Phenotyping the level of blood pressure by telemetry in mice

Improved method for surgical induction of chronic hypertension in mice

Chronic hypertension can be induced in mice by one-kidney one-clip (1K1C) or two-kidney one-clip surgery, transgenic overexpression of angiotensinogen and renin, administration of deoxycorticosterone acetate-salt, supplying Nitro-L-arginine methyl-ester in the drinking water and Angiotensin-II infusion. Although each model has its own pros and cons, selection of a model that mimics human hypertensive disease accurately is essential to ensure rigor and reproducibility in hypertension research. 1K1C mice represent an efficient, budget-friendly, and translationally capable model; however, their use in preclinical research has remained largely hindered due to concerns about potential technical complexity and lack of reported information regarding procedure-related mortality rates. Here, we describe in detail an improved version of the 1K1C surgery in mice that has zero intraoperative mortality and excellent survival rates in a long-term setting and permits the development of stable chronic hypertension and its target organ complications. Key to this outcome is unilateral nephrectomy 1 week after renal artery clipping to decelerate the blood pressure (BP) increase, which allows the organism to adapt better to the BP rise. The technical and animal welfare improvements presented here may promote the acceptance of the 1K1C model.

Harmonic Distortion of Blood Pressure Waveform as a Measure of Arterial Stiffness

Aging and disease alter the composition and elastic properties of the aortic wall resulting in shape changes in blood pressure waveform (BPW). Here, we propose a new index, harmonic distortion (HD), to characterize BPW and its relationship with other in vitro and in vivo measures. Using a Fourier transform of the BPW, HD is calculated as the ratio of energy above the fundamental frequency to that at the fundamental frequency. Male mice fed either a normal diet (ND) or a high fat, high sucrose (HFHS) diet for 2–10 months were used to study BPWs in diet-induced metabolic syndrome. BPWs were recorded for 20 s hourly for 24 h, using radiotelemetry. Pulse wave velocity (PWV), an in vivo measure of arterial stiffness, was measured in the abdominal aorta via ultrasound sonography. Common carotid arteries were excised from a subset of mice to determine the tangent modulus using biaxial tension-inflation test. Over a 24-h period, both HD and systolic blood pressure (SBP) show a large variability, however HD linearly decreases with increasing SBP. HD is also linearly related to tangent modulus and PWV with slopes significantly different between the two diet groups. Overall, our study suggests that HD is sensitive to changes in blood pressure and arterial stiffness and has a potential to be used as a noninvasive measure of arterial stiffness in aging and disease.

The sodium/proton exchanger NHA2 regulates blood pressure through a WNK4-NCC dependent pathway in the kidney

NHA2 is a sodium/proton exchanger associated with arterial hypertension in humans, but the role of NHA2 in kidney function and blood pressure homeostasis is currently unknown. Here we show that NHA2 localizes almost exclusively to distal convoluted tubules in the kidney. NHA2 knock-out mice displayed reduced blood pressure, normocalcemic hypocalciuria and an attenuated response to the thiazide diuretic hydrochlorothiazide. Phosphorylation of the thiazide-sensitive sodium/chloride cotransporter NCC and its upstream activating kinase Ste20/SPS1-related proline/alanine rich kinase (SPAK), as well as the abundance of with no lysine kinase 4 (WNK4), were significantly reduced in the kidneys of NHA2 knock-out mice. In vitro experiments recapitulated these findings and revealed increased WNK4 ubiquitylation and enhanced proteasomal WNK4 degradation upon loss of NHA2. The effect of NHA2 on WNK4 stability was dependent from the ubiquitylation pathway protein Kelch-like 3 (KLHL3). More specifically, loss of NHA2 selectively attenuated KLHL3 phosphorylation and blunted protein kinase A- and protein kinase C-mediated decrease of WNK4 degradation. Phenotype analysis of NHA2/NCC double knock-out mice supported the notion that NHA2 affects blood pressure homeostasis by a kidney-specific and NCC-dependent mechanism. Thus, our data show that NHA2 as a critical component of the WNK4-NCC pathway and is a novel regulator of blood pressure homeostasis in the kidney.

