Kirsi Karjala

Effects of Dietary Sodium and Magnesium on Cyclosporin A–Induced Hypertension and Nephrotoxicity in Spontaneously Hypertensive Rats

Arterial hypertension, nephrotoxicity, and magnesium loss are common side effects of the immunosuppressive agent cyclosporin A (CsA). In the present study, the effects of dietary sodium and magnesium on CsA toxicity were examined in spontaneously hypertensive rats. A 6-week treatment with CsA during a moderately low-sodium diet (Na 0.3%, Mg 0.2% of the dry weight of the chow) raised blood pressure only slightly, without evidence of nephrotoxicity. By contrast, CsA during a high-sodium diet (Na 2.6%) produced a pronounced rise in blood pressure as well as marked nephrotoxicity, comprising decreased creatinine clearance, increased levels of serum creatinine and urea, and increased urinary protein excretion. During the high-sodium diet, CsA decreased myocardial and bone magnesium concentration and increased myocardial and renal calcium concentration. Magnesium supplementation (Mg 0.6%) protected against the CsA-induced hypertension and nephrotoxicity during the high-sodium diet. Magnesium supplementation also completely prevented the CsA-induced myocardial magnesium depletion and calcium accumulation in the heart and kidney during the high-sodium diet. Our findings indicate a detrimental interaction between increased sodium intake and CsA treatment and a marked protection by concomitant oral magnesium supplementation.

Effects of calcium and potassium supplements on arterial tone in vitro in spontaneously hypertensive rats

Calcium and potassium intakes inversely correlate with blood pressure in experimental hypertension. Therefore, we examined the effects of calcium and potassium supplements alone and in combination on arterial tone in spontaneously hypertensive rats (SHR). Wistar‐Kyoto (WKY) rats served as normotensive controls. Calcium and potassium contents in the control diet were both 1%, while those in supplemented chows were 3% and 3.5%, respectively. The sodium content of all diets was moderately elevated to 1.1%. After 12 weeks of the study systolic blood pressures in SHR on high calcium and on high potassium diets were markedly lower (about 53 and 58 mmHg, respectively) than in hypertensive controls, while combined supplementation of these cations reduced blood pressure even further (about 69 mmHg). Responses of mesenteric arterial rings in vitro were examined at the end of the study. Both high calcium and high potassium diets improved the impaired relaxation to acetylcholine (ACh) in SHR, while the combination of these supplements completely normalized this response. Cyclo‐oxygenase inhibition by diclofenac augmented the relaxation to ACh in hypertensive controls but not in the other groups. Nevertheless, enhanced endothelium‐mediated dilatation was still observed in the presence of diclofenac and the nitric oxide synthase inhibitor NG‐nitro‐L‐arginine methyl ester (L‐NAME) in all supplemented groups. Interestingly, additional blockade of Ca2+‐activated K+ channels by tetraethylammonium abolished the improved relaxation to ACh in SHR on high calcium and on high potassium, but distinct responses were still observed in WKY rats and SHR on the combined supplement. When hyperpolarization of smooth muscle was prevented by precontraction of the preparations with 50 mM KCl, only marginal differences were observed in the diclofenac and L‐NAME‐resistant relaxations to ACh between the study groups. Finally, endothelium‐independent vasorelaxations of noradrenaline‐precontracted rings to nitroprusside, isoprenaline and cromakalim were comparably augmented by all supplements. In conclusion, the vascular mechanisms underlying the antihypertensive effect of high calcium and high potassium diets during moderately elevated sodium intake in SHR may involve enhanced arterial hyperpolarization, increased smooth muscle sensitivity to nitric oxide and decreased production of vasoconstrictor prostanoids. The administration of these cations in combination was more effective than either of them alone in reducing blood pressure and restoring arterial tone.

