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

Efficacy of Dynamics-based Features for Machine Learning Classification of Renal Hemodynamics

Different machine learning approaches for analyzing renal hemodynamics using time series of arterial blood pressure and renal blood flow rate measurements in conscious rats are developed and compared. Particular emphasis is placed on features used for machine learning. The test scenario involves binary classification of Sprague-Dawley rats obtained from two different suppliers, with the suppliers' rat colonies having drifted slightly apart in hemodynamic characteristics. Models used for the classification include deep neural network (DNN), random forest, support vector machine, multilayer perceptron. While the DNN uses raw pressure/flow measurements as features, the latter three use a feature vector of parameters of a nonlinear dynamic system fitted to the pressure/flow data, thereby restricting the classification basis to the hemodynamics. Although the performance in these cases is slightly reduced in comparison to that of the DNN, they still show promise for machine learning (ML) application. The pioneering contribution of this work is the establishment that even with features limited to hemodynamics-based information, the ML models can successfully achieve classification with reasonably high accuracy.

Comparison of the Surgical Resection and Infarct 5/6 Nephrectomy Rat Models of Chronic Kidney Disease

The 5/6 nephrectomy rat remnant kidney model is commonly employed to study chronic kidney disease (CKD). This model requires removal of one whole kidney and two-thirds of the other. The two most common ways of producing the remnant kidney are surgical resection of poles, known as the polectomy (Pol) model, or ligation of upper and lower renal arterial branches, resulting in pole infarction (Inf). These models have much in common, but also major phenotypic differences, and thus respectively model unique aspects of human CKD. The purpose of this review is to summarize phenotypic similarities and differences between these two models and their relation to human CKD, while emphasizing their vascular phenotype. In this article we review studies that have evaluated arterial blood pressure, the renin-angiotensin-aldosterone-system (RAAS), autoregulation, nitric oxide, single nephron physiology, angiogenic and anti-angiogenic factors, and capillary rarefaction in these two models. Phenotypic similarities: both models spontaneously develop hallmarks of human CKD including uremia, fibrosis, capillary rarefaction, and progressive renal function decline. They both undergo whole-organ hypertrophy, hyperfiltration of functional nephrons, reduced renal expression of angiogenic factor VEGF, increased renal expression of the anti-angiogenic thrombospondin-1, impaired renal autoregulation, and abnormal vascular nitric oxide physiology. Key phenotypic differences: the Inf model develops rapid-onset, moderate-to-severe systemic hypertension, and the Pol model early normotension followed by mild-to-moderate hypertension. The Inf rat has a markedly more active renin-angiotensin-aldosterone-system. Comparison of these two models facilitates understanding of how they can be utilized for studying CKD pathophysiology (e.g., RAAS dependent or independent pathology).

Salt-Sensitive Hypertension, Renal Injury, and Renal Vasodysfunction Associated With Dahl Salt-Sensitive Rats Are Abolished in Consomic SS.BN1 Rats

Background

Abnormal renal hemodynamic responses to salt‐loading are thought to contribute to salt‐sensitive (SS) hypertension. However, this is based largely on studies in anesthetized animals, and little data are available in conscious SS and salt‐resistant rats.

Methods and Results

We assessed arterial blood pressure, renal function, and renal blood flow during administration of a 0.4% NaCl and a high‐salt (4.0% NaCl) diet in conscious, chronically instrumented 10‐ to 14‐week‐old Dahl SS and consomic SS rats in which chromosome 1 from the salt‐resistant Brown‐Norway strain was introgressed into the genome of the SS strain (SS.BN1). Three weeks of high salt intake significantly increased blood pressure (20%) and exacerbated renal injury in SS rats. In contrast, the increase in blood pressure (5%) was similarly attenuated in Brown‐Norway and SS.BN1 rats, and both strains were completely protected against renal injury. In SS.BN1 rats, 1 week of high salt intake was associated with a significant decrease in renal vascular resistance (−8%) and increase in renal blood flow (15%). In contrast, renal vascular resistance failed to decrease, and renal blood flow remained unchanged in SS rats during high salt intake. Finally, urinary sodium excretion and glomerular filtration rate were similar between SS and SS.BN1 rats during 0.4% NaCl and high salt intake.

