A model of chronic heart failure in spontaneous hypertensive rats (SHR)

Common models of chronic heart failure (CHF) do not always result in parameters and symptoms that can be extrapolated to the clinical situation of patients with end-stage heart failure. The aim of this study was to establish and validate a new model of CHF in the rat. CHF was induced in Wistar Kyoto (WKY/NHsd) and spontaneously hypertensive (SHR/NHsd) rats by creating a permanent (8-week) occlusion of the left coronary artery 2 mm distal to the origin from the aorta by a modified technique. This resulted in a large infarction of the free left ventricular wall. The focus of attention was the validation of the geometric properties of the left ventricle and its contractility. The validation of the geometric properties of the left ventricle was done by a non-invasive magnetic resonance imaging (MRI) technique and by planimetry (stereology). Cardiodynamics (e.g. contractility) were evaluated in the isolated 'working heart' model. We were able to establish a new and predictive model of heart failure in the spontaneously hypertensive rat 8 weeks after coronary artery ligation. At this time point, the WKY rat did not show any symptoms of CHF. The model represents characteristic parameters and symptoms that can be extrapolated to the clinical situation of patients with end-stage heart failure (NYHA III-IV). Upon inspection, severe clinical symptoms of congestive heart failure were prominent, such as dyspnoea, subcutaneous oedema, pale-bluish limbs and impaired motion. Non-invasive sequential measurements by NMR techniques showed lung oedema, hydrothorax, large dilated left and right ventricular chambers and hypertrophy of the septum. The infarcted animals showed a reduced heart power, diminished contractility and enhanced heart work, much more so in the SHR/NHsd rat than in the WKY/NHsd rat. Furthermore the infarcted animals showed enhanced levels of hydroxyproline/proline ratios, again much more so in the SHR/NHsd rat than in the WKY/NHsd rat.     

Collagen in the aortae of spontaneously hypertensive (SHR) rats

A biphasic pattern of collagen biosynthesis was found in the aortae of spontaneously hypertensive (SHR) rats; the time course of the rate of biosynthesis is similar to that described in the heart by Sen and Bumpus. In comparison to age-matched controls, collagen biosynthesis is elevated in the SHR rats, diminishes during the first fourteen weeks and rises again at the stage of established hypertension. In the period of established hypertension, the increased rate of collagen biosynthesis was associated with a pronounced rise of the collagen type I to type III ratio. On the other hand, in the pre-hypertensive stage, the proportion of collagen type III clearly exceeds the proportion of collagen type I in SHR rats.     

Atrial natriuretic polypeptide (ANP) in the development of spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP)

In order to investigate the pathophysiological role of atrial natriuretic polypeptide (ANP) in genetic hypertensive rats, the atrial content and plasma concentration of ANP were measured by a sensitive radioimmunoassay (RIA) for rat ANP in 5-, 10- and 20-week-old spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) and compared to age-matched Wistar Kyoto rats (WKY). Atrial content of immunoreactive ANP (ir-ANP) tended to be higher in SHR and was already significantly higher in SHRSP than in WKY at 5 weeks of age. Atrial content in the hypertensive strains became significantly higher than in WKY when hypertension developed at 10 and 20 weeks. On the other hand, plasma ir-ANP in SHR was significantly lower than in WKY at 5 weeks, however, it became significantly higher in both SHR and SHRSP than in WKY at 10 and 20 weeks. These findings suggest that ANP release may increase to compensate for the elevation of blood pressure in SHR and SHRSP and that biosynthesis of ANP may be concomitantly stimulated, resulting in an increase in atrial ANP.     

Genetic control of blood pressure in spontaneously hypertensive rats (SHR)

Genetic control of blood pressure in the SHR strain was studied by three separate experiments which consist of cross analysis between the SHR and Donryu, two-way selecton for high and low blood pressure levels, and successive backcrosses to the parental strains. The results obtained were as follows. 1. The data from genetic crosses between the SHR and Donryu showed the phenotype segregation ratio of 1:1 at the backcross and 1:2:1 at the F2 generation. 2. Two-way selection for high and low blood pressure levels was performed from the F2 generation onward. The separation between the two lines occurred immediately after the first selection. Thereafter, the difference increased gradually with generation. The blood pressure level at the seventh generation of selection became approximately equal to those of the parental strains. 3. Two types of the successive backcross were performed from the F1 hybrids by mating the males showing the highest blood pressure level to Donryu females and the females showing the lowest blood pressure level to SHR males on the other. Bimodality was observed in the distribution of blood pressure levels at each generation. Their phenotypic segregation ratios were accordant with 1:1 on the whole. At the intercross generation during successive backcrosses, a trimodal distribution was observed. 4. These results confirmed that the hypertensive trait of the SHR is regulated by a single major gene and other several genes with minor effect. A gene symbol ht was proposed for this major gene. Concurrently, a congenic strain having the ht gene on the genetic background of the Donryu was developed by the successive backcross system.     

