Differential aging of median and ulnar sensory nerve parameters.

INTRODUCTION: Nerve conduction velocity slows and amplitude declines with aging. METHODS: Median and ulnar sensory nerves were tested at the annual meetings of the American Dental Association. Seven hundred four subjects had at least two observations. The rate of change in the nerve parameters was estimated while controlling for gender, age, change in hand temperature, baseline body mass index (BMI), and change in BMI. RESULTS: Amplitudes of the median sensory nerve action potentials decreased by 0.58 µV per year, whereas conduction velocity decreased at a rate of 0.41 m/s per year. Corresponding values for the ulnar nerve were 0.89 µV and 0.29 m/s per year. The rates of change in amplitudes did not differ, but the median nerve demonstrated a more rapid loss of conduction velocity. CONCLUSIONS: The rate of change for the median conduction velocity was higher than previously reported. The rate of change of median conduction velocity was significantly greater than for the ulnar nerve.

Factors associated with weaning in the first 3 months postpartum.

OBJECTIVE: To determine the demographic, behavioral, and clinical factors associated with breastfeeding termination in the first 12 weeks postpartum. STUDY DESIGN: This was a prospective cohort study. POPULATION: Breastfeeding women in Michigan and Nebraska were interviewed by telephone at 3, 6, 9, and 12 weeks postpartum or until breastfeeding termination. OUTCOMES MEASURED: We measured associations of demographic, clinical, and breastfeeding variables with weaning during the first 12 weeks postpartum. RESULTS: A total of 946 women participated; 75% breastfed until 12 weeks. Women older than 30 years and women with at least a bachelor's degree were more likely to continue breastfeeding in any given week. Mastitis, breast or nipple pain, bottle use, and milk expression in the first 3 weeks were all associated with termination. Beyond 3 weeks, women who expressed breast milk were 75% less likely to discontinue breastfeeding than women who did not. Women who used a bottle for some feedings during weeks 4 to 12 were 98% less likely to discontinue breastfeeding than women who did not use a bottle. "Not enough milk" was the most common reason given for termination in weeks 1 through 3 (37%) and weeks 4 through 6 (35%); "return to work" was the most common reason given in weeks 7 through 9 (53%) and weeks 10 through 12 (58%). CONCLUSIONS: Younger women and less educated women need additional support in their breastfeeding efforts. Counseling and assistance should be provided to women with pain and mastitis. Exclusive breastfeeding for the first 3 weeks should be recommended. After the first 3 weeks, bottles and manual expression are not associated with weaning and may improve the likelihood of continuing breastfeeding, at least until 12 weeks.

Weight loss due to energy restriction suppresses cholesterol biosynthesis in overweight, mildly hypercholesterolemic men.

Mechanisms explaining the decrease in circulatory cholesterol levels after weight loss remain ill defined. The objective was to examine effects of weight loss as achieved through energy restriction upon human in vivo cholesterol biosynthesis. Six subjects (64-77 y, body mass index, 30.3 +/- 3.8 kg/m(2)) were recruited into a two-phase prospective clinical trial. In the first phase, subjects complied with American Heart Association (AHA) Step I diets for 3 mo with no change in their usual energy intake. After this weight-stable phase, subjects consumed an AHA Step I diet with a targeted reduction in energy intake of approximately 1000 kJ/d for 6 mo to achieve negative energy balance leading to weight loss. The incorporation rate of deuterium from body water into erythrocyte membrane free cholesterol over 24 h was utilized as an index of cholesterogenesis at the end of both phases. Subjects' mean weights decreased (P < 0.05) from 89.3 +/- 12.5 kg to 83.2 +/- 11.5 kg (6.8 +/- 2.6% of initial body weight) across phases. Circulating concentrations of total and LDL-cholesterol, and triglycerides also decreased (P < 0. 05) across phases. HDL-cholesterol concentrations were unchanged (P > 0.05). Cholesterol fractional synthetic rate (FSR) after phase 2 (3.04 +/- 1.90%/d) was lower (P < 0.05) than that after phase 1 (8. 42 +/- 3.90%/d). Absolute synthesis rate (ASR) after phase 2 [0.59 +/- 0.38 g/(kg. d)] also was lower (P < 0.05) than that after phase 1 [1.66 +/- 0.84 g/(kg. d)]. These data suggest that, in obese men, energy restriction resulting in even modest weight loss suppresses endogenous cholesterol synthesis, which contributes to a decline in circulating lipid concentrations.

High fat, high cholesterol diets alter low density lipoprotein size and binding affinity in monkeys.

