Phospholipids and fatty acid profile of brain synaptosomal membrane from normotensive and hypertensive rats

1. The main synaptosomal membrane phospholipids and their acyl group profiles, from 3-4 month-old spontaneously hypertensive rats (SHR), were compared with those of age-matched normotensive Wistar Kyoto (WKY) rats. 2. The contents of the main or total phospholipids were not found to be significantly different between these two groups. It was also true for the membrane cholesterol contents in these two groups. 3. The acyl groups of the main phospholipids from hypertensive rats were significantly higher in the saturated fatty acids: such as palmitic acid or stearic acid, and lower in polyunsaturated fatty acids: such as undecylenic acid or docosahexaenoic acid, when compared to the corresponding normotensive controls. 4. The differences in the acyl group profile of the brain membrane phospholipids of the hypertensive rats seem to reflect an abnormality in the genetically related lipolytic process.     

Lipolysis and beta-adrenergic receptor binding on adipocytes of spontaneously hypertensive rats

Adipocytes from spontaneously hypertensive rats demonstrated a blunted lipolytic response to isoproterenol and dibutyryl cyclic AMP. (-)-[3H]Dihydroalprenolol binding was examined in adipocytes from normotensive and spontaneously hypertensive rats. Increasing concentrations of isoproterenol decreased total (-)-[3H]dihydroalprenolol binding to intact cells from normotensive rats, and the efficacy of competition was decreased in adipocytes from spontaneously hypertensive rats. Scatchard analysis indicated that the number of (-)-[3H]dihydroalprenolol binding sites and the affinity of dihydroalprenolol binding were comparable between normotensive and spontaneously hypertensive rats. Isoproterenol- and Gpp(NH)p-stimulated adenylate cyclase activity was consistently depressed in adipocyte membranes from spontaneously hypertensive rats as compared to normotensive rats. No difference in fluoride-stimulated adenylate cyclase activity was observed. The blunted lipolytic and cyclic AMP response to isoproterenol in these cells suggest a postreceptor lesion of the lipolytic pathway (possibly the guanine nucleotide regulatory protein) in adipocytes from spontaneously hypertensive rats. The blunted lipolytic response to dibutyryl cyclic AMP suggests defective regulation of lipolytic enzymes at the protein kinase-hormone-sensitive lipase level.     

Effect of coenzyme Q10 on structural alterations in the renal membrane of stroke-prone spontaneously hypertensive rats

To test the hypothesis that structural abnormalities exist in the kidney membrane of spontaneously hypertensive rats, we examined the effect of long-term administration of coenzyme Q10 on membrane lipid alterations in the kidney of stroke-prone spontaneously hypertensive rats (SHRSP). As compared with normotensive Wistar-Kyoto rats, renal membrane phospholipids, especially phosphatidylcholine and phosphatidylethanolamine, decreased and renal phospholipase A2 activity was enhanced with age in untreated SHRSP. Treatment with coenzyme Q10 attenuated the elevation of blood pressure, the membranous phospholipid degradation, and the enhanced phospholipase A2 activity. These results suggest that one factor contributing to the progress of hypertension is a structural membrane abnormality that alters the physical and functional properties of the cell membrane, and coenzyme Q10 might protect the renal membrane from damage due to hypertension in SHRSP.     

The characteristics of the oxygen supply to the skeletal muscle of spontaneously hypertensive rats during starvation

Peculiarities of oxygen supply of a skeletal muscle under normal alimentary conditions and under conditions of alimentary starvation have been studied on spontaneously hypertensive rats (SHR) and normotensive rats (NTR). Calculations of oxygen permeability through hematoparenchymatous barrier (HPB) have shown that it is higher (by 26%) in SHR than in NTR. This difference can be a result of higher content of arachidonic acid and intensity of lipid peroxidation in phospholipids of plasma membranes. After 5-day starvation tension of O2 in skeletal muscle of SHR increased due to a decrease of oxygen demand and increase of oxygen permeability through HPR. The observed modification of fatty-acid spectrum of plasma membrane phospholipids and a sharp decrease of cholesterol content in them can be responsible for an increase of oxygen permeability through HPB.     

