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Biomedical subjects

R J Barnard

Publications and source records attributed to R J Barnard.

At least 37 records · Page 2Linked to original sources
PubMed1998

Effects of diet and exercise on insulin, sex hormone-binding globulin, and prostate-specific antigen.

A diet high in fat has been linked to prostate cancer, possibly through an influence on hormones. Sex hormone-binding globulin (SHBG) binds androgens and is regulated in part by insulin. Diet and exercise can modify insulin levels, potentially affecting SHBG and the biologically available levels of androgens. To determine the effects of a low-fat (< 10% of calories), high-fiber diet plus daily exercise on insulin, SHBG, prostate-specific antigen (PSA), and serum lipids, we measured the levels of these factors in the serum of 27 obese men undergoing a three-week diet-and-exercise program. Insulin decreased from 222 +/- 30 to 126 +/- 21 pmol/l (p < 0.01), and SHBG increased from 18 +/- 2 to 25 +/- 3 nmol/l (p < 0.01). Body mass index decreased from 35 +/- 1.9 to 33.4 +/- 1.8 kg/m2 (p < 0.01). PSA levels were normal and did not change significantly, although in a small subset of men (n = 3) with slightly elevated PSA levels (> 2.5 ng/ml) all showed a decrease. The three-week diet-and-exercise intervention decreased insulin and lipid levels while increasing SHBG. The increase in SHBG would result in more testosterone being bound and, therefore, less of the androgen available to act on the prostate. The decrease in insulin might also decrease mitogenic activity in the prostate. The diet-and-exercise regimen did not have a significant impact on normal PSA levels. Although modest, these changes may be protective against the development of prostate cancer.

Body Mass Index↗
PubMed1998

Diet-induced insulin resistance precedes other aspects of the metabolic syndrome.

This study was designed to examine the effects of a high-fat refined-sugar (HFS) or a low-fat complex-carbohydrate (LFCC) diet on insulin-stimulated skeletal muscle glucose transport, plasma insulin, blood pressure, plasma triglycerides, plasma glycerol, body weight, and body fat in female Fischer rats. Insulin-stimulated glucose transport was significantly reduced in the HFS group at 2 wk, 2 mo, and 2 yr, whereas serum insulin was significantly elevated at all time points. Blood pressure was not significantly elevated in the HFS group until 12 mo, and all HFS animals were hypertensive by 18 mo. Glycerol, triglycerides, and abdominal fat cell size were not significantly different at 2 wk but were significantly elevated in the HFS rats at 2 and 6 mo. Body weight was similar in both groups until 20 wk on the diet, when the HFS rats started to gain more weight. These results demonstrate that insulin resistance and hyperinsulinemia occur before the other manifestations of the metabolic syndrome and that diet, not obesity, is the underlying cause.

Adipose Tissue↗
PubMed1997

Stimulation of NSF ATPase activity by alpha-SNAP is required for SNARE complex disassembly and exocytosis.

N-ethylmaleimide-sensitive fusion protein (NSF) and alpha-SNAP play key roles in vesicular traffic through the secretory pathway. In this study, NH2- and COOH-terminal truncation mutants of alpha-SNAP were assayed for ability to bind NSF and stimulate its ATPase activity. Deletion of up to 160 NH2-terminal amino acids had little effect on the ability of alpha-SNAP to stimulate the ATPase activity of NSF. However, deletion of as few as 10 COOH-terminal amino acids resulted in a marked decrease. Both NH2-terminal (1-160) and COOH-terminal (160-295) fragments of alpha-SNAP were able to bind to NSF, suggesting that alpha-SNAP contains distinct NH2- and COOH-terminal binding sites for NSF. Sequence alignment of known SNAPs revealed only leucine 294 to be conserved in the final 10 amino acids of alpha-SNAP. Mutation of leucine 294 to alanine (alpha-SNAP(L294A)) resulted in a decrease in the ability to stimulate NSF ATPase activity but had no effect on the ability of this mutant to bind NSF. alpha-SNAP (1-285) and alpha-SNAP (L294A) were unable to stimulate Ca2+-dependent exocytosis in permeabilized chromaffin cells. In addition, alpha-SNAP (1-285), and alpha-SNAP (L294A) were able to inhibit the stimulation of exocytosis by exogenous alpha-SNAP. alpha-SNAP, alpha-SNAP (1-285), and alpha-SNAP (L294A) were all able to become incorporated into a 20S complex and recruit NSF. In the presence of MgATP, alpha-SNAP (1-285) and alpha-SNAP (L294A) were unable to fully disassemble the 20S complex and did not allow vesicle-associated membrane protein dissociation to any greater level than seen in control incubations. These findings imply that alpha-SNAP stimulation of NSF ATPase activity may be required for 20S complex disassembly and for the alpha-SNAP stimulation of exocytosis.