Conclusions

Our data support the concept that renal vasodysfunction contributes to blood pressure salt sensitivity in Dahl SS rats, and that genes on rat chromosome 1 play a major role in modulating renal hemodynamic responses to salt loading and salt‐induced hypertension.

BP Fluctuations and the Real-Time Dynamics of Renal Blood Flow Responses in Conscious Rats

BACKGROUND

Renal autoregulation maintains stable renal function despite BP fluctuations and protects glomerular capillaries from hypertensive injury. However, real-time dynamics of renal autoregulation in conscious animals have not been characterized.

METHODS

To develop novel analytic methods for assessing renal autoregulation, we recorded concurrent BP and renal blood flow in conscious rats, comparing animals with renal autoregulation that was intact versus impaired (from 3/4 nephrectomy), before and after additional impairment (from the calcium channel blocker amlodipine). We calculated autoregulatory indices for adjacent short segments of increasing length (0.5, 1, 2.5, 5, 10, and 20 seconds) that exhibited a mean BP difference of at least 5 mm Hg.

RESULTS

Autoregulatory restoration of renal blood flow to baseline after BP changes in conscious rats occurs rapidly, in 5-10 seconds. The response is significantly slower in states of impaired renal autoregulation, enhancing glomerular pressure exposure. However, in rats with severe renal autoregulation impairment (3/4 nephrectomy plus amlodipine), renal blood flow in conscious animals (but not anesthetized animals) was still restored to baseline, but took longer (15-20 seconds). Consequently, the ability to maintain overall renal blood flow stability is not compromised in conscious rats with impaired renal autoregulation.

CONCLUSIONS

These novel findings show the feasibility of renal autoregulation assessment in conscious animals with spontaneous BP fluctuations and indicate that transient increases in glomerular pressure may play a greater role in the pathogenesis of hypertensive glomerulosclerosis than previously thought. These data also show that unidentified mechanosensitive mechanisms independent of known renal autoregulation mechanisms and voltage-gated calcium channels can maintain overall renal blood flow and GFR stability despite severely impaired renal autoregulation.

Interactions between the complement and endothelin systems in normal pregnancy and following placental ischemia

Preeclampsia is characterized by new onset hypertension and fetal growth restriction and is associated with aberrant activation of the innate immune complement system and stressed or ischemic placenta. Previous studies have suggested a role for both endothelin and complement system activation products in new onset hypertension in pregnancy, but inter-relationships of the pathways are unclear. We hypothesized that complement activation following placental ischemia stimulates the endothelin pathway to cause hypertension and impair fetal growth. The Reduced Uterine Perfusion Pressure (RUPP) model results in hypertension and fetal growth restriction in a pregnant rat due to placental ischemia caused by mechanical obstruction of blood flow to uterus and placenta. The effect of inhibitor of complement activation soluble Complement Receptor 1 (sCR1) and endothelin A receptor (ET_A) antagonist atrasentan on hypertension, fetal weight, complement activation (systemic circulating C3a and local C3 placental deposition) and endothelin [circulating endothelin and message for preproendothelin (PPE), ET_A and endothelin B receptor (ET_B) in placenta] in the RUPP rat model were determined. Following placental ischemia, sCR1 attenuated hypertension but increased message for PPE and ET_A in placenta, suggesting complement activation causes hypertension via an endothelin independent pathway. With ET_A antagonism the placental ischemia-induced increase in circulating C3a was unaffected despite inhibition of hypertension, indicating systemic C3a alone is not sufficient. In normal pregnancy, inhibiting complement activation increased plasma endothelin but not placental PPE message. Atrasentan treatment increased fetal weight, circulating endothelin and placental ET_A message, and unexpectedly increased local complement activation in placenta (C3 deposition) but not C3a in circulation, suggesting endothelin controls local placental complement activation in normal pregnancy. Atrasentan also significantly decreased message for endogenous complement regulators Crry and CD55 in placenta and kidney in normal pregnancy. Results of our study indicate that complement/endothelin interactions differ in pregnancies complicated with placental ischemia vs normal pregnancy, as well as locally vs systemically. These data clearly illustrate the complex interplay between complement and endothelin indicating that perturbations of either pathway may affect pregnancy outcomes.