Sympathetic hyperfunction causes increased sensitivity of the autonomic nervous system to whole-body X irradiation

Although the etiology of radiation sickness is still unknown, disturbance of the autonomic nervous system is suggested to be a factor. This study was designed to compare the radiosensitivity of spontaneously hypertensive rats possessing sympathetic hyperfunction and control Wistar-Kyoto rats, and to analyze the effects of radiation on the autonomic nervous system in both strains. After a 7.5-Gy dose of whole-body X irradiation, the blood pressure decreased significantly at 8 h and 2 days in the spontaneously hypertensive rats, but not in the Wistar-Kyoto rats. Epinephrine levels in the adrenal gland of spontaneously hypertensive rats decreased at 4, 8 and 24 h, unlike the Wistar-Kyoto rats. Radiation evoked a stronger increase in norepinephrine in the jejunum and colon of spontaneously hypertensive rats than in Wistar-Kyoto rats. Acetylcholine levels in the jejunum of spontaneously hypertensive rats decreased, in contrast to the increase in Wistar-Kyoto rats within 24 h after irradiation. The survival rate of spontaneously hypertensive rats was lower than that of Wistar-Kyoto rats and weight loss, appetite loss and morphological changes in the jejunum were greater in spontaneously hypertensive rats than in Wistar-Kyoto rats after irradiation. These results indicated that X irradiation caused greater activities in autonomic nervous function and severe radiation injury in spontaneously hypertensive rats. Sympathetic hyperfunction may be associated with a higher sensitivity to radiation, including radiation injury and radiation sickness.     

Ontogenetic development of isoproterenol subsensitivity of myocardial adenylate cyclase and beta-adrenergic receptors in spontaneously hypertensive rats

[3H]Dihydroalprenolol binding and adenylate cyclase activity in the myocardial membranes of Kyoto Wistar normotensive rats and spontaneously hypertensive rats were compared at various stages of postnatal development ranging from 2 to 36 weeks. Basal as well as agonist-stimulated myocardial adenylate cyclase activity was consistently decreased in spontaneously hypertensive rats as compared to normotensive rats as early as 2 weeks of age with significant differences (P < 0.05) observed after 6 weeks of age. When results were expressed as percent stimulation over the basal activity, only isoproterenol plus GTP-stimulated enzyme activity was reduced by 25--30% in spontaneously hypertensive rats, suggesting a specific loss of stimulation by isoproterenol in hypertensive animals. The number of [3H]dihydroalprenolol binding sites of KD for dihydroalprenolol binding were comparable between spontaneously hypertensive and normotensive rats at 3, 6 and 12 weeks of age. The competition of isoproterenol with [3H]dihydroalprenolol for the specific binding sites showed that the affinity of isoproterenol binding was decreased 3--4-fold in spontaneously hypertensive compared with normotensive rats. With postnatal development in age, basal as well as agonist-stimulated activities decreased progressively in both spontaneously hypertensive and normotensive rats. Similarly, the number of [3H]dihydroalprenolol binding sites decreased with the development in age, whereas affinity of dihydroalprenolol binding increased up to 12 weeks of age. These results therefore suggest that adenylate cyclase activity and the number of beta-adrenergic receptors in rat heart, decrease with age and that in hypertension, specific decrease in isoproterenol stimulation of cyclase appears at all stages of development.     

Content of prostaglandin biosynthesis precursors in the kidney lipids in the development of spontaneous arterial hypertension

The content of linoleic (18 : 2 omega 6), arachidonic; (20 : 4 omega 6) and eicosatrienic (20 : 3 omega 9) acids was studied and compared in lipids of the renal cortex and papilla of spontaneously hypertensive Okamoto-Aoki rats (SHR) and normotensive Wistar rats (NR) aged 10 days, 1, 2 and 4 months. The level of 18 : 2 omega 6 in lipids of the renal cortex and papilla of SHR was lower at the prehypertensive stage (10 days) and at the stage of persistent hypertension as compared to that seen in NR. The content of 20 : 4 omega 6 in phospholipids and triglycerides of the cortex and in phospholipids of the papilla of SHR did not differ from that in NR. In triglycerides of the papilla of SHR of all age groups, the content of 20 : 4 omega 6 was higher than in NR. In phospholipids of SHR cortex, the content of 20 : 3 omega 9 was higher than that in NR. As for lipids of the papilla, 20 : 3 omega 9 was not detectable either in NR or SHR. It is concluded that the data obtained are of interest for the characteristics of the renal prostaglandin system in SHR.     