Dietary habits affect the susceptibility of low-density lipoprotein to oxidation

Objective: To study, if there are differences in the fatty acid composition of low‐density lipoprotein (LDL) in people eating three different long‐standing habitual diets: vegetarian, high fish intake, or high saturated fat (milk fat) diet as a control group, and to study if these differences influence the oxidation susceptibility of LDL.Design: Cross‐sectional study using blood samples and a validated dietary frequency questionnaire with illustrations.Setting: Helsinki University Central Hospital, Finland.Subjects: The effect of three different types of long‐standing diets of different fatty acid content (a strict vegetarian diet, n=11; a high fish intake diet, n=9; and a high saturated fat (milk fat) diet, controls, n=7) on the serum and LDL fatty acid content, and on the susceptibility of LDL to oxidation in vitro, was studied in healthy normocholesterolemic volunteers who had been on these diets for years. Oxidation of LDL was carried out by using CuSO4 as a pro‐oxidant.Results: There were no statistically significant differences in the serum lipids or lipoproteins, though the vegetarian group exhibited lowest mean values of total, high‐density lipoprotein (HDL) and LDL cholesterol levels. Both the serum and LDL eicosapentaenoic, docosapentaenoic and docosahexaenoic acid proportions were highest in the fish and lowest in the vegetarian groups. Linoleic acid was highest among the vegetarians. In the fish group, the vitamin A concentration in serum was higher than in vegetarians and controls and β-carotene lower than in controls, but in α‐tocopherol, or lycopene concentrations there were no statistically significant differences. The lag phase of LDL oxidation was shortest (116 min) in the fish group and longest (165 min) in the vegetarian group, and the control group was between them (129 min). The mean oxidation percentage after 2.5 h of copper‐induced oxidation was highest (44%) in the fish group and lowest (22%) in the vegetarian group and intermediate (31%) in the control group.Conclusion: Long‐term dietary habits predict the fatty acid composition of serum and LDL, and influence the susceptibility of LDL to oxidation. In the fish group with the highest content of omega‐3 fatty acids in LDL, the oxidation susceptibility of LDL was highest. In the vegetarian group with less omega‐3 fatty acids in LDL, the LDL was more resistant to oxidation.Sponsorship: Helsinki University Central Hospital.

Comparison of the effects of supplementation with whey mineral and potassium on arterial tone in experimental hypertension

OBJECTIVE The aim of this work was to compare the effects of supplementation of rat chow diet with potassium (K+) and whey mineral concentrate (Whey), a diet rich in milk minerals, on blood pressure and arterial responses in vitro in spontaneously hypertensive rats (SHR). METHODS Thirty young SHR and twenty Wistar-Kyoto rats (WKY) were allocated into five groups: SHR, Whey-SHR, K(+)-SHR, WKY and Whey-WKY. Whey-supplementation was performed by adding 25% whey mineral concentrate to the chow, which in particular increased the intake of potassium (from 1.0% to 3.6%) and also that of calcium (from 1.0% to 1.3%) and magnesium (from 0.2% to 0.3%) in the rats. The K(+)-SHR were given extra potassium chloride (KCl) so that the final potassium content in the chow was 3.6%. Blood pressures were measured indirectly by the tail-cuff method. Responses of mesenteric arterial rings were examined in standard organ chambers after 12 study weeks. RESULTS During the 12-week study systolic blood pressures in control SHR increased steadily from 160 to about 230 mmHg, while supplementation with either Whey or potassium had a clear antihypertensive effect of about 50 mmHg in the hypertensive rats. Blood pressures in the WKY and Whey-WKY groups remained comparable during the whole study. In noradrenaline-precontracted arterial rings, endothelium-dependent relaxation to acetylcholine (ACh), as well as endothelium-independent relaxations to nitroprusside and isoprenaline were attenuated in untreated SHR, while all these dilatory responses were similarly improved by Whey and potassium supplementation. The cyclooxygenase inhibitor diclofenac, which reduces the synthesis of dilatory and constricting prostanoids, clearly enhanced the relaxation to ACh in untreated SHR, but was without effect in the other groups. In the presence of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester the relaxation to ACh was markedly reduced in all SHR groups, whereas in the two WKY groups, distinct relaxations to ACh were still present. The remaining responses were partially prevented by tetraethylammonium, an inhibitor of calcium-activated potassium channels, and the difference between untreated and potassium-supplemented SHR was abolished. When endothelium-mediated hyperpolarization of smooth muscle was prevented by precontracting the preparations with 50 mM KCl, only marginal differences were observed in relaxations to ACh between untreated SHR and the other groups. Interestingly, the impaired endothelium-independent relaxations to cromakalim, a hyperpolarizing vasodilator acting via ATP-sensitive potassium channels, were normalized by Whey mineral and potassium diets. CONCLUSION Supplementation with Whey mineral and a comparable dose of potassium similarly opposed the development of experimental genetic hypertension, an effect which was associated with improved arterial dilatory properties. Both supplements augmented the hyperpolarization-related component of arterial relaxation, increased the sensitivity of smooth muscle to nitric oxide, and decreased the production of vasoconstrictor prostanoids. Therefore, the beneficial effects of the Whey diet could be attributed to increased intake of potassium in SHR.