Adenosine Triphosphatases↗
PubMed1997

Effects of intensive diet and exercise intervention in patients taking cholesterol-lowering drugs.

Patients taking cholesterol-lowering drugs were placed on a very low fat, high-complex-carbohydrate diet with daily aerobic exercise and achieved 19%, 20% and 29% reductions in total cholesterol, LDL-cholesterol and triglycerides, respectively. Fifty-one percent of the primary care physicians had not used diet therapy before initiating drugs and 29% did not use diet therapy along with the drugs as recommended by the National Cholesterol Education Program.

Adult↗
PubMed1997

Exercise-stimulated glucose transport in skeletal muscle is nitric oxide dependent.

It has been suggested that there are separate insulin-stimulated and contraction-stimulated glucose transport pathways in skeletal muscle. This study examined the effects of nitric oxide on glucose transport in rat skeletal muscle by use of an isolated sarcolemmal membrane preparation and the nitric oxide synthase inhibitor N omega-nitro-L-arginine methyl ester (L-NAME), administered in the drinking water (1 mg/ml). Female Sprague-Dawley rats were divided into five groups: control, acute exercise, acute exercise+L-NAME, insulin stimulated, and insulin stimulated+L-NAME. Exercise (45 min of exhaustive treadmill running) increased glucose transport (37 +/- 2 to 76 +/- 5 pmol.mg-1.15 s-1) and this increase was completely inhibited by L-NAME (40 +/- 4 pmol.mg-1.15 s-1). A maximum dose of insulin increased glucose transport (87 +/- 10 pmol.mg-1.15 s-1), and adding L-NAME had no effect (87 +/- 11 pmol.mg-1.15 s-1). In addition, exercise, but not exercise+L-NAME, increased sarcolemma GLUT-4 content. This study confirms that there are separate pathways for contraction- and insulin-stimulated glucose transport. More importantly, although exercise and insulin both significantly increased glucose transport, L-NAME had no effect on insulin-stimulated glucose transport but blocked the exercise-stimulated transport. We conclude that nitric oxide is involved in the signal transduction mechanism to increase glucose transport during exercise.

Administration, Oral↗
PubMed1996

Similar effects of alpha- and beta-SNAP on Ca(2+)-regulated exocytosis.

Soluble N-ethylmaleimide-sensitive fusion protein attachment proteins (SNAP) proteins function in Ca(2+)-regulated exocytosis. Recent work (Schiavo et al. (1996) Nature 378, 733-736) based on in vitro protein interactions has raised the possibility that alpha- and beta-SNAPs have distinct roles in exocytosis. We have examined this possibility by comparing the activities of recombinant alpha- and beta-SNAPs. Both of these proteins were able to similarly bind NSF and activate its ATPase activity but to a lesser extent than gamma-SNAP. When introduced into digitoninpermeabilised chromaffin cells, both alpha- and beta-SNAP stimulated Ca(2+)-regulated exocytosis in a MgATP-dependent manner. The dose-response relationships for these proteins were essentially the same and addition of both proteins did not lead to any further increase in exocytosis above that due to each protein alone. We conclude that alpha- and beta-SNAPs are interchangeable isoforms with similar functions in regulated exocytosis.

Adenosine Triphosphatases↗
PubMed1996

Domains of alpha-SNAP required for the stimulation of exocytosis and for N-ethylmalemide-sensitive fusion protein (NSF) binding and activation.

