High-salt diet and hypertension: focus on the renin-angiotensin system.

A high-salt diet is one of the major risk factors in the development and maintenance of hypertension. Numerous experimental and observational studies have confirmed the association of sodium intake with blood pressure levels. The effects of a high-salt diet are related to the function of the renin-angiotensin system, which is normally suppressed by a high-salt diet. Endothelial dysfunction probably plays an important role in the influence of high sodium intake on blood pressure, although the exact mechanisms remain elusive. Genetic factors are known to be very important, and various consomic and congenic rat strains as animal models have proven to be very useful in bringing us a step closer to understanding the interaction between salt intake and hypertension. In this article, experimental data obtained in studies on animals and humans, as well as epidemiological data are reviewed.

Genetic determinants on rat chromosome 6 modulate variation in the hypercapnic ventilatory response using consomic strains.

To understand the genetic basis of pathways involved in the control of breathing, a large scale, high-throughput study using chromosomal substitution strains of rats is underway. Eight new consomic rat stains (SS-2(BN), SS-4(BN), SS-6(BN), SS-7(BN), SS-8(BN), SS-11(BN), SS-12(BN), SS-14(BN), SS-Y(BN)), containing one homozygous BN/NHsdMcwi (BN) chromosome on a background of SS/JrHsdMcwi (SS), were created by PhysGen (http://pga.mcw.edu) Program for Genomic Applications. Male and female rats were studied using standard plethysmography under control conditions and during acute hypoxia (inspired oxygen fraction = 0.12) and hypercapnia (inspired CO(2) fraction = 0.07). The rats were also studied during treadmill exercise. Both male and female BN rats had a significantly lower ventilatory response during 7% CO(2) compared with SS rats of the same gender. SS-6(BN) female rats had a significantly reduced ventilatory response, similar to BN rats due primarily to a reduced tidal volume. Male SS-6(BN) rats had a significantly reduced tidal volume response to hypercapnia but a slightly increased frequency response during hypercapnia. Gene(s) on the Y chromosome may play a role in this increased frequency response in the male rats because the SS-Y(BN) hypercapnic ventilatory response involves a significantly increased frequency response. Several chromosomal substitutions slightly altered the ventilatory responses to hypoxia and exercise. However, genes on chromosomes 6 and Y of those studied are of primary importance in aspects of ventilatory control currently studied.

Use of FemoStop system for arterial puncture site closure after coronary angioplasty.

Different protocols exist concerning the method and timing of post-coronary angioplasty arterial puncture site closure. Easy handling and good effectiveness are well-documented for the Femostop femoral artery compression system; however, no hard data exist concerning the relationship between heparin anticoagulation level and femoral artery compression time (FSCT). Thus, we prospectively randomized 267 patients after elective percutaneous transluminal coronary angioplasty (PTCA) into two groups [group A (n=137) had early sheath removal 6 to 8 hours after PTCA; group B (n=130) had late sheath removal 14 to 16 hours after PTCA] and analyzed the dependence of the FSCT on the heparin anticoagulation level (aPTT) and the incidence of vagal reactions and puncture site complications. FSCT was significantly longer in group A (69+/-27 minutes versus 45+/-15 minutes; p<0.001) with high heparin anticoagulation level (aPTT, 88+/-46 seconds) in comparison to group B with low heparinization (aPTT, 59+/-34 seconds). Vagal reactions occurred more frequently in group A (15.3% versus 10.0%; p<0.01) and the incidence of minor hemorrhage at the arterial puncture site was also increased (9.5% versus 3.1%; p<0.05). In the clinical setting of intensive heparin anticoagulation and early sheath removal after PTCA (<8 hours), the FemoStop system cannot be recommended due to prolonged femoral artery compression times.

Cytochrome P-450 omega-hydroxylase: a potential O(2) sensor in rat arterioles and skeletal muscle cells.

