Comparison of various genetic hypertensive rat strains

Comparative studies on nine genetic hypertensive rat strains [two stroke-prone spontaneously hypertensive rats (SHRSP) and Dahl salt-sensitive (DS) strains, and one strain each of spontaneously hypertensive rats (SHR), Lyon hypertensive rats (LH), Milan hypertensive strain (MHS), genetically hypertensive rats (GH) and Sabra hypertensive rats (SBH)] and their respective controls [two Dahl salt-resistent (DR) strains and one strain each of Wistar-Kyoto rats (WKY), Lyon normotensive rats (LN); Lyon low blood pressure rats (LL), Milan normotensive strain (MNS), genetically normotensive rats (GN) and Sabra normotensive rats (SBN) and their original strain, Sabra rats (SB)], in groups consisting of 6-10 males from each strain, were carried out at 10-12 weeks of age under the same experimental conditions. After checking the developmental course of blood pressure and changes in body weight, they were killed at 12 weeks of age for blood analysis and organ-weight examinations. The SHRSP and SHR showed markedly higher blood pressure levels and earlier blood pressure rises in comparison with other hypertensive strains, although they had higher blood pressure than their respective controls. Among various organ weights examined, all hypertensive strains commonly showed increases in left ventricular weight in proportion to blood pressure rises. Kidney weights were significantly decreased only in MHS compared with MNS, while they were either unchanged or significantly greater in other hypertensive strains. Weights of adrenal glands were greater in the two strains of DS and in LH than in their respective control strains. These comparative data indicate possible differences in the pathogenic mechanism involved in these genetic hypertensive rat strains.

Sympathetic factors in the cardiovascular complications of hypertension: evidence in genetic models for hypertension, stroke and atherosclerosis

The role of the nervous system in the pathogenesis of cardiovascular complications in hypertension has been clarified to a great extent in genetic rat models for hypertension, stroke and atherosclerosis, especially in the evolution of cardiovascular hypertrophy in hypertension, the most common process related to the pathogenesis and complications of hypertension, in the development of stroke, one of the most common sequelae of hypertension itself and in the pathogenesis of atherosclerotic vascular diseases, the most usual cause of myocardial infarction.

Biochemical aspects of salt-induced, pressure-independent left ventricular hypertrophy in rats

In an attempt to investigate the effect of chronic salt loading on heart size and biochemical composition, sixty 3-month-old male Wistar-Kyoto rats (WKY) were equally divided into two groups: One group was given 1% NaCl in drinking water, and the other group was given tap water as the control. After 7 months, five randomly selected rats from each group were examined for body weight (BW), indirect blood pressure (BP), hematocrit (Hct), and organ weights. Ventricles of the heart, aorta, and mesenteric arteries were biochemically analyzed for collagen (C) and noncollagenous protein NC) and deoxyribonucleic acid (DNA). Although here was no difference between the salt and control groups in BP (129 +/- 3 mmHg vs. 125 +/- 4 mmHg, mean +/- SE), BW (376 +/- 8 g vs. 372 +/- 5 g) and Hct (42.8% +/- 1.0% vs. 44.3% +/- 0.8%), left ventricular weight (857 +/- 19 mg vs. 788 +/- 8 mg) and kidney weight (2.59 +/- 00.9 g vs 2.31 +/- 0.05 g) were both significantly (P less than 0.01) greater in the salt group, whereas the weights of the right ventricle, aorta, and adrenal glands were equal. Biochemical analysis showed significant increase in NC/DNA ratio and total collagen content as well as decreased DNA concentration in the left ventricle of the salt group compared with the control, suggesting hypertrophy rather than hyperplasia of myocardial cells with concomitant activation of collagen synthesis. Since the manner of reactive collagen production appeared different from that reported for spontaneously hypertrophic rats (SHR) or in hypoxia- or aortic constriction-induced cardiac hypertrophy, some unique mechanism may be involved in salt-induced cardiac hypertrophy.

