Role of CaMKII in diabetes induced vascular injury and its interaction with anti-diabetes therapy.

Diabetes mellitus is a metabolic disorder denoted by chronic hyperglycemia that drives maladaptive structural changes and functional damage to the vasculature. Attenuation of this pathological remodeling of blood vessels remains an unmet target owing to paucity of information on the metabolic signatures of this process. Ca2+/calmodulin-dependent kinase II (CaMKII) is expressed in the vasculature and is implicated in the control of blood vessels homeostasis. Recently, CaMKII has attracted a special attention in view of its chronic upregulated activity in diabetic tissues, yet its role in the diabetic vasculature remains under investigation.This review highlights the physiological and pathological actions of CaMKII in the diabetic vasculature, with focus on the control of the dialogue between endothelial (EC) and vascular smooth muscle cells (VSMC). Activation of CaMKII enhances EC and VSMC proliferation and migration, and increases the production of extracellular matrix which leads to maladaptive remodeling of vessels. This is manifested by activation of genes/proteins implicated in the control of the cell cycle, cytoskeleton organization, proliferation, migration, and inflammation. Endothelial dysfunction is paralleled by impaired nitric oxide signaling, which is also influenced by CaMKII signaling (activation/oxidation). The efficiency of CaMKII inhibitors is currently being tested in animal models, with a focus on the genetic pathways involved in the regulation of CaMKII expression (microRNAs and single nucleotide polymorphisms). Interestingly, studies highlight an interaction between the anti-diabetic drugs and CaMKII expression/activity which requires further investigation. Together, the studies reviewed herein may guide pharmacological approaches to improve health-related outcomes in patients with diabetes.

From waste to wealth: Repurposing slaughterhouse waste for xenotransplantation.

Slaughterhouses produce large quantities of biological waste, and most of these materials are underutilized. In many published reports, the possibility of repurposing this form of waste to create biomaterials, fertilizers, biogas, and feeds has been discussed. However, the employment of particular offal wastes in xenotransplantation has yet to be extensively uncovered. Overall, viable transplantable tissues and organs are scarce, and developing bioartificial components using such discarded materials may help increase their supply. This perspective manuscript explores the viability and sustainability of readily available and easily sourced slaughterhouse waste, such as blood vessels, eyes, kidneys, and tracheas, as starting materials in xenotransplantation derived from decellularization technologies. The manuscript also examines the innovative use of animal stem cells derived from the excreta to create a bioartificial tissue/organ platform that can be translated to humans. Institutional and governmental regulatory approaches will also be outlined to support this endeavor.

Neuronal nitric oxide synthase, nNOS, regulates renal hemodynamics in the postnatal developing piglet.

INTRODUCTION: Nitric oxide (NO) vasodilation critically modulates renal hemodynamics in the neonate compared with the adult. Based on the postnatal expression pattern of renal neuronal nitric oxide synthase (nNOS), the hypothesis was that nNOS is the major NOS isoform regulating renal hemodynamics in the immature, but not mature, kidney. RESULTS: NOS inhibitors did not alter mean arterial pressure (MAP) in either group. Intrarenal S-methyl-L-thiocitrulline (L-SMTC) in newborns significantly reduced renal blood flow (RBF) 38 ± 4%, glomerular filtration rate (GFR) 42 ± 6%, and increased renal vascular resistance (RVR) 37 ± 7%, whereas intrarenal L-nitro-arginine methyl ester (L-NAME) affected RBF, GFR, and RVR equivalent to L-SMTC treatment. When L-NAME was administered after L-SMTC treatment, newborn renal hemodynamic changes were not further altered from what was observed when L-SMTC was administered alone. In contrast, in the adult, only intrarenal L-NAME, and not L-SMTC, affected renal hemodynamic responses. DISCUSSION: In conclusion, these studies demonstrate that nNOS is an important regulator of renal hemodynamics in the newborn kidney, but not in the adult. METHODS: Experiments compared renal hemodynamic responses with intrarenal infusion of L-NAME, an inhibitor of all NOS isoforms, with the selective nNOS inhibitor L-SMTC in the newborn piglet and the adult pig.

Structural and Electrical Remodeling of the Sinoatrial Node in Diabetes: New Dimensions and Perspectives.