Reproducibility in animal models of hypertension: a difficult problem

In 2016, the National Institutes of Health mandated that all grant proposals enhance reproducibility through rigor and transparency. In the past few years, physiological outcomes in established animal models of hypertension, in particular in regard to sex differences, have varied from study to study or laboratory to laboratory. The aim of this commentary is to increase investigator awareness of caveats related to animal models that may be sensitive to vendor-, barrier-, or diet-specific changes that result in an inability to sustain the genotype and/or phenotype of well-established experimental models. These considerations are critical in order for investigators to make informed and educated decisions in regard to their hypothesis-driven research, in particular as it relates to experimental design and interpretation, and the reporting of results.

Beneficial Effects of Paeoniflorin Enriched Extract on Blood Pressure Variability and Target Organ Damage in Spontaneously Hypertensive Rats

Blood pressure variability (BPV) is associated with the development and progression of severe target organ damage (TOD). This study aims to evaluate the protective effect of paeoniflorin enriched extract from Radix Paeoniae Alba (PG) on BPV and TOD in spontaneously hypertensive rats (SHR). All SHR were orally treated with distilled water, metoprolol (MP, 20 mg/kg), and PG (PG-H, 90 mg/kg or PG-L, 30 mg/kg) for a single time or daily for 7 weeks. The 24-hour dynamic blood pressure was monitored and then calculated BPV including long- and short-term systolic blood pressure variability (SBPV), diastolic blood pressure variability (DBPV), mean blood pressure variability (MBPV), and heart rate variability (HRV) as well as the 24-hour-SBP, 24-hour-DBP, and 24-hour-MBP. The protective effects of PG on TOD were observed by histopathologic and biochemical detection. The results indicated that long- and short-term SBPV, DBPV, MBPV, and HRV as well as 24-hour-SBP, 24-hour-DBP, and 24-hour-MBP showed no significant changes after single-dose administration of PG and significantly decreased after administration with PG for 7 weeks. PG could also markedly improve the damage of aorta, heart, kidney, and brain. This study suggested that PG could notably reduce BPV, stabilize blood pressure, and mitigate TOD in SHR.

Na+-sensitive elevation in blood pressure is ENaC independent in diet-induced obesity and insulin resistance

The majority of patients with obesity, insulin resistance, and metabolic syndrome have hypertension, but the mechanisms of hypertension are poorly understood. In these patients, impaired sodium excretion is critical for the genesis of Na(+)-sensitive hypertension, and prior studies have proposed a role for the epithelial Na(+) channel (ENaC) in this syndrome. We characterized high fat-fed mice as a model in which to study the contribution of ENaC-mediated Na(+) reabsorption in obesity and insulin resistance. High fat-fed mice demonstrated impaired Na(+) excretion and elevated blood pressure, which was significantly higher on a high-Na(+) diet compared with low fat-fed control mice. However, high fat-fed mice had no increase in ENaC activity as measured by Na(+) transport across microperfused cortical collecting ducts, electrolyte excretion, or blood pressure. In addition, we found no difference in endogenous urinary aldosterone excretion between groups on a normal or high-Na(+) diet. High fat-fed mice provide a model of metabolic syndrome, recapitulating obesity, insulin resistance, impaired natriuresis, and a Na(+)-sensitive elevation in blood pressure. Surprisingly, in contrast to previous studies, our data demonstrate that high fat feeding of mice impairs natriuresis and produces elevated blood pressure that is independent of ENaC activity and likely caused by increased Na(+) reabsorption upstream of the aldosterone-sensitive distal nephron.

Basal mTORC2 activity and expression of its components display diurnal variation in mouse perivascular adipose tissue

