A SIMPLE METHOD FOR DETERMINING THE SYSTOLIC BLOOD PRESSURE OF THE UNANESTHETIZED RAT

Tail-Cuff Technique and Its Influence on Central Blood Pressure in the Mouse

Background

Reliable measurement of blood pressure in conscious mice is essential in cardiovascular research. Telemetry, the “gold‐standard” technique, is invasive and expensive and therefore tail‐cuff, a noninvasive alternative, is widely used. However, tail‐cuff requires handling and restraint during measurement, which may cause stress affecting blood pressure and undermining reliability of the results.

Methods and Results

C57Bl/6J mice were implanted with radio‐telemetry probes to investigate the effects of the steps of the tail‐cuff technique on central blood pressure, heart rate, and temperature. This included comparison of handling techniques, operator's sex, habituation, and influence of hypertension induced by angiotensin II. Direct comparison of measurements obtained by telemetry and tail‐cuff were made in the same mouse. The results revealed significant increases in central blood pressure, heart rate, and core body temperature from baseline following handling interventions without significant difference among the different handling technique, habituation, or sex of the investigator. Restraint induced the largest and sustained increase in cardiovascular parameters and temperature. The tail‐cuff readings significantly underestimated those from simultaneous telemetry recordings; however, “nonsimultaneous” telemetry, obtained in undisturbed mice, were similar to tail‐cuff readings obtained in undisturbed mice on the same day.

Conclusions

This study reveals that the tail‐cuff technique underestimates the core blood pressure changes that occur simultaneously during the restraint and measurement phases. However, the measurements between the 2 techniques are similar when tail‐cuff readings are compared with telemetry readings in the nondisturbed mice. The differences between the simultaneous recordings by the 2 techniques should be recognized by researchers.

Impaired Neovascularization and Reduced Capillary Supply in the Malignant vs. Non-malignant Course of Experimental Renovascular Hypertension

Malignant hypertension develops in some cases of hypertension but not in others. We hypothesized that an impaired neovascularization and a reduced capillary supply characterizes the malignant course of experimental hypertension. Two-kidney, one-clip renovascular hypertension was induced in rats; controls (sham) were sham operated. To distinguish malignant hypertension from non-malignant hypertension, we considered two factors: weight loss, and the number of typical vascular lesions (onion skin lesions and fibrinoid necroses) per kidney section of the nonclipped kidney. Animals in the upper half for both criteria were defined as malignant hypertensives. After 5 weeks, mean arterial blood pressure was elevated to the same degree in malignant hypertension and non-malignant hypertension whereas plasma renin and aldosterone were significantly higher in malignant hypertensives. The expression of plasminogen activator inhibitor-1 was elevated (up to 14-fold) in non-malignant but significantly more increased (up to 36-fold) in malignant hypertensive rats, compared to sham. As a bioassay for neovascularization, the area of granulation tissue ingrowth in polyvinyl discs (implanted subcutaneously) was reduced in malignant hypertension compared to non-malignant hypertension and sham, while there was no difference between non-malignant hypertension and sham. The number of renal and left ventricular capillaries was significantly lower in malignant hypertension compared to non-malignant hypertension, as was the number of proliferating endothelial cells. We conclude that an impaired neovascularization and capillarization occurs in malignant renovascular hypertension but not in the non-malignant course of the disease despite comparable blood pressure levels. This might contribute to the unique vascular lesions and progressive target organ damage observed in malignant hypertension.

Antihypertensive Effect of Quercetin in Rats Fed with a High-Fat High-Sucrose Diet

The effects of different levels of quercetin on the blood pressure were studied in 6-week-old male Sprague-Dawley rats. The rats were fed with a control diet or a high-fat high-sucrose (HFS) diet containing 0, 0.02, 0.07, 0.2, or 0.5% quercetin for 4 weeks. The systolic blood pressure and the lipid peroxides in the plasma were both higher in the rats fed with the HFS diet without quercetin than in the rats fed with the control diet. The nitric oxide synthase (NOS) activity in the vascular tissues and nitric oxide (NO) metabolites in the plasma and urine were both lower in these rats. A distinct depression of the increase in blood pressure was found in the rats fed with the HFS diets containing quercetin. Each level of quercetin examined was effective, the 0.5% level being much more effective than other levels. Dietary quercetin decreased lipid peroxidation in the plasma of the rats fed with the HFS diets. Quercetin also suppressed the decrease in NO metabolites in the plasma and urine, and the NOS activity in the vascular tissues of these rats. These results suggest that the increased NO availability caused by the elevated NOS activity, and the antioxidative activity in these rats fed with quercetin may be sources of the antihypertensive effect of quercetin.

Antioxidative and Antihypertensive Effects of Welsh Onion on Rats Fed with a High-Fat High-Sucrose Diet

The effects of Welsh onion on the development of hypertension and autoxidation were studied in 6-week-old male Sprague-Dawley rats. The rats were fed with a control diet or a high-fat high-sucrose (HFS) diet with or without 5% Welsh onion (green-leafy type or white-sheath type) for 4 weeks. The systolic blood pressure was elevated and the thiobarbituric acid reactive substances (TBARS) in plasma were increased in the rats fed with the HFS diet without Welsh onion. The rats fed with the HFS diet containing Welsh onion, especially the green-leafy type, had lower blood pressure. They also had a higher level of nitric oxide (NO) metabolites in both the urine and plasma, lower activity of NADH/NADPH oxidase in the aorta, and suppressed angiotensin II production. The effect of white Welsh onion on decreasing the blood pressure was not significant, although the effects on increasing NO metabolites in the urine and decreasing NADH oxidase activity in the aorta were significant. The TBARS value in the plasma was lowered in the rats fed with either green or white Welsh onion, but the in vitro radical scavenging and ferric reducing antioxidative activities were much higher with green Welsh onion than with the white type. These results suggest that the green-leafy Welsh onion, but not the white type, reduced superoxide generation by suppressing the angiotensine II production and then the NADH/NADPH oxidase activity, increasing the NO availability in the aorta, and consequently lowering the blood pressure in the rats fed with the HFS diet. The radical scavenging and reducing antioxidative activities of green Welsh onion may also be effective in decreasing superoxide.