Minerals in renal and SHR hypertensive rats

References to individual trace minerals in hypertensive rats have been made; however, data on multiple minerals in SHR hypertensive rats is lacking. The purpose of this study was to investigate five trace minerals in normotensive, chronic renal and SHR hypertensive rats. Blood samples were drawn to measure serum levels of Ca, Fe, K, Mg, and Na. Serum K values were elevated in the chronic renal hypertensive animals. Iron levels were decreased in both the renal and SHR hypertensive animals. No difference was observed in levels of Ca, Mg, and Na between normotensive and chronic renal or SHR hypertensive rats. Further study of multiple trace minerals in experimental hypertension is recorded in order to extend these deviations.     

Changes in the blood vessel wall elastin of spontaneously hypertensive (SHR) rats

It has been demonstrated that both elastin and tropoelastin preparations obtained from aortae of spontaneously hypertensive rats at the stage of established hypertension differ in their amino acid composition from age-matching controls. The differences refer to an increased proportion of polar amino acids, particularly aspartic and glutamic acid (about a two-fold increase compared to the controls) and arginine and tyrosine (1.5 times the control value). On the other hand, this increase is compensated for by a decrease in the valine concentration. Furthermore, direct estimation of the number of val-pro sequence in different elastin preparations indicated a drop from 49.3 to 29.2 per 1,000 residues in normotensive controls and preparations obtained from spontaneously hypertensive rats respectively.     

Changes in elastin composition in aorta of spontaneously hypertensive rats (SHR)

Tropoelastin and elastin preparations obtained from aortae of spontaneously hypertensive rats (SHR) show an increased proportion of polar amino acids (aspartic acid, glutamic acid, arginine and tyrosine). The content of these amino acids is 1.43-3.04 times higher in SHR rats than in similar elastin or tropoelastin preparations obtained from normotensive animals. On the other hand elastin and tropoelastin preparations obtained from SHR rats show a lower frequency of the Val-Pro sequence; this was found to be 35.93 per 1000 amino acid residues in SHR rats as compared to 51.04 per 1000 amino acids in the preparations obtained from control animals. Since similar differences were found not only in elastin preparations but also in tropoelastin, contamination of these preparations with an acidic protein seems unlikely. In general the results obtained are similar to those seen in animals kept on a long term high fat diet. It appears feasible to suggest that these differences are caused by a changed proportion of two different elastin type.     

Intestinal calcium transport in spontaneously hypertensive rats (SHR) and their genetically matched WKY rats

Calcium transport across the basolateral membranes of the enterocyte represents the active step in calcium translocation. This step occurs by two mechanisms, an ATP-dependent pump and a Ca2+/Na+ exchange process. These studies were designed to investigate these two processes in jejunal basolateral membrane vesicles (BLMV) of the spontaneously hypertensive rats (SHR) and their genetically matched controls, Wistar-Kyoto (WKY) rats. The ATP-dependent calcium uptake was stimulated several-fold compared with no ATP condition in both SHR and WKY, but no differences were noted between rate of calcium uptake in SHR and WKY. Kinetics of ATP-dependent calcium uptake at concentrations between 0.01 and 1.0 microM revealed a Vmax of 0.67 +/- 0.03 nmol/mg protein/20 sec and a Km of 0.2 +/- 0.03 microM in SHR and Vmax of 0.69 +/- 0.12 and a Km of 0.32 +/- 0.14 microM in WKY rats. Ca2+/Na+ exchange in jejunal BLMV of SHR and WKY was investigated in two ways. First, sodium was added to the incubation medium (cis-Na+). Second, Ca2+ efflux from BLMV was studied in the presence of extravesicular Na+ (trans-Na+). Both studies suggest a decreased exchange of calcium and Na+. Kinetic parameters of Na(+)-dependent Ca2+ uptake at concentrations between 0.01 and 1.0 microM exhibited Vmax of 0.05 +/- 0.01 nanmol/mg protein/5 sec and a Km of 0.21 +/- 0.13 microM in SHR and Vmax of 0.11 +/- 0.02 nanmol/mg protein/5 sec and a Km of 0.09 +/- 0.05 in WKY, respectively. These results confirm that the intestinal BLMV of SHR and WKY rats have two mechanisms for calcium extrusion, an ATP-dependent Ca2+ transport process and a Na+/Ca2+ exchange process. The ATP-dependent process appears to be functional in SHR; however, the Ca2+/Na+ exchange mechanism appears to have a marked decrease in its maximal capacity. These findings suggest that calcium extrusion via Ca2+/Na+ is impaired in the SHR, which may lead to an increase in intracellular calcium concentration. These findings may have relevance to the development of hypertension.     