Electronmicroscopic autoradiographic study of the distribution of 3H-diltiazem in myocardial cells

The distribution of 3H-diltiazem in myocardial cell organelles was studied using an electronmicroscopic autoradiographic technique. At 3, 5 and 10 min after 3H-diltiazem injection, silver grains, which indicate the existence of diltiazem, were detected in plasma membranes and intracellular organelles. Silver grains in T systems were observed more frequently at 3 min than at 5 and 10 min. In contrast, silver grains in sarcoplasmic reticula and mitochondria apparently increased with the passage of time. These findings suggest that diltiazem is transported through the T system and may accumulate within the sarcoplasmic reticula and mitochondria. Furthermore, our study revealed morphologically for the first time that the intracellular sites of action where diltiazem was directed were possibly the mitochondria.

Sodium preference and excretion in spontaneously hypertensive rats on various diets

Stroke-prone spontaneously hypertensive rats (SHRSP) and stroke-resistant SHR (SHRSR) exhibited an increased preference for a 2% NaCl solution, relative to water, in comparison with normotensive Wistar-Kyoto (WKY), but the preference was lost quickly in SHRSP with unbroken exposure. Neither a high protein diet (50% fish protein) nor a low protein diet (5% protein) changed the salt water preference in SHRSR and the former abolished the preference more quickly in SHRSP. The fish protein diet, however, increased the ratio of urinary sodium excretion to dietary sodium intake in the first three days of exposure to a high salt intake in all groups. Results from this experiment suggest that an increased dietary protein intake can facilitate sodium excretion and may possibly ameliorate the adverse effect of a high sodium diet.

Common cellular disposition to hypertension and atherosclerosis

The genetically hypertensive rat models, spontaneously hypertensive rats (SHR) and especially stroke-prone SHR (SHRSP), both develop arterial fat deposits quickly when fed high cholesterol diets. Therefore the morphological and functional characteristics of cultured vascular smooth muscle cells (SMC) from the aorta of SHR, SHRSP and normotensive Wistar-Kyoto (WKY) rats have been compared in order to demonstrate the common cellular mechanisms which induce hypertension and atherosclerosis. Cultured SMC became differentiated after short-term foetal calf serum exclusion from the medium, and despite the general concept of their noncontractility there was opticometric evidence that subcultured SMC contract spontaneously. Smooth muscle cells from SHR, but especially from SHRSP, showed enhanced proliferation which was inhibited by a Ca-antagonist, and accelerated lipid incorporation. It is concluded that these SMC are primarily predisposed to hypertension as well as to atherosclerosis.

Effect of dietary urea on blood pressure in spontaneously hypertensive rats

The feeding of a normal diet containing 13.5% urea (in place of protein in a high protein diet) attenuated the development of severe hypertension and decreased the incidence of stroke in spontaneously hypertensive rats (SHR), when 1% NaCl solution was given to them. The urea not only increased urine volume, but also increased urinary sodium excretion in SHR given 1% NaCl for drinking. Although there was no obvious difference in erythrocyte size between the urea and the control groups, there was a significant inverse correlation between plasma urea level and erythrocyte size. These results suggest that a high protein diet reduced blood pressure partly through the diuretic effect of urea, the common metabolite of various proteins.

Humoral trophic influence on cardiovascular structural changes in hypertension

Since the early development of structural cardiovascular change in spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) indicated the involvement of non-pressure-dependent factors in this process in hypertension, smooth muscle cells (SMC) from the aorta of SHR, SHRSP, and normotensive Wistar-Kyoto rats (WKY) were investigated under tissue culture conditions free from blood pressure and humoral factors in vivo. By the observation of such factors as growth rate and DNA or protein synthesis vascular SMC from these rats with genetic hypertension were proved to have intrinsically greater growth activity independently of blood pressure. Although serum from SHR and SHRSP had no specific stimulative effect on SMC growth, circulating epinephrine may accelerate cardiovascular structural changes because isoproterenol added to the culture media enhanced ornithine decarboxylase (ODC) activity. Moreover, SMC from SHR and SHRSP showed greater thymidine incorporation than those from WKY even in response to lower extracellular Na+ concentration. Local nutritional conditions of SMC, which were proved to have a great effect on the morphology and structure of cultured SMC, may be a basic determinant of the development of hypertension-induced structural vascular changes or lesions.