Resveratrol did not alter blood pressure in rats with nitric oxide synthase-inhibited hypertension

Background:

Inhibition of nitric oxide synthase (NOS) is a well-known experimental model of hypertension (HT). It was shown that oxidative stress contributes to the pathogenesis of HT. Resveratrol is a potent anti-oxidant that is found in red grapes, peanuts and red wine. It improves the NO response and increases endothelial NOS expression, which causes endothelium-dependent vasorelaxation as well as renal vasodilation. We aimed to explore the effects of resveratrol on blood pressure, the water–salt balance and sodium excretion as a reflection of renal function in NOS-inhibited rat models.

Methods:

Thirty-five male Sprague-Dawley rats (200–250g) were used in this study. In order to obtain hypertension models, an NOS inhibitor, N-nitro-L-arginin (L-NNA) was used. The rats were randomly divided into five groups: controls (given water and 0.8% salty diet) and four groups [given L-NNA, resveratrol (RSV) eluent, RSV, and L-NNA + RSV]. Blood pressures were measured indirectly by the tailcuff method on the first, seventh and 10th days. At the end of the study protocol (10th day), fluid balance, glomerular filtration rate, fractional sodium excretion, and blood and urinesodium and creatinine levels were measured.

Results:

At the end of the study protocol, blood pressures were higher in only the L-NNA group (117.8 ± 3.5 vs 149.5 ± 2.1 mmHg; p < 0.05), as expected. Additional applications of RSV with L-NNA could not prevent the increase in blood pressure (122.8 ± 7.3 vs 155.4 ± 4.4 mmHg; p < 0.05). There were no remarkable changes in water–salt balance and renal function with the application of resveratrol.

Conclusion:

Resveratrol was unable to prevent or reverse blood pressure increase in NOS-inhibited rats.

Renal endothelial function is associated with the anti-proteinuric effect of ACE inhibition in 5/6 nephrectomized rats

In healthy rats, the physiological variation of baseline endothelial function of intrarenal arteries correlates with the severity of renal damage in response to a subsequent specific renal injury. However, whether such a variation in endothelial function may also condition or predict the variable response to angiotensin-converting enzyme-inhibiting treatment in these individuals has not been addressed before. To study this, 5/6 nephrectomy was performed to induce renal injury and chronic kidney disease in a group of healthy Wistar rats. At the time of nephrectomy, interlobar arteries were obtained from the extirpated right kidney and studied in vitro for endothelium-dependent relaxation to acetylcholine. Six weeks thereafter, treatment with lisinopril was started (n = 11) and continued for 9 wk. Proteinuria (metabolic cages) and systolic blood pressure (SBP; tail cuff) were evaluated weekly, and these were analyzed in relation to renal endothelial function at baseline. 5/6 Nephrectomy induced an increase in SBP and progressive proteinuria. Treatment with lisinopril reduced SBP and slowed proteinuria, albeit to a variable degree among individuals. The acetylcholine-induced renal artery dilation at baseline negatively correlated with lisinopril-induced reduction of proteinuria (r(2) = 0.648, P = 0.003) and with the decrease in SBP (r(2) = 0.592, P = 0.006). Our data suggest that angiotensin-converting enzyme-inhibitor attenuates the progression of renal damage the most in those individuals with decreased basal renal endothelial-mediated vasodilation.