Fasudil attenuates sympathetic nervous activity in the adrenal medulla of spontaneously hypertensive rats

We investigated the effects of fasudil, a Rho kinase inhibitor, on hypertension in spontaneously hypertensive rats and on the catecholamine synthetic pathway. Ten-week-old male SHR and Wistar-Kyoto rats were administered fasudil (10 mg/kg/day s.c.) for 4 days. Systolic blood pressure was measured using the tail-cuff method. Catecholamine levels were measured with high-performance liquid chromatography-ECD methods. Tyrosine hydroxylase protein levels were measured in Western blot analysis. The tyrosine hydroxylase mRNA level was measured using real-time PCR methods. Fasudil significantly decreased systolic blood pressure in spontaneously hypertensive rats, but not in Wistar-Kyoto rats. Fasudil also significantly decreased catecholamine, tyrosine hydroxylase protein, and tyrosine hydroxylase mRNA levels in the adrenal medulla of spontaneously hypertensive rats. These results suggest that the depressor effects of fasudil on hypertension in spontaneously hypertensive rats may be related to inhibition of the catecholamine synthetic pathway.     

Chronic effect of prazosin and yohimbine on the renal epinephrine content of DOCA-sodium and SHR-hypertensive rats

The chronic effect of two alpha-adrenergic receptor blockers, prazosin and yohimbine, on the renal noradrenaline (NA) content was investigated in two models of hypertensive rats, the DOCA-salt and the spontaneously hypertensive rats (SHR). In DOCA-salt rats an inversal relation exists between the level of blood pressure and renal NA content in all groups studied, except those treated with yohimbine and prazosin plus yohimbine. In SHR rats a decreased renal NA content has been detected with respect to their normotensive Wistar-Kyoto (WKY) rat controls. The administration of prazosin and/or yohimbine did not alter the renal NA content of the SHR rats, while on the contrary these agents produced an elevation of these levels in kidneys from normotensive WKY rats. These results suggest that the alpha-selective blocker agents used, demonstrate a different effect on the renal NA content in the two models of hypertension studied.     

Prolactin and LH release in response to vasoactive intestinal peptide (VIP) administration in spontaneously hypertensive and normotensive rats.

Vasoactive intestinal peptide (VIP) was injected intravenously at a dose of 10 micrograms in spontaneously hypertensive and normotensive Wistar-Kyoto rats. In order to evaluate the hemodynamic and hormonal effects of this peptide, the mean arterial pressure, heart rate as well as a serum rLH and rPRL levels, the contents of LH-RH in hypothalamus and the content of LH in pituitary tissue were determined. The same procedure was applied in rats receiving placebo. Serum rPRL concentration was measured additionally after combined administration of VIP+dopamine. VIP injection produced a decrease in mean arterial pressure and an increase in heart rate in both spontaneously hypertensive and normotensive rats. Serum rPRL concentration was significantly increased at 10 minutes after injection. The combined therapy (VIP+dopamine) partially inhibited this response. Serum rLH concentration, the content of LH-RH in hypothalamic tissue as well as the content of pituitary LH after VIP injection in spontaneously hypertensive and normotensive rats did not differ from the values obtained for the control group. Conclusions: 1. VIP injection produced the dramatic hypotensive effects in hypertensive rats; 2. A marked increase in PRL concentration in response to VIP was partially inhibited by dopamine in hypertensive and normotensive rats; 3. VIP injection did not change LH-RH and LH release in both hypertensive and normotensive rats.     

Reduced number of adrenal angiotensin II receptors in the spontaneously hypertensive rat

[¹²⁵I]angiotensin II binding to adrenal subcellular particles was compared between spontaneously hypertensive and Wistar-Kyoto normotensive control rats. The number of angiotensin II receptors was reduced in adrenals of spontaneously hypertensive rats (P < 0.05) without a change in the affinity of angiotensin II for the binding sites at animal ages of 5, 10 and 15 weeks. This decline of receptor content antedated the abrupt rise in blood pressure noted between 5 and 10 weeks. The data suggest the presence of an alteration of the receptor number in the renin-angiotensin- aldosterone system in the spontaneously hypertensive rat.     

Accelerated entry of aortic smooth muscle cells from spontaneously hypertensive rats into the S phase of the cell cycle.

The present study was designed to characterize the growth kinetics of the exaggerated proliferative response to mitogens of vascular smooth muscle cells from spontaneously hypertensive rats compared with cells from normotensive Wistar-Kyoto controls. Cellular DNA content, analyzed by flow cytometry, demonstrated a 4-h accelerated entry into the S phase of the cell cycle of vascular smooth muscle cells from spontaneously hypertensive rats; the significant (4.5-fold) increase in the percentage of cells in the S phase occurred between 8 and 12 h after calf serum stimulation. A 3.9-fold increase of cells in the S phase was seen in the normotensive controls only between 12 and 16 h. Transit through the cell cycle was quantitated by flow cytometry using the Hoechst 33,342--bromodeoxyuridine substitution technique. Vascular smooth muscle cells from spontaneously hypertensive rats went through the cell cycle 4 h ahead of cells from normotensive Wistar-Kyoto rats. This accelerated transit of spontaneously hypertensive rat cells was mostly due to an earlier entry into the S phase. Persistence of this new intermediate phenotype in cell culture suggests its primary pathogenetic role in spontaneous hypertension.     