The purposes of this study were to 1) further evaluate the possible role that vasoconstrictor metabolites of cytochrome P-450 (CYP) omega-hydroxylase plays in O(2)-induced constriction of arterioles in the rat skeletal muscle microcirculation, 2) determine whether omega-hydroxylases are expressed in rat cremaster muscle, and 3) determine whether the enzyme is located in the parenchyma or the arterioles. O(2)-induced constriction of third-order arterioles in the in situ cremaster muscle of Sprague-Dawley rats was significantly inhibited by the CYP inhibitors N-methyl-sulfonyl-12,12-dibromododec-11-enamide (DDMS; 50 microM) and 17-octadecynoic acid (ODYA; 10 microM). Immunoblot analysis with antibody raised against CYP4A protein indicated the presence of immunoreactive proteins in the cremaster muscle and in isolated arterioles and muscle fibers from this tissue. However, the molecular mass of the immunoreactive proteins was 85 kDa instead of the expected 50--52 kDa for CYP4A omega-hydroxylase isolated from rat liver or kidney. Treatment of the cremaster muscle with deglycosidases shifted the bands to the expected range which indicates that these proteins are likely glycosylated in skeletal muscle. Immunohistochemistry revealed intense staining of both muscle fibers and microvessels in the cremaster muscle. The results of this study indicate that O(2) sensing in the skeletal muscle microcirculation may be mediated by CYP4A omega-hydroxylases in both arterioles and parenchymal cells.

Differential effect of cytochrome P-450 omega-hydroxylase inhibition on O2-induced constriction of arterioles in SHR with early and established hypertension.

OBJECTIVE: To determine whether two structurally and mechanistically different inhibitors of cytochrome P-450 omega-hydroxylase would alter the enhanced vasoconstrictor response to elevated PO2 in arterioles of spontaneously hypertensive rats (SHR). Cytochrome P-450 omega-hydroxylases, which catalyze the formation of the vasoconstrictor 20-hydroxyeicosatetraenoic acid from arachidonic acid, have been proposed to serve as microvascular O2 sensors. METHODS: Arteriolar diameters were measured in the in situ cremaster muscle of 4- to 6- and 12- to 16-week-old SHR and normotensive Wistar-Kyoto (WKY) controls during superfusion with physiological salt solution (PSS) equilibrated with 0% O2 and 21% O2 before and after P-450 enzyme inhibition. RESULTS: The P-450 omega-hydroxylase inhibitors 17-octadecynoic acid (17-ODYA) and N-methylsulfonyl-12, 12-dibromododec-11-enamide (DDMS) significantly reduced O2-induced constriction of arterioles of 12- to 16-week-old SHR and WKY and eliminated the difference in the response between the two groups. In contrast, both enzyme inhibitors attenuated the O2-induced constriction of arterioles in the younger WKY, but not in the 4- to 6-week-old SHR. CONCLUSIONS: These results support the hypothesis that cytochrome P-450 4A may act as an O2 sensor in the skeletal muscle microcirculation and suggest that 20-hydroxyeicosatetraenoic acid plays an important role in the enhanced response to elevated PO2 in the SHR with established hypertension. Other mechanisms seem to contribute to the enhanced sensitivity of arterioles to elevated PO2 in young SHR during the early development of hypertension.

Improvement of cardiac output in patients with severe heart failure by use of ACE-inhibitors combined with the AT1-antagonist eprosartan.

BACKGROUND: The efficacy of ACE-inhibitor therapy is well documented in the treatment of chronic heart failure. As pharmacological mechanisms of ACE-inhibition and angiotensin II AT1-receptor-antagonists differ, an additional positive effect concerning left ventricular function can be expected in combining both classes of drugs. METHODS: Twenty patients (64.9+/-8.5 years) with advanced chronic heart failure (NYHA class III) receiving long-term medication with digitalis, diuretics and ACE-inhibitors were randomized to either eprosartan (540+/-96 mg/day) or placebo, according to a blinded protocol. Hemodynamic measurements by impedance cardiography were performed at baseline and after 8.85+/-1. 5 days of study medication treatment. RESULTS: Additional treatment with eprosartan resulted in a higher cardiac output than in the control group (P<0.05). While in the active treatment group cardiac output increased significantly from baseline (2.27-3.24 l/min, P=0. 039), there was no change in the control group. CONCLUSIONS: The additional treatment with the AT1-receptor antagonist eprosartan, given to severe heart failure patients, who received digitalis, diuretics and ACE-inhibitors, resulted in a beneficial effect by increasing cardiac output. This effect may be due to eprosartan's additional property of blocking the autocrine interaction of locally and not ACE-generated angiotensin II with their respective vascular and myocardial AT1-receptors as well as the influence on prejunctional AT1-receptors located on sympathetic nerve terminals.