Interrelationships between blood pressure, sodium, potassium, serum cholesterol, and protein intake in Japanese

Interrelationships among blood pressure (BP), sodium (Na), potassium (K), dietary protein, and serum cholesterol level (Chol) were examined in 62% (1120) of 1818 Japanese inhabitants of both sexes aged over 30 years who lived in a rural village in Japan. Fasting single-spot urine specimens were collected in the morning to measure Na, K, urea nitrogen (UN), inorganic sulfate (SO4), and creatinine (Cr). The Cr ratios of Na, K, UN, SO4, Na/K, and SO4/UN were analyzed by multiple regression analysis to determine independent associations with BP together with age, obesity index, hematocrit (Hct), Chol, triglyceride (TG), and fasting serum glucose level (Glu). Except for Na/Cr in men, Na/Cr and Na/K were found to be independently and positively related to BP, particularly to systolic BP (SBP). In contrast, K/Cr and SO4/UN (an index related to the dietary score of sulphur-containing amino acids derived mainly from animal protein) were both negatively associated with SBP, and UN/Cr (an index of total protein intake) was positively associated with SBP in men. Chol was linked to BP negatively in men but positively in women. Age, obesity index, TG, and Hct were generally positively and significantly related to BP in both sexes. The results confirmed on epidemiological grounds the positive link of Na and the negative link of K to BP within a single population in Japan. They further suggest, although only in men, that there is a negative relationship of Chol and dietary animal protein with BP.

Dietary effect on platelet aggregation in men with and without a family history of essential hypertension

Platelet aggregation induced by 5 microM adenosine 5'-diphosphate (ADP) was significantly higher in men with a family history of essential hypertension than in men without such a history when they were fed a low fat-cholesterol diet with low salt. Platelet aggregation activity was remarkably increased in both groups when the diet was changed from low salt into high salt. Platelet aggregation activity was higher in the group with a positive family history of hypertension on the low fat-cholesterol plus high salt diet than in the group without a family history under the same conditions. The activity was slightly increased in both groups when fed a high fat-cholesterol diet with low salt. There was no significant difference in the platelet aggregation between the two groups. The activity was significantly increased in both groups on the high fat-cholesterol diet after the diet was changed from low salt to high salt. Under both the low and high fat-cholesterol diets, the mean blood pressure was significantly elevated in response to excessive salt intake in the group with a family history of essential hypertension, but it was not elevated in the group without such a family history.

Simple method for sampling consecutive 24-hour urine for epidemiological and clinical studies

'Aliquot cups' a newly devised tool for collecting 24-hour urine samples were useful and accurate enough for the estimation of individual 24-hour excretion of sodium and potassium. Data from 24-hour collections for 31 days for 5 healthy volunteers showed relatively large intra- and inter-individual variation. These data suggest that at least 5 consecutive days of urine collection would be needed to make a reasonable estimate of daily intake.

Possible role of nutritional factors in the incidence of cerebral lesions in stroke-prone spontaneously hypertensive rats

The incidence of cerebral lesions in stroke-prone spontaneously hypertensive rats appears to depend on the severity of the hypertension and nutritional factors. Comparison of American and Japanese commercial rat diets revealed a much higher incidence of stroke in rats receiving the Japanese diet (88% vs 30% by 9 months of age). Analyses of the diets indicate that perhaps the most important difference in the two diets is the protein content. Based on complete amino acid analyses of the protein in these diets, it appears that the American diet contains about 22% protein as compared to about 15% for the Japanese diet. Minor differences in vitamin and mineral contents are not remarkable. Comparison of the findings in this experimental rat model with epidemiologic studies suggest that nutritional factors may also play a role in the incidence of stroke in humans.