The sinoatrial node (SAN) is composed of highly specialized cells that mandate the spontaneous beating of the heart through self-generation of an action potential (AP). Despite this automaticity, the SAN is under the modulation of the autonomic nervous system (ANS). In diabetes mellitus (DM), heart rate variability (HRV) manifests as a hallmark of diabetic cardiomyopathy. This is paralleled by an impaired regulation of the ANS, and by a pathological remodeling of the pacemaker structure and function. The direct effect of diabetes on the molecular signatures underscoring this pathology remains ill-defined. The recent focus on the electrical currents of the SAN in diabetes revealed a repressed firing rate of the AP and an elongation of its tracing, along with conduction abnormalities and contractile failure. These changes are blamed on the decreased expression of ion transporters and cell-cell communication ports at the SAN (i.e., HCN4, calcium and potassium channels, connexins 40, 45, and 46) which further promotes arrhythmias. Molecular analysis crystallized the RGS4 (regulator of potassium currents), mitochondrial thioredoxin-2 (reactive oxygen species; ROS scavenger), and the calcium-dependent calmodulin kinase II (CaMKII) as metabolic culprits of relaying the pathological remodeling of the SAN cells (SANCs) structure and function. A special attention is given to the oxidation of CaMKII and the generation of ROS that induce cell damage and apoptosis of diabetic SANCs. Consequently, the diabetic SAN contains a reduced number of cells with significant infiltration of fibrotic tissues that further delay the conduction of the AP between the SANCs. Failure of a genuine generation of AP and conduction of their derivative waves to the neighboring atrial myocardium may also occur as a result of the anti-diabetic regiment (both acute and/or chronic treatments). All together, these changes pose a challenge in the field of cardiology and call for further investigations to understand the etiology of the structural/functional remodeling of the SANCs in diabetes. Such an understanding may lead to more adequate therapies that can optimize glycemic control and improve health-related outcomes in patients with diabetes.

Neurotransmitters, neuropeptides and calcium in oocyte maturation and early development.

A primary reason behind the high level of complexity we embody as multicellular organisms is a highly complex intracellular and intercellular communication system. As a result, the activities of multiple cell types and tissues can be modulated resulting in a specific physiological function. One of the key players in this communication process is extracellular signaling molecules that can act in autocrine, paracrine, and endocrine fashion to regulate distinct physiological responses. Neurotransmitters and neuropeptides are signaling molecules that renders long-range communication possible. In normal conditions, neurotransmitters are involved in normal responses such as development and normal physiological aspects; however, the dysregulation of neurotransmitters mediated signaling has been associated with several pathologies such as neurodegenerative, neurological, psychiatric disorders, and other pathologies. One of the interesting topics that is not yet fully explored is the connection between neuronal signaling and physiological changes during oocyte maturation and fertilization. Knowing the importance of Ca2+ signaling in these reproductive processes, our objective in this review is to highlight the link between the neuronal signals and the intracellular changes in calcium during oocyte maturation and embryogenesis. Calcium (Ca2+) is a ubiquitous intracellular mediator involved in various cellular functions such as releasing neurotransmitters from neurons, contraction of muscle cells, fertilization, and cell differentiation and morphogenesis. The multiple roles played by this ion in mediating signals can be primarily explained by its spatiotemporal dynamics that are kept tightly checked by mechanisms that control its entry through plasma membrane and its storage on intracellular stores. Given the large electrochemical gradient of the ion across the plasma membrane and intracellular stores, signals that can modulate Ca2+ entry channels or Ca2+ receptors in the stores will cause Ca2+ to be elevated in the cytosol and consequently activating downstream Ca2+-responsive proteins resulting in specific cellular responses. This review aims to provide an overview of the reported neurotransmitters and neuropeptides that participate in early stages of development and their association with Ca2+ signaling.

Interaction of SARS-CoV-2 with cardiomyocytes: Insight into the underlying molecular mechanisms of cardiac injury and pharmacotherapy.

SARS-CoV-2 causes respiratory illness with a spectrum of systemic complications. However, the mechanism for cardiac infection and cardiomyocyte injury in COVID-19 patients remains unclear. The current literature supports the notion that SARS-CoV-2 particles access the heart either by the circulating blood cells or by extracellular vesicles, originating from the inflamed lungs, and encapsulating the virus along with its receptor (ACE2). Both cardiomyocytes and pericytes (coronary arteries) express the necessary accessory proteins for access of SARS-CoV-2 particles (i.e. ACE2, NRP-1, TMPRSS2, CD147, integrin α5ß1, and CTSB/L). These proteins facilitate the SARS-CoV-2 interaction and entry into the pericytes and cardiomyocytes thus leading to cardiac manifestations. Subsequently, various signaling pathways are altered in the infected cardiomyocytes (i.e. increased ROS production, reduced contraction, impaired calcium homeostasis), causing cardiac dysfunction. The currently adopted pharmacotherapy in severe COVID-19 subjects exhibited side effects on the heart, often manifested by electrical abnormalities. Nonetheless, cardiovascular adverse repercussions have been associated with the advent of some of the SARS-CoV-2 vaccines with no clear mechanisms underlining these complications. We provide herein an overview of the pathways involved with cardiomyocyte in COVID-19 subjects to help promoting pharmacotherapies that can protect against SARS-CoV-2-induced cardiac injuries.

