This review summarizes our findings concerning the altered balance of vasoactive systems (namely sympathetic nervous system and nitric oxide) in various forms of experimental hypertension – genetic hypertension (SHR, HTG rats), salt hypertension (Dahl rats) and NO-deficient hypertension (L-NAME-treated rats). An attempt is made to define relative NO deficiency (compared to the existing level of sympathetic vasoconstriction), to describe its possible causes and to evaluate particular indicators of its extent. A special attention is paid to reactive oxygen species, their interaction with NO metabolism, cell Ca2+ handling and blood pressure regulation. Our current effort is focused on the investigation of abnormal regulation of cytosolic Ca2+ levels in smooth muscle and endothelium of hypertensive animals. Such a research should cl
arify the mechanisms by which genetic and/or environmental factors could chronically modify blood pressure level.
High plasma triglyceride (TG) level is a major independent risk factor of coronary heart disease. A newly identified Apolipoprotein A5 (Apoa5) gene has been shown to play an important role in determining plasma TG concentrations in humans and mice. Prague hereditary hypertriglyceridemic (HTG) rats are a useful model of human hypertriglyceridemia and other symptoms of metabolic syndrome. Thus, the variation of Apoa5 gene and its expression were studied in this strain under normal conditions and after chronic fructose loading. Lewis and Wistar rats served as normotriglyceridemic controls. Plasma TG were significantly higher in HTG rats in comparison with both control strains. Sequence analysis of the rat Apoa5 gene revealed the existence of two introns. However, screening of the coding regions and intron-exon boundaries of Apoa5 gene did not indicate any mutation of this gene in HTG rats in comparison with Lewis and Wistar ones. Under the basal conditions the expression of Apoa5 was lower in all age groups of HTG rats compared to Wistar animals. Furthermore, during chronic fructose loading there were no significant changes of Apoa5 expression in HTG rats, although plasma TG levels rose 3-4 times within first two days of fructose loading and were increased during the whole period of fructose treatment. In conclusion, Apoa5 does not seem to be a genetic determinant of hypertriglyceridemia in HTG rats. The absence of significant changes in Apoa5 gene expression during chronic fructose-induced TG elevation excludes its major role in mechanisms compensating severe hypertriglyceridemia.
Our studies in hypertensive Ren-2 transgenic rats (TGR) demonstrated that chronic administration of atrasentan (ETA receptor antagonist) decreased blood pressure by reduced Ca2+ influx through L-type voltage-dependent calcium channels (L-VDCC) and attenuated angiotensin II-dependent vasoconstriction. We were interested whether bosentan (nonselective ETA/ETB receptor antagonist) would have similar effects. Young 4-week-old (preventive study) and adult 8-weekold (therapeutic study) heterozygous TGR and their normotensive Hannover Sprague-Dawley (HanSD) controls were fed normal-salt (NS, 0.6 % NaCl) or high-salt (HS, 2 % NaCl) diet for 8 weeks. An additional group of TGR fed HS was treated with bosentan (100 mg/kg/day). Bosentan had no effect on BP of TGR fed highsalt diet in both the preventive and therapeutic studies. There was no difference in the contribution of angiotensin II-dependent and sympathetic vasoconstriction in bosentan-treated TGR compared to untreated TGR under the condition of high-salt intake. However, bosentan significantly reduced NO-dependent vasodilation and nifedipine-sensitive BP component in TGR on HS diet. A highly important correlation of nifedipine-induced BP change and the BP after L-NAME administration was demonstrated. Although bosentan did not result in any blood pressure lowering effects, it substantially influenced NO-dependent vasodilation and calcium influx through L-VDCC in the heterozygous TGR fed HS diet. A significant correlation of nifedipine-induced BP change and the BP after L-NAME administration suggests an important role of nitric oxide in the closure of L-type voltage dependent calcium channels.
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.
The insertion of mouse renin gene (Ren-2) into the genome of
normotensive rats causes a spontaneous rise of blood pressure
(BP), leading to an angiotensin II (Ang II)-dependent form of
hypertension in transgenic (mRen-2)27 rats (TGR). However,
enhanced sympathetic BP component was demonstrated in
heterozygous TGR aged 20 weeks. In the present study we used
another model, i.e. Cyp1a1-Ren-2 transgenic rats (iTGR) in which
hypertension can be induced by natural xenobiotic indole-3
carbinol (I3C) added to the diet. We investigated whether the
development of high blood pressure (BP) in 5-month-old iTGR
animals fed I3C diet for 10 days is solely due to enhanced
Ang II-dependent vasoconstriction or whether enhanced
sympathetic vasoconstriction also participates in BP maintenance
in this form of hypertension. Using acute sequential blockade of
renin-angiotensin system (RAS), sympathetic nervous system
(SNS) and NO synthase (NOS) we have demonstrated that the
observed gradual increase of BP in iTGR fed I3C diet was entirely
due to the augmentation of Ang II-dependent BP component
without significant changes of sympathetic BP component. Thus,
the hypertension in iTGR resembles to that of homozygous TGR
in which high BP was entirely dependent on Ang II-dependent
vasoconstriction. Moreover, our measurements of acute BP
response to Rho kinase inhibitor fasudil in animals subjected to
a combined blockade of RAS, SNS and NOS indicated the
attenuation of basal calcium sensitization in both iTGR and
homozygous TGR.