In adipose tissue mTOR complex 2 (mTORC2) contributes to the regulation of glucose/lipid metabolism and inflammatory molecule expression. Both processes display diurnal variations during the course of the day. RICTOR and mSIN1 are unique and essential components of mTORC2, which is activated by growth factors including insulin. To assess whether mTORC2 components display diurnal variations, we analyzed steady state mRNA expression levels of Rictor, mSin1, and mTor in various adipose tissues during a 24 h period. Diurnally regulated expression of Rictor was detected in brown adipose tissues displaying highest mRNA expression levels at the beginning of the 12 h light period (zeitgeber time 2, ZT2). Gene expression patterns of mSin1 and mTor displayed a similar diurnal regulation as Rictor in PVAT while smaller changes were detected for these genes in aorta during the course of the day. Basal mTORC2 activity was measured by phosphorylation of protein kinase C (PKC) α at serine 657 was higher at ZT14 as compared with ZT2 in PVAT. In line, gene expression of inflammatory molecules nitric oxide synthase 2 and tumor necrosis factor α was lower at ZT 14 compared to ZT2. Our findings provide evidence for a diurnal regulation of expression of mTORC2 components and activity. Hence, mTORC2 is possibly an integral part of diurnally regulated signaling pathways in PVAT and possibly in other adipose tissues.

Pro-atherogenic role of smooth muscle Nox4-based NADPH oxidase

Nox4-based NADPH oxidase is a major reactive oxygen species-generating enzyme in the vasculature, but its role in atherosclerosis remains controversial.

OBJECTIVE

Our goal was to investigate the role of smooth muscle Nox4 in atherosclerosis.

APPROACH AND RESULTS

Atherosclerosis-prone conditions (disturbed blood flow and Western diet) increased Nox4 mRNA level in smooth muscle of arteries. To address whether upregulated smooth muscle Nox4 under atherosclerosis-prone conditions was directly involved in the development of atherosclerosis, mice carrying a human Nox4 P437H dominant negative mutation (Nox4DN), specifically in smooth muscle, were generated on a FVB/N ApoE deficient genetic background to counter the effect of increased smooth muscle Nox4. Nox4DN significantly decreased aortic stiffness and atherosclerotic lesions, with no effect on blood pressure. Gene analysis indicated that soluble epoxide hydrolase 2 (sEH) was significantly downregulated in Nox4DN smooth muscle cells (SMC), at both mRNA and protein levels. Downregulation of sEH by siRNA decreased SMC proliferation and migration, and suppressed inflammation and macrophage adhesion to SMC.

CONCLUSIONS

Downregulation of smooth muscle Nox4 inhibits atherosclerosis by suppressing sEH, which, at least in part, accounts for inhibition of SMC proliferation, migration and inflammation.

Conditional knockout of collecting duct bradykinin B2 receptors exacerbates angiotensin II-induced hypertension during high salt intake

We elucidated the role of collecting duct kinin B2 receptor (B2R) in the development of salt-sensitivity and angiotensin II (ANG II)-induced hypertension. To this end, we used a Cre-Lox recombination strategy to generate mice lacking Bdkrb2 gene for B2R in the collecting duct (Hoxb7-Cre(tg/+):Bdkrb2(flox/flox)). In 3 groups of control (Bdkrb2(flox/flox)) and 3 groups of UB(Bdkrb2-/-) mice, systolic blood pressure (SBP) responses to high salt intake (4 or 8% NaCl; HS) were monitored by radiotelemetry in comparison with standard salt diet (0.4% NaCl) prior to and during subcutaneous ANG II infusion (1000 ng/min/kg) via osmotic minipumps. High salt intakes alone for 2 weeks did not alter SBP in either strain. ANG II significantly increased SBP equally in control (121 ± 2 to 156 ± 3 mmHg) and UB(Bdkrb2-/-) mice (120 ± 2 to 153 ± 2 mmHg). The development of ANG II-induced hypertension was exacerbated by 4%HS in both control (125 ± 3 to 164 ± 5 mmHg) and UB(Bdkrb2-/-) mice (124 ± 2 to 162 ± 3 mmHg) during 2 weeks. Interestingly, 8%HS caused a more profound and earlier ANG II-induced hypertension in UB(Bdkrb2-/-) (129 ± 2 to 166 ± 3 mmHg) as compared to control (128 ± 2 to 158 ± 2 mmHg) and it was accompanied by body weight loss and increased mortality. In conclusion, targeted inactivation of B2R in the renal collecting duct does not cause salt-sensitivity; however, collecting duct B2R attenuates the hypertensive actions of ANG II under conditions of very high salt intake.