The Biological Assay of Rauwolfia Schueli

The biological effects of Rauwolfia schueli are essentially the same as those of the pure alkaloid reserpine and the crude compound R. serpentina in the rat. No difference in relative potency between the small and large roots of large trees of the R. schueli species was apparent when either reserpine or R. serpentina was employed as the standard. R. schueli was estimated to be about 1/630 as active as reserpine. In terms of reserpine-like activity, this species appeared to be more potent than R. serpentina and by comparison with the results of others about as potent as R. canescens but more potent than R. heterophylla. Within the range of doses selected, blood pressure did not appear to be an adequate index for measuring reserpine-like activity in the rat.

WATER METABOLISM IN HYPERTENSIVE RATS

The water intake in hypertensive rats was investigated. Rats made hypertensive by renal ischemia increased their water consumption by 75 per cent over the preoperative level. Polyuria was associated with this polydipsia and the independence of these occurrences from a number of other factors was demonstrated. It was found that the presence of a normal kidney exerted a compensatory influence which may mask either hypertension or polyuria or both. The appearance or exacerbation of the changes upon removal of the normal kidney, on the one hand, and the elimination or mitigation of the symptoms upon removal of the ischemic kidney on the other support the view that the changes observed cannot have been due to passive elimination of the kidney tissue by ischemia, but to active malfunction of the renal, and especially the tubular, mechanism upon withdrawal of oxygen. The view is put forward that polyuria is a primary sequel of ischemia rather than secondary to the intra- and extrarenal effects of hypertension. A number of concomitant observations are in harmony with this hypothesis.

DESOXYCORTICOSTERONE ACETATE : THE POTENTIATION OF ITS ACTIVITY BY SODIUM CHLORIDE

1. Desoxycorticosterone acetate (DCA) and NaCl, in the dosage employed in normal rats, caused renal and cardiac hypertrophy, characteristic changes in the renal tubular epithelium, atrophic changes in the subcapsular zone of the adrenal cortex, and serum electrolyte changes characterized by a rise in sodium and fall in potassium. 2. In rats rendered nephritic with a rabbit anti-rat-kidney serum, the same regimen caused similar changes. In addition, DCA given concurrently with NaCl greatly intensified the nephritic process and gave rise to striking arterial hypertension. 3. A diet, virtually sodium-free, administered to normal and nephritic rats receiving daily injections of DCA abolished or reduced to a minimum the effects of this steroid; i.e., a liberal ingestion of NaCl was essential for the potentiation of the action of DCA. 4. The addition of KCl to the drinking water of rats receiving DCA and NaCl tended to correct the depression of the level of potassium in the serum, but had no effect upon the hypertension in nephritic animals nor upon the anatomical lesions. 5. The mechanism by which the sodium ion potentiates the activity of DCA has not been established.

A METHOD TO DETERMINE THE PERIPHERAL ARTERIAL BLOOD PRESSURE IN THE MOUSE

Advantage has been taken of the relative transparency of the claw of the mouse to devise a method, here described, to measure the blood pressure in the animal's leg. Direct measurements of the systolic blood pressure from the carotid arteries of anesthetized mice have also been made. Simultaneous blood pressure readings by both these methods applied to the same animal showed close agreement. The systolic pressure ranged from 60 to 126 mm. Hg, according to the conditions.

REDUCTION OF ARTERIAL BLOOD PRESSURE OF HYPERTENSIVE PATIENTS AND ANIMALS WITH EXTRACTS OF KIDNEYS

1. Extracts of kidneys have been prepared containing a substance which lowers arterial blood pressure for prolonged periods in patients with essential and malignant hypertension, and in hypertensive dogs and rats. 2. Several different chemical procedures are proposed for the preparation of the extract. The best one has not been decided upon. 3. The quantity of original fresh whole kidney required to yield enough extract to lower blood pressure from hypertensive levels (200 mm. Hg mean pressure) to normal levels is roughly 600 to 900 gm. in dogs within 4 to 8 days. In hypertensive patients the yield from 700 to 1000 gm. daily for several weeks may be necessary. 4. Lowering of the blood pressure too rapidly in animals results in a shock syndrome which may be fatal. If overdosage is avoided, no appreciable rise in blood urea nitrogen occurs, nor do other signs of toxicity appear. 5. Lowering of blood pressure to nearly normal levels has been accomplished in 60 hypertensive dogs, and in some of these it has been allowed to rise and was again reduced as many as five times. Similar results have been obtained with hypertensive rats. 6. Six patients with essential hypertension have been treated resulting in prolonged reduction of blood pressure. Clinically the patients appear improved. 7. Five patients with malignant hypertension have been treated, with reduction of the blood pressure in all instances. One patient was treated despite urea clearance of 5 per cent of normal. His blood pressure was sharply reduced, but death in uremia occurred. The second patient also exhibited sharp reduction of pressure and died after treatment was discontinued. The other three are much improved after treatment, as indicated by increase in vision and mental activity, loss of dyspnea, improvement in the electrocardiogram, etc. 8. The length of time the blood pressure remains lowered varies greatly in both animals and man. The trend is usually upwards after discontinuing treatment for 4 to 6 days. 9. Increasing experience with this treatment suggests that it is of value in the management of hypertension, but it is yet in the experimental stage.

NUTRITIONAL DEFICIENCIES AS A CAUSE OF ELEVATED BLOOD PRESSURE IN RATS (WITH ESPECIAL REFERENCE TO THE VITAMIN B(2) COMPLEX)

The effects of dietary deficiencies on the blood pressure of rats were studied, with especial reference to vitamin B deficiencies. A deficiency of the entire vitamin B complex was followed by a slight fall in blood pressure. A deficiency of only thse heat-stable fractions was followed by a significant and persistent rise in pressure, which could be reversed by restoring these factors to the diet. Partial deficiencies were followed by a higher rise of blood pressure than were complete deficiencies, perhaps because of the debilitating effects of the latter. Even an excessive intake of the heat-stable fractions of the vitamin B complex did not prevent entirely a rise of pressure if the diet was otherwise deficient. Under the latter conditions, the rise in pressure was slower and less marked than in those animals with a deficiency of the vitamin B₂ complex only. It therefore appears that, while a deficiency of the vitamin B₂ complex plays a dominant rôle in causing a rise of blood pressure in rats, other dietary factors as yet undefined are also involved. From analogy with other deficiency states, it is possible that thsese undefined nutritional factors cause their effects by interfering with absorption and utilization of the vitamin B₂ complex.

