We investigated glucose tolerance and left ventricular contractile performance in 4 frequently used mouse strains (Swiss, C57BL/6J, DBA2, and BalbC) at 24 weeks. Glucose tolerance was tested by measuring blood glucose levels in time after intraperitoneal glucose injection (2 mg/g body weight). Left ventricular contractility was assessed by pressure-conductance analysis. Peak glucose levels and glucose area under the curve were higher (all
Multiple transgenic mouse models have been and are being developed in cardiovascular research to study hypertension [
Evaluating these disease models can be confounded not only by differences in gender [
We hypothesize that four frequently used mice strains (C57BL/6J, Swiss, BalbC, and DBA2 mice) exhibit a significantly different baseline left ventricular contractility and that glucose handling capacity is also different between these 4 strains. As glucose handling capacity could play an important role in the development of diabetes mellitus type 2 [
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Although it is thus clear that these 4 strains have different metabolic characteristics, with influence on cardiovascular disease development, no direct comparison of glucose tolerance has been published in these strains, nor was left ventricular contractility systematically compared. We therefore performed in vivo intraperitoneal glucose tolerance testing and cardiac pressure-conductance measurements in Swiss, C57BL/6J, DBA2, and BalbC mice at 24 weeks.
19 C57BL/6J, 14 BalbC, 14 DBA2, and 18 Swiss mice were investigated. All animals were purchased form Jackson Laboratories (Bar Harbour, Maine, USA) and housed at 22°C on a fixed 12-hour light-dark cycle. The investigation conforms with the Guide for the Care and Use of Laboratory Animals published by the US National Institutes of Health (NIH Publication no. 85-23, revised 1996). All experimental protocols were approved by the Institutional Animal Care Commission and Ethical Committee of the K.U.Leuven.
Intraperitoneal glucose tolerance testing was performed at 23 weeks with a bolus glucose injection of 2 mg/g body weight and followed by measuring the blood glucose levels at fixed timepoints (fasting and after 15, 30, 60, 120, and 240 minutes, resp.).
At 24 weeks, mice were anesthetized with a mixture of urethane (1.2 g/kg) and alpha-chloralose (50 mg/kg) injected intraperitoneally. Mice were placed on a heating pad, and rectal temperature was kept between 36.0 and 37.5°C. Surgery was performed under a surgical microscope. Through a midline neck incision, a tracheostomy was performed, and mechanical ventilation started with room air (Minivent 845; Hugo Sachs/Harvard Apparatus, March-Hugstetten, Germany). Subsequently, a 1.4 Fr high-fidelity pressure-conductance catheter (1.4-Fr, SPR-839; Millar Instruments, Houston, TX) was inserted through the right carotid artery into the left ventricle, and left ventricular pressure-conductance measurements were started. After stabilization of the hemodynamic situation, baseline pressure-volume (PV) loops were recorded (PowerLab/4SP ADInstruments, Castle Hill, Australia), while the ventilation was momentarily turned off to avoid respiratory fluctuation of cardiac signals. The inferior caval vein was compressed between liver and diaphragm with a cotton swab without opening the abdomen, while PV loops were recorded to obtain occlusion loops with progressively lowering preload. Afterwards a 24G catheter was introduced in the right jugular vein, and parallel volume was determined by a bolus injection of 3
Analysis after IPGTT testing included calculation of peak glucose levels and area under the curve. Peak glucose levels were obtained 30 minutes after bolus injection and expressed as mg/dL. Areas under the curve were calculated as the sum of the measured values, normalized for the time interval, and expressed in mg·h/dL.
