Fritz R. Bühler

Atrial Natriuretic Peptide and Atrial Pressure in Patients with Congestive Heart Failure

To define the relation between atrial pressures and the release of atrial natriuretic peptide, we measured plasma concentrations of the peptide in 26 patients with cardiac disease--11 with normal atrial pressures and 15 with elevated atrial pressures (11 of these 15 had elevated pressures in both atria). Mean peptide levels (+/- SEM) in the peripheral venous blood were increased in the 11 patients with cardiac disease and normal atrial pressures, as compared with 60 healthy controls (48 +/- 14 vs. 17 +/- 2 pmol per liter). In the patients with elevated atrial pressures, peptide concentrations were increased twofold in peripheral venous, right atrial, pulmonary arterial, and systemic arterial plasma, as compared with the concentrations in the patients with normal atrial pressures. A step-up in peptide concentration was seen between the venous and right atrial plasma (P less than 0.002) and between the pulmonary and systemic arterial plasma (P less than 0.01), suggesting release of the peptide from the atria. A linear relation was found between right atrial pressure and right atrial peptide concentration (r = 0.835, P less than 0.001) and between pulmonary wedge pressure and the systemic arterial peptide concentration (r = 0.866, P less than 0.001). Right atrial pressure and the peptide concentration both increased with exercise testing in the nine patients evaluated. We conclude that the release of atrial natriuretic peptide is at least partly regulated by right and left atrial pressures. Distinguishing the relative contributions of the two atria and defining the role of peptide release in the pathogenesis of heart failure will require further investigation.

Correlation of platelet calcium with blood pressure: effect of antihypertensive therapy

Intracellular free calcium has been implicated in vascular smooth-muscle contraction and in the pathophysiology of essential hypertension. We studied free-calcium levels in blood platelets, which have many features in common with vascular smooth-muscle cells. With use of an intracellularly trapped fluorescent dye, the free-calcium concentration in platelets was found to be elevated in 9 patients with borderline hypertension and 45 patients with established essential hypertension, who were compared with 38 normotensive subjects. There was a close correlation between the free-calcium level and both systolic and diastolic blood pressure (n = 92; r = 0.883 for systolic pressure and 0.931 for diastolic pressure; P less than 0.001 for both). Antihypertensive treatment with calcium-entry blockers (n = 15), beta-adrenoceptor blockers (n = 12), or a diuretic (n = 6) resulted in a reduction in free calcium, and this correlated with the fall in blood pressure (P less than 0.001). The intracellular free-calcium concentration in platelets may be determined by the same humoral or pharmacologic factors that determine the height of blood pressure.

Endothelin stimulated by angiotensin II augments contractility of spontaneously hypertensive rat resistance arteries.

In cultured endothelial cells, endothelin is produced after stimulation with angiotensin II. The effects of angiotensin II and endothelin-1 on vascular sensitivity to norepinephrine were studied in perfused rat mesenteric resistance arteries. Expression of endothelin messenger RNA (mRNA) was determined in endothelial cells obtained from the mesenteric circulation. Perfusion (5 hours) of the arteries with angiotensin II (10(-7) M) potentiated contractions in arteries with endothelium induced by norepinephrine in spontaneously hypertensive rats but not Wistar-Kyoto rats. The potentiation was inhibited by phosphoramidon and an endothelin antibody. Short-term stimulation (1 hour) with angiotensin II did not cause the potentiation. Stimulation with angiotensin I (10(-7) M; 5 hours) caused a potentiation prevented by captopril. In endothelial cells collected from the mesenteric arterial bed of spontaneously hypertensive rats, endothelin-specific mRNA was constitutively expressed, and the level of endothelin transcripts was increased by angiotensin II (10(-7) M). Threshold concentrations of exogenous endothelin-1 potentiated contractions induced by norepinephrine in arteries with and without endothelium of spontaneously hypertensive rats but not Wistar-Kyoto rats. Thus, angiotensin II stimulates the endothelial production of endothelin in situ and therapy potentiates contractions to norepinephrine in mesenteric resistance arteries of spontaneously hypertensive rats. This suggests that vascular endothelin production acts as an amplifier of the pressor effects of the renin-angiotensin system that may play an important role in hypertension.

Endothelin stimulates phospholipase C in cultured vascular smooth muscle cells.

Cultured vascular smooth muscle cells from bovine and rat thoracic aortae and from human omental vessels have been examined for cellular responses to endothelin. In myo-[3H]-inositol-prelabelled cells endothelin induced a rapid (within 30 sec) and protracted increase of [3H]-inositol content in inositol bis- and tris-phosphates. Concomitantly, significant polyphosphoinositide hydrolysis occurred within 30 sec. Accumulation of [3H]-inositol monophosphate and hydrolysis of phosphatidylinositol were delayed. In cells prelabelled with [3H]-arachidonic acid endothelin promoted rapid production of [3H]-diacylglycerol which decayed slowly toward control values after reaching maximum levels (1-2 min). Half-maximally effective concentrations of endothelin for all these cellular responses were comparable (approximately 3-7 nM) and not significantly different between the vascular cell isolates. The involvement of the phospholipase C-signal transduction pathway in mediating endothelin-induced vasoconstriction is invoked.