The binding of alpha-SNAP to the membrane proteins syntaxin, SNAP-25, and synaptobrevin leads to the recruitment of the N-ethylmaleimide-sensitive fusion protein (NSF). ATP hydrolysis by NSF has been suggested to drive conformational changes in one or more of these membrane proteins that are essential for regulated exocytosis. Functional evidence for a role of alpha-SNAP in exocytosis in adrenal chromaffin cells comes from the ability of this protein to stimulate Ca(2+)-dependent exocytosis in digitonin-permeabilized cells. Here we examine the effect of a series of deletion mutants of alpha-SNAP on exocytosis, and on the ability of alpha-SNAP to interact with NSF, to define essential domains involved in protein-protein interactions in exocytosis. Deletion of extreme N- or C-terminal regions of alpha-SNAP produced proteins unable to bind to syntaxin or to stimulate exocytosis, suggesting that these domains participate in essential interactions. Deletion of C-terminal residues abolished the ability of alpha-SNAP to bind NSF. In contrast, deletion of up to 120 N-terminal residues did not prevent the binding of NSF to immobilized alpha-SNAP and such mutants were also able to stimulate the ATPase activity of NSF. These results suggest that the C-terminus, but not the N-terminus, of alpha-SNAP is crucial for interactions with NSF. The involvement of the C-terminus of alpha-SNAP, which contains a predicted coiled-coil domain, in the binding of both syntaxin and NSF would place the latter two proteins in proximity in a ternary complex whereupon the energy derived from ATP hydrolysis by NSF could induce a conformational change in syntaxin required for exocytosis to proceed.

Adenosine Triphosphatases↗
PubMed1996

Effects of diet and exercise on qualitative and quantitative measures of LDL and its susceptibility to oxidation.

The purpose of this study was to investigate the effects of an intensive diet and exercise program on the quantity and quality of LDL as well as its susceptibility to in vitro oxidation. The diet was low in fat (< 10% kcal) and cholesterol (< 100 mg/d), while high in complex, unrefined carbohydrates (> 70% kcal) and fiber (35 g/1000 kcal). The study was composed of 80 participants in a 3-week residential program where food was provided ad libitum and there was daily aerobic exercise, primarily walking. In each subject, preparticipation and postparticipation fasting blood samples were drawn and LDL was isolated via density gradient ultracentrifugation. LDL particle diameter was determined by gradient gel electrophoresis of serum (n = 23). Isolated LDL was either separated into 6 subfractions by saline gradient equilibrium ultracentrifugation (n = 26) or subjected to in vitro copper oxidation (n = 32). Significant reductions (P < .01) in serum levels of cholesterol (20%). LDL-cholesterol (20%), HDL-cholesterol (17%), triglycerides (26%), and glucose (16%) as well as in body weight (4%) were noted for the total population. The mean particle diameter of the LDL increased (24.2 +/- 0.2 to 25.1 +/- 0.14 nm, P < .01) and was correlated with the reduction in serum triglycerides (r = .58, P < .01). Six of 22 subjects changed in LDL phenotype from B (< or = 25.5 nm) to A (> 25.5 nm). The percentage of LDL-cholesterol carried in the more dense subfractions fell significantly, while that carried by the less dense fractions increased. Initial oxidation levels fell (21%), while the lag time before copper-induced oxidation increased (13%). Reductions were observed in both the rate of oxidation (16%) and peak oxidation (20%). All of these changes should result in a dramatic reduction in the risk for atherosclerosis and its clinical sequelae.

Centrifugation, Density Gradient↗
PubMed1996

Patch-clamp capacitance analysis of the effects of alpha-SNAP on exocytosis in adrenal chromaffin cells.

We have examined the effect of alpha-SNAP on exocytosis in adrenal chromaffin cells by direct assay of exocytosis using patch-clamp capacitance analysis. Cells were recorded using the whole cell patch-clamp configuration and the cells dialysed with control pipette solution or with a pipette solution containing alpha-SNAP or the deletion mutant alpha-SNAP(41-295). The deletion mutant was found to be unable to bind to syntaxin allowing a test of the requirement for syntaxin-binding for any effect of alpha-SNAP on exocytosis. Following cell dialysis for 10 minutes, cells were depolarised five times at 2 minute intervals. At each depolarisation step cells dialysed with alpha-SNAP showed a significant increase in both the initial rate and extent of exocytosis which was seen as a rise in membrane capacitance. This increase in exocytosis was not observed with alpha-SNAP(41-295) which instead produced some inhibition of the extent but had no effect on the initial rate of exocytosis. These results show directly that alpha-SNAP has a specific and marked stimulatory effect on exocytosis in chromaffin cells.