Cytochrome P-450 omega-hydroxylase senses O2 in hamster muscle, but not cheek pouch epithelium, microcirculation.

The goal of this study was to investigate the role of cytochrome P-450 omega-hydroxylase in mediating O2-induced constriction of arterioles in the microcirculation of the hamster. Male Golden hamsters were anesthetized with pentobarbital sodium, and the cremaster muscle or cheek pouch was prepared for observation by intravital microscopy. Arteriolar diameters were measured during elevations of superfusate PO2 from approximately 5 to 150 mmHg. Arteriolar responses to elevated PO2 were determined in the cremaster muscle, in the retractor muscle where it inserts on the cheek pouch, and in the epithelial portion of the cheek pouch. Elevation of superfusion solution PO2 caused a vigorous constriction of arterioles in the cremaster and retractor muscles and in the epithelial portion of the cheek pouch. Superfusion with 10 microM 17-octadecynoic acid, a suicide substrate inhibitor of cytochrome P-450 omega-hydroxylase, and intravenous infusion of N-methylsulfonyl-12,12-dibromododec-11-enamide, a mechanistically different and highly selective inhibitor of cytochrome P-450 omega-hydroxylase, caused a significant reduction in the magnitude of O2-induced constriction of arterioles in the cremaster and retractor muscles. However, arteriolar constriction in response to elevated PO2 was unaffected by 17-octadecynoic acid or N-methylsulfonyl-12,12-dibromododec-11-enamide in the epithelial portion of the cheek pouch. These data confirm that there are regional differences in the mechanism of action of O2 on the microcirculation and indicate that cytochrome P-450 omega-hydroxylase senses O2 in the microcirculation of hamster skeletal muscle, but not in the cheek pouch epithelium.

[Value of K+ and Mg2+ in treatment of acute myocardial infarct]. / Stellenwert von K+ und Mg2+ bei der Behandlung des akuten Myokardinfarktes.

A critical role analysis of literature concerning the effects of intravenous magnesium on arrhythmias and mortality in acute myocardial infarction shows discrepant results and often inappropriate methods. So far neither an antiarrhythmic efficacy nor prophylactic effects with respect to mortality could be demonstrated. In contrast, potassium substitution should be performed in the setting of acute myocardial infarction with documented hypokalemia (K+ < 3.5 mmol/l) because of increased risk of ventricular arrhythmias. According to the documented results of the trials reviewed in this article no recommendations for the routine use of magnesium in myocardial infarction can be given.

RSR-13, an allosteric effector of hemoglobin, increases systemic and iliac vascular resistance in rats.

Tissue O2 delivery in excess of metabolic demand may be a factor in the development of high vascular resistance in experimental models of volume-expanded hypertension. This hypothesis was previously tested in rats with an exchange transfusion of red blood cells treated with inositol hexaphosphate or an intravenous infusion of RSR-4, allosteric effectors of hemoglobin. The binding of these drugs with hemoglobin effect a conformational change in the molecule, such that the affinity for O2 is reduced. However, in both preparations, the changes in vascular resistance could have been nonspecific. The present studies used intravenous infusions of RSR-13, which did not share some of the problematic characteristics of RSR-4 and inositol hexaphosphate. Conscious instrumented rats (an electromagnetic flow probe on ascending aorta or an iliac, mesenteric, or renal Doppler flow probe) were studied for 6 h after an RSR-13 infusion of 200 mg/kg in 15 min. This dose significantly increased arterial P50 (PO2 at which hemoglobin is 50% saturated) from 38 +/- 0.8 to 58 +/- 1.4 mmHg at 1 h after the start of the infusion. In the 3rd h cardiac output fell significantly from a control value of 358 +/- 33 to 243 +/- 24 ml.kg-1.min-1 and total peripheral resistance significantly increased from 0.31 +/- 0.03 to 0.43 +/- 0.04 mmHg.ml-1.kg.min. Cardiac output and P50 returned toward control over the next few hours. Neither cardiac output nor total peripheral resistance changed in the group of rats receiving vehicle alone. In a separate group of rats, iliac flow decreased significantly to 60% of control and iliac resistance increased to 160% of control. Iliac flow increased significantly in the group of rats that received vehicle only. Although the mechanism of these changes has not been established, these results suggest that a decreased O2 affinity leads to an increased total peripheral resistance and regional vascular resistance and support the hypothesis that O2 plays a role in the metabolic autoregulation of blood flow.