Non-invasive and quantitative evaluation of peripheral vascular resistances in rats by combined NMR measurements of perfusion and blood pressure using ASL and dynamic angiography

The in vivo determination of peripheral vascular resistances (VR) is crucial for the assessment of arteriolar function. It requires simultaneous determination of organ perfusion (F) and arterial blood pressure (BP). A fully non-invasive method was developed to measure systolic and diastolic BP in the caudal artery of rats based on dynamic NMR angiography. A good agreement was found between the NMR approach and the gold standard techniques (linear regression slope = 0.98, R(2) = 0.96). This method and the ASL-MRI measurement of skeletal muscle perfusion were combined into one single NMR experiment to quantitatively evaluate the local vascular resistances in the calf muscle of anaesthetized rats, in vivo and non-invasively 1) at rest: VR = 7.0 +/- 1.0 mmHg x min 100 g x ml(-1), F = 13 +/- 3 ml min(-1) x 100 g(-1) and mean BP (MBP) = 88 +/- 10 mmHg; 2) under vasodilator challenge (milrinone): VR = 3.7 +/- 1.1 mmHg min x 100 g ml(-1), F = 21 +/- 4 ml min(-1) x 100 g(-1) and MBP = 75 +/- 14 mmHg; 3) under vasopressor challenge (norepinephrine): VR = 9.8 +/- 1.2 mmHg min 100 g ml(-1), F = 14 +/- 3 ml min(-1) x 100 g(-1) and MBP = 137 +/- 2 mmHg.

Observations on the pregnant rat injected with nephrotoxic rabbit anti-rat placenta serum and desoxycorticosterone acetate

1. Pregnancy enhances the susceptibility of the rat to intercurrent renal damage produced by anti-placenta serum. This is manifested by the development of renal hypertrophy and nephritis in a number of these animals. Both renal hypertrophy and nephritis are consistently intensified by the concomitant administration of DCA. 2. Hypertension develops in both pregnant and non-pregnant rats treated with the anti-placenta serum employed together with the daily administration of DCA. 3. Termination of pregnancy, in the face of continued DCA administration, fails to lower the blood pressure or to arrest the nephritic process.

The effect of oral protease administration in the rat remnant kidney model

It has been demonstrated that intraperitoneal administration of proteolytic enzymes ameliorates the progression of renal diseases in various animal models. In the present study, we employed the rat remnant kidney model to study the effectiveness of oral administration of proteases. Twenty male Wistar rats underwent sham operation (CTRL), while 25 were subjected to 5/6 nephrectomy (5/6 NX). Rats were randomised into placebo (PL) (2 ml tap water/day by gavage), or Phlogenzym (E; fixed mixture of trypsin 2.42 mg, bromelain 4.54 mg, and rutozid 5.04 mg added as antioxidant, in 2 ml tap water daily by gavage) treated group. Duration of the study was 45 days. Rats were pair-fed. Enzyme treatment exerted salutary effects on various functional and morphological parameters. Proteinuria was higher in both 5/6 NX group rats throughout the study. Administration of proteases ameliorated its rise effectively (data at sacrifice: CTRL-PL 6.27 +/- 1.25, CTRL-E 9.27 +/- 0.99, 5/6 NX-PL 74.04 +/- 21.33, 5/6 NX-E 39.09 +/- 7.93 mg/24 h; P < 0.01). Increased urinary excretion of the fibrogenic cytokine transforming growth factor (TGF-beta 1) was improved, too (CTRL-PL 0.349 +/- 0.051, CTRL-E 0.693 +/- 0.230, 5/6 NX-PL 3.044 +/- 0.540, 5/6 NX-E 1.390 +/- 0.238 ng/mumol creatinine; P < 0.05). At sacrifice, tubulointerstitial fibrosis was less pronounced in E-treated rats. Correspondingly, the volume fraction of tubulointerstitial tissue in the renal cortex was improved in 5/6 NX-E rats (CTRL-PL 9.9 +/- 0.2, CTRL-E 10.0 +/- 0.2, 5/6 NX-PL 17.9 +/- 1.8, 5/6 NX-E 13.8 +/- 0.9%; P < 0.05). The protein/DNA ratio in isolated glomeruli and tubules, as an estimate of glomerular matrix accumulation and hypertrophy of tubules, was enhanced in 5/6 NX groups and a tendency towards lower values was observed after E treatment. Renal function as evaluated by serum creatinine and urea levels was not influenced by the enzyme therapy. No between-group differences in blood pressure were observed. In summary, oral administration of proteolytic enzymes improved proteinuria and urinary TGF-beta 1 excretion, as well as the severity of tubulointerstitial fibrosis without signs of toxicity.

Effect of gamma-tocotrienol on blood pressure, lipid peroxidation and total antioxidant status in spontaneously hypertensive rats (SHR)