Analysis of the pressure-conductance data was performed using PVAN 3.2 software (Millar Instruments, Houston, TX). A conductance-volume calibration line was constructed with the cuvette data. All data were corrected for parallel volume and expressed in absolute volumes. Only technically acceptable loops were included in the analysis for each experiment [
Data are expressed as mean ± standard deviation. Significant changes were detected by single regression, and normality was assessed by the Shapiro-Wilk
Between 12 and 24 weeks of age, 1 BalbC, 1 DBA2, and 2 Swiss mice died a sudden unexplained death. During the experimental procedure, 1 Swiss mouse and 2 BalbC mice died during the baseline pressure-conductance measurements. Under increasing isoproterenol dose, in total, 4 Swiss, 6 C57BL/6J, 2 DBA2, and 7 BalbC mice died before 90 ng/kg/min isoproterenol was reached. Survival during the experimental protocol was significantly lower in BalbC mice versus the other strains and occurred mainly during isoproterenol infusion (
Heart weight (HW), body weight (BW), tibial length (TL), and HW/TL were significantly higher in Swiss mice at 24 weeks versus all other strains (
Morphology in 4 mice background strains. All data are expressed as mean ± standard deviation. Values marked with * are
Swiss | C57BL6/J | DBA2 | BalbC | |
---|---|---|---|---|
Body weight (BW) (g) | 44.8 ± 5.1* | 26.1 ± 4.6 | 27.1 ± 2.7 | 27.0 ± 2.8 |
Heart weight (g) | 0.19 ± 0.03* | 0.14 ± 0.02 | 0.14 ± 0.02 | 0.14 ± 0.01 |
Tibial length (um) | 193 ± 7* | 185 ± 7 | 175 ± 3 | 174 ± 4 |
HW/TL (g/100 um) | 99.36 ± 16.08* | 77.62 ± 10.99 | 82.94 ± 14.21 | 79.64 ± 8.66 |
HW/BW (mg/g) | 4.26 ± 0.41* | 5.51 ± 0.31 | 5.31 ± 0.48 | 5.13 ± 0.31 |
Fasting glucose levels at 24 weeks were comparable between the four studied strains. During intraperitoneal glucose tolerance testing, all mice showed a strong increase in blood glucose values (Figure
Intraperitoneal glucose tolerance testing in 4 background strains at 23 weeks. Lean values are similar between the studied groups. Values after 15, 30, and 60 minutes are significantly higher in C57BL/6J mice versus other strains. Values with
At baseline, Swiss mice had the fastest
Pressure-conductance analysis in 4 mice background strains. All data are expressed as mean ± standard deviation. Values marked with
Heart rate (bpm) | 623 ± 71* | 569 ± 43 | 545 ± 40 | 566 ± 35 |
Ves (uL) | 10.9 ± 5.1 | 16.5 ± 6.2∆ | 9.0 ± 3.1 | 18.0 ± 4.6∆ |
Ved (uL) | 30.7 ± 9.1 | 31.8 ± 7.2 | 25.8 ± 7.1∆ | 30.0 ± 9.9 |
Pes (mmHg) | 69.5 ± 9.9 | 76.8 ± 8.2 | 71.9 ± 8.0 | 84.2 ± 13.6* |
Ped (mmHg) | 1.2 ± 1.7 | 1.9 ± 2.0 | 1.2 ± 1.2 | 2.9 ± 2.9 |
90 ± 5 | 84 ± 6∆ | 88 ± 7 | 89 ± 11 | |
EF (%) | 70.4 ± 11.2∆ | 55.9 ± 13.4 | 71.8 ± 9.2∆ | 47.8 ± 5.7 |
Cardiac output (uL/min) | 14038 ± 4530* | 10405 ± 2683 | 10438 ± 3251 | 8466 ± 3013 |
11746 ± 2105* | 7162 ± 1563 | 9420 ± 2268 | 7760 ± 1581 | |
−7738 ± 2098 | −7948 ± 1242 | −8204 ± 1458 | −8547 ± 1464 | |
Tau | 4.1 ± 0.7 | 5.2 ± 0.9∆ | 4.5 ± 0.7 | 5.2 ± 0.8∆ |
