Carvedilol Increases Atrial Natriuretic Peptide Plasma Levels in Hypertensive Patients

Twenty five patients with moderate essential hypertension were studied for 30 days in order to evaluate the medium term effects of carvedilol on atrial natriuretic peptide (ANP) levels. This drug blocks the β1 and β2 adrenenergic receptors as well as α1 adrenergic receptors. In addition, it has strong antioxidative and antiproliferative properties. The drug was given orally at a dose of 12.5 mg b.i.d. Quantitative determination of human ANP was made by radioimmunoassay procedure (RIA). At the end of this clinical trial, mean plasma levels of ANP had risen during treatment by 21.18% (from 37.60 pg/ml to 45.83 pg/ml) while both systolic (SBP) and diastolic (DBP) blood pressure as well as diameters of the left cardiac cavities had decreased in a statistically significant way. The ratio ANP/SBP was also increased by 46.6% in a statistically significant way. These findings support the suggestion that the increase in plasma ANP following the administration of β-adrenergic blockers to hypertensive patients is a primary effect of beta blockade and not a mechanical one secondary to a negative inotropic action on the left ventricle and obviously contributes to the anti-hypertensive action.

Nebivolol Increases Atrial Natriuretic Peptide/Systolic Blood Pressure Ratio in Hypertensive Patients

The aim of this study is to evaluate the medium term treatment effects of the beta-blocker nebivolol on the endogenous anti-hypertensive and anti-inflammatory agent Atrial Natriuretic Peptide (ANP) plasma levels in patients with moderate uncomplicated essential hypertension. The drug was given orally for 30 days to 25 patients. The daily dose was 5 mg once every morning. Quantitative determination of ANP was made by Radioimmunoassay (RIA). At the end of this clinical trial, plasma ANP levels showed a statistically non significant tendency to increase by 10.99% while both systolic (SBP) and diastolic (DBP) blood pressure as well as the diameters of the left cardiac cavities showed a statistically significant decrease. What was interesting was the fact that there was a statistically significant increase of 44.7% in the ratio ANP/SBP following the reduction of arterial blood pressure. This increase was the most important and essential finding as it indicated a real increase of ANP plasma levels. This result was obtained even though pressure and afterload, the homologous mechanical stimulatory parameters for ANP secretion, of the left cavities were diminished. These findings provide strong indications which were supported by several previous trials, that the increase in plasma ANP following the administration of beta-adrenergic blockers to hypertensive patients was a primary effect of beta blockade and not a mechanical one secondary to a negative inotropic action on the left ventricle. This primary action contributed to the anti-hypertensive effect of nebivolol during this trial.

Losartan Increases No Production from the Bovine Aortic Wall That is Stimulated by Angiotensin II

In these studies we investigated if losartan, an AT1- receptor blocker has any beneficial effect on NO production from the bovine aortic preparations in vitro while under stimulation from angiotensin II. Experiments were performed on intact specimens of bovine thoracic aorta, incubated in Dulbeco's MOD medium in a metabolic shaker for 24 hours under 95 % O2 and 5 % CO2 at a temperature of 37°C. We found that angiotensin II 1nM−10 μM does not exert any statistically significant action on NO production. On the contrary, angiotensin II 10nM increases the production of NO by 58.14 % (from 12.16 + 2.9 μm/l to 19.23 + 4.2 μm/l in the presence of losartan 1nM (P<0.05). Nitric oxide levels depend on both rate production and rate catabolism or chemical inactivation. Such an equilibrium is vital for the normal function of many systems including the cardiovascular one. The above results demonstrate that the blockade of AT1-receptors favors the biosynthesis of NO and indicate the protective role of losartan on the vascular wall.

The effect of losartan on calcium uptake by bovine aortic media in vitro

The action of losartan, an AT1-angiotensin II receptor antagonist, on Ca2+ uptake by bovine aortic media in vitro was studied. This action was compared with that of nifedipine, a Ca2+ entry blocker. Ca2+ uptake values were obtained by measuring small slices of thoracic aorta tissue incubated in Kreb's solution in the presence of 45Ca. After preparation stimulation with angiotensin II (10 microM), losartan (1 microM and 10 microM) was shown to have a weaker inhibiting effect on Ca2+ uptake than nifedipine in equal concentrations. It is known that angiotensin II contracts smooth muscle by mobilizing intracellular Ca2+. The stimulating action on Ca2+ entry might be a secondary mechanism, which was studied for the first time in tissue slices derived from the aorta media. Results seem to be reasonable, since nifedipine also inhibited the spontaneous entrance of Ca2+, while losartan's action was focused only on the effects of angiotensin II.