The aim of this study was to determine the effects of gamma tocotrienol on lipid peroxidation and total antioxidant status of spontaneously hypertensive rats (SHR), comparing them with normal Wistar Kyoto (WKY) rats. SHR were divided into three groups and treated with different doses of gamma tocotrienol (gamma1, 15 mg/kg diet; gamma2, 30 mg/kg diet and gamma3, 150 mg/kg diet). Normal WKY and untreated SHR were used as normal (N) and hypertensive control (HC). Blood pressure were recorded every fortnightly for three months. At the end of the trial, animals were killed and measurement of plasma total antioxidant status, plasma superoxide dismutase (SOD) activity and lipid peroxide levels in plasma and blood vessels were carried out following well established methods. Study shows that lipid peroxides were significantly higher in hypertensive plasma and blood vessels compared to that of normal rats (Plasma- N: 0.06+/-0.01, HC: 0.13+/-0.008; p<0.001, B1. Vessels - N: 0.47+/-0.17, HC: 0.96+/-0.37; p<0.001). SOD activity was significantly lower in hypertensive than normal rats (N = 148.58+/-29.56 U/ml, HC = 110.08+/-14.36 U/ml; p = 0.014). After three months of antioxidant trial with gamma-tocotrienol, it was found that all the treated groups have reduced plasma lipid peroxides concentration but was only significant for group gamma1 (gamma1: 0.109+/-0.026, HC: 0.132+/-0.008; p = 0.034). On the other hand, lipid peroxides in blood vessels reduced significantly in all treated groups (gamma1; p<0.05, gamma2; p<0.001, gamma3; p<0.005). All the three treated groups showed improve total antioxidant status (p<0.001) significantly. SOD activity also showed significant improvement in all groups (gamma1: p<0.001, gamma2: p<0.05, gamma3: p<0.001). Correlation studies showed that, total antioxidant status (TAS) and SOD were significantly negatively correlated with blood pressure in normal rats (p = 0.007; p = 0.008) but not in SHR control. This correlation regained in all three groups SHR's after treatment with tocotrienol. Lipid peroxides in blood vessel and plasma showed a positive correlation with blood pressure in normal and SHR control. This correlation also remains in treated groups significantly except that in gamma3 where positive correlation with plasma lipid peroxide was not significant. In conclusion it was found that antioxidant supplement of gamma-tocotrienol may prevent development of increased blood pressure, reduce lipid peroxides in plasma and blood vessels and enhanced total antioxidant status including SOD activity.

Spontaneous and renal hypertensive rats: responsiveness of isolated right and left atria to noradrenaline, isoprenaline and methoxamine

The adrenergic responsiveness of right and left atria isolated from spontaneously hypertensive rats (SHR) and renal hypertensive rats (RHR) was studied. Right atria isolated from SHR showed subsensitivity to the chronotropic effect of noradrenaline (21.3-fold at the EC50 level, P < 0.05) and isoprenaline (12.0-fold, P < 0.05). However, atria isolated from RHR did not exhibit any significant alteration (P > 0.05) in sensitivity to the chronotropic effect of noradrenaline or isoprenaline. Chronotropic responsiveness to theophylline was not altered in right atria isolated from SHR or RHR. alpha 1-Mediated inotropic responses to noradrenaline and methoxamine were blunted in left atria isolated from SHR. Left atria isolated from RHR showed supersensitivity to the inotropic effect of noradrenaline (5.4-fold at the EC50 level, P < 0.05) and subsensitivity to the inotropic effect of methoxamine (6.0-fold, P < 0.05). It is concluded that the present results could, at least partially, explain the reduced cardiac output observed during established hypertension in SHR and the increased cardiac output observed in the initial phase of renal hypertension in RHR.

Potassium channel activation improves blood flow pattern of conscious rats in cutaneous microcirculation

1. A dose-dependent mean arterial blood pressure reduction (tailcuff method) to an intravenously administered potassium channel activator (22 or 24 micrograms/kg bw) was found in conscious rats. 2. Intravital microscopic analysis of skin microcirculation in conscious rats was performed with respect to erythrocyte flow velocity and diameters of capillaries. There was a dose-dependent increase of erythrocyte flow velocity; diameters of capillaries were dilated following a dosage of 6 and 12 micrograms/kg bw, but constricted following a dosage of 24 micrograms/kg bw. 3. Frequency distributions of velocity ranges in capillaries under observation (real time video recordings) proved that the increase of microvascular perfusion is manifested by a shift of maximal values to increasing velocity ranges. 4. It is concluded that potassium channel activation plays an important role in the local regulation of perfusion on the peripheral circulation.

Proteinase activity in isolated glomeruli of Goldblatt hypertensive rats

In Goldblatt rats, the kidney exposed to high blood pressure reveals glomerulosclerosis. Moreover, in preexisting parenchymal renal disease, the development of glomerulosclerosis is accelerated in the unclipped kidney. Up to now, the pathogenetic mechanism underlying the development of glomerulosclerosis due to systemic hypertension has not completely been resolved. Traditionally, hemodynamic mechanisms have been discussed. This study was performed to investigate whether there might be a decreased activity of glomerular proteinases in the unclipped kidney of Goldblatt rats as a potential pathogenetic factor for glomerulosclerosis. 20 weeks after the surgical intervention, we found a reduced proteinase activity in ultrasonically destroyed isolated glomeruli obtained by differential sieving technique in comparison with the contralateral clipped kidney and the kidneys of sham-operated normotensive controls. This could be confirmed, when proteinase activity was related to DNA instead of protein. When investigating glomerular cathepsin B-content, a lysosomal enzyme, which is able to degrade glomerular structural as well as non-structural proteins, we found a decreased level in the kidney of Goldblatt rats exposed to systemic hypertension in comparison with normotensive control animals. Basing on these results we presume that glomerular protein accumulation and concomitant glomerulosclerosis due to systemic hypertension might be a result of a synergistical interaction between hemodynamic factors and biochemical ones; we suggest one of the latter to be a decreased glomerular proteinase activity.

Cardiac membrane vitamin E and malondialdehyde levels in heart muscle of normotensive and spontaneously-hypertensive rats

The vitamin E (alpha-tocopherol) and free and bound malondialdehyde (MDA) in ventricular heart muscle and myocardial membrane from Wistar-Kyoto (W/K) normotensive and spontaneously hypertensive (SH) rats have been measured directly by high performance liquid chromatography (HPLC). Thiobarbituric acid-reactive substance (TBA-RS) in the myocardium and heart-muscle membrane of the two strains was also quantified by a colorimetric TBA test. It was found that SH-rat myocardium and myocardial membrane contained more than 3-fold less alpha-tocopherol than did heart muscle and cardiac membrane of the normotensive rat. Coincident with this relative vitamin E deficiency were several-fold greater amounts of MDA and TBA-RS in SH-rat myocardium and myocardial membrane. Most (87%) of the MDA in SH-rat heart muscle, but only 40% in W/K-rat heart muscle, was free (i.e., unbound). These results offer direct evidence that SH-rat myocardium is vitamin E-deficient and highly peroxidative, relative to cardiac muscle of the normotensive W/K parent strain. The lower vitamin E content of SH-rat myocardium is particularly striking, because SH-rat myocardial membrane was found to contain approximately 35% more phospholipid than myocardial membrane in the W/K rat. Although the amounts of myocardial TBA-RS are greater in the SH strain, they do not reflect the actual MDA profiles of the heart muscles or the heart membranes and cannot be used as a quantitative index of cardiac oxidative-injury status due to non-MDA TBA-RS in both strains.