Challenges Faculty Faced Transitioning to e-Learning Platforms during the Current Pandemic in the United Arab Emirates.

The authors recount the challenges they overcame to deliver lecture content and assessments while engaging students at their newly established medical school. Faculty must multitask in new and added ways to achieve the same goal in e-learning platforms. Online course delivery introduces additional barriers to engaging students, atypical of face-to-face sessions. We received valuable feedback, adjusted our delivery, and allowed our students to access lecture recordings at their convenience. Our sessions with students were more than just a lecture but a way to help people through a unprecedented time. Remote learning platforms also provided faculty with opportunities to develop new pedagogical skills and alternative assessments.

Lessons Learned Transitioning from Traditional Premedical and Medical Education to E-learning Platforms during the COVID-19 Pandemic within the United Arab Emirates.

Educational systems across the globe were disrupted by the COVID-19 pandemic, and faculty, staff, and students had to rapidly transition to e-learning platforms. These groups had little preparation to cope with the challenges of this newly adopted system. However, as we begin to emerge from the COVID-19 era, efforts are being made to assess the impact of this transition and develop a framework of best practices to help educators prepare for possible future disruptions. This commentary aims to discuss some of the challenges associated with the rapid transition to the new academic environment, including the modes of instruction employed, technical obstacles encountered, student responses to change and efforts made to evaluate didactic and practical aspects of the curriculum in the contexts of premedical and medical education, at the newly established College of Medicine at Khalifa University of Science and Technology in the United Arab Emirates.

Intravital imaging of real-time endogenous actin dysregulation in proximal and distal tubules at the onset of severe ischemia-reperfusion injury.

Severe renal ischemia-reperfusion injury (IRI) can lead to acute and chronic kidney dysfunction. Cytoskeletal modifications are among the main effects of this condition. The majority of studies that have contributed to the current understanding of IRI have relied on histological analyses using exogenous probes after the fact. Here we report the successful real-time visualization of actin cytoskeletal alterations in live proximal and distal tubules that arise at the onset of severe IRI. To achieve this, we induced fluorescent actin expression in these segments in rats with hydrodynamic gene delivery (HGD). Using intravital two-photon microscopy we then tracked and quantified endogenous actin dysregulation that occurred by subjecting these animals to 60 min of bilateral renal ischemia. Rapid (by 1-h post-reperfusion) and significant (up to 50%) declines in actin content were observed. The decline in fluorescence within proximal tubules was significantly greater than that observed in distal tubules. Actin-based fluorescence was not recovered during the measurement period extending 24 h post-reperfusion. Such injury decimated the renal architecture, in particular, actin brush borders, and hampered the reabsorptive and filtrative capacities of these tubular compartments. Thus, for the first time, we show that the combination of HGD and intravital microscopy can serve as an experimental tool to better understand how IRI modifies the cytoskeleton in vivo and provide an extension to current histopathological techniques.

Enalapril treatment restores the decreased proximal tubule reabsorption in response to acute volume expansion in diabetic rats.