Decreased tyrosine hydroxylase activity in the adrenals of spontaneously hypertensive rats

Higher activity of the peripheral sympathetic nervous system, accompanied by higher tyrosine hydroxylase activity is frequently and consistently reported in human essential hypertension as well as in animal models of hypertension. However, results obtained in the adrenals, particularly in young animals before the development of hypertension, are scarce and controversial. In the present study tyrosine hydroxylase activity and catecholamine content in the adrenals of spontaneously hypertensive rats and of age-matched control Wistar Kyoto rats were evaluated before, during and after the development of hypertension (5, 12 and 22-week-old animals). Results show that both tyrosine hydroxylase activity and total amine content in the adrenals of spontaneously hypertensive rats were significantly reduced (35% reduction) at all studied ages. Determination of the kinetic parameters for tyrosine hydroxylase in the adrenals of 5 week-old spontaneously hypertensive rats revealed a 38% reduction in V(max) values (13.4 versus 21.3 nmol L-DOPA/mg prot/h in age-matched controls) accompanied by lower levels of expression of both tyrosine hydroxylase total protein and phosphoSer40 observed by Western-Blot. In contrast, norepinephrine content in both plasma and tail artery were significantly higher in the spontaneously hypertensive strain. In conclusion, contrary to the higher peripheral sympathetic activity, tyrosine hydroxylase activity and catecholamine content in the adrenals of spontaneously hypertensive rats are markedly reduced before, during and after the development of hypertension. End product, long-term feedback inhibition by the high norepinephrine plasma levels could be responsible for this reduction, establishing yet another regulatory mechanism of tyrosine hydroxylase operating in adrenal cromaffin cells.     

Involvement of brain stem noradrenergic neurons in the development of hypertension in spontaneously hypertensive rats

This study attempted to investigate the possible involvement of the brain stem noradrenergic system in the development of hypertension in spontaneously hypertensive rats. Steady-state norepinephrine, dopamine, serotonin and 5-hydroxyindoleacetic acid concentrations and norepinephrine turnover were determined in the individual brain stem nuclei using high performance liquid chromatography with electrochemical detection. Decreased norepinephrine contents in the nucleus tractus solitarii in spontaneously hypertensive rats compared with Wistar-Kyoto rats at the age of 4, 8, and 16 weeks were demonstrated. In later stages (8 and 16 weeks), increased norepinephrine levels were observed in the nucleus reticularis gigantocellularis, the A1 and A5 areas. Norepinephrine turnover was not different between spontaneously hypertensive rats and Wistar-Kyoto rats in the nucleus tractus solitarii at the age of 4 and 16 weeks and increased in the nucleus reticularis gigantocellularis of spontaneously hypertensive rats at 16 weeks. Our results indicate that altered norepinephrine metabolism in the specific brain stem nuclei, especially the consistently decreased norepinephrine in the nucleus tractus solitarii of spontaneously hypertensive rats, contribute to the development of genetic hypertension.     

Hypotensive effects of a methanol extract of Bidens pilosa Linn on hypertensive rats

Bidens pilosa Linn is highly regarded in some parts of Cameroon in traditional folk medical practices. The hypotensive effects of the leaf methanol extract from Bidens pilosa Linn (Asteraceae) were evaluated in spontaneously hypertensive rats (SHR), salt-loading hypertensive rats (SLHR) and normotensive Wistar rats (NTR) using the indirect (tail-cuff) method. Acute changes in urine volume and urinary excretion of Na+ and K+ were also studied. The hypotensive effect of the extract was more remarkable in hypertensive than in normotensive rats. Bidens pilosa did not provoke significant changes in the heart rate and urine volume. Urinary excretion of Na+ was decreased by 36% in spontaneously hypertensive rats and the excretion of K+ increased by 35% in normotensive rats but the effects were not statistically significant. These results suggest that the extract is a useful antihypertensive drug which has no effect on the heart frequency. The hypotensive effects of the extract may be induced by vasodilation.     