Animals↗
PubMed1995

Effects of a very low fat, high fiber diet on serum hormones and menstrual function. Implications for breast cancer prevention.

BACKGROUND: Low fat, high fiber dietary interventions that decrease blood estrogen levels may reduce breast cancer risk. Asian women consuming their traditional low fat, high fiber diets have lower blood estrogen levels before and after menopause and lower rates of breast cancer compared with Western women. The current controlled feeding study of premenopausal women was designed to determine the effects of a very low fat (10% of calories) and high fiber (35-45 g/day) diet on blood estrogen levels and menstrual function. METHOD: Twelve healthy premenopausal women with regular ovulatory cycles were followed for 3 months. Subjects consumed a diet providing 30% of their energy from fat and 15-25 g of dietary fiber per day for 1 month, and they consumed a very low fat, high fiber and libitum diet providing 10% of their energy from fat and 25-35 g of dietary fiber per day for 2 months. RESULTS: At the end of the second month of the very low fat, high fiber diet, there was a significant reduction in serum estrone and estradiol levels during the early follicular and late luteal phases. There were no significant changes observed in serum estrone sulfate, sex hormone binding globulin, or progesterone. Despite a significant decrease in serum estradiol and estrone levels after 2 months of a very low fat, high fiber diet, there was no interference with ovulation or the magnitude of the mid-cycle leuteinizing hormone surge. Small changes in menstrual cycle length of up to 3 days were not ruled out due to the small sample size of the study. CONCLUSIONS: A very low fat, high fiber diet in healthy premenopausal women can reduce estradiol and estrone levels without affecting ovulation, thereby providing a rationale for the prevention of breast cancer through a very low fat, high fiber diet.

Adult↗
PubMed1995

Calcineurin feedback inhibition of agonist-evoked cAMP formation.

The effects of immunosuppressant blockers of calcineurin (protein phosphatase 2B) on cAMP formation and hormone release were investigated in mouse pituitary tumor (AtT20) cells. Immunosuppressants enhanced corticotropin-releasing factor- and isoproterenol-evoked cAMP production in proportion with their potency to block calcineurin. Further analysis of cAMP production revealed that intracellular Ca2+ derived through voltage-regulated calcium channels reduces cAMP formation induced by corticotropin releasing-factor or beta 2-adrenergic stimulation and that this effect of Ca2+ is inhibited by blockers of calcineurin. AtT20 cells were found to express at least three species of adenylyl cyclase mRNA-encoding types 1 and 6 as well as a novel isotype, which appeared to be the predominant species. In two cell lines expressing very low or undetectable levels of the novel cyclase mRNA (NCB20 and HEK293 cells respectively), corticotropin-releasing factor-induced cAMP formation was not altered upon blockage of calcineurin activity. These data identify calcineurin as a Ca2+ sensor that mediates the negative feedback effect of intracellular Ca2+ on receptor-stimulated cAMP production. Furthermore, the effect of calcineurin on cAMP synthesis appears to be associated with the expression of a novel adenylyl cyclase isotype, which is highly abundant in AtT20 cells.

1-Methyl-3-isobutylxanthine↗
PubMed1995

Effect of short-term cardiovascular conditioning and low-fat diet on myocardial blood flow and flow reserve.