The renin-angiotensin system (RAS) plays an important role in the regulation of blood pressure, fluid and electrolyte homeostasis. The RAS is activated and renal interstitial hydrostatic pressure (RIHP) is decreased in diabetic rats. The objective of this study was to evaluate the roles of proximal tubule reabsorption and RAS in the decreased RIHP and blunted natriuretic and diuretic responses to acute saline volume expansion (VE) in diabetic rats. Enalapril was utilized to inhibit angiotensin II (AII) formation. Diabetes mellitus (DM) was induced by a single intraperitoneal (i.p.) injection of streptozotocin (STZ, 65 mg/kg). RIHP was measured by a polyethylene (PE) matrix that was chronically implanted in the left kidney. Fractional excretion of phosphate (FE(Pi)) and fractional excretion of lithium (FE(Li)) were used as indexes for proximal tubule reabsorption. VE significantly increased both FE(Li) and FE(Pi) in all groups of rats studied. However, the increase in FE(Li) (DeltaFE(Li)=17.26+/-3.83%) and FE(Pi) (DeltaFE(Pi)=7.38+/-2.37%) in diabetic rats (DC, n=12) were significantly lower as compared with those in nondiabetic control rats (NC, n=8; DeltaFE(Li)=32.15+/-4.71% and DeltaFE(Pi)=20.62+/-3.27%). The blunted increases in FE(Li) and FE(Pi) were associated with an attenuated increase in RIHP (DeltaRIHP) in DC (1.8+/-0.4 mm Hg) compared with NC rats (4.3+/-0.3 mm Hg). Enalapril treatment (25 mg/kg/day in drinking water) had no effect on nondiabetic rats (NE, n=8) as compared with untreated NC rats, but significantly improved RIHP response (DeltaRIHP) to VE in diabetic rats (DE, n=9; 2.8+/-0.5 mm Hg). Both DeltaFE(Li) and DeltaFE(Pi) were restored by enalapril treatment in diabetic rats and no significant differences were found in DeltaFE(Li) and DeltaFE(Pi) between DE (DeltaFE(Li)=26.81+/-4.94% and DeltaFE(Pi)=10.45+/-4.67%) and NC groups of rats in response to VE. These data suggest that the activated RAS and the decrease in RIHP may play an important role in the increased proximal tubule reabsorption, and the attenuated natriuretic and diuretic responses to acute volume expansion in diabetic rats.

Renal interstitial hydrostatic pressure and natriuretic response to high doses of angiotensin II in pregnant rats.

BACKGROUND: Administration of high doses of angiotensin II (Ang II) results in natriuretic and diuretic responses that are mediated by increases in renal perfusion pressure (RPP). Elevations in renal interstitial hydrostatic pressure (RIHP) caused by increases in mean arterial pressure (MAP) or RPP are associated with significant increases in urinary sodium excretion (U(Na)V) and urine flow rate (V). In pregnant rats the renin-angiotensin system (RAS) is activated and basal RIHP is reduced. The exact relationship among MAP, RIHP, U(Na)V, and V in response to a high pressor dose of Ang II during normal pregnancy is not known. METHODS: The objective of this study was to evaluate the relationship between MAP and RIHP, and determine the role of RIHP in the natriuretic and diuretic responses to administration of high dose of Ang II in midterm pregnant (MP) and nonpregnant (NP) Sprague-Dawley (SD) rats. RESULTS: Intravenous infusion of Ang II (200 ng/kg/min) significantly increased MAP (DeltaMAP), DeltaU(Na)V, and DeltaV in anesthetized MP and NP rats. The DeltaMAP, DeltaU(Na)V, and DeltaV were 12 +/- 2 mm Hg, 27.9 +/- 2.7 microEq/min, and 197 +/- 23 microL/min for MP rats and were similar (15 +/- 3 mm Hg, 34.1 +/- 4.3 microEq/min, and 242 +/- 34 microL/min, respectively) for NP rats. The RIHP decreased significantly (P < .05) with Ang II infusion in NP (from 6.1 +/- 0.2 to 3.9 +/- 0.4 mm Hg) but not in MP (from 3.3 +/- 0.3 to 4.1 +/- 0.4 mm Hg) groups of rats. Acute renal decapsulation eliminated the change in RIHP mediated by high doses of Ang II infusion in the NP group, but did not affect MAP or the natriuretic and diuretic responses to Ang II in either the MP or NP groups of rats. CONCLUSIONS: The natriuretic and diuretic responses to high doses of Ang II are not mediated by changes in RIHP in pregnant or nonpregnant rats.

Natriuretic response to direct renal interstitial volume expansion (DRIVE) in pregnant rats.