Low-affinity hemoglobin increases tissue PO2 and decreases arteriolar diameter and flow in the rat cremaster muscle.

The hypothesis that tissue oxygen delivery in excess of metabolic demand results in vasoconstriction and reduced blood flow was tested in the cremaster muscle of anesthetized Sprague-Dawley rats by studying the effects of an intravenous infusion of RSR-13, an allosteric effector of hemoglobin. RSR-13 reduces the affinity of hemoglobin for oxygen, causing a right shift in the oxygen dissociation curve. Thus, oxygen delivery to the tissues was increased without elevations in blood flow or blood pressure. Tissue PO2, arteriolar diameter, and RBC velocity were measured and volume flow was calculated from diameter and RBC velocity in third-order arterioles. In rats receiving RSR-13 at a rate of 200 mg kg-1 in 15 min (n = 18) P50 (the PO2 at which hemoglobin is 50% saturated) increased from 36 +/- 1 to 52 +/- 3 mm Hg, and tissue PO2 increased to a maximum of 146 +/- 12% above its control value. P50 and tissue PO2 did not change in the control group (n = 8) receiving vehicle at a rate equivalent to that in the experimental group. In a separate group of rats receiving RSR-13 (n = 7), P50 increased from 38 +/- 1 to 51 +/- 3 mm Hg, calculated arteriolar flow decreased from 9 +/- 3 to a minimum of 1.4 +/- 1 nl sec-1, and arteriolar diameter decreased from 27 +/- 3 to a minimum of 13 +/- 3 micrograms P50, volume flow, and arteriolar diameter did not change in the control group (n = 10). These results suggest that an increased tissue oxygen delivery, caused by a right shift in the oxygen dissociation curve, may cause an increase in vascular resistance independent of an elevated blood flow.

-Value of activated blood coagulation time in monitoring anticoagulation during coronary angioplasty-. / Der Stellenwert der aktivierten Gerinnungszeit (ACT) in der Uberwachung der Antikoagulation bei Koronarangioplastie.

Accurate heparin anticoagulation assessment is important to prevent complications (hemorrhage, thrombotic coronary occlusion) during and after coronary angioplasty (PTCA). Paired ACT-, aPTT- and prothrombin time (PT) measurements have not been studied after PTCA using a high dose heparin management. For that reason we analyzed in 150 consecutive patients (115 m., 35 f., 61 +/- 10 y.) immediately after PTCA and at the time of arterial sheath removal aPTT-(Neothromtin, Behring), PT- (Thromborel S, Behring) and ACT-(HR-ACT, HemoTec) values after application of 20,000 U of heparin (5,000 U intravenous, 15,000 U intracoronary) followed by a heparin-infusion (15,000-25,000 U/24 h). Immediately after PTCA in all patients a aPTT above the upper limit of >180 s was found. The average postprocedural ACT was 330 +/- 82 s. Only 9 patients showed an ACT below 200 s. All coronary reocclusions (n = 3) immediately after PTCA occurred in this group. Arterial sheaths were removed 13 +/- 3 h after PTCA. The incidence of minor peripheral bleeding complications at that time was 21% and was related to the anticoagulation level. Major bleeding complications requiring transfusion were noted in only one case. Our findings suggest that after high dose heparinization for PTCA the ACT test provides a reliable and broad range for the assessment of heparin anticoagulation. In contrast to the aPTT the ACT is ideally suited to determine the dosage of heparin infusion and the time of arterial sheath removal after PTCA. ACT measurements are superior to aPTT measurements in heparin anticoagulation assessment during and direct after PTCA.

Hemodynamic changes induced by low blood oxygen affinity in dogs.