The 24 h pattern of arterial pressure in mice is determined mainly by heart rate-driven variation in cardiac output

Few studies have systematically investigated whether daily patterns of arterial blood pressure over 24 h are mediated by changes in cardiac output, peripheral resistance, or both. Understanding the hemodynamic mechanisms that determine the 24 h patterns of blood pressure may lead to a better understanding of how such patterns become disturbed in hypertension and influence risk for cardiovascular events. In conscious, unrestrained C57BL/6J mice, we investigated whether the 24 h pattern of arterial blood pressure is determined by variation in cardiac output, systemic vascular resistance, or both and also whether variations in cardiac output are mediated by variations in heart rate and or stroke volume. As expected, arterial pressure and locomotor activity were significantly (P < 0.05) higher during the nighttime period compared with the daytime period when mice are typically sleeping (+12.5 ± 1.0 mmHg, [13%] and +7.7 ± 1.3 activity counts, [254%], respectively). The higher arterial pressure during the nighttime period was mediated by higher cardiac output (+2.6 ± 0.3 mL/min, [26%], P < 0.05) in association with lower peripheral resistance (-1.5 ± 0.3 mmHg/mL/min, [-13%] P < 0.05). The increased cardiac output during the nighttime was mainly mediated by increased heart rate (+80.0 ± 16.5 beats/min, [18%] P < 0.05), as stroke volume increased minimally at night (+1.6 ± 0.5 μL per beat, [6%] P < 0.05). These results indicate that in C57BL/6J mice, the 24 h pattern of blood pressure is hemodynamically mediated primarily by the 24 h pattern of cardiac output which is almost entirely determined by the 24 h pattern of heart rate. These findings suggest that the differences in blood pressure between nighttime and daytime are mainly driven by differences in heart rate which are strongly correlated with differences in locomotor activity.

Effects of a domain-selective ACE inhibitor in a mouse model of chronic angiotensin II-dependent hypertension

The somatic isozyme of ACE (angiotensin I-converting enzyme) comprises two distinct zinc-dependent catalytic domains with different substrate specificities for angiotensin I (cleaved selectively by the C-domain) and bradykinin (cleaved equally efficiently by both the N- and C-domains). Classical ACEIs (ACE inhibitors) target both domains, with side effects such as cough and angio-oedema being attributed, in part, to N-domain inhibition, probably through bradykinin accumulation. We questioned whether a novel C-domain-selective ACEI (lisW-S) has anti-hypertensive effects without influencing bradykinin status. AngII (angiotensin II)-dependent hypertension was studied in mice that express active human renin in the liver (TtRhRen). Compared with wild-type littermates, TtRhRen mice displayed cardiac hypertrophy and had significantly elevated SBP [systolic BP (blood pressure)] as determined by tail cuff sphygmomanometry (150±3 compared with 112±5 mmHg; P<0.05) and telemetry (163±3 compared with 112±2 mmHg; P<0.01). Treatment with the non-selective ACEI lisinopril (1 mg/kg of body weight per day via an osmotic mini-pump for 2 weeks) reduced SBP (127±3 compared with. 154±6; P<0.05). Similarly, treatment with the C-domain selective ACEI lisW-S (lisinopril-tryptophan; 3.6 mg/kg of body weight per day via an osmotic mini-pump for 2 weeks) reduced BP. Treatment with lisinopril or lisW-S significantly reduced levels of AngII in kidneys (~4-fold; P<0.001). Ang-(2-8) [angiotensin-2-8)] was significantly reduced by lisinopril, but not by lisW-S. Plasma bradykinin levels were significantly increased only in the lisinopril group. These data suggest that C-domain-selective ACEIs reduce BP and AngII levels similarly to classical ACEIs. C-domain-selective ACEIs have the potential to avoid undesirable effects on the bradykinin system common to classic ACEIs and may represent a novel approach to the treatment of hypertension.

American Thyroid Association Guide to investigating thyroid hormone economy and action in rodent and cell models

BACKGROUND

An in-depth understanding of the fundamental principles that regulate thyroid hormone homeostasis is critical for the development of new diagnostic and treatment approaches for patients with thyroid disease.

