The renin-angiotensin-aldosterone system in volume control

Augmented transcripts of kidney injury markers and renin angiotensin system in urine samples of overweight young adults

Obesity has been firmly established as a major risk factor for common disease states including hypertension, type 2 diabetes mellitus, and chronic kidney disease. Increased body mass index (BMI) contributes to the activation of both the systemic and intra-tubular renin angiotensin systems (RAS), which are in turn associated with increased blood pressure (BP) and kidney damage. In this cross-sectional study, 43 subjects of normal or increased body weight were examined in order to determine the correlation of BMI or body fat mass (BFM) with blood pressure, fasting blood glucose (FBG), and urinary kidney injury markers such as interleukin-18 (IL-18), connective tissue growth factor (CTGF), neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 (KIM-1). Our results showed that: (1) subjects with increased body weight showed significantly higher BP, BFM, total body water and metabolic age; (2) BMI was positively correlated to both systolic (R² = 0.1384, P = 0.01) and diastolic BP (R² = 0.2437, P = 0.0008); (3) BFM was positively correlated to DBP (R² = 0.1232, P = 0.02) and partially correlated to urine protein (R² = 0.047, P = 0.12) and FBG (R² = 0.07, P = 0.06); (4) overweight young adults had higher urinary mRNA levels of renin, angiotensinogen, IL-18 and CTGF. These suggest that BMI directly affects BP, kidney injury markers, and the activation of the intra-tubular RAS even in normotensive young adults. Given that BMI measurements and urine analyses are non-invasive, our findings may pave the way to developing a new and simple method of screening for the risk of chronic kidney disease in adults.

Angiotensin, bradykinin and the endothelium

Angiotensins and kinins are endogenous peptides with diverse biological actions; as such, they represent current and future targets of therapeutic intervention. The field of angiotensin biology has changed significantly over the last 50 years. Our original understanding of the crucial role of angiotensin II in the regulation of vascular tone and electrolyte homeostasis has been expanded to include the discovery of new angiotensins, their important role in cardiovascular inflammation and the development of clinically useful synthesis inhibitors and receptor antagonists. While less applied progress has been achieved in the kinin field, there are continuous discoveries in bradykinin physiology and in the complexity of kinin interactions with other proteins. The present review focuses on mechanisms and interactions of angiotensins and kinins that deal specifically with vascular endothelium.

Effects of Dietary Salt Load and Salt Depletion on the Course of Hypertension and Angiotensin II Levels in Male and Female Heterozygous Ren-2 Transgenic Rats

BACKGROUND

In the present study we evaluated plasma and kidney angiotensin II (ANG II) levels in female and male Ren-2 transgenic rats (TGR) in comparison to age-matched female and male normotensive Hannover Sprague-Dawley rats.

METHODS

The rats were maintained on a normal sodium (NS) diet (0.6% NaCl) or fed a high sodium (HS) diet (2% NaCl) for 4 days or were sodium depleted by administration of 40 mg furosemide per liter drinking water overnight followed by 3 days of low sodium diet (0.01% NaCl) (LS + F). ANG II levels were determined by radioimmunoassay.

RESULTS

Female TGR at the age of 38 days were already hypertensive and had developed cardiac hypertrophy, whereas male TGR at this age still exhibited a normotensive phenotype. HS diet increased the blood pressure (BP) but did not alter the ANG II levels in TGR at any age. LS + F decreased the BP without significant change in ANG II concentrations in TGR. Female TGR responded to salt loading and salt depletion by more pronounced changes in BP than male TGR.

CONCLUSIONS

Female TGR develop hypertension more rapidly and the salt-sensitive component of hypertension is more pronounced in female than in male TGR.

c-Jun NH2-terminal kinase mediation of angiotensin II-induced proliferation of human mesangial cells

Angiotensin II (ANG II) has been shown to activate c-Jun NH2-terminal kinase (JNK) in cultured mesangial cells, but the functional implication of this phenomenon remains to be determined, largely due to the lack of an effective approach to block JNK. Therefore, the present study was carried out to examine whether JNK is involved in ANG II-induced cell proliferation in cultured human mesangial cells (HMCs) with the use of a newly developed JNK-selective blocker, SP-600125. Within minutes, treatment with 100 nM ANG II activated all three members of MAP kinase family, including extracellular signal-regulated protein kinase (Erk) 1/2, JNK, and p38 in cultured HMCs, as assessed by immunoblotting detection of phosphorylation of MAP kinases. ANG II-dependent activation of JNK was further confirmed by detection of increased phosphorylation and transcription activity of c-Jun after the ANG II treatment. SP-600125 ranging from 5 to 10 μM almost completely abolished the activation of JNK by ANG II without affecting the activities of Erk1/2 and p38. After treatment with 100 ng ANG II, there was a steady increase in [3H]thymidine incorporation that was blocked by SP-60025 in a dose- and time-dependent manner. Similarly, SP-600125 dose dependently reduced the ANG II-induced increase in cell number. The antiproliferative effect of SP-60025 was further determined by cell-cycle analysis with flow cytometry. Twenty-four hours after ANG II treatment, 50% of the quiescent HMCs (G0/G1) progressed into the S phase, and the cell cycle progression was almost completely prevented in the presence of SP-60025. Our data suggest that JNK mediates the proliferative effect of ANG II in cultured HMCs and thus represents a novel therapeutic target for treatment of chronic renal diseases.

