Cardiovascular effects of felodipine are not antagonized by dietary salt

Influence of dietary salts on the cardiovascular effects of low-dose combination of ramipril and felodipine in spontaneously hypertensive rats

1 In spontaneously hypertensive rat (SHR) we examined over a 4-week period the influence of control low sodium diet, common salt-enriched diet (sodium chloride 6% of the dry weight of the chow) and a novel mineral salt-enriched diet (potassium-, magnesium-, and l-lysine-enriched mineral salt added at a 75% higher level of 10.5% to produce the same sodium chloride concentration of 6%) on the cardiovascular effects produced by a low-dose combination of an angiotensin converting enzyme inhibitor ramipril (0.25 mg kg(-1) day(-1) in the food) and a calcium channel blocker felodipine (0.4 mg kg(-1) day(-1) subcutaneously via an osmotic minipump). 2 Common salt, but not the mineral salt, accelerated the development of hypertension and induced left ventricular and renal hypertrophy in SHR. Neither common salt nor mineral salt significantly affected heart rate. 3 The combination of ramipril and felodipine decreased systolic blood pressure and prevented the development of left ventricular hypertrophy effectively during the common salt diet without any significant effect on the heart rate. The cardiovascular effects of the drug combination were improved by the low sodium diet or by replacement of high common salt in the diet by mineral salt. 4 Responses of endothelium-intact mesenteric arterial rings in vitro were examined at the end of the four-week study. The combination of ramipril and felodipine markedly improved the endothelium-dependent vascular relaxation responses to acetylcholine and enhanced the endothelium-independent vascular relaxation responses to sodium nitroprusside in SHR on control and common salt diets. Replacement of common salt in the diet by mineral salt improved the endothelium-dependent vascular relaxation responses to acetylcholine. The drug combination attenuated the alpha-adrenoceptor-mediated vascular contractile responses to noradrenaline during the common salt diet. 5 Ramipril and felodipine in combination increased plasma renin activity by 1.9-3.2 fold without affecting serum aldosterone levels. 6 Our findings suggest that the cardiovascular effect of the low-dose combination of ramipril and felodipine was maintained during high salt intake. However, salt restriction or replacement of common salt in the diet by the potassium- and magnesium-enriched mineral salt improved the cardiovascular effects of the drug combination. In the face of a high intake of sodium, a part of the beneficial cardiovascular effects of the drug combination is apparently mediated by improved endothelium-dependent and endothelium-independent vascular relaxation responses and attenuated alpha-adrenoceptor-mediated vascular contractile responses.

Cardiovascular effects of a low-dose combination of ramipril and felodipine in spontaneously hypertensive rats

1. Cardiovascular effects of submaximal antihypertensive doses of the angiotensin converting enzyme inhibitor, ramipril (0.25 mg kg-1 day-1 in the food), and the calcium channel blocker, felodipine (0.4 mg kg-1 day-1 subcutaneously by osmotic minipump), both alone and in combination, were examined in spontaneously hypertensive rats (SHR) in a four-week study. 2. Both ramipril and felodipine as monotherapy decreased systolic blood pressure. The antihypertensive effect of the drug combination was more than that of ramipril treatment alone, but not significantly better than that of felodipine monotherapy. Ramipril or felodipine treatments did not significantly affect the heart rate, either alone or in combination. 3. The beneficial effect of ramipril monotherapy on left ventricular hypertrophy was more prominent than that of felodipine. The cardioprotective effect of felodipine was improved when combined to ramipril. The systolic blood pressure at the end of the experimental period correlated only weakly with left ventricular hypertrophy. 4. Responses of mesenteric arterial rings in vitro were examined at the end of the four-week study. Ramipril and felodipine monotherapies as well as their combination markedly improved the endothelium-dependent vascular relaxation responses to acetylcholine. The combination of ramipril and felodipine slightly enhanced the endothelium-independent vascular relaxation responses to sodium nitroprusside. Ramipril treatment alone slightly diminished the vascular contractile responses to noradrenaline. Neither ramipril nor felodipine alone or in combination affected the vascular contractile responses to potassium chloride. 5. Ramipril treatment, both alone and in combination with felodipine, caused a three fold increase in plasma renin activity. Serum aldosterone, fasting blood glucose level, serum insulin and the 24 hour urinary excretions of sodium, potassium, magnesium, calcium, phosphorus or protein were not significantly affected by the drug treatments. 6. Our findings suggest that a better overall control of hypertension and end-organ damages, without an increase in adverse effects, can be achieved by the combination of submaximal antihypertensive doses of felodipine and ramipril than by monotherapy with either drug alone.

Interrelationships between salt and fish oil in stroke-prone spontaneously hypertensive rat

The cardiovascular effects of a partially purified extract of fish oil, enriched in the n-3 series fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), were studied in stroke-prone spontaneously hypertensive rats (SHR-SP) fed with high- and low-sodium diets during 5 weeks. Addition of salt to the low-salt control diet at a level commonly found in human food items (6% NaCl of the dry weight of the diet) produced a remarkable rise in blood pressure, an increase in left ventricular weight-to-body weight ratio (LVH-index) and an increase in kidney weight-to-body weight ratio (RH-index). Fish oil (20% of the dry weight of the diet) did not significantly influence the blood pressure or LVH-index or RH-index during the low-salt control diet. However, fish oil completely prevented the remarkable rise in blood pressure and clearly antagonized the rise of both LVH- and RH-indices, induced by the high-salt diet. The fish oil supplementation increased the levels of the polyunsaturated fatty acids of the n-3 series and decreased those of the n-6 series in plasma and kidney, irrespective of the salt content of the diet. Fish oil lowered serum thromboxane B2 concentration by approximately 75%. During the high-salt diet, fish oil markedly decreased water intake and urine volume, and increased urinary sodium concentration by about 60%. Our findings show that, in addition to an antihypertensive effect, fish oil also decreases LVH and RH. These effects appear to be due to an improved ability to excrete sodium and could be explained by the observed changes in the fatty acid composition and metabolism.

Antihypertensive drugs reduce noradrenaline-induced hypertrophy of cultured myocardial cells

The cellular mechanisms of cardiac hypertrophy are still largely unknown. In-vivo studies have demonstrated that antihypertensive drugs can regress hypertrophy independently of reductions in blood pressure. The antihypertrophic effects of metoprolol, propranolol, felodipine, verapamil and captopril were studied in neonatal cardiac myocyte culture. Prazosin was used as a positive control. Hypertrophy was defined as an increase in protein content measured by [3H]leucine incorporation. Noradrenaline induced a 1.5-fold increase in protein synthesis over 48 h. Prazosin prevented the hypertrophic effect of noradrenaline. Adrenergic beta-receptor blocking agents and calcium antagonists reduced myocyte hypertrophy in a dose-dependent manner. The angiotensin-converting enzyme inhibitor captopril was ineffective. These results indicate that adrenergic beta-receptor blockers and calcium antagonists may have direct nonhaemodynamic effects on the growth of cultured cardiac myocytes.