An impedance method for blood pressure measurement in awake rats without preheating

The tail-cuff methods for measuring systolic blood pressure in the rat usually require preheating of the animal to obtain recordable pulse signals. To find a more sensitive method, we applied the principle of differentiated impedance (dZ/dt) to the tail-cuff measurement of systolic blood pressure. We obtained clear pulse signals from the tail in awake rats without preheating the animals, and the systolic blood pressure obtained by this method had an excellent correlation with the directly measured femoral artery pressure (correlation coefficient = 0.98). Heating the animals at 40 degrees C for 5 minutes increased systolic blood pressure by a mean of 6 mm Hg as compared with that determined at the ambient temperature of 21 to 24 degrees C. Mean systolic blood pressure in young female diabetic rats was 122 +/- 3 mm Hg, which was significantly higher than the 111 +/- 2 mm Hg of normal rats. It is concluded that the technique of electrical impedance as applied to the tail-cuff method is simple and highly sensitive and is suitable for measurement of tail systolic blood pressure in awake rats without preheating.

Myocardial biochemical, contractile, and electrical performance after imposition of hypertension in young and old rats

The effects of renovascular hypertension on the biochemical, contractile, and electrical performance of myocardial tissue from rats of various ages has been examined. Male Fischer rats, 2, 7, 12, and 17 months old, were made hypertensive by constriction of the left renal artery. Ten weeks after the onset of hypertension, left ventricular papillary muscles were isolated from those four groups when 5, 10, 15, and 20 months old, respectively. Mechanical performance and transmembrane electrical events were recorded simultaneously. Contractile protein enzyme activity was determined in the same hearts from which papillary muscles were used for acquisition of mechanical and electrical information. There was a slight increase in blood pressure in control groups as a function of age while blood pressure maintained a range of approximately 179-188 mm Hg for all hypertensive groups. Heart weight of control animals increased significantly from 5 months to 20 months of age from 539 +/- 26 to 1088 +/- 56 mg, representing an increase of 101%. In hypertensive animals, heart weight increased 50% in 5-month-, 15% in 10-month-, 50% in 15-month-, and 11.7% in 20-month-old animals. Although control groups revealed alterations in mechanical, electrical, and biochemical parameters that increased as a function of age, the magnitude of the biochemical, contractile, and electrical response to hypertension varied monotonically with the extent of myocardial hypertrophy, rather than age per se. Adaptation to the stress of hypertension was observed in each age group, and was revealed as prolongation of mechanical and electrical timing parameters, depression of the load-velocity relation, and contractile protein enzyme activity. Thus, the stress of hypertension, which was tolerated by the 10- and 20-month-old animals with lesser relative hypertrophy and lesser changes in measured parameters, may represent a differential adaptation to the stress of hypertension.

Renal hypertensive hypertrophy in the rat: a substrate for arrhythmogenicity

We investigated the ability of ouabain to produce lethal arrhythmias in rats with myocardial hypertrophy resulting from chronic renal hypertension. A gradual pressure overload was produced in female Wistar rats by left renal artery stenosis (two kidney, one clip, Goldblatt hypertension). Hypertension (systolic blood pressure greater than 150 mm Hg) developed within three weeks after clipping of the left renal artery and blood pressure continued to increase for the next five weeks. At ten weeks after the onset of hypertension animals were anesthetized with sodium pentobarbital (40 mg/kg) and artificially ventilated with room air while ECG was continually monitored and recorded. Continuous infusion of ouabain was maintained (0.7 mg/kg/min) through the inferior vena cava. Body weight and heart rate of control animals (C) was not significantly different from hypertensive (H) values, while systolic blood pressure in animals hypertensive for ten weeks was considerably greater (187 +/- 8.4 mm Hg) than their age-matched normotensive counterparts (123 +/- 6.0 mm Hg). Heart weight in hypertensive animals was elevated by 69% +/- 2.5 by time of study. Serological evaluation of both groups of animals revealed no significant differences in electrolytes and blood gases while significant differences were noted in glucose, BUN and creatinine. The average time to the first premature ventricular contraction was significantly shorter in H animals (3.5 +/- 0.2 min) when compared to C rats (6.0 +/- 0.2 min). The average time to ventricular tachycardia, ventricular fibrillation and death were also significantly shorter in H rats when compared to C animals (7.5 +/- 0.6 vs. 13.5 +/- 0.3; 13.5 +/- 0.5 vs. 21.0 +/- 0.5; 15.6 +/- 0.4 vs. 24.0 +/- 0.6 min). Thus, the hypertensive hypertrophied myocardium displays an increased propensity for lethal cardiac arrhythmias due to ouabain.

Involvement of lymphocytes in non-immune inflammation: dual effect of glucocorticoids

Leucopenia induced by the administration of methotrexate reduced the volume of inflammatory exudate and the number of cells entering the pleural cavity during a 4-h carrageenin pleurisy when compared with that of non-leucopenic controls. The depressed response was partially but markedly restored when leucopenic animals were intravenously injected, immediately before the initiation of pleurisy, with spleen lymphocytes (or their products) obtained from normal, adrenal-demedullated or mock-operated rats. In contrast spleen lymphocytes (or their products) obtained from adrenalectomized rats or from rats receiving metyrapone, an inhibitor of adrenal glucocorticoid biosynthesis, were completely inactive. It is concluded that in physiologic concentrations glucocorticoids are essential for the production of lymphocyte-derived factors involved in the development of acute, non-immune inflammation. In pharmacologic concentrations, however, glucocorticoids suppress the release of such pro-inflammatory factors.