The purpose of this study was to examine the effects of various dietary fats on low density lipoprotein (LDL) binding in an in vitro system where receptor number is not regulated. Cynomolgus monkeys were fed diets containing 37% of energy from fat, with various degrees of saturation, and 0.4 mg/kcal cholesterol or low-fat (13% of energy), low cholesterol (0.03 mg/kcal) chow. Plasma LDL was isolated after 16 weeks. The fatty acid composition of LDL showed enrichment corresponding to the dietary fats consumed, and the high fat, high cholesterol diets produced marked hypercholesterolemia compared to chow feeding. Of those fed the high fat diets, monkeys fed the fish oil diet had the highest LDL cholesterol concentrations, 13.25 +/- 0.77 mmol/l, while those fed the safflower oil diet had the lowest, 7.51 +/- 3.31. LDL from chow fed monkeys had the lowest binding affinity; the Kd was 26.2 +/- 8.7 microg/ml, nearly twice that of the high fat diets (P = 0.003). No significant differences in binding were found between the different high fat diets, although there was a trend toward lower affinity in the diets enriched in polyunsaturated fat. LDL size was affected by diet with chow fed monkeys having the smallest average LDL, 259.3 +/- 1.7 A compared to the other groups (P = 0.03). Monkeys fed the fish oil diet tended to have smaller LDL, but this was not significantly different from the other high fat diets. Binding affinity was correlated with LDL size, r = 0.54, P < 0.01. LDL composition, as measured by apo B/cholesterol ratio, was altered by feeding a high fat, high cholesterol diet. The ratio was reduced in the LDL samples from monkeys fed the high fat diets compared to those fed chow, but this ratio was not significantly correlated with binding. Thus, it appears that increasing dietary fat and cholesterol intake increases LDL size and binding affinity, such that LDL metabolism may be altered independently from effects on receptor number; the type of dietary fat does not seem to influence this process when fat and cholesterol content is very high.

The relationship between weight and response to cholesterol-lowering diets in women.

OBJECTIVE: To determine whether factors related to body weight might influence the cholesterol lowering response to diet. DESIGN: Run-In diet followed by crossover to low fat diets; average response is reported. SUBJECTS: Sixty-three subjects (30 men and 33 women) with moderately elevated plasma cholesterol levels. MEASUREMENTS: Lipid and anthropometric measurements. Data were analyzed as a repeated measures analysis of variance with lipid lowering response in all combined cholesterol lowering diets compared to baseline. RESULTS: LDL cholesterol lowering was significantly affected by BMI in women (P = 0.01) but not in men (P = 0.54). There was also a weak effect of waist-hip (W/H) ratio on response (P = 0.127) in women, with the lower responders having a higher W/H ratio but there was no effect of W/H ratio in men (P = 0.86). CONCLUSION: These results suggest that overweight women with elevated plasma cholesterol may be less responsive to reducing their cholesterol levels with diet.

Fatty acid modification of membrane fluidity in Chinese hamster ovary (TR715-19) cells.

Dietary saturated fatty acids, especially lauric (12:0), myristic (14:0) and palmitic (16:0) acids, which are hypercholesterolemic, influence cell membrane fatty acid composition and affect LDL receptor function. When membrane phospholipid fatty acids in Chinese hamster ovary cells, containing the human LDL receptor, were modified (Hannah J. S. et al., 1995 Metabolism 44, 1428-1434), LDL receptor function was affected, but correlations with DPH-determined membrane fluidity were weak. The role of fluidity in various membrane domains with respect to the LDL receptor is examined here. Membrane fluidity was assessed by measuring steady-state fluorescence polarization of diphenylhexatriene (DPH) and its polar propionic acid (DPH-PA) and trimethylammonium (TMA-DPH) derivatives from 38 to 4 degrees C in fatty acid modified Chinese hamster ovary cells. Fatty acid changes modulated mid-bilayer fluidity as determined with DPH, but fluidity in phospholipid headgroup domains, assessed with DPH-PA and TMA-DPH, was independent of fatty acyl composition. The DPH fluidity was related to membrane unsaturation (P < 0.02), oleate contents (P < 0.009) in particular, but inversely related (P < 0.0002) to the longer chain (> or = 20 C atoms) unsaturated fatty acids with from four to six double bonds. The LDL binding was independent of fluidity, but there were weak relations between LDL internalization and DPH-PA anisotropy and between LDL degradation and TMA-DPH anisotropy. It was concluded that LDL binding was not related to mid-bilayer fluidity, but the results with the polar probes suggest a role of fluidity in modulating vertical displacement of the LDL/LDL receptor complex across the plasma membrane.