BACKGROUND: Basal renal interstitial hydrostatic pressure (RIHP) is lower in pregnant rats, suggesting an increase in renal interstitial compliance during pregnancy. The RIHP responses to increases in renal perfusion pressure (RPP) and acute saline volume expansion (VE) are attenuated in pregnant rats. Pressure natriuresis and diuresis responses are significantly attenuated during normal pregnancy, whereas the natriuretic and diuretic responses to VE remain intact. METHODS: The objectives of this study were to use direct renal interstitial volume expansion (DRIVE) to selectively increase RIHP and determine the renal interstitial compliance and the relationship between RIHP, natriuretic, and diuretic responses in nonpregnant (NP; n = 8), midterm pregnant (MP; n = 8), and late-term pregnant (LP; n = 8) Sprague-Dawley (SD) rats. RESULTS: DRIVE resulted in significant increases in RIHP, fractional excretion of sodium (FE(Na)), and urine flow rate (V) in all groups of rats. The increase in RIHP (DeltaIHP) was greatest for NP (3.3 +/- 0.2 mm Hg) as compared to MP (1.3 +/- 0.1 mm Hg; P < .05 v NP) and LP (1.4 +/- 0.2 mm Hg; P < .05 v NP) in response to DRIVE showing that renal interstitial compliance was greater in MP and LP as compared to the NP group of rats. The increase in fractional excretion of sodium (DeltaFE(Na)) was similar in NP (3.1% +/- 0.3%) and LP (3.6% +/- 0.8%), but was significantly lower in MP (1.5% +/- 0.4%; P < .05 v NP and LP) in response to DRIVE. CONCLUSIONS: These data suggest that the blunted increase in RIHP and natriuresis in response to DRIVE in midterm pregnant rats may play an important role in the gradual plasma volume expansion that is occurring during this stage of pregnancy.

Role of RIHP and renal tubular sodium transporters in volume retention of pregnant rats.

BACKGROUND: Normal pregnancy is characterized by sodium and water conservation and an increase in plasma volume that is required for an uncomplicated pregnancy. Renal interstitial hydrostatic pressure (RIHP) is significantly decreased in pregnant rats. This decrease in RIHP may play an important role in the sodium and water retention that characterizes normal pregnancy. Paradoxically this enhanced renal sodium and water reabsorption appear to conflict with the consistent findings of a general decrease in abundance of renal tubular sodium transporters during normal pregnancy. The objective of this review is to examine the apparent discrepancy between the increases in renal tubular sodium and water reabsorption, facilitated by decreases in RIHP, and the seemingly discordant decreases in abundance of renal tubular transporters during normal pregnancy in rats. METHODS: Western blots and immunohistochemistry were used to evaluate abundance and localization of renal tubular transporters. RIHP was measured directly and continuously via a polyethylene (PE) matrix that was implanted in the left kidney of rats at the age of 11 to 16 weeks. RESULTS: Average basal RIHP and fractional excretion of sodium (FENa) were found to be significantly lower (P < .05) in midterm pregnant (MP; n = 18) and late-term pregnant (LP; n = 20) rats compared with nonpregnant (NP; n = 16) rats (3.5 +/- 0.3 mm Hg and 1.46 +/- 0.24% for MP; 3.3 +/- 0.1 mm Hg and 1.41 +/- 0.21% for LP; and 7.6 +/- 0.6 mm Hg and 3.67 +/- 0.24% for NP). Cortical Na+-K+-ATPase and Na-Pi2a cotransporter (Na-Pi) protein expression tend to decline with pregnancy. Also cortical Na+-H+ exchanger-1 (NHE-1) protein expression declines steadily during the course of pregnancy from MP to LP compared with that in NP rats, and cortical Na+-H+ exchanger-3 (NHE-3) protein expression is significantly lower in MP and LP compared with NP rats. CONCLUSIONS: We propose that during normal uncomplicated pregnancy, simultaneous decreases in RIHP and in net abundance of renal tubular sodium transporters occur. The effects of decreased RIHP exceed those of the reduction in net abundance, and presumably activity, of renal tubular transporters resulting in an enhanced net sodium and water retention during pregnancy.

Cardiovascular and renal characteristics, and responses to acute volume expansion of a rat model of diabetic pregnancy.

