Direct monitoring pressure overload predicts cardiac hypertrophy in mice

Pressure overload (POL) is a classical model for studying cardiac hypertrophy, but there has been no direct measure of hemodynamics in a conscious ambulatory mouse model of POL. We used abdominal aortic constriction to produce POL and radiotelemetry to measure the blood pressure and heart rate for three weeks. The cardiac size correlated with the systolic pressure in the last week is better than other hemodynamic parameters. Cardiac fibrosis was more correlated to the cardiac size than to the systolic pressure. The expression of the cardiac genes that are typically associated with cardiac hypertrophy was correlated with both cardiac size and systolic pressure. In conclusion, the systolic pressure is the major determinant of cardiac hypertrophy in the murine POL model. In contrast, cardiac fibrosis shows the influence of other factors besides systolic pressure. The combination of the POL model with continuous direct measurements of hemodynamics represents a significant technological advance and will lead to an extended usefulness of POL methodologically.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/58150/2/pm7_11_001.pd

Packed Red Blood Cells Are an Abundant and Proximate Potential Source of Nitric Oxide Synthase Inhibition

<div><p>Objective</p><p>We determined, for packed red blood cells (PRBC) and fresh frozen plasma, the maximum content, and ability to release the endogenous nitric oxide synthase (NOS) inhibitors asymmetric dimethylarginine (ADMA) and monomethylarginine (LNMMA).</p><p>Background</p><p>ADMA and LNMMA are near equipotent NOS inhibitors forming blood’s total NOS inhibitory content. The balance between removal from, and addition to plasma determines their free concentrations. Removal from plasma is by well-characterized specific hydrolases while formation is restricted to posttranslational protein methylation. When released into plasma they can readily enter endothelial cells and inhibit NOS. Fresh rat and human whole blood contain substantial protein incorporated ADMA however; the maximum content of ADMA and LNMMA in PRBC and fresh frozen plasma has not been determined.</p><p>Methods</p><p>We measured total (free and protein incorporated) ADMA and LNMMA content in PRBCs and fresh frozen plasma, as well as their incubation induced release, using HPLC with fluorescence detection. We tested the hypothesis that PRBC and fresh frozen plasma contain substantial inhibitory methylarginines that can be released chemically by complete <i>in vitro</i> acid hydrolysis or physiologically at 37°C by enzymatic blood proteolysis.</p><p>Results</p><p><i>In vitro</i> strong-acid-hydrolysis revealed a large PRBC reservoir of ADMA (54.5 ± 9.7 µM) and LNMMA (58.9 ± 28.9 μM) that persisted over 42-d at 6° or -80°C. <i>In vitro</i> 5h incubation at 37°C nearly doubled free ADMA and LNMMNA concentration from PRBCs while no change was detected in fresh frozen plasma.</p><p>Conclusion</p><p>The compelling physiological ramifications are that regardless of storage age, 1) PRBCs can rapidly release pathologically relevant quantities of ADMA and LNMMA when incubated and 2) PRBCs have a protein-incorporated inhibitory methylarginines reservoir 100 times that of normal free inhibitory methylarginines in blood and thus could represent a clinically relevant and proximate risk for iatrogenic NOS inhibition upon transfusion.</p></div

Potential role of intermittent functioning of baroreflexes in the etiology of hypertension in spontaneously hypertensive rats

The spontaneously hypertensive rat (SHR) is a genetic model of primary hypertension with an etiology that includes sympathetic overdrive. To elucidate the neurogenic mechanisms underlying the pathophysiology of this model, we analyzed the dynamic baroreflex response to spontaneous fluctuations in arterial pressure in conscious SHRs, as well as in the Wistar-Kyoto (WKY), the Dahl salt-sensitive, the Dahl salt-resistant, and the Sprague-Dawley rat. Observations revealed the existence of long intermittent periods (lasting up to several minutes) of engagement and disengagement of baroreflex control of heart rate. Analysis of these intermittent periods revealed a predictive relationship between increased mean arterial pressure and progressive baroreflex disengagement that was present in the SHR and WKY strains but absent in others. This relationship yielded the hypothesis that a lower proportion of engagement versus disengagement of the baroreflex in SHR compared with WKY contributes to the hypertension (or increased blood pressure) in SHR compared with WKY. Results of experiments using sinoaortic baroreceptor denervation were consistent with the hypothesis that dysfunction of the baroreflex contributes to the etiology of hypertension in the SHR. Thus, this study provides experimental evidence for the roles of the baroreflex in long-term arterial pressure regulation and in the etiology of primary hypertension in this animal model

ADMA scaled against hemoglobin concentration over storage time at 6°C or -80°C.

<p>In an attempt to account for any dehydration of the samples under either storage condition (6°C or -80°C), we measured hemoglobin concentrations paired with each ADMA measurement to calculate ADMA to hemoglobin ratio. The time course and pattern remained unchanged over time suggesting no measurable desiccation effect on sample concentration over the 42-day storage.</p

Incubation-induced release of Free ADMA over 5h by Blood Product type.

<p>Incubation of defrosted fresh frozen plasma (open triangles), supernatants of PRBC alone (solid squares), a mixture of 1:1 PRBC and fresh frozen plasma (open circles), and a mixture of 1:3 PRBC and fresh frozen plasma (open diamonds). Repeated measures Two-way ANOVA shows significant differences of ADMA among PRBC and PRBC: fresh frozen plasma groups over the incubation period (p<0.006). Tukey’s <i>post-hoc</i> multiple comparison test revealed significant differences of ADMA (α = 0.05) among groups at individual sampling points. At three and five hour time points, ADMA in PRBC and 1:1 PRBC: fresh frozen plasma was significantly (*) higher than 1:3 PRBC: fresh frozen plasma. Hemoglobin measurements confirmed PRBC concentration and dilutions.</p

Relative methylated arginine release over 5 h from PRBC incubation.

<p>All three methylated arginines, ADMA, LNMMA, and symmetric dimethylarginine were released in proportionately similar amounts during the 5h incubation at 37°C. The starting free concentrations were different (0.58 ± 0.12, 0.08 ± 0.02, and 0.20 ± 0.12 respectively). Free ADMA, LNMMA and symmetric dimethylarginine increased significantly from baseline by 5h. Linear regression analysis failed to detect differences among methylated arginines over 5h.</p

Total methylarginines obtained by strong acid hydrolysis of pre-aliquoted PRBCs stored at 6°C or -80°C.

<p>No statistically significant differences were detected between 6°C or -80°C storage at any time (pooled to 5, 14, 28 and 42 d) for ADMA, LNMMA and symmetric dimethylarginine and no change from control was detected. It is likely that neither PRMT activity nor DDAH-induced hydrolysis was a dominating effect under these storage conditions. However, equal formation and hydrolysis cannot be ruled out.</p