SUMMARY

Important clinical practices in use today for the treatment of patients with hypothyroidism, hyperthyroidism, or thyroid cancer are the result of laboratory discoveries made by scientists investigating the most basic aspects of thyroid structure and molecular biology. In this document, a panel of experts commissioned by the American Thyroid Association makes a series of recommendations related to the study of thyroid hormone economy and action. These recommendations are intended to promote standardization of study design, which should in turn increase the comparability and reproducibility of experimental findings.

CONCLUSIONS

It is expected that adherence to these recommendations by investigators in the field will facilitate progress towards a better understanding of the thyroid gland and thyroid hormone dependent processes.

Effects of chronic in-vivo treatments with protease-activated receptor 2 agonist on endothelium function and blood pressures in mice

Short-term treatments with protease-activated receptor 2-activating peptides (PAR2-AP) induce endothelium-dependent vasodilation and decrease blood pressure. In this study, we tested the effect of chronic in-vivo treatment with PAR2-AP on the blood pressure and endothelium function of mice. Male PAR2 wild-type (WT) and par2-deficient (KO) mice received subcutaneous infusions of either saline, low (PAR2-LD), or high (PAR2-HD) doses of 2-furoyl-LIGRLO-amide for 1 or 2 weeks. In each treatment group, endothelium function was assessed in isolated arteries. Blood pressure, heart rate, and locomotor activity were recorded by radiotelemetry, and levels of tumour nercrosis factor α (TNF-α) and interkeukin 1β (IL-1β) were measured in plasma samples by ELISA. The relaxation of WT aortas and mesenteric arteries induced by PAR2-AP was decreased by PAR2-LD and PAR2-HD. In mesenteric arteries, PAR2-LD and PAR2-HD decreased the relaxation induced by acetylcholine, but not by nitroprusside; in aortas, PAR2-LD and PAR2-HD caused differential decreases in the relaxations induced by acetylcholine and nitroprusside. Only PAR2-HD lowered systolic arterial pressures in WT, when compared with all of the other groups. TNF-α and IL-1β plasma concentrations were not different among the groups. We conclude that the systolic blood pressure of unrestrained mice can be lowered by chronic in-vivo activation of PAR2; however, this effect is countered by receptor desensitization and the concomitant development of endothelium and vascular dysfunction.

Role of mutation of the circadian clock gene Per2 in cardiovascular circadian rhythms

Alterations in the circadian blood pressure pattern are frequently observed in hypertension and lead to increased cardiovascular morbidity. However, there are no studies that have investigated a possible implication of the Period2 gene, a key component of the molecular circadian clock, on the circadian rhythms of blood pressure and heart rate. To address this question, we monitored blood pressure, heart rate, and locomotor activity 24 h a day by telemetry in mice carrying a mutation in the Period2 gene and in wild-type control mice. Under a standard 12:12-h light-dark cycle, mutant mice showed a mild cardiovascular phenotype with an elevated 24-h heart rate, a decreased 24-h diastolic blood pressure, and an attenuation of the dark-light difference in blood pressure and heart rate. Locomotor activity was similar in both groups and did not appear to explain the observed hemodynamic differences. When mice were placed under constant darkness during eight consecutive days, wild-type mice maintained 24-h rhythms, whereas there was an apparent progressive loss of 24-h rhythm of blood pressure, heart rate, and locomotor activity in mutant mice. However, a chi square periodogram revealed that circadian rhythms were preserved under complete absence of any light cue, but with shorter periods by approximately 40 min, leading to a cumulative phase shift toward earlier times of approximately 5 h and 20 min by the end of the 8th day. When heart rate, mean arterial pressure, and activity were recalculated according to the endogenous circadian periods of each individual mouse, the amplitudes of the circadian rhythms ("subjective night"-"subjective day" differences) were maintained for all variables studied. Our data show that mutation of the Period2 gene results in an attenuated dipping of blood pressure and heart rate during both light-dark cycles and constant darkness, and in shorter circadian periods during constant darkness.