Vascular reactivity in diabetes mellitus: possible role of insulin on the endothelial cell

The response to vasoactive agents of microvessels of the rat was tested in vivo by direct microscopic observation of the exteriorized mesentery and assessment of cutaneous vascular permeability changes with Evans blue. The constrictor response to a standard amount of noradrenaline in mesenteric microvessels was fully antagonized by acetylcholine in normal, diabetic, adrenalectomized and diabetic-adrenalectomized rats. In contrast, the minimum doses of histamine or bradykinin, effective in normal or adrenalectomized animals, had to be increased about 20 fold to be active in diabetic or diabetic-adrenalectomized animals. Topical application of insulin to mesenteric microvessels of diabetic animals, in amounts not causing any increase in serum insulin levels, improved or restored the capacity of the animals to respond to histamine or bradykinin, acting as antagonists of the vasoconstrictor response to noradrenaline. Topical insulin, however, was ineffective in normal animals given 2-deoxyglucose, the acute effects of which result from cellular glucopaenia unrelated to insulin deficiency. Vascular permeability responses to intracutaneous histamine or bradykinin were decreased in animals pretreated with 2-deoxyglucose as much as in diabetic animals. Pretreatment of normal animals with indomethacin produced no effect on the responses of these animals to histamine or bradykinin, tested as antagonists of noradrenaline on mesenteric microvessels, or as vascular permeability-increasing factors in the skin. Pretreatment of normal animals with chloroquine, mepacrine or dexamethasone had no effect on the reactivity of mesenteric microvessels to histamine and bradykinin, acting as antagonists to noradrenaline. 7 It is suggested that vasoactive substances, endowed with permeability-increasing properties, evoke relaxation of microvessels through an insulin-dependent action on endothelial cells, unrelated to the release of arachidonic acid metabolites. This action would lead to increased vascular permeability, with opening of interendothelial junctions, and temporary changes in composition of extravascular fluid, which in turn, would provide the basis for vasodilatation. Diabetes mellitus apparently impairs such responses as a result of the accompanying cellular glucopaenia. Adrenal corticosteroids are not involved in the impaired responses.

Hypertension and cardiovascular hypertrophy during chronic catecholamine infusion in rats

Chronic continuous infusion of norepinephrine (NE) or epinephrine (Epi) subcutaneously in rats resulted in rapid elevation of systolic blood pressure (SBP) by 40 mm Hg. Pressure remained high for the duration of the infusion but rapidly returned to control levels after its termination. Pronounced hypertrophy of the thoracic aorta, abdominal aorta and heart was evident within 2 days of the initiation of NE infusion and a plateau was attained by 5 days of infusion. The activity of tissue ornithine decarboxylase (ODC), the rate limiting enzyme in polyamine biosynthesis, was elevated preceeding the onset of tissue hypertrophy, and returned to control levels coincidentally with the cessation of accelerated tissue growth. It is concluded that high blood pressure in this animal model of hypertension is dependent upon the continued presence of exogenous catecholamine, and that pronounced cardiovascular hypertrophy per se is not sufficient to maintain the hypertension. The elevation and decline of vascular ODC activity is consistent with reports that in other tissues an elevation of ODC activity is an obligatory early event in hypertrophy.

Vascular reactivity in diabetes mellitus: role of the endothelial cell

The response to vasoactive agents of microvessels in situ and large arteries in vitro was compared in normal and alloxan-diabetic rats. Noradrenaline was equally effective in evoking a constrictor response of mesenteric microvessels in normal and diabetic animals. The constrictor response to a standard amount of noradrenaline in such vessels was fully antagonized by acetylcholine or papaverine, the minimum effective doses being equivalent in normal and diabetic animals. In contrast, the minimum doses of histamine or bradykinin, effective in normal animals, had to be increased about 20 fold to be active in diabetic animals. Increased osmolarity of extracellular fluid caused a significant and equivalent increase in latency of the vasoconstrictor response of microvessels to noradrenaline in normal and diabetic animals. Concentration-effect curves, constructed from the response of isolated aortae to noradrenaline, were similar in normal and diabetic animals, provided the endothelium was removed. Diabetes only affected preparations in which the endothelium was left intact. In these, the median effective concentrations of noradrenaline were greatly increased in comparison with normal values. Precontracted aortae from normal and diabetic animals were equally relaxed by acetylcholine and histamine, provided the endothelium was left intact. Loss of the relaxant response of the preparations in all groups of animals was observed following removal of endothelial cells. It is suggested that different mechanisms may be involved in the effects of vasodilator agents on large arteries in vitro or small vessels in situ. Histamine and bradykinin which are potent permeability-increasing factors, may antagonize the vasoconstrictor response of microvessels to noradrenaline through an action on endothelial cells with increased vascular permeability and temporary changes in composition of extracellular fluid. The reactive process of endothelial cells to permeability factors was affected by diabetes mellitus. However, the response of microvessels to acetylcholine and papaverine which are devoid of permeability-increasing properties, was not influenced by diabetes.

Facts and fallacies about measuring blood pressure in rats

Although blood pressure can easily be measured in anesthetized rats by simply connecting a catheter to a pressure transducer, repeated measurements taken over long periods of time in awake rats are much more difficult to make. For chronic experiments two methods are now commonly used: direct recording from chronically-implanted arterial catheters, or indirect measurement with the tail-cuff method. Direct recording of intraarterial pressure can be done continuously and is more accurate, but technically more demanding. On the other hand, although tail-cuff measurements are less accurate, they do not require surgery and can be repeated almost indefinitely. With most tail-cuff methods the rats are preheated to dilate the tail vessels and thereby facilitate pulse detection, but with the new IITC photoelectric sensor indirect measurements of systolic as well as of mean arterial pressure can be made without external preheating. Even with a properly validated tail-cuff method, however, errors can still occur particularly when it is used to quantify modest blood pressure changes like those during development of hypertension, or following administration of vasoactive drugs. To safeguard against such errors, each laboratory should always validate its own tail-cuff method under uniform experimental conditions similar to those existing when the method is actually used. Additionally, all blood pressure differences thereby detected should be verified by direct measurement of intraarterial pressure in the same rats.