Light and electron microscopic localization of atrial natriuretic peptide in the heart of spontaneously hypertensive rat

Atrial natriuretic peptide (ANP) is a newly discovered peptide hormone present mainly in the atria. We investigated the occurrence and distribution of ANP immunoreactivity in the myocardiocytes of the ventricles of spontaneously hypertensive rats by use of immunocytochemistry at both light and electron microscopic level. ANP immunoreactivity was found in the specific granules in the cytoplasm of the cardiocytes in the subendocardium and the myocardium of the ventricles, as well as in the atria. The specific granules found in the ventricles of hypertensive rats were similar in size, shape, and ANP immunoreactive content to those in the atria. The abundance of ANP immunoreactivity in the left ventricle is greater than that in the right, and appears to increase with increasing severity of hypertension. Conversely, the overall content of ANP in the atria of hypertensive rats was decreased when compared with that in age-matched normotensive rats. The present findings indicate that ventricles may become a major source for ANP synthesis and release during hypertension, and may play important roles in cardiac endocrine pathology and cardiac hypertrophy.     

Action of 3-beta adrenolytics on plasma renin activity measured by radioimmunology in genetically hypertensive rats]

Spontaneously hypertensive rats (SHR) have basal levels of plasma renin activity (PRA) lower than the ones observed in normal Sprague Dawley rats. Three beta blocking agents are orally administered to unanesthetized spontaneously hypertensive and normotensive rats. Propranolol and S 464 reduce PRA in spontaneously hypertensive and normotensive control rats. Pindolol do not lower PRA in normotensive rats but increases levels of PRA in spontaneously hypertensive rats. These results are discussed.     

Effect of dietary alpha-linolenate/linoleate balance on mean survival time, incidence of stroke and blood pressure of spontaneously hypertensive rats

Following the suckling period, stroke-prone spontaneously hypertensive rats (SHR-SP) were fed semi-purified diets supplemented either with safflower seed oil (rich in linoleic acid) or with perilla seed oil (rich in alpha-linolenic acid). The mean survival time of male SHR-SP fed the perilla diet was longer than that fed the safflower diet by 17% (p less than 0.001) while the difference was 15% in female SHR-SP (p less than 0.05). The mean survival times of female SHR-SP were more than 40% longer than those of male SHR-SP in both dietary groups. Post-mortem examinations of brains revealed apoplexy-related symptoms as the major cause of the death in both dietary groups. The systolic blood pressure was lower by ca. 10% (21 mmHg) in the perilla group than in both the safflower group and conventional diet group. The eicosapentaenoate (20:5 n-3)/arachidonate (20:4 n-6) ratio of platelet phospholipids in spontaneously hypertensive rat (SHR), a measure of platelet aggregability, was much higher in the perilla group than in the safflower group. Thus, increasing the dietary alpha-linolenate/linoleate ratio resulted in an increased mean survival time of SHR-SP rats, possibly by lowering blood pressure and platelet aggregability.     

Antioxidant activity of propionyl-L-carnitine in liver and heart of spontaneously hypertensive rats

Oxidative stress plays an important role in arterial hypertension and propionyl-L-carnitine (PLC) has been found to protect cells from toxic reactive oxygen species. In this work, we have evaluated the antioxidant capacity of chronic PLC treatment in spontaneously hypertensive rats (SHR) by measuring the activity of antioxidant enzymes and the lipid peroxidation in liver and cardiac tissues. The activity of glutathione peroxidase was decreased in liver and cardiac tissues of SHR when compared with their normotensive controls, Wistar- Kyoto (WKY) rats, this alteration being prevented by PLC treatment. Glutathione reductase activity was increased in hypertensive rats and no effect was observed after the treatment. No significant changes in superoxide dismutase activity were observed among all experimental groups. Liver of hypertensive rats showed higher catalase activity than that of normotensive rats, and PLC enhanced this activity in both rat strains. Thiobarbituric acid reactive substances, determined as a measure of lipid peroxidation, were increased in SHR compared with WKY rats, and PLC treatment decreased these values not only in hypertensive rats but also in normotensive ones. The content of carnitine in serum, liver and heart was higher in PLC-treated rats, but PLC did not prevent the hypertension development in young SHR. In addition, triglyceride levels, which were lower in SHR than WKY rats, were reduced by chronic PLC treatment in both rat strains. These results demonstrate: i) the hypotriglyceridemic effect of PLC and ii) the antioxidant capacity of PLC in SHR and its beneficial use protecting tissues from hypertension-accompanying oxidative damage.