Optimized surgical techniques and postoperative care improve survival rates and permit accurate telemetric recording in exercising mice

Background

The laboratory mouse is commonly used as a sophisticated model in biomedical research. However, experiments requiring major surgery frequently lead to serious postoperative complications and death, particularly if genetically modified mice with anatomical and physiological abnormalities undergo extensive interventions such as transmitter implantation. Telemetric transmitters are used to study cardiovascular physiology and diseases. Telemetry yields reliable and accurate measurement of blood pressure in the free-roaming, unanaesthetized and unstressed mouse, but data recording is hampered substantially if measurements are made in an exercising mouse. Thus, we aimed to optimize transmitter implantation to improve telemetric signal recording in exercising mice as well as to establish a postoperative care regimen that promotes convalescence and survival of mice after major surgery in general.

Results

We report an optimized telemetric transmitter implantation technique (fixation of the transmitter body on the back of the mouse with stainless steel wires) for subsequent measurement of arterial blood pressure during maximal exercise on a treadmill. This technique was used on normal (wildtype) mice and on transgenic mice with anatomical and physiological abnormalities due to constitutive overexpression of recombinant human erythropoietin. To promote convalescence of the animals after surgery, we established a regimen for postoperative intensive care: pain treatment (flunixine 5 mg/kg bodyweight, subcutaneously, twice per day) and fluid therapy (600 μl, subcutaneously, twice per day) were administrated for 7 days. In addition, warmth and free access to high energy liquid in a drinking bottle were provided for 14 days following transmitter implantation. This regimen led to a substantial decrease in overall morbidity and mortality. The refined postoperative care and surgical technique were particularly successful in genetically modified mice with severely compromised physiological capacities.

Conclusion

Recovery and survival rates of mice after major surgery were significantly improved by careful management of postoperative intensive care regimens including key supportive measures such as pain relief, administration of fluids, and warmth. Furthermore, fixation of the blood pressure transmitter provided constant reliable telemetric recordings in exercising mice.

Blood pressures, heart rate and locomotor activity during salt loading and angiotensin II infusion in protease-activated receptor 2 (PAR2) knockout mice

Background

In this study we used radiotelemetry to measure hemodynamic variables and locomotor activity in conscious unrestrained male Protease-Activated Receptor 2 (PAR-2) knockout mice in order to provide a detailed assessment of their blood pressure phenotype. In addition we tested for an influence of PAR-2 on salt-sensitivity (8% versus 0.5% NaCl diet, 2.5 weeks) and angiotensin II-induced hypertension (1 μg Ile⁵-angiotensin II/kg/min versus 0.25 μl/h saline, 2 weeks).

Results

Systolic arterial pressures of PAR-2 -/- (129 ± 1 mmHg, n = 21, P < 0.05) were statistically higher than those of C57BL/6J (124 ± 1 mmHg, n = 33) throughout the 24 h period under baseline conditions. Pulse pressures in PAR-2 -/- were also significantly elevated (33 ± 1 mmHg versus 30 ± 1 mmHg, P < 0.05), whereas diastolic arterial pressures were not. Heart rates in PAR-2 -/- were not significantly different than controls, with the exception that heart rate of PAR-2 -/- was 23 beats per min higher than controls (P < 0.001) during periods of nocturnal activity. The diurnal pattern and intensity of locomotor activity were not found to differ between strains. A high salt diet led to increased blood pressures, decreased heart rates, increased time spent active and decreased intensity levels of locomotor activity. Salt-induced changes in systolic and pulse pressures in PAR-2 -/- were less than in C57B/6J. Angiotensin II treatment increased pressures, decreased heart rates, decreased time spent active and decreased intensity levels of activity of PAR-2 -/-, all to the same extent as C57BL/6J. A trend of lower blood pressures during the middle period of angiotensin II treatment period was observed in individual PAR-2 -/-.

Conclusion

The data indicated gene knockout of PAR-2 was associated with a modest change in blood pressure phenotype. PAR-2 -/- mice exhibited moderate elevation of systolic arterial and pulse pressures, yet no increased diastolic arterial pressure, no increased blood pressure responses to high salt diet and a subtle difference in the time course of the blood pressure responses to angiotensin II infusion.

Sampling of cardiovascular data; how often and how much?

