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In renovascular hypertensive rats, low doses of angiotensin converting enzyme (ACE) inhibitors have been found to prevent myocardial hypertrophy independent of blood pressure level. This finding would suggest humoral rather than mechanical control of myocyte growth. The aim of this study was to examine the effect of nonantihypertensive doses of ACE inhibitor on myocardial hypertrophy and necrosis in hypertensive rats. Renovascular hypertension (RHT) was induced in four-week-old Wistar rats. Twenty-eight animals were treated for four weeks with three doses of ramipril (0.01, 0.1 or 1. 0 mg/kg/day, which are unable to lower blood pressure. Fourteen animals were not treated (RHT group). A sham operated, age/sex-matched group was used as control (n = 10). Myocardial histology was analysed in 3 microm thick sections of the ventricle stained with either haematoxylin-eosin, reticulin silver stain or Masson's trichrome. There was a significant correlation between systolic blood pressure and left ventricular to body weight ratio in both sets of animals: untreated plus controls and ramipril-treated rats. ACE inhibition prevented myocyte and perivascular necrosis and fibrosis in a dose-dependent manner. We conclude that myocardial hypertrophy in rats with renovascular hypertension is directly related to arterial pressure, and that this relationship is not affected by nonantihypertensive doses of ACE inhibitor. Myocardial necrosis/fibrosis and coronary artery damage induced by angiotensin II are prevented by ACE inhibitor in a dose-dependent manner, despite the presence of arterial hypertension.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=10469264&dopt=Abstract
Hypertension. 1993 Nov;22(5):699-704.
Angiotensin II increases norepinephrine release from atria by acting on angiotensin subtype 1 receptors.
Brasch H, Sieroslawski L, Dominiak P.
Institute of Pharmacology, Medical University of Lubeck, FRG.
Norepinephrine stores in electrically driven guinea pig isolated atria were loaded with [3H]norepinephrine, and norepinephrine release was deduced from the radioactivity efflux. Electrical field stimulation of sympathetic nerve endings was applied during the refractory period of atrial contractions. The stimulation-induced release of norepinephrine was increased by angiotensin II (Ang II) (10(-8) to 10(-6) mol/L) in a concentration-dependent manner. The maximum observed effect was a 55% augmentation. The effects of 10(-7) and 10(-6) mol/L Ang II were abolished by 10(-6) and 10(-5) mol/L of the subtype 1 Ang II receptor antagonist losartan, respectively. Losartan by itself (10(-6) mol/L) caused a 14% reduction of norepinephrine release. The subtype 2 Ang II receptor ligand PD 123319 (1-[[4-(dimethylamino)-3-methylphenyl]methyl]-5-(diphenylacetyl)- 4,5,6,7-tetrahydro-1H-imidazo[4,5-c]pyridine-6-carboxylic acid ditrifluoroacetate) in a concentration of 10(-4) mol/L had no detectable influence on transmitter release and did not antagonize the effect of Ang II. Angiotensin I (10(-6) and 10(-5) mol/L) increased norepinephrine release maximally by 23%. This effect was antagonized by 10(-5) mol/L losartan and did not appear in the presence of 10(-6) mol/L of the converting enzyme inhibitor ramiprilat. These results suggest that Ang II increases norepinephrine release by an activation of subtype 1 receptors, whereas angiotensin I is converted to Ang II to become effective.
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8225530&dopt=Abstract
Br J Pharmacol. 1994 Apr;111(4):1189-97.
Replacement of salt by a novel potassium- and magnesium-enriched salt alternative improves the cardiovascular effects of ramipril.
Mervaala EM, Paakkari I, Laakso J, Nevala R, Teravainen TM, Fyhrquist F, Vapaatalo H, Karppanen H.
Department of Pharmacology and Toxicology, University of Helsinki, Finland.
1. The influence of salt (sodium chloride; NaCl) (an additional 6% in the diet) and that of a novel sodium-reduced, potassium-, magnesium-, and L-lysine-enriched salt alternative on the cardiovascular effects of ramipril was studied in stroke-prone spontaneously hypertensive rats in a 6-week study. The intake of sodium chloride was adjusted to the same level by adding the salt alternative at a 1.75 times higher amount than regular salt. 2. Salt produced a marked rise in blood pressure and induced cardiac hypertrophy and significant mortality, while the salt alternative neither increased blood pressure nor caused any mortality and produced less cardiac hypertrophy than salt. 3. Ramipril treatment at a daily dose of 3 mg kg-1 normalized blood pressure and prevented the development of cardiac hypertrophy of rats on control diet. These effects of ramipril were blocked by the addition of salt but were only slightly attenuated by the addition of the salt alternative. The mortality in the salt group was prevented by ramipril. 4. Responses of mesenteric arterial rings in vitro were examined at the end of the study. Salt, but not the salt alternative, increased vascular contractile responses to noradrenaline. Ramipril treatment improved the arterial relaxation responses to acetylcholine and to sodium nitroprusside. The vascular relaxation enhancing effect of ramipril was blocked by salt but only slightly attenuated by the salt alternative. 5. Ramipril treatment did not significantly increase plasma renin activity in the presence or in the absence of salt supplementation. The salt alternative did not cause hyperkalaemia, either alone or in combination with ramipril treatment.(ABSTRACT TRUNCATED AT 250 WORDS)
online pharmacy ref source: www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=8032605&dopt=Abstract
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