Binding affinity and particle size of LDL in subjects with moderate hypercholesterolemia: relationship with in vivo LDL metabolism.

The aim of this study was to examine relationships between low density lipoprotein (LDL) metabolism, in vitro binding, and particle size. Twenty four study subjects, 17 men and 7 women, had elevated plasma total cholesterol (TC), ranging from 174 to 232 mg/dl, and LDL cholesterol (LDLC) ranging from 113 to 195 mg/dl after 12 weeks on a Step I diet. The fractional clearance rate (FCR) for LDL ranged from 0.233 to 0.619 pools/day (0.366 +/- 0.021) and was significantly correlated with plasma triglycerides (TG) (P < 0.05). Although there was no relation between FCR and binding in the study group as a whole, those subjects with an FCR within the normal range (< 0.45, n = 20), showed a significant negative correlation between FCR and the KD for LDL binding, (r = 0.52). A subset of four subjects with an elevated FCR (> 0.45) had higher production rate (PR) (P < 0.005) and a significant positive correlation between the KD for LDL binding and FCR (P < 0.05). LDL size varied from 240.0 to 265.8 A and was significantly inversely correlated with plasma TG (P < 0.001) but there was no relation between LDL size and metabolism or binding affinity. Thus, there appears to be a correlation between binding affinity and clearance for subjects who had normal LDL production and clearance rates. On the other hand, mechanisms other than binding affinity appear to influence clearance in subjects with elevated rates of production and clearance.

Effects of Acipimox on the metabolism of free fatty acids and very low lipoprotein triglyceride.

The mechanism of triglyceride lowering by Acipimox, a nicotine acid analogue, was examined in a group of five moderately hypertriglyceridemic male rhesus monkeys. Two experiments were designed to examine the effect of the drug on lipid and glucose metabolism in nondiabetic, insulin-resistant animals. A single dose of Acipimox (8 mg/kg) given with a meal lowered the plasma free fatty acids (FFA) significantly at 4 h (0.102 +/- 0.008 vs 0.154 +/- 0.020 g/l; mean +/- SEM; P < 0.03); however, FFA concentrations returned to control levels at 6 h. Chronic administration of Acipimox (16 mg/kg q. i. d.) for 2 months produced a 31% reduction in triglyceride concentration (P < 0.05) and a significant decrease in low density lipoprotein (LDL)-cholesterol (P < 0.04), without changes in insulin action as measured by the hyperinsulinemic euglycemic clamp. Fasting FFA concentrations were not significantly altered by chronic treatment (0.163 +/- 0.013 versus 0.140 +/- 0.034 g/l). Fatty acid metabolic studies indicated increases in FFA transport (203.7 +/- 59.1 versus 136.1 +/- 26.6 microEq/min; P < 0.05), while FFA fractional clearance rate (FCR) was unchanged. Very low density lipoprotein triglyceride (VLDL-Tg) metabolic experiments, using [3H]glycerol, showed increases in production and FCR with the drug. Increased VLDL-Tg clearance, in spite of increased production of VLDL, appears to be the mechanism by which triglycerides are lowered upon chronic Acipimox administration.

In vitro regulation of low-density lipoprotein receptor interaction by fatty acids.

Low-density lipoprotein (LDL) receptor binding is the initial step in receptor-mediated clearance. Dietary fat composition is known to affect LDL clearance, but the mechanism of the effect is unknown. We have examined the effects of altered membrane fatty acid composition, as might occur when specific dietary fats are consumed, on LDL binding using a Chinese hamster ovary (CHO) line that constitutively expresses the human LDL receptor. Binding of pooled human LDL to its receptor was compared in cells enriched with various fatty acids. Binding affinity was greater (lower Kd) for cells grown in 16:0-, 18:0-, or 18:1-enriched media than for those grown in 18:2 (P < .0001). The apparent receptor number (Bmax) was lower for cells enriched in saturated fatty acids and 18:1. Fluidity was assessed by measuring diphenylhexatriene (DPH) fluorescence anisotropy (rs). Cells enriched in 18:1 or 18:2 were the most fluid (P < .003). The correlation between binding and fluidity (r = .24, P = .27) was weak and did not appear to explain the effects of fatty acid modification on LDL receptor binding. Thus, it appears that cellular enrichment in 16:0, 18:0, and 18:1 increases binding affinity by affecting properties other than membrane fluidity. Changes in Bmax may also contribute to the observed differences in LDL binding.

Polyunsaturated fatty acids result in greater cholesterol lowering and less triacylglycerol elevation than do monounsaturated fatty acids in a dose-response comparison in a multiracial study group.