Some evidence of enhanced alimentary motivation in spontaneously hypertensive rats (SHR)

The consumption of a wet mash of biscuits or pellets, outside the home cage, was determined in adult spontaneously hypertensive (SHR) and normotensive (NT) Wistar rats. Rats were deprived of food for 24 h or satiated. Regardless of the testing conditions, SHR showed a higher food interest than NT rats, which was reflected in a shorter latency to start eating, a longer time of eating to the first interval as well as to the 30 sec interval which terminated the trial, and a larger amount of food consumed during the test trial. The speed of eating was greater in SHR. In the competition for food SHR won almost all encounters with NT rats. The mean time of eating by SHR increased over the consecutive encounters up to 90%. These findings indicate that alimentary motivation of SHR was higher than that of NT rats. The results are discussed in terms of hyperreactivity of SHR.     

Increased immunoreactive neuropeptide Y in platelets of spontaneously hypertensive rats (SHR)

A high concentration of immunoreactive neuropeptide Y was observed in rat platelets using a specific and sensitive radioimmunoassay for neuropeptide Y. Three kinds of high performance liquid chromatography combined with radioimmunoassay for neuropeptide Y showed that immunoreactive neuropeptide Y in rat platelets is identical to rat authentic neuropeptide Y. To investigate the pathological role of platelet neuropeptide Y in genetic hypertensive rats, the platelet content and plasma concentration of neuropeptide Y were measured by a sensitive radioimmunoassay for rat neuropeptide Y in 5-, 10- and 15-wk old spontaneously hypertensive rat and age-matched Wistar Kyoto rat. Platelet content of immunoreactive neuropeptide Y in 5-, 10- and 15-wk old spontaneously hypertensive rat was higher than that in Wistar Kyoto rat at each age. No difference was observed in plasma concentration of immunoreactive neuropeptide Y between spontaneously hypertensive rat and Wistar Kyoto rat at each age.     

Ontogeny of mitochondrial calcium transport in spontaneously hypertensive (SHR) and WKY rats

The current studies were designed to investigate calcium uptake by intestinal jejunal sacs as well as in intestinal mitochondria of spontaneously hypertensive rats and their genetically matched WKY control rats. Kinetics of jejunal calcium uptake by jejunal sacs of adult SHR and WKY rats showed a significant decrease in Vmax of calcium uptake in SHR (227 +/- 24 versus 423 +/- 22 nmol.g tissue-1.3 min-1) compared to WKY rats P less than 0.001. To explore the intracellular handling of calcium by the intestinal mitochondria, calcium uptake was characterized by intestinal mitochondria before (suckling and weanling periods) and after (adult period) development of hypertension. Calcium uptake by intestinal mitochondria was driven by ATP in the presence of succinate as a respiratory substrate. Calcium uptake was stimulated several fold by the presence of ATP compared to no ATP conditions. Maximal calcium uptake occurred between 15-30 min and was significantly greater in adult SHR and WKY rats compared to corresponding values in weanling and suckling rats. Maximal ATP dependent calcium uptake in adult, weanling and suckling WKY rats was significantly greater compared to corresponding mean values in each age group in SHR (P less than 0.001). Oligomycin (10 micrograms/mg protein) inhibited calcium uptake partially. Ruthenium red (0.25 microM), 1 mM sodium azide and 0.5 mM dinitrophenol inhibited calcium uptake by more than 80% in both SHR and WKY rats. Kinetic parameters for ATP stimulated calcium uptake at 10 s revealed a Vmax of 0.56 +/- 0.6, 3.46 +/- 0.23 and 3.95 +/- 0.52 nmol/mg protein/10 s in suckling, weanling and adult WKY rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Congenital abnormality of pituitary-thyroid axis in spontaneously hypertensive rats (SHR) and stroke-prone rats (SPR).