Haemodynamic and renal sympathetic responses to V1b vasopressin receptor activation within the paraventricular nucleus

NEW FINDINGS

What is the central question of this study? Does antagonism of V1b receptors prevent the haemodynamic and renal sympathetic nerve responses that occur with application of exogenous vasopressin into the paraventricular nucleus (PVN) of conscious, chronically instrumented rats? What is the main finding and its importance? Microinjection of vasopressin into the PVN increased mean arterial pressure, heart rate and renal sympathetic nerve activity, all of which were inhibited by pre-injection of the PVN with the V1b antagonist, nelivaptan. The administered vasopressin did not enter the peripheral circulation or increase plasma vasopressin. Ganglionic blockade prevented each of the responses, consistent with mediation by enhanced sympathetic output rather than an increase in circulating vasopressin. Vasopressin (VP) participates in regulation of haemodynamics and volume. Besides more classical actions as a circulating hormone, VP may act via release from axons and dendrites within the CNS. The paraventricular nucleus (PVN) possesses vasopressinergic neurons and a dense complement of VP receptors, including the V1b receptor, which has been implicated in several types of stress responses. We tested the hypothesis that antagonism of V1b receptors will prevent VP-induced increases in mean arterial pressure (MAP), heart rate (HR) and renal sympathetic nerve activity (RSNA). Studies were performed in conscious male Sprague-Dawley rats chronically instrumented with vascular catheters, renal nerve electrodes and a cannula stereotaxically directed into the PVN. Unilateral microinjection of VP into the PVN significantly increased MAP, HR and RSNA, peaking at 10 min. Pre-injection of the PVN with the selective V1b receptor antagonist, nelivaptan, did not alter baseline values but blocked the responses to VP. Ganglionic blockade with chlorisondamine decreased MAP and HR and abolished their increase in response to subsequent PVN application of VP. Injection of VP into the PVN did not alter plasma VP levels. Paraventricular nucleus injection with radiolabelled VP resulted in negligible radiolabelled VP in peripheral blood. These findings support the concept that, in basal conditions, PVN V1b receptor activation (rather than VP release into the periphery) may be implicated in the increases in MAP, HR and RSNA due to increased sympathetic outflow. While the role of V1a and oxytocin receptors cannot be excluded, these data suggest that further studies of the role of V1b receptor activation by endogenous VP during stress to effect neuroexcitation are warranted.

Neutrophil Depletion Attenuates Placental Ischemia-Induced Hypertension in the Rat

Preeclampsia is characterized by reduced placental perfusion with placental ischemia and hypertension during pregnancy. Preeclamptic women also exhibit a heightened inflammatory state and greater number of neutrophils in the vasculature compared to normal pregnancy. Since neutrophils are associated with tissue injury and inflammation, we hypothesized that neutrophils are critical to placental ischemia-induced hypertension and fetal demise. Using the reduced uteroplacental perfusion pressure (RUPP) model of placental ischemia-induced hypertension in the rat, we determined the effect of neutrophil depletion on blood pressure and fetal resorptions. Neutrophils were depleted with repeated injections of polyclonal rabbit anti-rat polymorphonuclear leukocyte (PMN) antibody (antiPMN). Rats received either antiPMN or normal rabbit serum (Control) on 13.5, 15.5, 17.5, and 18.5 days post conception (dpc). On 14.5 dpc, rats underwent either Sham surgery or clip placement on ovarian arteries and abdominal aorta to reduce uterine perfusion pressure (RUPP). On 18.5 dpc, carotid arterial catheters were placed and mean arterial pressure (MAP) was measured on 19.5 dpc. Neutrophil-depleted rats had reduced circulating neutrophils from 14.5 to 19.5 dpc compared to Control, as well as decreased neutrophils in lung and placenta on 19.5 dpc. MAP increased in RUPP Control vs Sham Control rats, and neutrophil depletion attenuated this increase in MAP in RUPP rats without any effect on Sham rats. The RUPP-induced increase in fetal resorptions and complement activation product C3a were not affected by neutrophil depletion. Thus, these data are the first to indicate that neutrophils play an important role in RUPP hypertension and that cells of the innate immune system may significantly contribute to pregnancy-induced hypertension.