Cholesterol-lowering effects of polyunsaturated and monounsaturated fatty acids were compared as they were varied in a reciprocal dose-dependent fashion in the context of a National Cholesterol Education Program (NCEP) Step 1 diet. The study population comprised 63 moderately hypercholesterolemic African American and white men and women. After a 6-wk baseline diet containing 37% of energy from total fat and 15% from saturated fat, participants consumed four diets for 6 wk each, in random order, containing 10% of energy as saturated fatty acids; 3%, 6%, 10%, and 14% of energy as polyunsaturated fatty acids; and 17%, 14%, 10%, and 6% of energy as monounsaturated fatty acids. Dietary cholesterol, fiber, plant sterol, and squalene contents were constant with all four diets. There was a progressive decrease in total (P = 0.028) and low-density-lipoprotein cholesterol (P = 0.184) across the four diets, with the greatest decrease observed in the diet with the highest content of polyunsaturated fatty acids; a small but significant decrease in high-density-lipoprotein (HDL) cholesterol that did not show a trend between the polyunsaturated and monounsaturated diets; and a trend between the four diets in triacylglycerol elevations (P = 0.029), with the smallest increment occurring in the diets highest in polyunsaturates. The magnitude of the cholesterol-lowering response was greater in those with higher baseline cholesterol and less in those who were more obese. The dietary response was similar in both ethnic groups and in both sexes. In conclusion, in an NCEP Step 1 diet containing 30% total fat, with all other known cholesterol-influencing dietary factors held constant, the substitution of polyunsaturated fatty acid for monounsaturated fatty acid from 3% to 14% resulted in a progressive decline in total cholesterol and less triacylglycerol elevations, without effect on HDL cholesterol.

Effects of sex and ethnicity on responses to a low-fat diet: a study of African Americans and whites.

The effects of sex and ethnicity on plasma lipoprotein changes that occur with low-fat diets were studied in 34 African American subjects (20 women, 14 men) and 29 white subjects (13 women, 16 men) aged 25-62 y with moderate hypercholesterolemia. A baseline diet containing 37% fat (15% saturated) was compared with four experimental diets containing 30% fat (10% saturated) with reciprocally varying contents of polyunsaturated and monounsaturated fatty acids. Diets were fed for 6 wk each, and all food and beverages provided and compliance were intensively monitored. Body weight and physical activity were held constant. Lowering of total and low-density-lipoprotein cholesterol were similar between women and men and between African Americans and whites. Small differences were observed between women and men in the extent of high-density lipoprotein lowering and triacylglycerol elevations. Additionally, African American subjects had slightly higher triacylglycerol elevations than did white subjects. Results suggest that men and women of varied ethnic backgrounds should respond similarly to cholesterol-lowering diets. Studies are required to develop strategies for achieving dietary changes that consider diverse eating patterns and cultural barriers to dietary adherence.

Dietary fats, insulin resistance, and diabetes.

Although population-based studies suggest that a high-fat diet may increase the incidence of diabetes, the mechanism of this association is not clear. Controlled metabolic studies indicate that changes in fat content of the diet within the range that people normally consume have little or no effect on insulin-mediated glucose disposal. Thus, the effects of a high-fat diet on the incidence of non-insulin-dependent diabetes mellitus (NIDDM) may be mediated by inducing obesity, a known cause of insulin resistance and a risk factor for NIDDM. More research is needed in this area.

Central obesity in rhesus monkeys: association with hyperinsulinemia, insulin resistance and hypertriglyceridemia?

Total body fat and anthropometric assessments of fat distribution were examined in 23 lean and obese rhesus monkeys (Macaca mulatta). In addition, the relationships of central obesity to hyperinsulinemia, insulin resistance, glucose intolerance and hyperlipidemia were studied. Total body fat (as determined by the tritiated water dilution method), plasma glucose, insulin, lipoproteins (triglyceride, cholesterol and HDL- and LDL-cholesterol) and free fatty acids (FFA), and glucose disappearance rate (KG) and peripheral insulin-stimulated glucose uptake (M) were obtained. Results showed that abdominal circumference was the best predictor of body fat (r = 0.90; P < 0.001). There were strong linear relationships between abdominal circumference and plasma insulin (r = 0.66), glucose tolerance (r = -0.53), and M rate (r = -0.59) (all P < 0.05) but not to plasma glucose, lipoprotein fractions, or free fatty acids. When the subjects were grouped according to degree of obesity and insulin resistance (lean normals, obese insulin sensitive, and obese insulin resistant), the obese resistant monkeys had significantly higher plasma insulin levels, lower glucose tolerance, and significantly higher plasma triglyceride levels. We conclude that the spontaneously obese rhesus monkey is an excellent model of central obesity. Furthermore, in this model upper body obesity appears to be facilitative in the development of hyperinsulinemia, glucose intolerance and hypertriglyceridemia but does not appear to be causally related. In the rhesus monkey and in humans as well, we propose that the link between central obesity and these metabolic abnormalities may be peripheral insulin resistance.