Inducibleendothelin mRNA expression and peptide secretion in cultured human vascular smooth muscle cells

Abstract This study demonstrates the induction of endothelin (ET) mRNA expression and synthesis of functional ET -peptide in cultured human vascular smooth muscle cells (hVSMC). Compounds eliciting such responses in hVSMC include the vasoconstrictor hormones angiotensin II and arginine-vasopressin and the growth factors transforming growth factor s, platelet derived growth factor AA and epidermal growth factor. Induction of ET mRNA expression in hVSMC exhibited transient kinetics (peak at 3–5 hrs. and return to basal within 7 hrs.) which differed from the more sustained ET transcript induction observed for porcine endothelial cells. ET peptide (determined by both radioimmuno-and radioreceptor assays) produced by stimulated hVSMC attained levels (∼ 120–160 pg/10 6 cells/4 hrs.; concentration ∼ 3 × 10 −11 M) within the biologically effective concentration range of ET. Stimulated secretion of ET from hVSMC was abolished in the presence of the protein synthesis inhibitor cycloheximide. Sep-pak C 18 extracts of medium from stimulated hVSMC elicited a concentration-dependent phosphoinositide catabolic response in myo-[2- 3 H]-inositol-prelabelled hVSMC. Our findings invoke a role for ET which extends beyond the paracrine regulation by peptide synthesized and secreted by endothelial cells. We propose that VSMC-synthesized ET may function in an autocrine manner to regulate both tone and structural modelling of vasculature.

Activation of human peripheral monocytes by angiotensin II

This study has investigated the ability of the vasoconstrictor peptide angiotensin II to activate human peripheral blood monocytes. Activation was monitored by measuring both the release of tumor necrosis factor α from monocytes and their adhesion to monolayers of human endothelial cells. Angiotensin II‐elicited activation of monocytes was dose‐dependent (half‐maxiinally effective concentration ≈ 0.2 nM), saturable (maximally effective concentration ≈ 5 nM), and sensitive to inhibition by the angiotensin type 1 receptor antagonist ZD 7155. Such direct actions imply that angiotensin II is an important candidate stimulus for the subendothelial infiltration of monocytes observed in atherogenesis and hypertension.

Activation of phospholipase A2 by endothelin in cultured vascular smooth muscle cells

The ability of endothelin to promote phospholipid hydrolysis has been studied in myo-[2-3H]-inositol-, [3H]-arachidonic acid- or methyl-[3H]choline chloride-prelabelled cultured vascular smooth muscle cells (VSMC) from rat and bovine thoracic aortae and human omental vessels. The biochemical responses to endothelin were comparable between the different VSMC isolates. Endothelin promoted the accumulation of glycerolphospho[3H]inositol and concomitant loss of [3H]-inositol label from phosphatidylinositol. Exposure of [3H]choline-labelled VSMC to endothelin resulted in a loss of radioactivity from phosphatidylcholine that was inversely parallelled by an increase in water-soluble [3H]-choline metabolites. In [3H]-arachidonic acid ([3H]-AA)-labelled VSMC, endothelin induced extracellular release of [3H]-AA which derived from both phosphatidylcholine and phosphatidylinositol. Half-maximally effective concentrations of endothelin for all these responses were approximately 2-7 nM and did not vary between VSMC types. Endothelin-induced release of [3H]-AA into VSMC medium-overlay was inhibited by quinacrine and nordihydroguaiaretic acid but not by neomycin or indomethacin. The data herein implicate activation of phospholipase A2 by endothelin with subsequent metabolism of arachidonic acid via the lipoxygenase pathway.

Age, race, blood pressure and renin: Predictors for antihypertensive treatment with calcium antagonists

Age, race, pretreatment blood pressure and plasma renin activity have been related to the antihypertensive response to calcium antagonists in studies that included 215 patients with mild to moderate essential hypertension. Adverse effects necessitated withdrawal from therapy in about 10% of the patients. All calcium antagonists lowered blood pressure significantly and comparably without weight gain or reflex tachycardia. In a multiple linear regression analysis of 138 white patients, age, pretreatment blood pressure and renin activity were of independent and significant predictive value for the antihypertensive response. Stratification of patients into 3 age groups disclosed a greater effect in patients older than 60 years compared with those between 40 and 60 years and those below 40 years, respectively (p less than 0.01). In 16 middle-aged black patients, antihypertensive therapy with a calcium antagonist proved highly efficacious. Monotherapy with a calcium antagonist may become a first-line treatment for essential hypertension, particularly in older patients who have low renin activity and possibly in black patients as well.

Renin Profiling to Select Anti hypertensive Baseline Drugs: Renin Inhibitors for High-Benin and Calcium Entry Blockers for Low-Benin Patients

Renin profiling stimulated research into the pathophysiology of essential hypertension and influenced the development of antihypertensive treatment strategies. Patients with a high renin value and usually younger age respond better to drugs that interfere with the renin-angiotensin system, that is, beta blockers or converting enzyme inhibitors. Patients with a low renin value and often older age respond better to calcium entry blockers or diuretics. Patients with normal renin levels exhibit mixed but, on average, equal responses to these types of drugs. A pathophysiology-oriented antihypertensive treatment strategy is proposed in which beta blockers or converting enzyme inhibitors are used as one and calcium entry blockers--in the place of diuretics when possible--as the other baseline drug, and this approach may provide a cardiac-protective effect.

Nailfold microcirculation in normotensive and essential hypertensive subjects, as assessed by video-microscopy

Objective: To compare morphological and hemodynamic parameters of skin microcirculation in the fingertip in patients with essential hypertension and normotensive control subjects. Design: Consecutive sample of patients. Methods: Digital capillary blood flow measurements under normal and cooled conditions were assessed by nailfold video capillaroscopy using the technique of flying spot. Results: There was a significant reduction in capillary density in hypertensive patients, compared with normotensive subjects There was a correlation between capillary density and mean diastolic blood pressure. After local cooling, the frequency of the blood flow stop was significantly higher in hypertensive patients. Conclusion: The finding of abnormal vasoconstriction in finger microcirculation in essential hypertension suggests a vasospastic tendency in the disease.