In an attempt to study whether TSH abnormality was genetically determined in SHR and SPR, plasma T4, T3, TSH and prolactin concentrations were measured in the animals with intervals of 1 to 3 months. Hypertension was found in 6-month-old SHR and SPR, but it was not found in younger animals. In contrast, a decrease of plasma T3 and an increase of plasma TSH were found in 15-day-old SHR. Also, an increase of TSH was found in 1-month-old SPR in spite of normal plasma T3 concentration. These abnormalities in SHR and SPR increased progressively with age. It is suggested that thyroid-pituitary abnormality was genetically determined in SHR and SPR.     

The carotid bodies of spontaneously hypertensive rats (SHR): a functional and morphologic study

The parameters of the acid-base-state of the arterial blood were measured in spontaneously hypertensive rats of the Okamoto-strain (SHR) and in normotensive Wistar rats (NWR) of a random-bred strain. The animals were anaesthetized with chloralose-urethane and breathed normal air under sea-level conditions. Structure and size of their carotid bodies were studied by light-microscopic methods. When compared with the NWR, the SHR showed a respiratory alkalosis and enlarged carotid bodies. In the SHR, never in the NWR, the lumen of the branches of the glomic arteries was narrowed by pad-like structures. The data suggest that systemic hypertension leads to morphologically and functionally detectable alterations of both carotid body structure and function. The interdependence of arterial chemoreceptor activity, sodium household, and the adjustment of systemic arterial blood pressure is briefly discussed.     

Clonidine action in spontaneously hypertensive rats (SHR) depends on the GABAergic system function

Summary The effect of -aminobutyric acid (GABA)_A antagonists (bicuculline, picrotoxin) on clonidine hypotension in spontaneously hypertensive (SHR) and Wistar Kyoto (WKY) rats were examined. The GABA turnover changes after clonidine injection in both strains were also studied. Administration of clonidine alone induced the stronger decrease of systolic blood pressure (SBP) in SHR. Co-dosage of clonidine with these agents reduced its hypotensive effect in dose dependent manner and the effectiveness of both antagonists was higher in SHR. We find that clonidine stimulates GABA synthesis in the hypothalamus and the pons-medulla in both strains but the GABA turnover rate is significantly slower in SHR. Therefore, the differences in inhibitory action of GABAA receptor anatgonists between WKY and SHR rats may be explained by central GABAergic system dysfunction in the hypertension. Our results indicate that the down regulation of the GABAergic system observed in hypertension may be compensated by the action of clonidine.     

The effect of CpG-rich DNA fragments on the development of hypertension in spontaneously hypertensive rats (SHR)

In this study we have investigated properties of blood plasma extracellular DNA (cell-free DNA, cfDNA) from patients with essential arterial hypertension (AH). Concentration of cell-free DNA was basically the same as in healthy donors, however, the content of the marker, CpG-rich cell-free DNA fragments (CpG-DNA) of the transcribed area of the ribosomal repeat (TArDNA, CpG-DNA) was higher in AH patients. For evaluation of the effect of CpG-DNA on the development of arterial hypertension 2-day-old SHR rat pups and corresponding controls of normotensive WKY rats received a single subcutaneous injection of human TArDNA (700 ng) to generate anti-CpG-DNA antibodies (and thus to alter the CpG-DNA content in total cfDNA). After 9 weeks blood pressure (BP) in SHR rats immunized with CpG-DNA was significantly lower than in control SHR rats and was basically the same as in WKY rats. However, subsequently, BP of the immunized SHR exhibited age-related increase, which reached the stably high values typical for mature SHR 8 weeks later compared with control SHR. Analysis of cfDNA has shown that in 17-week-old immunized SHR rats concentrations of cell-free DNA and its small DNA fragments are lower and the content of CpG-DNA (rat TArDNA) is higher than in corresponding controls. These changes were accompanied by a 3.5-fold increase in blood endonuclease activity and the decrease in content of free (unbound to cfDNA) anti-CpG-DNA antibodies. Total content of anti-CpG-DNA antibodies in the immunized rats was the same as in control animals. Thus, the delayed age-related increase in stable BP observed in immunized SHR rats is obviously not associated with increased generation of anti-CpG-DNA antibodies. Possible reasons of this effect are discussed.     

Protein kinase C activity in platelets from spontaneously hypertensive rats (SHR) and normotensive Wistar Kyoto rats (WKY)

Calcium-activated phospholipid dependent protein kinase (protein kinase C) activity in platelets was measured in 4, 12, and 20-week-old SHR and WKY. At age 4-weeks, there was no significant difference in protein kinase C activity and systolic blood pressure between SHR and WKY. In 12 and 20-week-old SHR, both protein kinase C activity and systolic blood pressure were significantly higher than in the age-matched WKY. These results suggest that protein kinase C may be involved in the control of blood pressure in SHR and WKY.