The renin-angiotensin-aldosterone system: cardiorenal effects and implications for renal and cardiovascular disease states

The renin-angiotensin-aldosterone system (RAAS) plays an integral role in maintaining vascular tone, optimal salt and water homeostasis, and cardiac function in humans. However, it has been recognized in recent years that pathologic consequences may also result from overactivity of the RAAS. Clinical disease states such as renal artery stenosis, hypertension, diabetic and nondiabetic nephropathies, left ventricular hypertrophy, coronary atherosclerosis, myocardial infarction, and congestive heart failure (CHF) are examples. Part of the adverse cardiorenal effects of the RAAS may be related to the prominent role that this system plays in the activation of the sympathetic nervous system, the dysregulation of endothelial function and progression of atherosclerosis, as well as inhibition of the fibrinolytic system. Also, direct profibrotic actions of angiotensin II and aldosterone in the kidney and heart promote end organ injury. Current basic science and clinical research supports the use of inhibitors of the RAAS, including angiotensin converting enzyme inhibitors, angiotensin receptor blockers, and aldosterone antagonists in treating hypertension, improving diabetic nephropathy and other forms of chronic kidney disease, preventing or ameliorating CHF, and optimizing prognosis after myocardial infarction.

Lack of control of renin release by adrenergic nervous system in the aglomerular toadfish

Aglomerular toadfish, Opsanus tau, release renin in response to hemorrhage or vasodilator drugs, presumably by stimulating a renal arterial baroreceptor. We aimed to determine whether the adrenergic nervous system and prostaglandins play a role in the control of renin release in unanesthetized toadfish kept in 50% seawater. Isoproterenol (1 microgram/kg) increased plasma renin activity (PRA) fourfold and decreased blood pressure (BP); both effects were abolished by a concomitant infusion of propranolol. Propranolol itself slightly decreased the basal level of heart rate and BP, but not that of PRA. Norepinephrine (1 microgram/kg) increased BP, but did not change PRA. Repeated injection of 6-hydroxydopamine did not alter resting levels of either PRA or BP. Monoamine-specific nerve fluorescence activity could not be demonstrated in association with arterioles of kidneys from intact toadfish or from those treated with monoamine oxidase inhibitor and norepinephrine (5 mg/kg). Furthermore, treatment of toadfish with indomethacin (10 or 20 mg/kg) prevented neither the increase in PRA nor the reduction in BP after a massive hemorrhage. These results indicate that renin release in toadfish primarily occurs in response to a reduction in renal arterial pressure, whereas it appears unlikely that the adrenergic nervous system or prostaglandins have a significant role in the control of renin release.

Low molecular weight hydroxyethyl starch 6% compared to albumin 4% during intentional hemodilution

Intentional normovolemic hemodilution was chosen as the model to compare a 6% low molecular weight hydroxyethyl starch (LMW HES) to 4% albumin. The study ran over the plasma exchange period for 24 h. Nine patients, scheduled for abdominal aortic surgery, were included in each group. After basal measurements, blood was withdrawn and simultaneously replaced by either 4% albumin (Group 1) or 6% LMW HES (Group 2) to achieve a final hematocrit of approximately 30%. Hemodynamic blood oxygen gas and hormonal plasma levels were determined before hemodilution then at 30 min, 1, 2, 3, and 24 h after the end of hemodilution. Basal value for total blood volume was 4377 +/- 162 ml in group 1 and 4138 +/- 315 ml in group 2. As in both groups the decrease in blood cell volume was exactly compensated by the increase in plasma volume, no significant change in total blood volume (respectively 4432 +/- 159 and 4305 +/- 267 ml) was observed. Throughout the study, in both groups, no significant change in mean arterial and right atrial pressures was observed. In group 2 (LMW HES), a significant increase of pulmonary capillary wedge pressure was noted 120 min after hemodilution. After hemodilution, despite a significant decrease in arterial oxygen O2 content, systemic oxygen transport did not significantly vary until 24 h in relation to the increased cardiac index. An increase in O2 extraction was observed after the exchange but no further increase was observed until the 24 h. No significant changes either in global O2 consumption or in lactate concentration were detected.(ABSTRACT TRUNCATED AT 250 WORDS)