A new approach to assessing the structural total peripheral resistance amplifier in renal (Page) hypertension in conscious rabbits

Estimation of the vascular resistance amplifier in the renal vascular bed in conscious hypertensive rabbits: comparison with the total peripheral vasculature

Objectives

The vascular amplifier in hypertension is a result of structural changes in resistance arteries. We estimated the vascular amplifier hypertensive:normotensive (H:N) ratio in the renal bed compared with the total peripheral bed in conscious rabbits during infusion of vasoconstrictor and vasodilator stimuli.

Methods

Rabbits were subjected to bilateral renal cellophane wrap or sham operation. A perivascular ultrasonic flow probe was implanted on the left renal artery to measure renal blood flow. A catheter was inserted into the thoracic aorta for agonist administration. Blood pressure, heart rate and renal blood flow were measured on three separate days in conscious rabbits with intact effectors, ganglionic block or neurohumoral block. Dose-response curves were constructed to intra-arterial infusion of noradrenaline, angiotensin II, adenosine and acetylcholine.

Results

Resting renal vascular resistance in hypertensive rabbits was markedly decreased by ganglionic block and further by neurohumoral block. With effectors intact, ganglionic block or neurohumoral block, the H:N ratio for renal vascular resistance was 2.32, 1.72 or 1.72, respectively. The ratio was generally maintained during the infusion of constrictor and dilator drugs although distortions occurred at higher concentrations of constrictor or dilator drugs.

Conclusions

Estimation of the renal resistance amplifier in renal wrap hypertension with neurohumoral block accords with our earlier estimates of the total peripheral resistance amplifier (1.79). This vascular resistance amplifier is consistent with a decrease in internal radius through structural remodelling in the renal vascular bed as is reflected in the total arterial circulation in hypertension.

Thymoquinone protection from amikacin induced renal injury in rats

We investigated whether thymoquinone (TQ) exerts a beneficial effect on renal injury due to amikacin (AK) administration in rats. To generate kidney damage with AK, a single 1.2 g/kg dose of AK was administered intraperitoneally. TQ was administered orally to the AK treated group at a dose of 40 mg/kg for five days. At the end of the experiment, rats were sacrificed and blood samples were used to measure blood urea nitrogen (BUN) and creatinine (Cr) levels. Kidney samples were taken to measure the oxidative stress biomarker, malondialdehyde (MDA), and expression of the antioxidant enzymes, superoxide dismutase (SOD) and catalase (CAT). Because reactive oxygen species (ROS) and apoptosis contribute to tissue damage associated with NADPH oxidase (NOX), we also investigated NOX-2, NOX-4 and apoptosis marker, caspase-3, expression using immunohistochemistry. MDA, BUN, Cr, NOX-2, NOX-4 and caspase-3 production were increased, and SOD and CAT were decreased in the AK treated group compared to controls. MDA, BUN, Cr, NOX-2, NOX-4 and caspase-3 levels were decreased, and SOD and CAT levels were increased in TQ + AK treated rats compared to AK treated animals. TQ appears to protect the kidney from the toxic effects of AK.

Central aortic pressure improves prediction of cardiovascular events compared to peripheral blood pressure in short-term follow-up of a hypertensive cohort