Glomerulosclerosis in the diet-induced obesity model correlates with sensitivity to nitric oxide inhibition but not glomerular hyperfiltration or hypertrophy

The diet-induced obesity (DIO) model is frequently used to examine the pathogenesis of obesity-related pathologies; however, only minimal glomerulosclerosis (GS) has been reported after 3 mo. We investigated if GS develops over longer periods of DIO and examined the potential role of hemodynamic mechanisms in its pathogenesis. Eight-week-old male obesity-prone (OP) and obesity-resistant (OR) rats (Charles River) were administered a moderately high-fat diet for 5 mo. Radiotelemetrically measured blood pressure, proteinuria, and GS were assessed. OP (n=10) rats developed modest hypertension (142±3 vs. 128±2 mmHg, P<0.05) and substantial levels of proteinuria (63±12 vs. 12±1 mg/day, P<0.05) and GS (7.7±1.4% vs. 0.4±0.2%) compared with OR rats (n=8). Potential hemodynamic mechanisms of renal injury were assessed in additional groups of OP and OR rats fed a moderately high-fat diet for 3 mo. Kidney weight (4.3±0.2 vs. 4.3±0.1 g), glomerular filtration rate (3.3±0.3 vs. 3.1±0.1 ml/min), and glomerular volume (1.9±0.1 vs. 2.0±0.1 μm3×10(-6)) were similar between OP (n=6) and OR (n=9) rats. Renal blood flow autoregulation was preserved in both OP (n=7) and OR (n=7) rats. In contrast, Nω-nitro-L-arginine methyl ester (L-NAME) administration in conscious, chronically instrumented OP (n=11) rats resulted in 15% and 39% increases in blood pressure and renal vascular resistance, respectively, and a 16% decrease in renal blood flow. Minimal effects of L-NAME were seen in OR (n=9) rats. In summary, DIO-associated GS is preceded by an increased hemodynamic sensitivity to L-NAME but not renal hypertrophy or hyperfiltration.

Hemodynamic basis for the limited renal injury in rats with angiotensin II-induced hypertension

ANG II is thought to increase the susceptibility to hypertension-induced renal disease (HIRD) via blood pressure (BP)-dependent and BP-independent pathways; however, the quantitative relationships between BP and HIRD have not been examined in ANG II-infused hypertensive rats. We compared the relationship between radiotelemetrically measured BP and HIRD in Sprague-Dawley rats (Harlan) chronically administered ANG II (300-500 ng·kg(-1)·min(-1), n = 19) for 4 wk versus another commonly employed pharmacological model of hypertension induced by the chronic administration of N(ω)-nitro-l-arginine methyl ester (l-NAME, 50 mg·kg(-1)·day(-1), n = 23). [DOSAGE ERROR CORRECTED]. Despite the significantly higher average systolic BP associated with ANG II (191.1 ± 3.2 mmHg) versus l-NAME (179.9 ± 2.5 mmHg) administration, the level of HIRD was very modest in the ANG II versus l-NAME model as evidenced by significantly less glomerular injury (6.6 ± 1.3% vs. 11.3 ± 1.5%, respectively), tubulointerstitial injury (0.3 ± 0.1 vs. 0.7 ± 0.1 injury score, respectively), proteinuria (66.3 ± 10.0 vs. 117.5 ± 10.1 mg/day, respectively), and serum creatinine levels (0.5 ± 0.04 vs. 0.9 ± 0.07 mg/dl, respectively). Given that HIRD severity is expected to be a function of renal microvascular BP transmission, BP-renal blood flow (RBF) relationships were examined in additional conscious rats administered ANG II (n = 7) or l-NAME (n = 8). Greater renal vasoconstriction was observed during ANG II versus l-NAME administration (41% vs. 23% decrease in RBF from baseline). Moreover, administration of ANG II, but not l-NAME, led to a unique BP-RBF pattern in which the most substantial decreases in RBF were observed during spontaneous increases in BP. We conclude that the hemodynamic effects of ANG II may mediate the strikingly low susceptibility to HIRD in the ANG II-infused model of hypertension in rats.