The objective of this study was to characterize the cardiovascular and renal alterations that occur during diabetic pregnancy, and to evaluate the effect of insulin treatment in 12-14 days pregnant diabetic rats. Four groups of female Sprague Dawley rats were studied: virgin control group (NP), pregnant control group (CP), diabetic pregnant group (DP), and diabetic pregnant group with insulin treatment (DPI). Systolic arterial pressure (SAP) was increased on day 12, whereas heart rate (HR) decreased starting with day 3 in DP group of rats. DP rats exhibited marked renal hypertrophy with greater kidney weight (wt) and kidney wt/body wt ratio. Insulin treatment normalized blood glucose (BG) concentration, SAP and HR, and prevented the increase in kidney wt/body wt ratio in DPI rats. At the time of the terminal acute experiment, acute saline volume expansion (VE, 5% body wt/30 min) significantly increased renal interstitial hydrostatic pressure (RIHP), urinary sodium excretion (U(Na)V) and urine flow rate (V) in all groups, but the increases (Delta) were significantly attenuated in both CP (1.7 +/- 0.2mmHg, 12.0 +/- 1.5 microEq.min(-1).g kidney wt(-1) and 76.2 +/- 10.9 microl.min(-1).g kidney wt(-1) for DeltaRIHP, DeltaU(Na)V and DeltaV respectively) and DP (1.3 +/- 0.1 mmHg, 6.8 +/- 1.8 microEq.min(-1).g kidney wt(-1) and 32.3 +/- 9.3 microl.min(-1).g kidney wt(-1) for DeltaRIHP, DeltaU(Na)V and DeltaV respectively) group of rats as compared to NP (4.0 +/- 0.6 mmHg, 21.6 +/- 1.4 microEq.min(-1).g kidney wt(-1)and 136.8 +/- 10.5 microl.min(-1).g kidney wt(-1) for DeltaRIHP, DeltaU(Na)V and DeltaV respectively) group of rats. Although RIHP response to VE was similar in DP and CP group of rats, the natriuretic and diuretic responses to VE were significantly lower in DP as compared to CP group of rats. Insulin treatment had no effect on RIHP response (DeltaRIHP = 1.5 +/- 0.3 mmHg), but restored most of the natriuretic (DeltaU(Na)V = 15.7 +/- 2.9 microEq.min(-1).g kidney wt(-1)) and diuretic (DeltaV = 100.2 +/- 19.3 microl.min(-1).g kidney wt(-1)) responses to VE in DPI as compared with CP group of rats. These data suggest that with VE, the restoration of the increase in U(Na)V and V with insulin treatment in diabetic pregnant rats is not mediated by changes in RIHP.

Renal interstitial hydrostatic pressure and sodium excretion in hypertension and pregnancy.

The kidney plays an important role in the long-term regulation of blood pressure and extracellular fluid volume through the regulation of sodium and water excretion. Increases in renal perfusion pressure (RPP) cause a potent natriuretic stimulus, referred to as 'pressure natriuresis', which is an important mechanism in the regulation of extracellular fluid volume and blood pressure. In normotensive animals, increases in RPP are transmitted to the renal interstitium and result in increases in renal interstitial hydrostatic pressure (RIHP), as well as in sodium and water excretion. However, pressure natriuresis is significantly attenuated in hypertensive and pregnant normotensive rats. Furthermore, this response is associated with an attenuated increase in RIHP with increases in RPP, suggesting that the renal interstitial compliance is greater in hypertension and during pregnancy than in normotensive non-pregnant states. In the absence of other mechanisms, this attenuated pressure natriuretic response can lead to volume retention. However, volume expansion also increases RIHP and sodium excretion. It is proposed that a compensatory increase in the natriuretic sensitivity to increases in RIHP counterbalances the volume retention that results from the attenuated pressure natriuresis in hypertensive rats, and thus may play an important role in maintaining normal plasma volume in these animals. Likewise, it is also proposed that the attenuated relationship between blood pressure, RIHP and sodium excretion that is observed during normal pregnancy is due to an increase in the compliance of the renal interstitium and leads to a reduction in sodium excretion and the gradual gestational volume expansion. During pregnancy, RIHP does not increase immediately due to the large renal interstitial compliance and therefore the increased sensitivity of the natriuretic response to increases in RIHP does not occur, and gradual volume expansion continues during normal pregnancy. However, the increased sensitivity of the natriuretic response to increases in RIHP takes effect only after the necessary volume is retained for a normal pregnancy. Below this requisite volume expansion, the increase in RIHP is not sufficient to activate the exaggerated natriuretic sensitivity to increases in RIHP. Failure of these adaptive mechanisms during pregnancy can lead to disturbances in the regulation of plasma volume which, in turn, can affect amniotic fluid volume and fetal growth and may result in premature labour and intrauterine growth restriction, as well as pre-eclampsia.

Different natriuretic responses in obese and lean rats in response to nitric oxide reduction.