CBF response to L-dopa influenced by peripheral decarboxylase inhibitor and serotonin in conscious SHR-SP, SHR-SR and WK rats

1. L-Dopa induced a 56% increase in frontal cortical blood flow (fcCBF) one hour after intraperitoneal administration in stroke-prone spontaneously hypertensive rats. The treatment with carbidopa did not alter the magnitude of the response but shortened the response time to half an hour. In stroke-resistant rats and in Wistar Kyoto rats, L-dopa decreased fcCBF. This response was reversed to different degree by carbidopa pretreatment. 2. Serotonin decreased fcCBF in all groups. L-Dopa administered one hour after serotonin resulted in a recovery to the control level in SHR-SR, an increase in fcCBF in WK but the decreased flow in SHR-SP was maintained till the end of the observation time. 3. The data suggest that the stroke-prone rats have an unusual response to L-dopa and that L-dopa and this combination with a peripheral decarboxylase inhibitor may have a beneficial effect on the improvement of cerebral blood flow especially when the pre-existing level of cerebral blood flow is reduced in severe hypertension.

Dietary risk factors of stroke and hypertension in Japan -- Part 2: Validity of urinalysis for dietary salt and protein intakes under a field condition

Utility of urinalysis as a method for estimating dietary salt and protein intakes was examined in volunteers from farming and fishing villages in Japan and the data was compared to findings in a survey on diets. We found that partial urine samples and even a fasting single spot urine in the a.m. could serve as valid substitutes for 24-hour (hr) urine collections. Further, significant correlations were obtained between levels of salt in the diet estimated by survey interviews and urinary sodium (Na) and between interview-estimated dietary total or animal protein and urinary inorganic sulfate (SO4). In comparative studies between farming and fishing villages, almost the same findings, higher salt in a farming village and higher animal protein in a fishing village, were obtained in the urinalysis and the survey on diets. These findings clearly indicate that urinalysis, as a method for estimating dietary salt and protein intake in population surveys, has distinct advantages.

Dietary risk factors of stroke and hypertension in Japan -- Part 1: Methodological assessment of urinalysis for dietary salt and protein intakes

In our attempt to design a method which would be more reliable than dietary survey interviews when estimating salt and protein intakes in a population survey, a urinalysis-related study was done on volunteers. Urinary sodium (Na), urea nitrogen (UN) and inorganic sulfate (SO4), all indices of dietary salt, protein and sulfoamino acids, respectively, were confirmed to reflect the nutritional condition. Interaction between salt and protein was not observed at least at the dietary levels used in the present study (for salt, 0.33 and 0.1 g/kg body weight/day; for protein, 1.6 and 0.7 g/kg body weight/day). Excretion of components was delayed several days or more after dietary ingestion, and nutritional estimation by urinalysis, therefore, may not be so much affected by daily variables in the diet intake. Further, partial urine samples proved to have a highly significant correlation with 24-hour (hr) urine, as for urinary Na, potassium (K), SO4, UN and their creatinine (Cr) ratios, thus indicating the availability of partial urine samples as substitutes for 24-hr urine specimens. Thus, urinalysis is a more readily facilitated, more scientific and more quantitative method for epidemiological nutritional surveys.