Critical blood pressure threshold dependence of hypertensive injury and repair in a malignant nephrosclerosis model

Most patients with essential hypertension do not exhibit substantial renal damage. Renal autoregulation by preventing glomerular transmission of systemic pressures has been postulated to mediate this resistance. Conversely, malignant nephrosclerosis (MN) has been postulated to develop when severe hypertension exceeds a critical ceiling. If the concept is valid, even modest blood pressure (BP) reductions to below this threshold regardless of antihypertensive class (1) should prevent MN and (2) lead to the healing of the already developed MN lesions. Both predicates were tested using BP radiotelemetry in the stroke-prone spontaneously hypertensive rats receiving 1% NaCl as drinking fluid for 4 weeks. Severe hypertension (final 2 weeks average systolic BP, >200 mm Hg) and MN (histological damage score 36±5; n=27) developed in the untreated stroke-prone spontaneously hypertensive rats but were prevented by all antihypertensive classes (enalapril [n=15], amlodipine [n=13], or a hydralazine/hydrochlorothiazide combination [n=15]) if the final 2-week systolic BP remained <190 mm Hg. More impressively, modest systolic BP reductions to 160 to 180 mm Hg (hydralazine/hydrochlorothiazide regimen) initiated at ≈4 weeks in additional untreated rats after MN had already developed (injury score 35±4 in the right kidney removed before therapy) led to a striking resolution of the vascular and glomerular MN injury over 2 to 3 weeks (post-therapy left kidney injury score 9±2, P<0.0001; n=27). Proteinuria also declined rapidly from 122±9.5 mg/24 hours before therapy to 20.5±3.6 mg 1 week later. These data clearly demonstrate the barotrauma-mediated pathogenesis of MN and the striking capacity for spontaneous and rapid repair of hypertensive kidney damage if new injury is prevented.

Genetic variants on rat chromosome 8 exhibit profound effects on hypertension severity and survival during nitric oxide inhibition in spontaneously hypertensive rats

BACKGROUND

Hypertension and mortality is aggravated by nitric oxide inhibition with N(G)-nitro-L-arginine methyl ester (L-NAME) in spontaneously hypertensive rats (SHRs) but not in Munich Wistar Frömter (MWF) rats. MWF rats carry major albuminuria quantitative trait loci on rat chromosome (RNO) 6 and RNO8; susceptibility of SHRs to L-NAME is enhanced by transfer of RNO6 from MWF rats into the SHR background. Here, we tested whether the sensitivity to L-NAME in SHRs is affected by transfer of RNO8 from MWF rats in consomic SHR-8(MWF) rats.

METHODS

In study 1, we analyzed survival in male SHR and SHR-8(MWF) rats in response to 18 weeks of treatment with either normal drinking water (vehicle-treated) or water containing 20mg/L L-NAME. In study 2, we analyzed blood pressure and renal damage in both strains in response to 6 weeks of treatment with L-NAME compared with vehicle-treated groups.

RESULTS

In study 1, starting after 6 weeks of treatment with L-NAME, mortality reached 90% in SHRs in contrast with the group of L-NAME treated SHR-8(MWF) rats (P < 0.0001) in which all rats survived similar to vehicle-treated rats. In study 2, L-NAME resulted in a more pronounced increase in mean arterial blood pressures in SHRs compared with SHR-8(MWF) rats (216 ± 6 vs. 180 ± 11 mm Hg; P < 0.05). In contrast, tubulointerstitial kidney damage was even lower in SHRs compared with SHR-8(MWF) rats after L-NAME treatment (P < 0.05), whereas albuminuria was not different between strains.

CONCLUSIONS

The blood pressure increase and impaired survival of SHRs in response to nitric oxide inhibition is profoundly influenced by genes on RNO8.