Arterial elastance (Ea) (mmHg/ | 3.4 ± 1.2 | 4.4 ± 1.2 | 4.1 ± 1.1 | 6.2 ± 1.9* |
Ees | 9.5 ± 5.0 | 6.1 ± 2.1 | 8.4 ± 3.8 | 8.2 ± 2.9 |
EDPVR (mmHg/ | 0.265 ± 0.082 | 0.218 ± 0.074 | 0.316 ± 0.079 | 0.415 ± 0.159* |
Preload recruitable stroke work (PRSW) (mmHg) | 92 ± 22 | 88 ± 21 | 94 ± 25 | 82 ± 23 |
Efficiency (SW/PVA) | 0.78 ± 0.054 | 0.70 ± 0.08 | 0.70 ± 0.13 | 0.60 ± 0.11* |
The load-independent
All species showed an
Pressure-conductance analysis in 4 mice background strains under increasing isoproterenol. All data are expressed as mean ± standard deviation. Values marked with * are
Isoproterenol |
HR |
Ves |
Ved |
Pes |
Ped |
EF |
CO | Ees |
EDPVR |
PRSW |
Efficiency | |
---|---|---|---|---|---|---|---|---|---|---|---|---|
Swiss | 0 | 623 ± 71 | 10.9 ± 5.1 | 30.7 ± 9.1 | 69.5 ± 9.9 | 1.2 ± 1.7 | 70 ± 11 | 14038 ± 4530 | 9.5 ± 5.0 | 0.265 ± 0.082 | 92 ± 22 | 0.78 ± 0.05 |
3 | 681 ± 77† | 10.3 ± 7.0 | 30.1 ± 9.7 | 65.9 ± 14.9 | −2.1 ± 2.2† | 72 ± 13 | 15832 ± 5374† | 8.9 ± 4.2 | 0.221 ± 0.065 | 101 ± 18 | 0.79 ± 0.04 | |
90 | 720 ± 79‡ | 6.8 ± 5.7 | 24.9 ± 7.2* | 56.1 ± 17.7‡ | −5.1 ± 2.1*‡ | 79 ± 16 | 15537 ± 5549 | 9.3 ± 6.1 | 0.239 ± .087 | 82 ± 39 | 0.76 ± 0.050 | |
C57BL6/J | 0 | 569 ± 43 | 16.5 ± 6.2 | 31.8 ± 7.2 | 76.8 ± 8.2 | 1.9 ± 2.0 | 56 ± 13 | 10405 ± 2683 | 6.1 ± 2.1 | 0.218 ± 0.074 | 88 ± 21 | 0.70 ± 0.08 |
3 | 586 ± 50* | 13.6 ± 7.1* | 31.2 ± 7.6 | 64.1 ± 9.6† | 0 ± 2.5 | 64 ± 17† | 12196 ± 3405 | 6.2 ± 1.8 | 0.216 ± 0.076 | 102 ± 24 | 0.69 ± 0.05 | |
90 | 681 ± 41*‡ | 4.7 ± 5.6*‡ | 24.7 ± 8.4‡ | 45.0 ± 13.8*‡ | −2.8 ± 2.5*‡ | 88 ± 14‡ | 16245 ± 4818‡ | 11.0 ± 5.5 | 0.256 ± 0.084 | 106 ± 30 | 0.77 ± 0.14 | |
DBA2 | 0 | 545 ± 40 | 9.0 ± 3.1 | 25.8 ± 7.1 | 71.9 ± 8.0 | 1.2 ± 1.2 | 72 ± 9 | 10438 ± 3251 | 8.4 ± 3.8 | 0.316 ± 0.079 | 94 ± 25 | 0.70 ± 0.13 |
3 | 615 ± 50† | 5.0 ± 3.8* | 21.4 ± 3.5* | 87.1 ± 23.4 | −1.3 ± 1.2† | 83 ± 16* | 11634 ± 3246 | 14.7 ± 6.9† | 0.266 ± 0.133 | 102 ± 23 | 0.75 ± 0.09 | |
90 | 671 ± 39‡ | 3.9 ± 3.0 | 15.3 ± 3.5†‡ | 61.5 ± 16.4 | −4.7 ± 2.0*‡ | 83 ± 15 | 9918 ± 3574* | 15.6 ± 5.8‡ | 0.239 ± 0.049 | 94 ± 27 | 0.74 ± 0.07 | |
BalbC | 0 | 566 ± 35 | 17.5 ± 4.6 | 30.0 ± 9.9 | 84.20 ± 13.62 | 2.9 ± 2.9 | 48 ± 6 | 8466 ± 3013 | 8.2 ± 2.9 | 0.415 ± 0.159 | 82 ± 23 | 0.60 ± 0.11 |
3 | 586 ± 26* | 16.4 ± 4.8 | 28.4 ± 9.9* | 86.2 ± 8.5 | 2.8 ± 3.1* | 49 ± 4 | 8464 ± 2804 | 8.5 ± 2.6 | 0.382 ± 0.113 | 93 ± 19* | 0.63 ± 0.11 | |
90 | 733 ± 50*‡ | 4.9 ± 4.1‡ | 19.3 ± 4.5‡ | 61.5 ± 19.5 | −2.0 ± 2.8*‡ | 81 ± 13‡ | 11760 ± 1958 | 11.1 ± 1.7‡ | 0.314 ± 0.105*‡ | 117 ± 6*‡ | 0.70 ± 0.06*‡ |
Illustration of the increase in heart rate under isoproterenol infusion in the four studied mice background strains.
Under isoproterenol,
This study shows that left ventricular contractility and glucose handling capacity are significantly different in four mice background strains frequently used in cardiovascular research. Overall survival under isoproterenol infusion with invasive left ventricular contractility measurements was different between the studied strains.