Increased tissue oxygen delivery may play a role in the increased vascular resistance that develops in volume-expanded hypertension. This hypothesis was tested by decreasing the affinity of hemoglobin for oxygen in dogs to increase unloading of oxygen to the tissues. Six chronically instrumented dogs were studied before and for 7 days after partial exchange transfusion with red blood cells modified by incorporation of inositol hexaphosphate, which, 1 h after exchange, increased the PO2 value at which hemoglobin is half-saturated with oxygen (P50) to 38.8 +/- 2.1 mmHg from a control value of 31 +/- 1.5 mmHg. Cardiac output (electromagnetic flowmeter) fell to 92.5 +/- 7.4 ml.kg-1.min-1 after 2-4 h from control values between 120.2 +/- 5.7 and 125.8 +/- 4.6 ml.kg-1.min-1. One day later, cardiac output was still significantly decreased to 104.0 +/- 5.9 ml.kg-1.min-1. As P50 returned to control over the next few days, so did cardiac output. Two to four hours after exchange, total peripheral resistance was increased to 1,144 +/- 73 mmHg.l-1.kg.min from control values between 762 +/- 26 and 790 +/- 32 mmHg.l-1.kg.min. It was still increased to 993 +/- 51 mmHg.l-1.kg.min after 1 day. Oxygen consumption did not change significantly. Cardiac output and peripheral resistance changes were significantly different from those measured in a control group of six dogs receiving exchange transfusion with sham-shifted red blood cells without significant P50 changes. These results suggest that an increase in tissue oxygen delivery can raise total peripheral resistance in dogs in the absence of primary changes in fluid volumes, blood flow, or blood pressure.

Allosteric modifiers of hemoglobin: 2-[4-[[(3,5-disubstituted anilino)carbonyl]methyl]phenoxy]-2-methylpropionic acid derivatives that lower the oxygen affinity of hemoglobin in red cell suspensions, in whole blood, and in vivo in rats.

Two new potent allosteric effectors of hemoglobin, RSR-4 [2-[4-[[(3,5-dichloroanilino)carbonyl]-methyl]phenoxy]-2- methylpropionic acid] and RSR-13 [2-[4-[[(3,5-dimethlanilino)carbonyl]methyl]-phenoxy]-2-methylp rop ionic, are compared to the previously reported compounds L3,5 and L3,4,5 [Lalezari, I., Lalezari, P., Poyart, C., Marden, M., Kister, J., Bohn, B., Fermi, G., & Perutz, M. F. (1990) Biochemistry 29, 1515]. Unlike L3,5 and L3,4,5, RSR-4 and RSR-13 are less impeded by physiological concentrations of serum albumin. RSR-4 has also been shown to be more effective than L3,5 in shifting the allosteric equilibrium of bovine Hb toward the low-affinity T-state. X-ray crystal studies show that both RSR-4 and RSR-13 bind to only one pair of symmetry-related sites in the Hb central water cavity whereas previous studies on L3,5 and L3,4,5 demonstrated a second pair of symmetry-related binding sites near Arg 104 beta. Three major interactions between these allosteric effectors and Hb include the acid group with the guanidinium group of C-terminal Arg 141 alpha, the effector's amide oxygen with the ammonium ion of Lys 99 alpha, and the phi electrons of the halogenated or methylated aromatic ring and Asn 108 beta. No explanation has been found for the difference in number of binding sites observed for RSR-4 and RSR-13 (two sites) compared to L3,5 and L3,4,5 (four sites); also no correlation has been made between the number of binding sites and degree of allosteric shift in the oxygen equilibrium curve.(ABSTRACT TRUNCATED AT 250 WORDS)

[Biofreezer BF 80--a universally employed apparatus in preservation at very low temperatures]. / Biofreezer BF 80--eine universell einsetzbare Tieftemperaturkonservierungsapparatur.

A computer-controlled freezing apparatus is described which uses liquid nitrogen (LN2) as coolant. The freezing equipment BF 80 consists of a big cryochamber (volume 24 l), a LN2 tank and a computer for the control of the freezing procedure. The biofreezer functions in the range from 40 to -180 degrees C. A complete cooling curve can be composed of up 15 linear segments with freezing rates between 0 and 45 K.min-1. In the computer up to 80 different freezing curves can be stored and activated by simple operations. The reliability of the biofreezer BF 80 was successfully tested for the cryopreservation of lymphocytes.