Comparison of felodipine and nitroglycerin actions on vasomotion physiology

Felodipine is a Calcium blocker and nitroglycerin, a nitrate vasodilating agent, were compared. Two parameters were studied in vitro on bovine aortic media. Calcium uptake and vascular tone. The Calcium uptake measurement was performed by incubating in Krebs solution small slices of the preparation in the presence of 45Ca. Studies on vascular tone were performed on deendothelialized bovine aortic rings suspended in Krebs solution. Felodipine (1nM-100microM) decreases Ca2+ uptake and relaxes the preparation while nitroglycerin's 1nM-100microM) action is also inhibiting but very weak. When the preparation is stimulated by alpha 1-adrenergic against phenylephrine 1microM, then nitroglycerin 100microM has a much stronger inhibiting effect on Call uptake and vascular tone than felodipine 100microM. These results are reversed when the preparation is stimulated by KC165.4mM. Then felodipine 100nM exerts a strong inhibiting effect on Ca2+ uptake and vascular tone while nitroglycerin's 100nM inhibiting action is very weak. It is well known that in cases of endothelium disfunction the adrenergic stimulation provokes vasoconstriction and ischemia. This ischemia induces a second phase of vasoconstriction that is due to a depolarization provoked by the increased levels of extracellular K+. Felodipine is able to antagonize the consequences of such a depolarization. Thus, felodipine may be useful as an additional agent to nitroglycerin's treatment and that is the clinical message of our findings.

Clonidine and vasomotion physiology

It is known that clonidine exerts a hyperpolarizing action and alpha 2-adrenergic activity. The experimental work investigates the conditions under which each action of clonidine is developed on vascular smooth muscle. Two parameters were studied in vitro on bovine aortic media, Ca2+ uptake and vascular tone. The Ca2+ uptake measurement was performed by incubating in Krebs' solution small slices of the preparation in the presence of 45Ca. Studies on vascular tone were performed on deendothelialized bovine aortic rings suspended in Krebs' solution. Low concentrations of clonidine (1 nM-1 microM) decrease Ca2+ uptake and relax the preparation, indicating dominance of the inhibiting action of clonidine may be due to an hyperpolarization. Clonidine 10 microM results in equalization of the opposing actions of Ca2+ uptake and vascular tone. When the preparation is stimulated by alpha 1-adrenergic against phenylephrine 1 microM, clonidine 1 nM-10 microM potentates the Ca2+ uptake and vascular contraction in a monophasic way, indicating that the depolarizing mechanisms connected with the alpha 1-adrenergic stimulation totally inhibit the relaxing action of clonidine possibly due to hyperpolarization. This action is restricted in the presence of yohimbine (alpha 2-adrenergic blocker).

Felodipine and vasomotion physiology

This study concerns the investigation of felodipine's influence on some parameters of vasomotion physiology. Felodipine is a new generation 1,4 dihydropyridine (1,4 DHP) Ca(2+)-entrance blocker with marked vascular selectivity. It was found that felodipine 1-10 microM presents a Ca2+ entrance-blocking activity when the bovine aortic smooth muscle is normal or stimulated by K+ 65.4 mM or the alpha-adrenoceptor agonist phenylephrine 1 microM. The same action is observed after nifedipine, a first-generation 1,4 DHP derivative with less angioselectivity in clinical practice. It was also found that felodipine 1-10 microM antagonizes the contraction of the bovine aortic ring that is induced by phenylephrine 10 microM or KCl 65.4 mM. On the contrary, felodipine 1-10 microM increases the contraction of the rat aortic ring that is induced by the same substances. It is known that some 1,4 DHP derivatives that are Ca2+ activators can also behave as Ca2+ blockers and that their final action is dependent upon membrane potential. Now it is also proved that the kind of animal species may also influence the action of the 1,4 DHP derivatives. It was finally found that felodipine increases the catecholamine stores of the sympathetic nerve terminal at the mouse heart (H) and liver (L). Obtained values were as following: control 15.00 +/- 7.7 (H) and 17.72 +/- 3.5 (L). Felodipine 54.50 +/- 4.9 (H) and 41.54 +/- 10.4 (L). Since catecholamine stores depend on secretion (Ca(2+)-dependent) and reabsorption (mostly Na(+)-dependent) rates, the increase after felodipine may be attributed to a decreased secretion due to a Ca2+ entry inhibition.(ABSTRACT TRUNCATED AT 250 WORDS)

The influence of amikacin on digoxin uptake by certain rabbit tissues in vitro

The influence of amikacin on digoxin uptake by various rabbit tissues was investigated in vitro. 125J-digoxin was used and radioactivity was counted in a gamma scintillation counter. Amikacin decreases digoxin uptake by the renal tissue and this action is probably due to a displacing effect. On the contrary, amikacin increases digoxin uptake by striated and cardiac muscle. It is suggested that the latter action is due to a vasodilating effect of the aminoglycoside antibiotic that favors the microcirculation of the above tissues.