Paraventricular nucleus control of blood pressure in two-kidney, one-clip rats: effects of exercise training and resting blood pressure

Exercise-induced changes in γ-aminobutyric acid (GABA) or nitric oxide signaling within the paraventricular nucleus (PVN) have not been studied in renovascular hypertension. We tested whether exercise training decreases mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA) in two-kidney, one-clip (2K-1C) hypertensive rats due to enhanced nitric oxide or GABA signaling within PVN. Conscious, unrestrained male Sprague-Dawley rats with either sham (Sham) or right renal artery clipping (2K-1C) were assigned to sedentary (SED) or voluntary wheel running (ExT) for 6 or 12 wk. MAP and angiotensin II (ANG II) were elevated in 2K-1C SED rats. The 2K-1C ExT rats displayed lower MAP at 6 wk that did not decline further by 12 wk. Plasma ANG II was lower in 2K-1C ExT rats. Increases in MAP, heart rate, and RSNA to blockade of PVN nitric oxide in 2K-1C SED rats were attenuated compared with either Sham group. Exercise training restored the responses in 2K-1C ExT rats. The increase in MAP in response to bicuculline was inversely correlated with baseline MAP. The rise in MAP was lower in 2K-1C SED vs. either Sham group and was normalized in the 2K-1C ExT rats. Paradoxically, heart rate and RSNA responses were not diminished in 2K-1C SED rats but were significantly lower in the 2K-1C ExT rats. Thus the decrease in arterial pressure in 2K-1C hypertension associated with exercise training is likely due to diminished excitatory inputs to PVN because of lower ANG II and higher nitritergic tone rather than enhanced GABA inhibition of sympathetic output.

An acute rat in vivo screening model to predict compounds that alter blood glucose and/or insulin regulation

INTRODUCTION

Drug-induced glucose dysregulation and insulin resistance have been associated with weight gain and potential induction and/or exacerbation of diabetes mellitus in the clinic suggesting they may be safety biomarkers when developing antipsychotics. Glucose and insulin have also been suggested as potential efficacy biomarkers for some oncology compounds. The objective of this study was to qualify a medium throughput rat in vivo acute Intravenous Glucose Tolerance Test (IVGTT) for predicting compounds that will induce altered blood glucose and/or insulin levels.

METHODS

Acute and sub-chronic studies were performed to qualify an acute IVGTT model. Double cannulated male rats (Han-Wistar and Sprague-Dawley) were administered vehicle, olanzapine, aripiprazole or other compounds at t=-44min for acute studies and at time=-44min on the last day of dosing for sub-chronic studies, treated with dextrose (time=0min; i.v.) and blood collected using an automated Culex® system for glucose and insulin analysis (time=-45, -1, 2, 10, 15, 30, 45, 60, 75, 90, 120, 150 and 180min).

RESULTS

Olanzapine significantly increased glucose and insulin area under the curve (AUC) values while aripiprazole AUC values were similar to control, in both acute and sub-chronic studies. All atypical antipsychotics evaluated were consistent with literature references of clinical weight gain. As efficacy biomarkers, insulin AUC but not glucose AUC values were increased with a compound known to have insulin growth factor-1 (IGF-1) activity, compared to control treatment.

DISCUSSION

These studies qualified the medium throughput acute IVGTT model to more quickly screen compounds for 1) safety - the potential to elicit glucose dysregulation and/or insulin resistance and 2) efficacy - as a surrogate for compounds affecting the glucose and/or insulin regulatory pathways. These data demonstrate that the same in vivo rat model and assays can be used to predict both clinical safety and efficacy of compounds.

Blood pressure-renal blood flow relationships in conscious angiotensin II- and phenylephrine-infused rats

