Increased bile acid pool inhibits cholesterol 7 alpha-hydroxylase in cholesterol-fed rabbits

BACKGROUND & AIMS: Cholesterol feeding unexpectedly inhibits cholesterol 7 alpha-hydroxylase in rabbits. The aim of this study was to explore the mechanism. METHODS: Twenty male New Zealand white rabbits were fed regular chow with and without 2% cholesterol for 10 days followed by 7 days of bile drainage. The activities of hepatic cholesterol 7 alpha-hydroxylase and sterol 27-hydroxylase that control bile acid synthesis in classic and alternative pathways were related to the size and composition of bile acid pool. RESULTS: After feeding cholesterol, plasma and hepatic cholesterol concentrations increased, the bile acid pool doubled (from 254 +/- 44 to 533 +/- 51 mg; P < 0.001), cholesterol 7 alpha-hydroxylase activity decreased 68% (P < 0.01), but sterol 27-hydroxylase activity increased 66% (P < 0.05) with increased cholic acid synthesis (P < 0.01). Bile drainage in the cholesterol-fed rabbits depleted the bile acid pool and stimulated down- regulated cholesterol 7 alpha-hydroxylase activity 11.4-fold (P < 0.001), although hepatic cholesterol remained elevated. Hepatic sterol 27-hydroxylase activity was unaffected. CONCLUSIONS: Feeding cholesterol increased hepatic cholesterol and stimulated sterol 27- hydroxylase and alternative bile acid synthesis, which expanded the bile acid pool and inhibited cholesterol 7 alpha-hydroxylase in rabbits. In distinction, hepatic sterol 27-hydroxylase was insensitive to changes in the bile acid pool. (Gastroenterology 1997 Dec;113(6):1958-65)     

Reduced thrombus formation in native blood of homozygous factor VII- deficient patients at high arterial wall shear rate

Inhibition of thrombin formation in flowing native blood reduces thrombus formation on subendothelium, dacron, or collagen fibrils at arterial wall shear rates of 450 to 650 s-1. In the present study, we have investigated the role of low levels of factor VII (FVII) in thrombus formation on collagen fibrils at arterial wall shear rates of 650 s-1 (coronary arteries), 2,600 s-1 (mildly stenosed arteries), and 10,510 s-1 (severely stenosed arteries) in parallel-plate perfusion chambers. In the perfusion chamber with the highest wall shear rate, thrombus formation took place at the apex of an eccentric stenosis, which reduced the cross-sectional area of the blood flow channel by 80%, thus simulating thrombus formation at an atherosclerotic plaque rupture. Native blood from 21 healthy volunteers and 12 homozygous FVII- deficient patients was drawn by a pump directly from an antecubital vein over a surface of fibrillar collagen positioned in the respective perfusion chambers. The patients had FVII coagulant activities ranging from 1.3% to 4.5% and FVII antigen levels of 16% to 23% of normal. Immunoaffinity purification of the patients' FVII followed by electrophoresis (sodium dodecyl sulfate-polyacrylamide gel electrophoresis [SDS-PAGE]) and immunoblotting showed a protein with similar molecular mass as normal FVII. In the perfusion studies, a reduction in thrombus volume of 54% of normal (P < .007) at 10,510 s-1 was observed. The deposition of fibrin on the thrombogenic surface and the plasma level of fibrinopeptide A (FPA) in blood samples collected distal to the perfusion chamber were concomitantly reduced (P < .002 and P < .04, respectively). The plasma FPA level was also reduced at 2,600 s-1 (P < .04), but not at 650 s-1. However, at the lower shear conditions, the thrombus volume and the fibrin deposition were within the ranges observed in normal blood. The platelet-collagen adhesion was not affected at any of the three shear conditions. Thus, low plasma levels of FVII result in significantly less formation of thrombin and fibrin in and around growing platelet masses at high shear condition. This may weaken the thrombus stability and reduce platelet recruitment, thereby lowering thrombus volume. In support of this theory, one patient with afibrinogenemia had an 83% reduction in thrombus volume at this high shear condition.     

Red cell antibody problems in 1000 liver transplants

Liver transplant patients frequently require large amounts of blood. The frequency and nature of their red cell (RBC) antibody problems were examined. Records were reviewed in 496 adults and 286 children undergoing 1000 consecutive transplants. Twenty-two percent of adults and 14 percent of children had RBC alloantibodies. Antibodies of potential clinical significance were found before transplant in 6.3 percent of adults and 1.0 percent of children; despite immunosuppression, they appeared 1 to 5 weeks after transplant in an additional 7.5 and 5.2 percent respectively. These antibodies probably represented secondary immune responses. Of 58 transplant patients with prior potentially significant antibodies, 8 required 7 to 110 units of antigen-untyped blood after 8 to 28 units of antigen-negative blood; of these patients, one had subsequent hemolysis. Positive direct antiglobulin tests in 24 percent of adults and 10 percent of children were most often thought to be due to nonspecific adsorption of IgG. Anti-recipient ABO antibodies developed in 22 of 60 (37%) evaluable ABO-unmatched grafts; 13 cases had associated hemolysis. In all, 36 percent of adults and 20 percent of children had diverse RBC antibody problems. Resolution of these problems is an important part of the laboratory support necessary for a liver transplantation program.     

