by the AT7 /Mas receptor and include reduced blood pressure, decreased oxidative stress, enhanced baroreflex sensitivity, and increased nitric oxide (NO). Ang-(1-7) is directly formed from Ang I by neprilysin (NEP). We identify a new pathway for Ang-(1-7) metabolism in the brain distinct from angiotensin-converting enzyme-dependent hydrolysis. The Ang-(1-7) endopeptidase (A7-EP) degrades the peptide to Ang-(1-4) and may influence central Ang-(1-7) tone.

Effects of aqueous leaf extract of Asystasia gangetica on the blood pressure and heart rate in male spontaneously hypertensive Wistar rats

Background

Asystasia gangentica (A. gangetica) belongs to the family Acanthaceae. It is used to treat hypertension, rheumatism, asthma, diabetes mellitus, and as an anthelmintic in South Africa, India, Cameroun, Nigeria, and Kenya respectively. It has also been reported to inhibit the angiotensin I converting enzyme (ACE) in-vitro. Therefore, the aim of this study is to investigate the in-vivo effect of aqueous leaf extract (ALE) of A. gangetica on the blood pressure (BP) and heart rate (HR) in anaesthetized male spontaneously hypertensive rats (SHR); and to elucidate possible mechanism(s) by which it acts.

Methods

The ALE of A. gangetica (10–400 mg/kg), angiotensin I human acetate salt hydrate (ANG I, 3.1–100 μg/kg) and angiotensin II human (ANG II, 3.1–50 μg/kg) were administered intravenously. The BP and HR were measured via a pressure transducer connecting the femoral artery to a Powerlab and a computer for recording.

Results

A. gangetica significantly (p<0.05), and dose-dependently reduced the systolic, diastolic, and mean arterial BP. The significant (p<0.05) reductions in HR were not dose-dependent. Both ANG I and ANG II increased the BP dose-dependently. Co-infusion of A. gangetica (200 mg/kg) with either ANG I or ANG II significantly (p<0.05) suppressed the hypertensive effect of both ANG I and ANG II respectively, and was associated with reductions in HR.

Conclusions

A. gangetica ALE reduced BP and HR in the SHR. The reduction in BP may be a result of actions of the ALE on the ACE, the ANG II receptors and the heart rate.

Protein phosphatase 1b in the solitary tract nucleus is necessary for normal baroreflex function

Despite positive metabolic effects, genetic deletion of protein phosphatase 1b (PTP1b) results in sympathetically mediated elevations in arterial pressure (AP) in mice. Because several PTP1b-regulated peptides also impair the baroreflex sensitivity (BRS) for control of heart rate (HR), we hypothesized that PTP1b in the solitary tract nucleus (NTS) participates in the maintenance of resting baroreflex function. To test this hypothesis, we performed acute bilateral microinjection of an allosteric PTP1b inhibitor (100 nM/120 nL) in the NTS of urethane/chloralose anesthetized Sprague-Dawley rats and assessed the BRS, responses to cardiac vagal chemosensitive fiber activation, and resting AP and HR before and after the injection. PTP1b inhibition impaired the BRS for bradycardia (n = 6; 0.93 ± 0.14 baseline vs. 0.48 ± 0.04 at 10 minutes vs. 0.49 ± 0.04 millisecond/mm Hg at 60 minutes; P < 0.01), with no significant effect on the BRS for tachycardia (0.30 ± 0.16 baseline vs. 0.24 ± 0.08 at 10 minutes vs. 0.24 ± 0.12 millisecond/mm Hg at 60 minutes). The reduced BRS for bradycardia was associated with a significant decrease in alpha-adrenergic responsiveness to phenylephrine at 60 minutes after PTP1b inhibition. Injection of the PTP1b inhibitor in the NTS elicited transient decreases in AP and HR in these animals. However, there was no effect of the inhibitor on depressor or bradycardic responses elicited by activation of cardiac vagal chemosensitive fibers, which converge with baroreceptor afferents in the NTS. These results suggest that PTP1b within the NTS may be a novel molecular mechanism for preservation of resting baroreflex function and provides further evidence for deleterious cardiovascular effects associated with PTP1b inhibition.