This study investigated the contribution of reactive oxygen species (ROS) to blood pressure regulation in conscious adult male Wistar rats exposed to acute stress. Role of ROS was investigated in rats with temporally impaired principal blood pressure regulation systems using ganglionic blocker pentolinium (P, 5 mg/kg), angiotensin converting enzyme inhibitor captopril (C, 10 mg/kg), nitric oxide synthase inhibitor L-NAME (L, 30 mg/kg) and superoxide dismutase mimeticum tempol (T,25 mg/kg). Mean arterial pressure (MAP) was measured by
the carotid artery catheter and inhibitors were administered intravenously. MAP was disturbed by a 3-s air jet, which increased MAP by 35.2±3.0 % vs. basal MAP after the first exposure. Air jet increased MAP in captopril-
and tempol-treated rats similarly as observed in saline-treated rats. In pentolinium-treated rats stress significantly decreased MAP vs. pre
-stressvalue. In L-NAME-treated rats stress failed to affect MAP
significantly. Treatment of rats with P+L+C resulted in stress-induced MAP decrease by 17.3±1.3 % vs. pre-stress value and settling time (20.1±4.2 s). In P+L+C+T-treated rats stress led to maximal MAP decrease by 26.4±2.2 % (p<0.005 vs. P+L+C) and prolongation of settling time to 32.6±3.3 s (p<0.05 vs. P+L+C). Area under the MAP curve was significantly smaller in P+L+C-treated rats compared to P+L+C+T-treated ones (167±43 vs. 433±69 a.u., p<0.008). In conclusion, in rats with temporally impaired blood pressure regulation, the lack of ROS resulted in greater stress-induced MAP alterations and prolongation of time required to reach new post-stress steady state.
Cardiovascular effects of LVV-hemorphin-7, a member of the family of fragments from β-chain of human or bovine hemoglobin, were studied in conscious spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats by radiotelemetry. Intraperitoneal injection of hemorphin in a dose of 100 g/kg significantly decreased blood pressure in SHR, whereas negligible effect was seen in normotensive WKY rats. Blood pressure changes were accompanied by reduction of heart rate. In conclusion, a direct effect of LVV-hemorphin-7 on blood pressure was demonstrated in SHR. These biologically active peptides could be involved in blood pressure regulation especially in hypertensive rats, but the precise mechanism should be elucidated.
Hypothalamic paraventricular nucleus (PVN) and rostral ventrolateral medulla (RVLM) play an important role in brain control of blood pressure (BP). One of the important mechanisms involved in the pathogenesis of hypertension is the elevation of reactive oxygen species (ROS) production by nicotine adenine dinucleotide phosphate (NADPH) oxidase. The aim of our present study was to investigate NADPH oxidase -mediated superoxide (O 2 - ) production and to search for the signs of lipid peroxidation in hypothalamus and medulla oblongata as well as in renal medulla and cortex of hypertensive male rats transgenic for the murine Ren -2 renin gene (Ren -2 TGR) and their age -matched normotensive controls ‒ Hannover Sprague Dawley rats (HanSD) . We found no difference in the activity of NADPH oxidase measured as a lucigenin -mediated O 2 - production in the hypothalamus and medulla oblongata. However, we observed significantly elevated NADPH oxidase in both renal cortex and medulla of Ren -2 TGR com pared with HanSD. Losartan (LOS) treatment (10 mg/kg body weight/day) for 2 months (Ren -2 TGR+LOS) did not change NADPH oxidase -dependent O 2 - production in the kidney. We detected significantly elevated indirect m arkers of lipid peroxidation measured as th iobarbituric acid -reactive substance s (TBARS) in Ren -2 TGR, while they were significantly decreased in Ren -2 TGR +LOS. In conclusion, the present study shows increased NADPH oxidase activities in renal cortex and medulla with significantly increased TBARS in renal cortex. No significant changes of NADPH oxidase and markers of lipid peroxidation were detected in the studied brain regions., M. Vokurková, H. Rauchová, L. Řezáčová, I. Vaněčková, J. Zicha., and Obsahuje bibliografii