The negative inotropic action of canrenone is mediated by L-type calcium current blockade and reduced intracellular calcium transients

Background and purpose:

Adding spironolactone to standard therapy in heart failure reduces morbidity and mortality, but the underlying mechanisms are not fully understood. We analysed the effect of canrenone, the major active metabolite of spironolactone, on myocardial contractility and intracellular calcium homeostasis.

Experimental approach:

Left ventricular papillary muscles and cardiomyocytes were isolated from male Wistar rats. Contractility of papillary muscles was assessed with force transducers, Ca²⁺ transients by fluorescence and Ca²⁺ fluxes by electrophysiological techniques.

Key results:

Canrenone (300–600 µmol·L⁻¹) reduced developed tension, maximum rate of tension increase and maximum rate of tension decay of papillary muscles. In cardiomyocytes, canrenone (50 µmol·L⁻¹) reduced cell shortening and L-type Ca²⁺ channel current, whereas steady-state activation and inactivation, and reactivation curves were unchanged. Canrenone also decreased the Ca²⁺ content of the sarcoplasmic reticulum, intracellular Ca²⁺ transient amplitude and intracellular diastolic Ca²⁺ concentration. However, the time course of [Ca²⁺]_i decline during transients evoked by caffeine was not affected by canrenone.

Conclusion and implications:

Canrenone reduced L-type Ca²⁺ channel current, amplitude of intracellular Ca²⁺ transients and Ca²⁺ content of sarcoplasmic reticulum in cardiomyocytes. These changes are likely to underlie the negative inotropic effect of canrenone.     

Macular pigment density in relation to serum and adipose tissue concentrations of lutein and serum concentrations of zeaxanthin

BACKGROUND: Macular pigment (MP), concentrated in the central area of the retina, contains the carotenoids lutein and zeaxanthin. A low MP density could be a risk factor for age-related macular degeneration. Little information is available regarding MP density in relation to serum lutein and zeaxanthin and adipose lutein concentrations in a general population. OBJECTIVE: The objective was to investigate the associations between MP density and serum lutein, serum zeaxanthin, and adipose lutein, taking into account potential confounders in a population. DESIGN: Volunteers (n = 376) aged 18-75 y were recruited. In a cross-sectional design, serum (n = 376) and adipose tissue (n = 187) were analyzed for carotenoids, and MP density was measured by spectral fundus reflectance. RESULTS: Mean MP density in the total study group was 0.33 +/- 0.15. MP density was 13% higher in men than in women (P < 0.05). Serum and blood concentrations of alpha-tocopherol, vitamin C, and all carotenoids except lycopene were significantly higher in women. Adipose lutein concentrations were also significantly higher in women than in men. Regression models showed a positive significant association between MP density and serum lutein, serum zeaxanthin, and adipose lutein concentrations in men after adjustment for age, but no relation in women. In men, serum lutein remained significantly associated with MP density after adjustment for age, total cholesterol, body mass index, and smoking. CONCLUSION: The associations between MP density and serum lutein, serum zeaxanthin, and adipose lutein concentrations are stronger in men than in women.     

Bedwetting and behavioural and/or emotional problems

Objective: To assess the link between enuresis nocturna and the severity of behavioural and/or emotional problems in Dutch children and the course of these problems. Setting: West-Mine Region in the Netherlands. Subjects and methods: Prospective cohort study involving 66 of the 80 bedwetting children from all 1652 children born in 1983 in this region. After 1 y, contact was still possible with 64 of the enuretics. We used the Dutch version of the Child Behaviour Checklist (CBCL) and a questionnaire about bedwetting. Results: The mean T-score for Total Problems (CBCL score) in 1992 (M1; mean age 8. 6) was 52. 1, and 1 y later was 49. 2 (M2). There was no significant difference in the CBCL scores for Ml, M2 and a matching group from the Dutch CBCL norm population, either in the group who remained wet or in the group who became dry. There were no differences between the sexes. There was no link between the severity of behavioural and emotional problems and the frequency of bedwetting. However, more children with bedwetting than expected were in the clinical range. Conclusion: There was no difference in behavioural and/or emotional problems between the first and the second measurement and the matching group from the CBCL norm group. There were no differences in behavioural and/or emotional problems between primary and secondary bedwetters, nor were there any consequences related to the frequency of bedwetting.