Losartan and enalapril therapies enhance vasodilatation in the mesenteric artery of spontaneously hypertensive rats.

We studied the effects of 10-week long enalapril and losartan treatments (4 and 15 mg kg(-1) day(-1), respectively) on mesenteric arterial function in vitro in spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). The relaxations of noradrenaline-precontracted rings to acetylcholine, nitroprusside and cromakalim were similar in WKY and enalapril- and losartan-treated SHR, and more pronounced than in untreated SHR. The responses to acetylcholine were attenuated by N(G)-nitro-L-arginine methyl ester in WKY and drug-treated SHR, but were completely inhibited in untreated SHR. When hyperpolarization of smooth muscle was prevented by KCl-induced precontractions, no differences were found in the relaxations to acetylcholine and nitroprusside between the groups, and the dilatations to cromakalim were abolished. Moreover, in noradrenaline-precontracted rings of drug-treated SHR, the addition of tetraethylammonium attenuated the nitric oxide synthase and cyclooxygenase-resistant relaxations to acetylcholine and abolished the enhanced dilatations to nitroprusside. In conclusion, since the enhancement of vasorelaxation in enalapril- and losartan-treated SHR was abolished by conditions preventing hyperpolarization, the improved vasodilatation following these therapies could be attributed to enhanced vasodilatation via K+ channels in this model of hypertension.

Influence of chronic ethanol consumption on arterial tone in young and aged rats

The aim of this work was to evaluate the effects of long-term ethanol consumption on arterial responses in vitro in young and aged rats. Therefore, Wistar rats (ages 3 and 29 mo, respectively) were allocated to six groups: control-young, sucrose-young, ethanol-young, control-aged, sucrose-aged, and ethanol-aged. The ethanol-fed groups were given 25% ethanol by intragastric gavage three times a day 4 days a week. Responses of mesenteric arterial rings were examined in standard organ chambers after 5 treatment weeks. In norepinephrine-precontracted arterial rings, endothelium-dependent relaxations to acetylcholine, as well as endothelium-independent relaxations to isoproterenol, were attenuated in aged rats when compared with young controls. Relaxation responses to isoproterenol, but not to acetylcholine and nitroprusside, were clearly improved by ethanol treatment in both young and aged rats. The cyclooxygenase inhibitor diclofenac, which reduces the synthesis of dilating and constricting prostanoids, enhanced the relaxation to acetylcholine in all three aged rat groups but was without significant effect in the young rats. In the presence of the nitric oxide synthase inhibitor N G-nitro-l-arginine methyl ester the relaxation to acetylcholine in control and sucrose-fed aged rats was markedly reduced compared with control rats, whereas in the young controls and in both young and aged ethanol-exposed groups, distinct relaxations to higher concentrations of acetylcholine were still present. The endothelium-independent relaxations to cromakalim, a hyperpolarizing vasodilator acting via ATP-sensitive potassium channels, were also markedly augmented by ethanol feeding in both young and aged rats. In conclusion, ethanol consumption in both young and aged rats was associated with markedly improved arterial relaxations to isoproterenol and cromakalim, as well as clearly augmented relaxation to acetylcholine during inhibition of cyclooxygenase and nitric oxide synthase. These findings suggest that especially the potassium channel-related component of arterial relaxation was augmented by long-term ethanol exposure.The aim of this work was to evaluate the effects of long-term ethanol consumption on arterial responses in vitro in young and aged rats. Therefore, Wistar rats (ages 3 and 29 mo, respectively) were allocated to six groups: control-young, sucrose-young, ethanol-young, control-aged, sucrose-aged, and ethanol-aged. The ethanol-fed groups were given 25% ethanol by intragastric gavage three times a day 4 days a week. Responses of mesenteric arterial rings were examined in standard organ chambers after 5 treatment weeks. In norepinephrine-precontracted arterial rings, endothelium-dependent relaxations to acetylcholine, as well as endothelium-independent relaxations to isoproterenol, were attenuated in aged rats when compared with young controls. Relaxation responses to isoproterenol, but not to acetylcholine and nitroprusside, were clearly improved by ethanol treatment in both young and aged rats. The cyclooxygenase inhibitor diclofenac, which reduces the synthesis of dilating and constricting prostanoids, enhanced the relaxation to acetylcholine in all three aged rat groups but was without significant effect in the young rats. In the presence of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester the relaxation to acetylcholine in control and sucrose-fed aged rats was markedly reduced compared with control rats, whereas in the young controls and in both young and aged ethanol-exposed groups, distinct relaxations to higher concentrations of acetylcholine were still present. The endothelium-independent relaxations to cromakalim, a hyperpolarizing vasodilator acting via ATP-sensitive potassium channels, were also markedly augmented by ethanol feeding in both young and aged rats. In conclusion, ethanol consumption in both young and aged rats was associated with markedly improved arterial relaxations to isoproterenol and cromakalim, as well as clearly augmented relaxation to acetylcholine during inhibition of cyclooxygenase and nitric oxide synthase. These findings suggest that especially the potassium channel-related component of arterial relaxation was augmented by long-term ethanol exposure.