The possible association of plasma lipids (triglycerides and cholesterol) with erythrocyte Na+ content (Na+j) and/or with alterations in red cell Na+ and K+ (Rb+) transport was studied in a population of F2 hybrids obtained by crossing hypertensive Prague hereditary hypertriglyceridaemic (HTG) rats with normotensive Lewis rats. The obtained data indicated a strong cosegregation (p<0.001) of plasma triglycerides with erythrocyte Na+ content. This was the cause for the close correlation of plasma triglycerides with the Ma+-K+ pump activity (measured as ouabain-sensitive Na+ extrusion). On the contrary, there was only marginal association (p<0.05) of erythrocyte Na+ content with plasma cholesterol which was significantly (p<0.01) related to bumetanide-sensitive Rb+ uptake mediated by the Ma+-K+ cotransport system. Na+ leak (bumetanide-resistant net Na+ uptake) correlated positively with blood pressure in female but not in male F2 rats. The close association between plasma triglycerides and erythrocyte Na+ content suggests that ion transport alterations might contribute to mechanisms responsible for the cosegregation of blood pressure with plasma triglycerides in HTG x Lewis F2 hybrids.
We have searched for polymorphism of inducible nitric oxide synthase gene (
Nos2 gene) in the Prague colony of salt-sensitive and salt-resistant Dahl/Rapp rats. Specific primers were used to confirm previously described Nos2 gene polymorphism because this gene was suggested to be a potential candidate gene for genetic hypertension. Phenotyping
(blood pressure, organ weight, plasma lipids) have confirmed the data known from other colonies of Dahl/Rapp rats. However, in our colony we were not able to find any Nos2 gene polymorphism between salt-sensitive and salt-resistant rats, which was previously described in animals from Harlan colony. Moreover, the genetic homogeneity of our salt-sensitive and salt-resistant rats in terms of Nos2 gene was the same as in the original Brookhaven colony of Dahl rats. This is surprising because our colony has been established from breeding pairs kindly provided by Prof. J.P. Rapp more
than 15 years ago. It seems that the polymorphism found in Harlan colony could be the result of previous contamination or genetic drift during the breeding conditions specific for this colony.
It was recognized that recombinant inbred strains are a very powerful system for the study of the genetics of hypertension, linkage analysis and gene mapping. Such set of recombinant inbred strains has been developed in the cooperation of Prof V. Křen and Dr. M. Pravenec in Prague. These recombinant inbred strains were used to search for the genes of spontaneous hypertension and to test the phenotypic differences. It was found that 1) the major histocompatibility compex of the rats showed a significant association with blood pressure, 2) the restriction fragment lenght polymorphism in kallikrein gene family as well as renin gene cosegregated with blood pressure, 3) Na+ leak in red blood cells cosegregated with blood pressure, 4) the relative heart and kidney weights are not closely related to mean arterial pressure and 5) the platelet aggregation and blood pressure are independent traits. The results indicate the usefulness of recombinant inbred strains in the analysis of the relationship between phenotype and genotype.