BACKGROUND: Cardiovascular conditioning reduces resting myocardial oxygen demand by lowering systolic blood pressure and heart rate. Lower myocardial oxygen demand at rest would be expected to be associated with a decrease in resting myocardial blood flow and, consequently, an increase in myocardial flow reserve as the ratio of hyperemic to resting blood flow. However, the effect of controlled exercise together with a low-lipid diet on myocardial blood flow and flow reserve has not been examined in humans. METHODS AND RESULTS: Myocardial blood flow at rest and after dipyridamole-induced hyperemia (0.56 mg/kg i.v.) was quantified with [13N]ammonia and positron emission tomography in 13 volunteers before and upon completion of a 6-week program of cardiovascular conditioning and a low-fat diet. Exercise capacity and serum lipid profiles were also assessed at the start and finish of the program. Eight normal volunteers of similar age not participating in the conditioning program served as a control group. Cardiovascular conditioning lowered the resting rate-pressure product (8859 +/- 2128 versus 7450 +/- 1496, P < .001), serum cholesterol (217 +/- 36 versus 181 +/- 26 mg/dL), LDL cholesterol (140 +/- 32 versus 114 +/- 24 mg/dL), and triglycerides (145 +/- 53 versus 116 +/- 33 mg/dL, all P < .05). Exercise tolerance (metabolic equivalent of the task, METs) improved significantly from 10.0 +/- 3.0 to 14.4 +/- 3.6 (P < .01). Resting blood flow decreased (0.78 +/- 0.18 versus 0.69 +/- 0.14 mL.g-1.min-1, P < .05), whereas hyperemic blood flow increased (2.06 +/- 0.35 versus 2.25 +/- 0.40 mL.g-1.min-1, P < .05), resulting in an improved myocardial flow reserve (2.82 +/- 1.07 versus 3.39 +/- 0.91, P < .05). Overall, the myocardial flow reserve was significantly related to exercise performance (METs). In the control group, no changes in resting rate-pressure product, serum cholesterol levels, exercise performance, resting or hyperemic myocardial blood flow, or flow reserve were observed. CONCLUSIONS: Short-term cardiovascular conditioning together with a low-fat diet results in an improved myocardial flow reserve by lowering resting blood flow and increasing coronary vasodilatory capacity. These changes are associated with an improved exercise capacity and may offer a protective effect in patients with coronary artery disease.

Ammonia↗
PubMed1995

Response of immature diabetic rat bone-ligament junctions to insulin and exercise.

The mechanical and morphological characteristics of femur-medial collateral ligament-tibia units and the histomorphometry of medial collateral ligament-tibial insertion were examined in female Sprague-Dawley rats with diabetes mellitus (type I, insulin-dependent diabetes). Diabetes was induced with the streptozotocin, a drug with toxic effects on insulin-producing islet cells in the pancreas. The groups studied included rats with untreated streptozotocin-induced diabetes mellitus (Diabetes), insulin-treated streptozotocin-induced diabetes (Diabetes-Insulin), exercise with streptozotocin-induced diabetes (Diabetes-Exercise), exercise with insulin-treated streptozotocin-induced diabetes (Diabetes-Insulin-Exercise), and age-matched sedentary-control rats (Control). Diabetes and Diabetes-Exercise groups had significantly lower body mass and higher blood glucose than Diabetes-Insulin, Diabetes-Insulin-Exercise, and Control groups, indicating that exercise alone did not prevent growth retardation or improve blood glucose control in the streptozotocin-induced diabetes. The strength of Diabetes femur-medial collateral ligament-tibia units was significantly less than Control, but exercise (with or without insulin treatment) maintained the bone-ligament-bone unit strength at a normal level. The load (per unit body mass) of Diabetes-Exercise femur-medial collateral ligament-tibia unit was significantly greater than Control, Diabetes, and Diabetes-Insulin groups. The tensile stiffness (per unit body mass) of the femur-medial collateral ligament-tibia unit for the Diabetes-Exercise group was also significantly greater than Control and Diabetes-Insulin groups. The fibroblast-like cell density in medial collateral ligament at its tibial-insertion site and medial collateral ligament insertion area was significantly less in Diabetes rats. RELEVANCE--:Diabetes mellitus can have deleterious effects on connective tissues, such as bone and ligament. Thus the bone-ligament junction becomes vulnerable. The results of this experiment suggest, however, that exercise, with or without insulin treatment, can have a positive effect on the bone-ligament interface in the rat with type I diabetes mellitus. Furthermore exercise (with insulin treatments) can mitigate growth retardation and many of the adverse effects of streptozotocin-induced diabetes on the structure and mechanical properties of immature bone-ligament junctions.

Journal Article↗
PubMed1995

Long-term, high-fat-sucrose diet alters rat femoral neck and vertebral morphology, bone mineral content, and mechanical properties.