Collagen metabolism and reversal of aortic medial hypertrophy in spontaneously hypertensive rats treated with methyldopa

Collagen synthesis, content, and concentration were determined in the hypertrophied intima media of thoracic aortas from 10-, 15-, and 20-week-old spontaneously hypertensive rats (SHR). Although the rates of aortic collagen synthesis declined with age, the dry weight of the intima media and the total collagen content increased proportionally. Collagen concentration thus remained unchanged. Methyldopa was administered orally to SHR when they were 12 to 15 weeks of age, when their body weight were identical to the untreated group. Blood pressure and the degree of aortic medial hypertrophy, judged by medial dry weight per kilogram body weight, were significantly lower compared with untreated SHR. Collagen synthesis was likewise decreased to a mean rate not significantly higher than age-matched normotensive Wistar-Kyoto controls. This reduction in collagen synthesis, however, was not sufficient to decrease measurably the total collagen content of the aortas compared with untreated SHR. Since medial dry weights were lower in the treated rats, collagen concentration in aortas from SHR given methyldopa for 3 weeks was actually increased. The increase in collagen concentration also suggests that medial hypertrophy was reversed.

Altered cyclic AMP levels in specific cardiovascular brain centers of spontaneously hypertensive rats (SHR)

The possible participation of cAMP in central regulation of arterial blood pressure was investigated in spontaneously hypertensive rats (SHR). Cyclic AMP concentrations of 36 microdissected individual brain areas-including primary and higher cardiovascular centers-were measured in adult SHR and compared with those of normotensive control rats of the same strain and age. In the adult SHR, elevated cAMP concentrations were found in brain areas which are in close connection with the central regulation of blood pressure: nucleus tractus solitarii, A1- and A2- catecholaminergic cell groups in the medulla oblongata, locus coeruleus, central grey matter (subnucleus medialis), and certain cortical areas (especially cingulate cortex and hippocampus). On the other hand, hypothalamic cell groups which have been also suggested to control blood pressure, such as paraventricular, anterior, ventromedial, dorsomedial and posterior hypothalamic nuclei, show lower concentrations of cAMP in the SHR than in normotensive controls. Cyclic AMP levels in 19 other brain areas of SHR which seem to be not involved in mechanisms of central blood pressure regulation practically do not differ from the values of normotensive rats. The results suggest that cAMP-dependent processes are involved in the regulatory mechanisms of central blood pressure control. The brain areas which show alterations of cAMP-levels are also distinguished by close neuronal connections to the baroreceptor reflex arc. It is supposed that these areas represent modulatory higher centers capable to affect baroreceptor reflex function.

Cardiac pumping ability following reversal of hypertrophy and hypertension in spontaneously hypertensive rats

Direct measurements of arterial pressure, stroke volume (SV), and cardiac output (CO) were obtained in ether-anesthetized rats with established spontaneous hypertension (SHR) treated with alpha-methyldopa and compared to both untreated hypertensive and normotensive Wistar-Kyoto (WKY) rats. Left ventricular pumping ability was determined by the maximum levels of SV and CO reached during rapid intravenous volume loading with blood. Treatment with methyldopa reduced the SHR arterial blood pressure (average 57 mm Hg) and reversed the cardiac hypertrophy toward normal. In comparison to untreated SHR, therapy increased heart rate and CO and decreased peripheral resistance. During volume-loading, the levels of SV and CO at matched left ventricular end-diastolic pressures were significantly higher in treated vs untreated SHR. To evaluate the role of blood pressure in the improved peak pumping ability observed in treated rats, a phenylephrine infusion was used to equalize pressures while repeating cardiac function studies. In normotensive WKY and untreated SHR, left ventricular pump function was not greatly affected. A pronounced depression in peak SV and peak CO was observed only in treated SHR. The data indicate that treatment with methyldopa is associated with improved ventricular function in part related to the reduction in arterial pressure.

Sympathetic nerve activity and blood pressure in normotensive backcross rats genetically related to the spontaneously hypertensive rat

The genetic basis of hyperactivity of the sympathetic nervous system (SNA) in spontaneously hypertensive rats (SHR) was assessed by measuring SNA in animals derived from a backcross (BC) breeding program designed to isolate single gene differences causing changes in blood pressure. Selective breeding of the male hypertensive rats with inbred normotensive female Wistar/Lewis rats yielded progeny with a range of blood pressures, but whose group mean pressures were lower than the group mean pressures of the original SHR. Progressive generations had progressively lower group mean pressures. There was a positive correlation between SNA and mean arterial pressure in BC rats. These results indicate that the genetic defect in SHR may be abnormality in SNA, and the hypertension in these animals is a secondary result of this primary defect. Baroreceptor function was also assessed in SHR and in BC rats. In young (8 to 24 weeks old) SHR, baroreceptor function was similar to that in BC rats, whereas SNA was markedly increased. Only in older (24 to 40 weeks old) SHR was there an abnormality in the gain of baroreceptors. The development of hypertension in SHR therefore appears to be due to increased SNA resulting from a defect in the central nervous system. Changes in baroreceptor function are secondary to the hypertension and occur after the hypertension is established.

Cardiac pumping ability in rats with experimental renal and genetic hypertension

In two experimental models of established hypertension in the rat (two kidney, one clip renal and genetic hypertension), the maximum by which stroke volume and cardiac output could be increased during an acute preload stress was significantly reduced despite the concomitant development of left ventricular hypertrophy. Reversal of cardiac hypertrophy by prolonged treatment with methyldopa (range 3 to 6 weeks) during the established phase of spontaneous hypertension normalized arterial blood pressure and improved ventricular pumping ability. The improved performance was in part due to reduced impedance to ventricular ejection because it did not persist when peripheral resistance was increased by an acute administration of phenylephrine hydrochloride. Thus, hemodynamic as well as structural factors contribute to alterations in cardiac function during the chronic established phase of arterial hypertension.