Objective: The aim of this study was to assess indices of a comprehensive panel of central aortic pressure and arterial stiffness for prediction of cardiovascular events in a hypertensive cohort.Methods: Noninvasive measurements of central aortic blood pressure, brachial pressure, wave reflection augmentation index, pressure amplification, pulse wave velocity (PWV) and carotid intima-media thickness (IMT) were obtained in 675 hypertensive patients (age 61 ± 9 years, 425 males) for a mean follow-up period 25 ± 4 months. The primary endpoints were defined as cardiovascular disease (CVD) events or death from CVD.Results: After adjusting for confounding factors, central systolic (cSBP) and pulse pressure (cPP) showed higher hazard ratios (HR/10 mmHg) for cardiovascular events (CV) compared to peripheral pressure indices (pSBP, pPP) at age >60 years (cSBP: HR = 1.18, pSBP: HR = 1.17, p = 0.034; cPP: HR = 1.28, pPP: HR = 1.2, p = 0.019). Each SD increase in IMT and in central augmented pressure (cAP) entailed a 1.4 times higher risk of increased total events in elderly patients (age >60 years). For males, each SD increase in cAP was associated with 1.36 times higher risk of increased total events. For females, each SD increase in cAIx and cAP was associated with 0.4 and 0.5 times lower risk of increased total and major CV, respectively. This sex difference is most likely due to lack of age-related increase of cAIx in females after age >60 years compared to males.Conclusions: Central pressure improved prediction of CVD compared to peripheral pressure during a relatively short-term follow up of approximately 2 years at age >60 years.

Vascular reactivity of rabbit isolated renal and femoral resistance arteries in renal wrap hypertension

In rabbits with cellophane renal wrap hypertension, hindquarter and total vascular resistance changes to pressor and depressor agents are amplified compared to those of normotensive rabbits. The aim of the present study was to evaluate the in vitro pharmacodynamics of hypertensive and normotensive rabbit small artery segments isolated from the renal and hindquarter vascular beds. Using wire myography, the full range (Emax) and sensitivity (EC50) to a range of agonists of segments of renal interlobar (≈ 600 µm i.d.), renal arcuate (≈ 250 µm i.d.) and deep femoral branch (≈ 250 µm i.d.) arteries were assessed under normalised conditions of passive tension. Interlobar arteries from hypertensive rabbits were more sensitive (EC50) than those from normotensive rabbits to noradrenaline (6-fold), methoxamine (3-fold) and angiotensin II (3-fold). Arcuate artery reactivity was largely unaffected by hypertension. Deep femoral arteries from hypertensive rabbits had enhanced sensitivity only to noradrenaline (2-fold) and methoxamine (4-fold). Sensitivity to relaxation by acetylcholine was unaffected by hypertension in all arteries. Deep femoral arteries from hypertensive rabbits were more sensitive to sodium nitroprusside than normotensive counterparts. Adenosine caused little relaxation in renal arteries, but full relaxation in deep femoral arteries, unaltered by hypertension. This study found substantial heterogeneity in the pharmacodynamic profile of vessels isolated from different vascular beds and between arterial segments within the kidney. These profiles were differentially affected by hypertension suggesting that hypertension per se is not a resultant of general vascular dysfunction.

Comparison of blood pressure and sympathetic activity of rabbits in their home cage and the laboratory environment

Methodological improvements in measuring cardiovascular parameters have meant that data can be collected from freely moving animals in their home cage. However, experiments in rabbits still often require them to be restrained in a laboratory setting. The aim of this study was to determine whether measurements collected when rabbits were placed in a holding box in the laboratory are representative of values obtained in freely moving conscious rabbits. Nine New Zealand White rabbits received two radiotelemetry implants to monitor mean arterial pressure (MAP) and renal sympathetic nerve activity (RSNA). The MAP measured in the laboratory (71 ± 1 mmHg) was similar to that in the home cage (69 ± 1 mmHg), but there was less MAP variability. The RSNA was also similar in both environments. In contrast, laboratory heart rate (HR) was 7% lower than home cage HR (181 ± 4 beats min(-1), P < 0.001), but HR variability was similar. Baroreflex gain, assessed by spectral analysis, was 19% higher in the laboratory than in the home cage due to lower MAP mid-frequency variability in the laboratory. Home cage circadian patterns of MAP and HR were strongly influenced by feeding and activity. Nevertheless, MAP and RSNA laboratory measurements were the same as average 24 h values and remained similar over several weeks. We conclude that while HR is generally lower in the laboratory, a valid representation of MAP and RSNA can be given by laboratory measurements.