Short-term exposure to diets high in fat and sucrose can induce hyperinsulinemia, affect calcium and magnesium metabolism, and alter bone mineralization and mechanical properties. The current study focused on the morphological and structural changes that result from long-term exposure to a high-fat sucrose (HFS) diet. Inbred, female Fischer 344 rats were assigned randomly to a low-fat, complex-carbohydrate (LFCC) diet group or a HFS diet for 24 months. At the end of the 2 years, each femoral neck (FN) was tested to failure in cantilever-bending, the sixth lumbar vertebra (L6) was tested in compression, and geometrical characteristics of the bones were determined. Although the HFS rats were significantly fatter and heavier than the LFCC rats, the HFS L6 had a significantly smaller average cross-sectional area. When L6 structural properties were normalised with respect to body mass, the HFS L6 had significantly lower loads, energies, and stiffnesses. The HFS L6 stress and strain energy density values were also significantly less than the LFCC L6. Compared to the LFCC FN, the HFS FN had a smaller cortical shell and larger trabecular core. The HFS FN also had significantly lower mass-normalised loads, energies, and stiffnesses. These results suggest that a long-term HFS diet has a significant adverse effect on rat bone morphology and mechanics.

Adaptation, Physiological↗
PubMed1995

Urinary tract obstruction and nephrostomy drainage in pelvic malignant disease.

OBJECTIVE: To determine the survival of patients after percutaneous nephrostomy drainage (PND) for obstructive uropathy secondary to pelvic malignant disease. PATIENTS AND METHODS: The records of 77 patients undergoing PND for obstructive uropathy were reviewed. Patients were classified according to the nature of the obstructing lesion: Group I (primary untreated malignancy, 31 patients); Group II (recurrent malignancy with further treatment, 15 patients); Group III (recurrent malignancy with no further treatment, 12 patients); and Group IV (benign disease as a consequence of previous treatment, 19 patients). Outcome was assessed by survival over a mean follow-up of 20 months (range 2 days-8.3 years). RESULTS: Overall median survival was 26 weeks, with a 5-year survival of 22%. The survival in Groups I and II was not significantly different (median survival 27 and 20 weeks, respectively; 5-year survival, 10% and 20%, respectively). Group III patients had a poor prognosis (median survival 6.5 weeks) with no patient surviving beyond one year, whilst Group IV patients fared best with a 5-year survival of 64%. The commonest primary tumour type was carcinoma of the cervix (42 patients), and these patients were analysed as a subset. Benign post-radiation fibrosis was found in 16 of 27 patients (59%). Survival was related to the diagnostic group. CONCLUSION: The nature and extent of the obstructing lesion and its potential for further treatment are the major determinants of post-nephrostomy survival. Every effort should therefore be made to identify the nature of the obstruction before deciding on PND.

Adult↗
PubMed1995

Effects of acute and chronic exercise on skeletal muscle glucose transport in aged rats.

The purpose of this study was to investigate the effects of acute and chronic exercise on skeletal muscle glucose transport in aged rats by using an isolated sarcolemmal membrane preparation. In 24-mo-old female Fischer 344 rats, a maximum dose of insulin increased glucose transport from 43 +/- 6 to 82 +/- 6 pmol.mg protein-1.15 s-1. A 45-min bout of exhaustive treadmill running increased glucose transport to the same maximum level (88 +/- 5 pmol.mg protein-1.15 s-1). Eight weeks of progressive exercise training resulted in a 65% increase in succinic dehydrogenase activity in hindlimb muscles and a 55% increase in total cellular GLUT-4 content. Despite these biochemical adaptations, there was no change in either basal or maximum insulin-stimulated glucose transport between control (43 +/- 6 and 82 +/- 6 pmol.mg protein-1.15 s-1, respectively) and trained (42 +/- 2 and 82 +/- 8 pmol.mg protein-1.15 s-1, respectively) animals. When hindlimb muscle succinate dehydrogenase activity and GLUT-4 content were compared for both the combined sedentary and trained groups, a significant correlation (r = 0.68) was obtained. This study demonstrates that the skeletal muscle glucose transport system of 24-mo-old rats is fully stimulated by acute exercise and that, although GLUT-4 levels are increased in aged animals after exercise training, this does not result in an enhancement of maximal insulin-stimulated glucose transport. Thus increases in GLUT-4 are not sufficient to improve muscle insulin responsiveness with training.

Aging↗