Role of protein kinase C in angiotensin II-induced constriction of renal microvessels

Role of protein kinase C in angiotensin II-induced constriction of renal microvesselsBackgroundAlthough angiotensin II (Ang II) exerts its action through multiple vasomotor mechanisms, the contribution of phosphoinositol hydrolysis products to Ang II-induced renal vasoconstriction remains undetermined.MethodsThe role of protein kinase C (PKC) in Ang II-induced afferent (AFF) and efferent (EFF) arteriolar constriction was examined using the isolated perfused hydronephrotic rat kidney.ResultsAng II (0.3 nmol/L)-induced EFF constriction was refractory to inhibition of voltage-dependent calcium channels by pranidipine (1 μmol/L, 19 ± 2% reversal) but was completely reversed by a PKC inhibitor, chelerythrine (1 μmol/L, 96 ± 2% reversal). Furthermore, direct PKC activation by phorbol myristate acetate (PMA; 1 μmol/L) caused prominent EFF constriction, and this constriction was inhibited by manganese and free calcium medium. In contrast, Ang II-induced AFF constriction was completely abolished by pranidipine (98 ± 4% reversal) and was partially inhibited by chelerythrine (55 ± 3% reversal). Although PMA elicited marked AFF constriction, this constriction was insensitive to the calcium antagonist, but was totally inhibited by manganese or free calcium medium.ConclusionsPKC plays an obligatory role in Ang II-induced EFF constriction that requires extracellular calcium entry through nonselective cation channels. In contrast, in concert with our recent findings demonstrating a complete dilation by thapsigargin, Ang II-induced AFF constriction is mainly mediated by inositol trisphosphate (IP3) and voltage-dependent calcium channel pathways, but could not be attributed to the PKC-activated calcium entry pathway (for example, nonselective cation channels). Rather, Ang II-stimulated PKC may cross-talk to the IP3/voltage-dependent calcium channel pathway and could modulate the vasoconstrictor mechanism of the AFF. Thus, the role of PKC during Ang II stimulation differs in AFF and EFF, which may constitute segmental heterogeneity in the renal microvasculature

Ovariectomy enhances renal cortical expression and function of cyclooxygenase-2

Ovariectomy enhances renal cortical expression and function of cyclooxygenase-2.BackgroundCyclooxygenase-2 (COX-2) inhibitors are used as analgesics in postmenopausal women, who develop edema and require a salt-restricted diet. This study was performed to determine the renal expression of COX-2 and on COX-2–dependent regulation of renal blood flow (RBF) in ovariectomized rats.MethodsSprague-Dawley rats were divided into 4 groups: sham-operated rats fed a normal-salt diet (Sh+NS) or a low-salt diet (Sh+LS), and bilaterally ovariectomized rats fed a normal-salt diet (Ox+NS) or a low-salt diet (Ox+LS) (N = 6 in each group). Estrogen replacement therapy was performed on other ovariectomized rats. A renal clearance study was performed in anesthetized animals.ResultsOvariectomy increased renal cortical COX-2 expression independently of dietary salt intake (Sh+NS <Ox+N; Sh+LS <Ox+LS). Inhibition of COX-2 by NS398 reduced the urinary excretion of 6-keto-prostaglandin F1α in all 4 groups, although the reduction was greater in the Ox+LS group than in the Ox+NS and Sh+LS groups, which in turn had a greater reduction than the Sh+NS group. RBF significantly decreased in every group except the Sh+NS group, but no effect on blood pressure, inulin clearance, or urinary sodium excretion was seen. The decrease in RBF was significantly greater in the Ox+LS group than in the Sh+LS and Ox+NS group. The decrease in RBF was dependent on cortical RBF in the Sh+LS and Ox+NS groups, and on both cortical and medullary RBF in the Ox+LS group. Estrogen replacement therapy reversed the ovariectomy-induced changes.ConclusionEstrogen-dependent COX-2 expression plays an important role in the RBF regulation in female rats

Is Pulse Pressure a Predictor of New-Onset Diabetes in High-Risk Hypertensive Patients?: A subanalysis of the Candesartan Antihypertensive Survival Evaluation in Japan (CASE-J) trial

OBJECTIVE: Hypertensive patients have an increased risk of developing diabetes. Accumulating evidence suggests a close relation between metabolic disturbance and increased arterial stiffness. Here, we examined the association between pulse pressure and the risk of new-onset diabetes in high-risk Japanese hypertensive patients. RESEARCH DESIGN AND METHODS: The Candesartan Antihypertensive Survival Evaluation in Japan (CASE-J) trial examined the effects of candesartan and amlodipine on the incidence of cardiovascular events in 4, 728 high-risk Japanese hypertensive patients. In the present study, we analyzed the relationship between pulse pressure at baseline and new-onset diabetes in 2, 685 patients without diabetes at baseline (male 1, 471; mean age 63.7 years; mean BMI 24.8 kg/m(2)) as a subanalysis of the CASE-J trial. RESULTS: During 3.3 +/- 0.8 years of follow-up, 97 patients (3.6%) developed diabetes. In multiple Cox regression analysis, pulse pressure was an independent predictor for new-onset diabetes (hazard ratio [HR] per 1 SD increase 1.44 [95% CI 1.15-1.79]) as were male sex, BMI, and additional use of diuretics, whereas age and heart rate were not. Plots of HRs for new-onset diabetes considering both systolic and diastolic blood pressure (DBP) revealed that a higher pulse pressure with a lower DBP, indicating that the increased pulse pressure was largely due to increased arterial stiffness, was strongly associated with the risk of new-onset diabetes. CONCLUSIONS: Pulse pressure is an independent predictor of new-onset diabetes in high-risk Japanese hypertensive patients. Increased arterial stiffness may be involved in the development of diabetes