Dietary risk factors of stroke and hypertension in Japan -- Part 3: Comparative study on risk factors between farming and fishing villages in japan

General medical examinations were performed in two rural areas of Shimane Prefecture in Japan, one was a farming village and the other a fishing village where incidences of death due to stroke differed, higher in the former and lower in the latter. Comparisons were made on salt and protein intake by analyzing the fasting single spot urine collected in the morning and by blood tests. Urine samples were analyzed for sodium (Na), potassium (K), urea nitrogen (UN), inorganic sulfate (SO4) and creatinine (Cr) and blood samples for cholesterol (Chl), triglyceride (TG), hematocrit (Ht) and hemoglobin (Hb). Blood pressure, Na/Cr, Na/K and Ht were higher in the farming village and K/Cr, UN/Cr, SO4/Cr, SO4/UN, Chl and TG were higher in the fishing village. These findings indicate the higher salt intake and lower intake of K, animal protein and fat in the farming village. This typical dietary pattern of the Japanese may explain the higher incidence of hypertension and stroke in the farming village.

Symptomatological classification in the development of stroke in stroke-prone spontaneously hypertensive rats

The developmental course of cerebrovascular diseases was examined by comparative neurological and pathological studies in stroke-prone SHR (SHRSP) which died spontaneously or were sacrificed. Behavioral status during their life span could be simply divided into 4 patterns, i.e., "no abnormalities", "irritable", "lethergic" and "akinetic" named Grades 0, I, II and III, respectively (Yamori's Classification). Grades I, II and III of behavioral status corresponded well to symptomato-pathoanatomically divided 3 stages (relating to brain edema), i.e., Stages I, II and III, respectively.

Effect of unilateral carotid ligation on brainstem PNMT activity

Phenylethanolamine N-methyltransferase (PNMT) activity in the C1 and C2 regions of the brainstem was assayed in normotensive Wistar-Kyoto rats (WKY) and spontaneously hypertensive rats (SHR) with or without unilateral carotid artery ligation. PNMT activity was significantly higher in SHR than in WKY (P less than 0.01). PNMT activity in the C1 and C2 regions on non-ligated side in both WKY and SHR was significantly elevated compared with that on the ligated side. These results indicate that the activity of PNMT in adrenergic neurons may respond to baroreflex activation and that adrenergic neurons may be involved in blood pressure regulation.

Mechanisms of structural vascular changes in genetic hypertension: analyses on cultured vascular smooth muscle cells from spontaneously hypertensive rats

1. The basic mechanism underlying the structural vascular changes occurring in hypertension was studied in cultured aortic smooth muscle cells (SMC) obtained by an explant method from spontaneously hypertensive rats (SHR) and stroke-prone SHR (SHRSP) and compared with that in normotensive Wistar--Kyoto (WKY) rats. 2. The growth rate of SMC from SHR and SHRSP at the age of 2.5--11 months was greater than that of SMC from WKY rats even after repeated passages. 3. [3H]Thymidine and [14C]leucine incorporation, and ornithine decarboxylase (ODC) activity of SMC were increased in SHR and SHRSP in comparison with WKY rats. 4. The application of isoprenaline but not noradrenaline to the culture media increased ODC activity acutely in SMC from WKY rats and this increase was blocked by propranolol. 5. These results indicate that SMC from SHR and SHRSP are more prone to proliferate than those from WKY rats and that a beta-adrenergic neurohumoral mechanism accelerates SMC growth independently of blood pressure.

Effect of acute and chronic reduction of cerebral blood flow on glucose metabolite levels in SHRSP

Glucose metabolites in the rat brain were measured under various stages of ischemia. In acute ischemia induced by bilateral carotid artery ligation, phosphocreatine and ATP levels were significantly decreased and lactate levels were significantly increased in stroke-prone spontaneously hypertensive rats (SHRSP). These extreme changes were not observed in normotensive Wistar-Kyoto rats (WKY) and stroke-resistant spontaneously hypertensive rats (SHRSR), under the same conditions. In chronic ischemia induced by long-lasting regional cerebral blood flow reduction due to severe hypertension, similar changes were observed only in SHRSP at the advanced stage. The levels of glucose metabolites in the brain were confirmed to be well maintained within control ranges even though the cerebral tissues were subjected to the chronic ischemia related to severe hypertension.