Changes in lipoprotein concentrations during the development of noninsulin-dependent diabetes mellitus in obese rhesus monkeys (Macaca mulatta).

Abnormalities in plasma lipoprotein concentrations commonly found in subjects with noninsulin-dependent diabetes may be related to insulin resistance, hyperinsulinemia, hyperglycemia, or other metabolic defects. The middle-aged obese rhesus monkey is an animal model in which these defects can be separated in time during the development of diabetes. It is, therefore, a model system for examining the sequence of metabolic changes which occur before and after the onset of diabetes. This sequence of changes was used in the present study to determine if lipoprotein changes occur in association with the development of diabetes in the rhesus monkey. Increases in plasma triglyceride, very low density lipoprotein (VLDL) triglyceride, and VLDL cholesterol, and decreases in high density lipoprotein cholesterol were observed across previously identified groups ranging from normal to diabetic. Plasma triglycerides increased from 0.54 +/- 0.09 (normal) to 1.27 +/- 0.50, 1.93 +/- 0.79, and 4.28 +/- 2.24 in three intermediate groups with progressive hyperinsulinemia and insulin resistance, to 7.59 +/- 2.73 mmol/L in the diabetic monkeys. Increases in VLDL triglyceride and VLDL cholesterol paralleled the plasma triglyceride increases. High density lipoprotein cholesterol decreased across the groups from 2.33 +/- 0.16 (normal) to 1.72 +/- 0.20, 1.17 +/- 0.13, and 1.09 +/- 0.20 mmol/L in the intermediate groups, and was lowest in the diabetic monkeys, 1.00 +/- 0.21. The obese rhesus monkey can therefore be used to study lipoprotein abnormalities as they occur both before and in noninsulin-dependent diabetes.

Postingestional effects of a high-protein diet on the regulation of food intake in monkeys.

Using a system in which the composition of an intragastric diet could be manipulated while oral factors were kept constant, we studied the effect of a high-protein diet on food intake. Four adult rhesus monkeys with chronically implanted intragastric cannulas were trained to use suction-activated food pumps that were monitored by computer so feeding pattern could be assessed over periods averaging 4 wk each. Each suck delivered the oral control diet while simultaneously activating a second pump, which delivered a second diet directly into the stomach, resulting in net diet compositions of either 14% or 50% protein. The calorie intake was consistently reduced by 24.7 +/- 1.6% when the high-protein diet was fed. The effect on intake was not due to increased diet osmolality. A doubling in plasma branched-chain amino acid concentration occurred when the high-protein diet was fed. These data indicate that feeding a high-protein diet results in a physiological appetite suppression, possibly mediated through branched-chain amino acids.

Modification of intracellular hemoglobin with pyridoxal and pyridoxal 5'-phosphate.

The aldehyde forms of vitamin B6, pyridoxal and pyridoxal 5'-phosphate (PLP) have aroused interest as antisickling agents because of their ability to modify hemoglobin (Hb) and their low toxicity. To study their rate of formation and stability inside red cells, pyridoxal-Hb and PLP-Hb were measured in lysates from treated normal and sickle erythrocytes using isocratic high pressure liquid chromatography on Bio-Rex 70. The validity of this assay was confirmed by isoelectric focussing, fluorescence scans of reduced globin, and treatment of cells with pyridoxal 14C. Optimal conditions were described for treatment of whole blood with pyridoxal and washed erythrocytes with PLP. Although there was competition between 2,3-DPG and PLP, but not pyridoxal, for binding to Hb, depletion of 2,3-DPG prior to treatment was unnecessary. No special requirements were noted for the anticoagulants or buffers used. Sickle erythrocytes formed PLP-Hb more rapidly than normal erythrocytes, but pyridoxal-Hb appeared at the same rate in both types of erythrocytes. During incubation of treated erythrocytes in untreated plasma, the stability of pyridoxal-Hb varied inversely with the hematocrit, but PLP-Hb was stable at all hematocrits tested. The absence of hemolysis during a 4 day incubation of treated normal red cells implies that treatment with pyridoxal or PLP did not severely impair red cell metabolism.