Decreased cAMP content of the hypothalamus of genetically hypertensive rats

In genetically hypertensive rats an altered catecholamine content of hypothalamic structures has been reported. In the present study cAMP was estimated in the hypothalamus and cortex of genetically hypertensive rats and compared with normotensive controls of the same strain. It is shown, that the cAMP content of the hypothalamus of the hypertensive animals was decreased to about 60% of control values, whereas there was no difference of the cAMP content in the cortical regions of the same animals. These results indicate an alteration of the adenyl cyclase-cAMP-phosphodiesterase system in hypothalamic structures of genetically hypertensive rats.

Hypertension: increase of collagen biosynthesis in arteries but not in veins

In two models of hypertension in rats, it was shown that collagen synthesis and deposition are increased in arteries where blood pressure is elevated. By contrast, there were no alterations in any of the markers of collagen synthesis in veins, where blood pressure was only slightly elevated. It would appear that the stimulus for vascular collagen synthesis is provided by a direct effect of the increased pressure on the arterial cells rather than by a humoral factor released into the general circulation.

Reduction of blood pressure and vascular collagen in hypertensive rats by beta-aminopropionitrile

beta-Aminopropionitrile, a specific inhibitor of lysyl oxidase prevented the rise in blood pressure induced by deoxycorticosterone-salt in rats. In addition, after the onset of hypertension, administration of beta-aminopropionitrile lowered the blood pressure. Concomitant with the lowering of blood pressure, there was a reduction in the more highly crosslinked form of vascular collagen. These findings would indicate that increases in vascular connective tissue are not only sequelae of hypertension, but may also contribute to the maintenance of elevated blood pressure.

Effect of 1-(m-chlorophenyl)-3-N,N-dimethyl-carbamoyl-5-methoxypyrazole (PZ-177) on drug-metabolizing enzyme on rat liver

Effect of 1-(m-chlorphenyl)-3-N,N-dimethylcarbamoyl-5-methoxypyrazole (PZ-177) (62.5 and 250 mg/kg) on rat liver was investigated by measuring liver weight and drug-metabolizing enzyme activity. The effects of PZ-177 were compared with those of phenobarbital, phenylbutazone, and tiaramide hydrochloride. Increase of liver weight and liver/body weight ratio was observed in the rats treated with PZ-177 or phenobarbital, however, normal values were reverted to 1--2 weeks after treatment. PZ-177 similar to phenobarbital, significantly enhanced the activity of aminopyrine demethylase and aniline hydroxylase after 1,2, and 4 weeks of treatment. In contrast, tiaramide hydrochloride decreased the activity of aminopyrine demethylase and aniline hydroxylase after 1 week of treatment, and significantly enhanced the activity of these enzymes after 4 weeks. The content of cytochrome P-450 and the activity of NADPH cytochrome C reductase were also increased by treatment with PZ-177. The sleeping time by hexobarbital was shortened significantly by the administration of PZ-177. Vmax for both aminopyrine demethylase and aniline hydroxylase increased by treatment with PZ-177. However, only the Km for aniline hydroxylase was increased by treatment with PZ-177. From the results of these experiments, PZ-177 may be classified as a phenobarbital-type inducer.

A proinflammatory factor in lymphocytes. Its role in the development of acute, non-immunological inflammatory reactions

Drug-induced leucopenia renders rats hyporeactive to various inflammatory stimuli. Administration to leucopenic rats of suspensions of lymphocytes, sufficient to apparently correct the induced lymphocytopenia, led to a partial but marked reversal of the inhibited responses. Similar results were observed when lysates of lymphocytes or filtrates of the disintegrated cells were injected. Suspensions of polymorphonuclear granulocytes, on the contrary, were ineffective in producing a reversal of inhibited inflammatory reactions in leucopenic rats. The presence of a proinflammatory factor (LpIF) in lymphocytes, which might be involved in the modulation of acute inflammatory responses is suggested.

Inhibition of dopamine beta-hydroxylase in blood vessels by picolinic acid derivatives in vivo and their anthypertensive effects

The effect of picolinic acid derivatives, 5-butylpicolinic (fusaric) acid (FA), 5-(3',4'-DIBROMOBUTYL)PICOLINIC ACID(BPR2FA)and 50(N'N-dimethyldithiocarbamoilmethyl)picolinic acid (YP-279) on dopamine beta-hydroxylase in blood vessels in vivo was studied. Maximum inhibition of the conversion of 14C-dopamine (14C-DA) to 14C-norepinephrine (14C-ne) in rat aorta, mesenteric artery and renal artery was detected 30 min after FA and Br2FA (75 mg/kg) and 60 min after YP-279 (75 MG/KG). NE synthesis from 14C-DA returned to near control values by 6 hr in the blood vessels. NE levels of the aorta and mesenteric artery were sigkificantly reduced by 30 to 50% at 4 hr after Br2FA or FA (75 mg/kg). Dopamine beta-hydroxylase (DBH) activity, using tyramine as substrate, in heart, aorta, mesenteric artery and renal artery was markedly reduced. The concentrations of FA, Br2FA and YP-279 in rat blood following a single i.p, injection of each drug increase rapidly, reaching highest values in 0 to 30 min and decreasing slowly to 0 after 6 hr. These compounds did not affect the uptake of 3H-NE into the rat heart. These three compounds were found to lower blood pressure effectively in normal Wistar rats (above 25 mg/kg).

Influence of neonatal thymectomy on blood pressure and hypertensive vascular disease in rats with renal hypertension

The effect of neonatal thymectomy on the degree and prognosis of hypertension and on the vascular lesions in rats with renal hypertension was studied. There were no differences between thymectomized and sham operated hypertensive rats. The degree of hypertension, the frequency of spontaneous death and heart infarcts were the same in both groups. The occurrence and degree of perivascular cell infiltrations, deposits of perivascular connective tissue and fibrinoid degenerations of the media were found to be the same in both the thymectomized and the sham operated hypertensive animals. The results do not support the assumption that delayed type immune reactions are important in the pathogenesis of hypertensive vascular disease in renal hypertensive rats.