Long-term measurement of cardiovascular variables by telemetry in laboratory animals has become indispensable in recent years. However, limited battery life and management of large volumes of recorded data are major drawbacks. These limitations can often be overcome by intermittent sampling of data. The question is, how much data does one need to collect to accurately reflect the underlying average value? To investigate this, 24-h continuous recordings of rabbit heart rate, arterial pressure, and integrated renal sympathetic nerve activity (RSNA) were resampled using a variety of protocols that differed with respect to the number of individual sampling periods used and the total amount of time that was sampled. The absolute percentage errors of estimates of the daily mean, standard deviation, and interquartile range were calculated for each sampling protocol. A similar analysis was repeated using arterial pressure data from rats. The results show that the number of sampling periods spread throughout the day had more effect than the total amount of data recorded. For example, just 2 h of total sampling time spread over 12 evenly spaced 10-min periods gave estimates of the daily mean of blood pressure and heart rate with < 1% error and RSNA with < 3% error. We show that accurate estimates of the daily mean of arterial pressure, heart rate, and RSNA can all be made using scheduled recording, and we recommend recording a minimum of 2 h/day spread over a number of periods throughout the day.

Maternal Endothelial Nitric Oxide Synthase Genotype Influences Offspring Blood Pressure and Activity in Mice

Deficiencies in maternal endothelial NO synthase (eNOS) have been associated with pregnancy complications, intrauterine growth retardation, and altered vascular function in offspring. In the present study, we investigated the influence of the maternal eNOS genotype on offspring's blood pressure, heart rate, and locomotor activity. The effect of maternal eNOS genotype was made by comparing telemetered blood pressure and activity between 2 groups of 13- to 16-week-old male heterozygous eNOS knockout mice, 1 produced by a cross of eNOS knockout (eNOS-/-) mothers and wild-type (eNOS+/+) fathers (eNOS(+/-MAT) offspring, N=11), the other by a cross of eNOS+/+ mothers and eNOS-/- fathers (eNOS(+/-PAT) offspring, N=10). Data were also collected for homozygous eNOS-/- and eNOS+/+ mice (N=15 each). Heterozygous eNOS knockout mice exhibited blood pressures that were intermediate to the eNOS+/+ and eNOS-/- groups. Relative to eNOS(+/-PAT) mice, eNOS(+/-MAT) mice exhibited significant increases in nocturnal diastolic arterial pressure and diurnal variations (dark-light difference) in systolic, mean, and diastolic arterial pressure. In addition, indices of spontaneous nocturnal locomotor activity, including both the proportion of time spent active and the intensity of activity when active, were also significantly increased. Heart rate did not differ between the groups. Our results suggest that the maternal eNOS genotype influences both blood pressure and behavior of offspring, possibly as a consequence of developmental programming associated with intrauterine growth retardation.

Persistence of PAR-2 vasodilation despite endothelial dysfunction in BPH/2 hypertensive mice

This study investigated relaxation of vascular smooth muscle by acetylcholine, bradykinin and protease-activated receptor 2 (PAR-2) to characterise endothelial dysfunction in spontaneously hypertensive mice (BPH/2). We hypothesised that PAR-2 induced vasodilation would be preserved in BPH/2 despite the presence of hypertension and impaired vasodilator responses to acetylcholine and bradykinin. Mean arterial blood pressure (MAP), heart rate and locomotor activity were assessed in conscious mice over 24-h periods by radiotelemetry. Relaxation responses of small mesenteric arteries to acetylcholine, bradykinin and the PAR-2 agonist, 2-furoyl-LIGRLO-amide (2fly), were assessed using wire myographs. MAP and heart rate of BPH/2 were 15 and 18%, respectively, higher than in controls (BPN/3). BPH/2 also exhibited increased locomotor activity. Maximal relaxations of arteries by acetylcholine and bradykinin in BPH/2 were reduced by 25-50% relative to BPN/3. In contrast, relaxation responses to 2fly were only slightly (6%), albeit significantly, reduced. Sodium nitroprusside-induced relaxations were not different between strains. Treatment of BPH/2 arteries with inhibitors of calcium-activated K(+) channels was sufficient to block persistent 2fly- and residual ACh- and bradykinin-induced relaxations, whereas NO synthase inhibitor failed to inhibit these relaxations. In BPH/2 mice, vascular smooth muscle relaxation by PAR-2 is well preserved despite the presence of hypertension and impaired vasodilation responses to acetylcholine and bradykinin.