Role of adenosine in the renal responses to contrast medium

Role of adenosine in the renal responses to contrast medium. Despite the development of non-ionic radiographic contrast media (CM), CM-induced nephropathy is a clinically important problem in patients with pre-existing renal insufficiency. We examined the effects of non-ionic CM (iohexol) on renal function in conscious dogs with and without renal insufficiency, and evaluated the effects of a non-selective (theophylline), an A1 selective (KW-3902), and an A2 selective adenosine antagonist (KF17837) on the renal responses to CM. In sham-operated group, iohexol (2ml/kg/min for 3min) increased effective renal plasma flow (ERPF) and glomerular filtration rate (GFR), whereas in renal insufficiency group (with subtotal nephrectomy), following transient increases in ERPF and GFR, CM markedly decreased ERPF (-46.5 ± 6.7%) and GFR (-51.2 ± 7.1%). In sham-operated group, theophylline and KF17837 markedly attenuated CM-induced increases in ERPF and GFR, while KW-3902 had no effects on CM-induced increases in ERPF or GFR. In renal insufficiency group, initial increases in ERPF and GFR were blunted by theophylline and KF17837. In contrast, the subsequent decreases in ERPF and GFR were attenuated by theophylline (%ΔERPF, -12.2 ± 3.2% vs. -46.6 ± 6.7%, P < 0.01; %ΔGFR, 4.3 ± 2.5% vs. -51.0 ± 7.1%, P < 0.01), and were completely prevented by KW-3902 (%ΔERPF, 10.8 ± 2.9%; %ΔGFR, 23.8 ± 4.4%), whereas KF17837 aggravated ERPF (-73.3 ± 5.3%) and GFR (-78.4 ± 5.3%). These data indicate that in normal renal function, iohexol elicits renal vasodilation by activating mainly the adenosine A2 receptors. In contrast, in impaired renal function, CM induces both A2 and A1 activation; the former is associated with the initial renal vasodilation, while the latter is responsible for the sustained aggravation of renal hemodynamics

Importance of rostral ventrolateral medulla neurons in determining efferent sympathetic nerve activity and blood pressure

Accentuated sympathetic nerve activity (SNA) is a risk factor for cardiovascular events. In this review, we investigate our working hypothesis that potentiated activity of neurons in the rostral ventrolateral medulla (RVLM) is the primary cause of experimental and essential hypertension. Over the past decade, we have examined how RVLM neurons regulate peripheral SNA, how the sympathetic and renin-angiotensin systems are correlated and how the sympathetic system can be suppressed to prevent cardiovascular events in patients. Based on results of whole-cell patch-clamp studies, we report that angiotensin II (Ang II) potentiated the activity of RVLM neurons, a sympathetic nervous center, whereas Ang II receptor blocker (ARB) reduced RVLM activities. Our optical imaging demonstrated that a longitudinal rostrocaudal column, including the RVLM and the caudal end of ventrolateral medulla, acts as a sympathetic center. By organizing and analyzing these data, we hope to develop therapies for reducing SNA in our patients. Recently, 2-year depressor effects were obtained by a single procedure of renal nerve ablation in patients with essential hypertension. The ablation injured not only the efferent renal sympathetic nerves but also the afferent renal nerves and led to reduced activities of the hypothalamus, RVLM neurons and efferent systemic sympathetic nerves. These clinical results stress the importance of the RVLM neurons in blood pressure regulation. We expect renal nerve ablation to be an effective treatment for congestive heart failure and chronic kidney disease, such as diabetic nephropathy

How to use marginal structural models in randomized trials to estimate the natural direct and indirect effects of therapies mediated by causal intermediates

Background. Although intention-to-treat analysis is a standard approach, additional supplemental analyses are often required to evaluate the biological relationship among interventions, intermediates, and outcomes. Therefore, we need to evaluate whether the effect of an intervention on a particular outcome is mediated by a hypothesized intermediate variable. Purpose. To evaluate the size of the direct effect in the total effect, we applied the marginal structural model to estimate the average natural direct and indirect effects in a large-scale randomized controlled trial. Method. The average natural direct effect is defined as the difference in the probability of a counterfactual outcome between the experimental and control arms, with the intermediate set to what it would have been, had the intervention been a control treatment. We considered 2 marginal structural models to estimate the average natural direct and indirect effects introduced by VanderWeele (Epidemiology 2009) and applied them in a large-scale randomized controlled trial - the Candesartan Antihypertensive Survival Evaluation in Japan (CASE-J trial) - that compared angiotensin receptor blockers and calcium-channel blockers in high-risk hypertensive patients. Results. There were no strong blood pressure-independent or dependent effects; however, a systolic blood pressure reduction of about 1.9 mmHg suppressed all events. Compared to the blood pressure-independent effects of calcium channel blockers, those of angiotensin receptor blockers contributed positively to cardiovascular and cardiac events, but negatively to cerebrovascular events. Limitations. There is a particular condition for estimating the average natural direct effect. It is impossible to check whether this condition is satisfied with the available data. Conclusion. We estimated the average natural direct and indirect effects through the achieved systolic blood pressure in the CASE-J trial. This first application of estimating the average natural effects in an RCT can be useful for obtaining an in-depth understanding of the results and further development of similar interventions