Body weight, heart weight, and left ventricular weight are significantly higher in Swiss versus the other studied strains. Although Swiss mice are at 24 weeks heavier than the other background strains, tibial length did not show an increase to the same extent as the heart weight increase, and this results in a higher HW/TL. In contrast, HW/BW was lower in Swiss mice, because BW increase was more pronounced than the HW increase. HW over body surface area did not show significant differences between the 4 groups. When LV hypertrophy is studied, it is probably more safe to report HW/TL, HW/BW, and HW/BSA simultaneously.
IPGTT in C57BL67/J showed higher peak glucose levels and a higher AUC versus the other strains. This suggests that capacity for glucose handling at 24 weeks is lower in C57BL/6J, although fasting glucose levels are not increased. These findings are in accordance with the findings of Gerich [
Swiss mice exhibited a higher heart rate than the other strains, despite their higher body weight. An increased cardiac output to meet the metabolic demands of a larger individual is thus obtained by a combination of a higher resting HR and a relatively high SV.
Arterial elastance (Ea), a parameter for afterload, was higher in BalbC mice. Afterload is influenced by peripheral vascular resistance, arterial compliance, aortic characteristic impedance, and systolic and diastolic time intervals, and therefore any increase in afterload results in a decreased stroke volume, unless contractility is increased. The higher Ea can partially be explained by the higher systolic blood pressures described in BalbC mice (Schlager and sides [
Isoproterenol affects the
These findings suggest that the cardiac
Glucose handling capacity was clearly reduced in C57BL/6J mice at 24 weeks. Although cardiac performance parameters were significantly different between the four studied strains, C57BL/6J mice did not show a difference in cardiac performance. Thus, the contractility changes that have been reported for experimental mice models of diabetes mellitus type 2 do not seem to precede the diabetic state. Most likely, pronounced and sustained hyperglycemia is required to clearly influence cardiac performance parameters.
Swiss mice were significantly larger at 24 weeks with inconsistent cardiac hypertrophy parameters. Glucose handling capacity was reduced in C57BL/6J mice, but this did not lead to a pronounced difference in cardiac performance. Survival under increasing isoproterenol dose was significantly lower in the BalbC mice. Although baseline cardiac performance was different between the 4 studied strains, the load-independent PRSW was comparable.
Wouter Oosterlinck received a Ph.D. fellowship of the Research Foundation-Flanders (FWO). This work was supported by a research grant of the Research Fund K.U.Leuven, PF/10/014, and a grant of the Scientific Research Fund-Flanders (F.W.O.-Vlaanderen G.0966.11).