BACKGROUND: Nitric oxide (NO) is an important regulator of renal sodium transport and participates in the control of natriuresis and diuresis. In obesity, the nitric oxide bioavailability was reportedly reduced, which may contribute to the maintenance of hypertension. The aim of this study was to determine the effect of NO depletion on renal sodium handling in a model of diet-induced obesity hypertension. METHODS: Obese hypertensive (obesity-prone (OP)) and lean normotensive (obesity-resistant (OR)) Sprague-Dawley rats were treated with 1.2 mg/kg/day N(G)-nitro-L-arginine-methyl ester (L-NAME) for 4 weeks to inhibit NO synthesis. Acute pressure natriuresis and diuresis were measured in response to an increase in perfusion pressure. NHE3 and Na(+), K(+)-ATPase protein expression were measured by Western blot and NHE3 activity was determined as the rate of pH change in brush border membrane vesicles. NHE3 membrane localization was determined by confocal microscopy. RESULTS: L-NAME did not significantly attenuate the natriuretic and diuretic responses to increases in renal perfusion pressure (RPP) in OP rats while inducing a significant reduction in OR rats. Following chronic NO inhibition, NHE3 protein expression and activity and Na(+), K(+)-ATPase protein expression were significantly increased in the OR but not in the OP group. Immunofluorescence studies indicated that the increase in NHE3 activity could be, at least in part, due to NHE3 membrane trafficking. CONCLUSIONS: Obese hypertensive rats have a weaker natriuretic response in response to NO inhibition compared to lean rats and the mechanism involves different regulation of the apical sodium exchanger NHE3 expression, activity, and trafficking.

Effects of insulin on renal interstitial hydrostatic pressure and natriuretic response to volume expansion in diabetic rats.

Diabetes mellitus (DM) is characterized by alterations in fluid balance and blood volume homeostasis. Renal interstitial hydrostatic pressure (RIHP) has been shown to play a critical role in mediating sodium and water excretion under various conditions. The objective of this study was to determine the effects of immediate and delayed initiation of insulin treatment on the restoration of the relationship between RIHP, natriuretic, and diuretic responses to acute saline volume expansion (VE) in diabetic rats. Diabetes was induced by an intraperitoneal injection of streptozotocin (STZ; 65 mg/kg body wt). Four groups of female Sprague-Dawley rats were studied: normal control group (C), untreated diabetic group (D), immediate insulin-treated diabetic group (DI; treatment with insulin for 2 wk was initiated immediately when diabetes was confirmed, which was 2 days after STZ injection), and delayed insulin-treated diabetic group (DDI; treatment with insulin for 2 wk was initiated 2 wk after STZ injection). RIHP and sodium and water excretions were measured before and during VE (5% body wt/30 min) in the four groups of anesthetized rats. VE significantly increased RIHP, fractional excretion of sodium (FE(Na)), and urine flow rate (V) in all groups of rats. Basal RIHP, RIHP response to VE (Delta RIHP), and FE(Na) and V responses to VE (Delta FE(Na) and Delta V) were significantly lower in the D group compared with the C group of rats. Delta RIHP was significantly higher in both DI and DDI groups compared with D group but was similar to that of the C group of rats. While in the DI group the Delta FE(Na) response to VE was restored, Delta FE(Na) was significantly increased in DDI compared with D group, but it remained lower than that of the C group. In conclusion, insulin treatment initiated immediately after the onset of diabetes restores basal RIHP and RIHP, natriuretic, and diuretic responses to VE; however, delayed insulin treatment restores the basal RIHP and RIHP response to VE but does not fully restore the natriuretic response to VE.

Role of nitric oxide in the natriuretic and diuretic responses in pregnant rats.

Normal pregnancy is characterized by sodium conservation and increase in plasma volume, yet the natriuretic response to acute saline volume expansion (VE) is intact in pregnant rats. Nitric oxide (NO) has been suggested to play a role in renal and cardiovascular adaptations to normal pregnancy. The objective of this study was to determine the role of NO in the natriuretic and diuretic responses to VE during pregnancy. Infusion of NG-monomethyl-l-arginine (l-NMMA) was used to inhibit NO synthesis. Nine groups of Sprague-Dawley (SD) rats were studied: nonpregnant (NP-VE, n = 7), midterm pregnant (MP-VE, n = 8), and late-term pregnant (LP-VE, n = 7) SD groups that underwent VE alone after a control period; NP-l-NMMA (n = 7), MP-l-NMMA (n = 8), and LP-l-NMMA (n = 7) SD groups that were infused with l-NMMA after a control period; and another three groups of SD rats (NP-VE-l-NMMA, n = 8; MP-VE-l-NMMA, n = 7; and LP-VE-l-NMMA, n = 12) that underwent simultaneous VE and l-NMMA infusion after a control period. The change in fractional excretion of sodium was 7.22 +/- 1.03% for NPVE, 9.89 +/- 1.85% for NP-l-NMMA, and 17.66 +/- 1.85% for NP-VE-l-NMMA (P < 0.05 vs. NP-VE and NP-l-NMMA); 6.61 +/- 1.07% for MP-VE, 7.99 +/- 1.92% for MP-l-NMMA, and 10.24 +/- 1.91% for MP-VE-l-NMMA [not significant (NS) vs. MP-VE and MP-l-NMMA]; 8.20 +/- 1.92% for LP-VE, 8.09 +/- 0.70% for LP-l-NMMA, and 7.57 +/- 1.11% for LP-VE-l-NMMA (both NS vs. LP-VE and LP-l-NMMA). The increase in renal interstitial hydrostatic pressure was significantly greater in all NP compared with pregnant groups with similar experimental intervention (i.e., VE, l-NMMA, or VE-l-NMMA). In conclusion, the natriuretic and diuretic responses to VE and l-NMMA infusion were additive in NP but not in pregnant rats, indicating a possible lower ability of pregnant rats to respond to combined significant natriuretic and diuretic stimuli.