Influence of different dietary salts on the cardiovascular and renal effects of moxonidine in spontaneously hypertensive rats

Abstract The influence of common salt (NaCl) and a novel potassium-, magnesium-, and L-lysine-enriched mineral salt on the cardiovascular and renal effects of the selective imidazoline I1-receptor agonist moxonidine was examined in spontaneously hypertensive rats (SHR). Common salt was added at the level of 6% of the dry weight of the chow, and mineral salt at a 75% higher level of 10.5% thereof to produce the same NaCl concentration of 6% as in the common salt group. During the control diet an 8-week oral treatment with moxonidine (117mg/1000g of the dry weight of the chow producing an approximate daily dose of 10mg/kg), lowered blood pressure by 13mmHg. The common salt diet alone raised blood pressure by 27mmHg. Moxonidine lowered blood pressure by 21mmHg during the common salt diet, but the blood pressure remained 19mmHg higher than in the moxonidine-treated SHR receiving the control diet (P<0.05). Unlike common salt, mineral salt alone did not raise blood pressure nor did it interfere with the antihypertensive effect of moxonidine. Moxonidine showed a kidney-protective effect during the control diet measured as decreased urinary protein excretion, but it did not affect the development of left ventricular hypertrophy. Moxonidine increased plasma renin activity during the control diet and it raised the serum aldosterone level both during the control and mineral salt diets. The vascular relaxation responses of the mesenteric arterial rings to both acetylcholine (an indicator of endothelium-dependent vascular relaxation) and nitroprusside and nitroprusside (an indicator of endothelium-independent vascular relaxation) were attenuated by the common salt diet alone but maintained during the moxonidine treatment.Our findings are consistent with the concept that moxonidine is able to improve the excretion of sodium. This effect might explain the maintenance of normal vascular relaxation during a high intake of common salt. These effects may partly account for the antihypertensive effect of moxonidine.

Proliferative effects of oxidized low-density lipoprotein on vascular smooth muscle cells: Role of dietary habits

The effects were studied of native, partially-oxidized and totally-oxidized human low-density lipoprotein (LDL) on the proliferation of cultured rat aortic smooth muscle cells (VSMC), measured as an altered DNA synthesis. The LDL was obtained from three different human long-term diet groups (a control diet rich in saturated fats, a vegetarian diet, and a fish diet). The oxidized LDLs were prepared by oxidizing the LDL with copper sulfate. The DNA synthesis was measured by [3H]-thymidine incorporation into the DNA. The partially-oxidized LDL was the most potent promoter of DNA synthesis compared to the native or totally-oxidized LDL of the same diet group. The partially-oxidized LDL had a true mitogenic effect in the absence of exogenous growth factors. The native and totally-oxidized LDL induced a significant increase in DNA synthesis, if they were obtained from the fish diet group. This study suggests an enhanced proliferative effect of partially-oxidized LDL on VSMC growth.