Our previous studies concerning the role of furosemide-resistant cation leaks in genetic hypertension demonstrated that blood pressure of recombinant inbred strains (derived from F2 hybrids of spontaneously hypertensive and normotensive Brown Norway rats) cosegregated with inward Na4 leak (determined in saline medium) but not with Na4" efflux (measured in Mg2+-sucrose medium) or with Rb+ uptake (found in either medium). In the present study the alterations of particular components of ouabain-resistant (OR) Na+ and K4 (Rb+) transport in erythrocytes of spontaneously hypertensive rats (SHR) were analyzed using saline and Na + -free (Mg24-sucrose or choline) incubation media. OR Na+ net uptake was elevated in SHR as compared to both normotensive strains — Brown Norway and Wistar rats. This was mainly due to an increased bumetanide- resistant (BR) Na4 inward leak. On the other hand, Wistar rats did not differ significantly from SHR in either OR Na4 efflux or OR Rb4 uptakes. Major augmentations of BR Na4 efflux and BR Rb4 uptake in SHR erythrocytes were seen not only in Mg24-sucrose medium but also in choline medium. In both Na4-free media there was a considerable saturable Na4¡-dependent component of BR Na4 and Rb4 fluxes which was more pronounced in SHR than in BN erythrocytes. A great caution is required for the interpretation of the data on "increased passive membrane permeability" obtained in SHR erythrocytes incubated in Na4-free media because of the presence of this saturable component which seems to be related to incompletely inhibited Na4-K4 pump. It can be concluded on the basis of BR fluxes seen in erythrocytes incubated in saline media which probably reflect true cation leaks that passive membrane permeability of SHR erythrocytes is increased for Na4 but not for Rb4(K+).
The imbalance between nitric oxide (NO) and reactive oxygen species (ROS) production appears to be a common feature of experimental and human hypertension. Previously, different antioxidants and/or scavengers of oxygen free radicals were shown to activate nitric oxide synthase (NO synthase, NOS) and to increase the expression of both endothelial and neuronal NO synthase isoforms leading to blood pressure reduction. On the other hand, various antihypertensive drugs have been documented to possess antioxidant properties, which may contribute to their beneficial effect on blood pressure. This review is focused on the effects of antioxidant treatment in different models of
experimental hypertension with a special attention to the prevention of oxidative damage and the augmentation of NO synthase activity and expression of NOS isoforms.
The growth response to angiotensin II (Ang II) was studied using cultured vascular smooth muscle cells (VSMC) isolated from the aortae of male and female spontaneously hypertensive rats (SHR). Systolic and mean arterial blood pressure of 10-week-old males was significantly higher when compared to age-matched females. The specific growth rate of male VSMC was significantly higher on the third and sixth day after synchronisation. Angiotensin II in concentration 10~7 M stimulated the specific growth rate only in male VSMC during the exponential phase of growth. Moreover, doubling time was 3 hours shorter in male VSMC in comparison with the females. Our results suggest that both the increased specific growth rate and augmented growth-response of male VSMC to Ang II may explain the higher sensitivity of males to hypertensive stimuli.
To evaluate the role of chloride in the pathogenesis of salt-dependent deoxycorticosterone (DOC) hypertension, we studied young Wistar rats chronically loaded with sodium bicarbonate (NaHCO3) or sodium chloride (NaCl) which were administered either in the diet or in the drinking fluid. Selective sodium loading (without chloride) increased blood pressure (BP) in DOC-treated animals only if NaHCO3 was provided in the diet. In contrast, no significant blood pressure changes were induced by DOC treatment in rats drinking NaHCO3 solution. Hypernatremia and high plasma osmolality occurred only in rats drinking NaCl or NaHCO3 solutions. Compared to great volume expansion in NaCl-loaded DOC-treated rats, the degree of extracellular fluid volume expansion (namely of its interstitial fraction) was substantially lower in both NaHCO3-loaded groups in which significant hypokalemia was observed. NaHCO3-drinking rats without significant blood pressure response to DOC treatment represented the only experimental group in which blood volume was not expanded. In conclusion, our data confirm previous observations that NaHCO3 loading is less potent in eliciting DOC hypertension than NaCl loading, but blood pressure rise in rats fed NaHCO3 diet clearly demonstrated that selective sodium loading could potentiate the development of DOC hypertension if NaHCO3 is offered within the appropriate dietary regimen. The reasons for the failure of NaHCO3-drinking rats to elevate blood pressure in response to chronic mineralocorticoid treatment are not obvious. However, the absence of a significant plasma volume expansion together with hypernatremia and increased plasma osmolality suggest a considerable degree of dehydration in these animals which fail to increase their fluid consumption compared to water drinking rats.