Chronic ANG II infusion in rodents is widely used as an experimental model of hypertension, yet very limited data are available describing the resulting blood pressure-renal blood flow (BP-RBF) relationships in conscious rats. Accordingly, male Sprague-Dawley rats (n = 19) were instrumented for chronic measurements of BP (radiotelemetry) and RBF (Transonic Systems, Ithaca, NY). One week later, two or three separate 2-h recordings of BP and RBF were obtained in conscious rats at 24-h intervals, in addition to separate 24-h BP recordings. Rats were then administered either ANG II (n = 11, 125 ng·kg(-1)·min(-1)) or phenylephrine (PE; n = 8, 50 mg·kg(-1)·day(-1)) as a control, ANG II-independent, pressor agent. Three days later the BP-RBF and 24-h BP recordings were repeated over several days. Despite similar increases in BP, PE led to significantly greater BP lability at the heart beat and very low frequency bandwidths. Conversely, ANG II, but not PE, caused significant renal vasoconstriction (a 62% increase in renal vascular resistance and a 21% decrease in RBF) and increased variability in BP-RBF relationships. Transfer function analysis of BP (input) and RBF (output) were consistent with a significant potentiation of the renal myogenic mechanism during ANG II administration, likely contributing, in part, to the exaggerated reductions in RBF during periods of BP elevations. We conclude that relatively equipressor doses of ANG II and PE lead to greatly different ambient BP profiles and effects on the renal vasculature when assessed in conscious rats. These data may have important implications regarding the pathogenesis of hypertension-induced injury in these models of hypertension.

Renal microvascular dysfunction, hypertension and CKD progression

PURPOSE OF REVIEW

Despite apparent blood pressure (BP) control and renin-angiotensin system (RAS) blockade, the chronic kidney disease (CKD) outcomes have been suboptimal. Accordingly, this review is addressed to renal microvascular and autoregulatory impairments that underlie the enhanced dynamic glomerular BP transmission in CKD progression.

RECENT FINDINGS

Clinical data suggest that failure to achieve adequate 24-h BP control is likely contributing to the suboptimal outcomes in CKD. Whereas evidence continues to accumulate regarding the importance of preglomerular autoregulatory impairment to the dynamic glomerular BP transmission, emerging data indicate that nitric oxide-mediated efferent vasodilation may play an important role in mitigating the consequences of glomerular hypertension. By contrast, the vasoconstrictor effects of angiotensin II are expected to potentially reduce glomerular barotrauma and possibly enhance ischemic injury. When adequate BP measurement methods are used, the evidence for BP-independent injury initiating mechanisms is considerably weaker and the renoprotection by RAS blockade largely parallels its antihypertensive effectiveness.

SUMMARY

Adequate 24-h BP control presently offers the most feasible intervention for reducing glomerular BP transmission and improving suboptimal outcomes in CKD. Investigations addressed to improving myogenic autoregulation and/or enhancing nitric oxide-mediated efferent dilation in addition to the more downstream mediators may provide additional future therapeutic targets.

Complement activation is critical for placental ischemia-induced hypertension in the rat

Preeclampsia is a major obstetric problem defined by new-onset hypertension and proteinuria associated with compromised placental perfusion. Although activation of the complement system is increased in preeclampsia compared to normal pregnancy, it remains unclear whether excess complement activation is a cause or consequence of placental ischemia. Therefore, we hypothesized that complement activation is critical for placental ischemia-induced hypertension. We employed the reduced utero-placental perfusion pressure (RUPP) model of placental ischemia in the rat to induce hypertension in the third trimester and evaluated the effect of inhibiting complement activation with a soluble recombinant form of an endogenous complement regulator, human complement receptor 1 (sCR1; CDX-1135). On day 14 of a 21-day gestation, rats received either RUPP or Sham surgery and 15 mg/kg/day sCR1 or saline intravenously on days 14-18. Circulating complement component 3 decreased and complement activation product C3a increased in RUPP vs. Sham (p<0.05), indicating complement activation had occurred. Mean arterial pressure (MAP) measured on day 19 increased in RUPP vs. Sham rats (109.8±2.8 mmHg vs. 93.6±1.6 mmHg). Treatment with sCR1 significantly reduced elevated MAP in RUPP rats (98.4±3.6 mmHg, p<0.05) and reduced C3a production. Vascular endothelial growth factor (VEGF) decreased in RUPP compared to Sham rats, and the decrease in VEGF was not affected by sCR1 treatment. Thus, these studies have identified a mechanistic link between complement activation and the pregnancy complication of hypertension apart from free plasma VEGF and have identified complement inhibition as a potential treatment strategy for placental ischemia-induced hypertension in preeclampsia.