Renal interstitial hydrostatic pressure and natriuretic responses to volume expansion in pregnant rats.

During normal pregnancy, a gradual plasma volume expansion (VE) occurs and reaches a maximum level at late term. Pressure natriuresis and renal interstitial hydrostatic pressure (RIHP) responses are attenuated in pregnant rats. Also, basal RIHP is lower in pregnant rats, suggesting an increase in renal interstitial compliance during pregnancy. This adaptation may contribute to the increase in plasma volume that is required for a normal pregnancy, because increases in RIHP have been consistently shown to produce natriuresis and diuresis. Acute saline VE (5% body wt/30 min) has been shown to increase RIHP in normal nonpregnant rats. Therefore, the objective of this study was to determine RIHP, natriuretic, and diuretic responses to VE in nonpregnant (n = 7), midterm pregnant (n = 8), and late-term pregnant (n = 8) Sprague-Dawley rats. Although VE significantly increased RIHP, fractional excretion of sodium (FE(Na)), and urine flow rate (V) in all groups, DeltaRIHP was highest for nonpregnant (3.0 +/- 0.3 mmHg) compared with midterm pregnant (1.6 +/- 0.1 mmHg; P < 0.05 vs. nonpregnant) and late-term pregnant rats (1.2 +/- 0.1 mmHg; P < 0.05 vs. both midterm pregnant and nonpregnant rats). DeltaFE(Na) and DeltaV were similar in all groups: 5.8 +/- 1.0% and 231 +/- 27 microl/min for nonpregnant, 6.8 +/- 1.3% and 173 +/- 16 microl/min for midterm pregnant, and 7.6 +/- 1.2% and 203 +/- 10 microl/min for late-term pregnant rats, respectively. In conclusion, basal RIHP and the increase in RIHP during VE were attenuated during pregnancy; however, the natriuretic and diuretic responses to VE remain intact during the course of pregnancy.

Pioglitazone prevents hypertension and reduces oxidative stress in diet-induced obesity.

The objective of this study was to determine the effect of pioglitazone on blood pressure (BP) and oxidative balance in obese, hypertensive, Sprague-Dawley rats and to identify some of the molecular mechanisms involved. After 12 weeks of a moderately high-fat diet, rats diverged into obesity-prone (OP) and obesity-resistant (OR) groups (n=6 per group). At the end of the diet, peroxisome proliferator activated receptor-gamma (PPARgamma) mRNA expression and activity in the renal cortex and medulla of OP rats were significantly lower compared with that in OR rats. Pioglitazone treatment increased PPARgamma expression and activity in OP rats, suggesting a possible direct ligand-related effect of pioglitazone. As opposed to the untreated OP group, which showed moderate hypertension (systolic BP=159+/-5.3 mm Hg) after 12 weeks, pioglitazone-treated rats were normotensive (systolic BP=123.9+/-2.7 mm Hg). Insulin production was reduced by 2-fold in the OP group treated with pioglitazone. Urinary isoprostanes and renal lipid peroxides were also reduced in OP rats treated with pioglitazone compared with untreated counterparts. Also, expression of p47phox and gp91phox, both increased in OP versus OR rats, was reduced in the former by pioglitazone treatment. In addition, pioglitazone treatment increased nitrate/nitrite excretion and expression of renal endothelial and neuronal nitric oxide synthase. Collectively, the results show that pioglitazone treatment prevented hypertension and renal oxidative stress both by reducing free-radical production and by increasing nitric oxide production/availability.