Concomitant supplemental vitamin A enhances the response to weekly supplemental iron and folic acid in anemic teenagers in urban Bangladesh

BACKGROUND

Iron deficiency is the most common micronutrient deficiency and affects >2 billion persons worldwide, leading to anemia in >40% of women of reproductive age in the developing world.

OBJECTIVE

The objective was to determine whether weekly supplementation with iron and folate would reduce the frequency of anemia in teenage women in urban Bangladesh before they became pregnant.

DESIGN

Participants with a hemoglobin concentration of 80-120 g/L were entered into a randomized, double-blind, placebo-controlled trial and received supplements of placebo, vitamin A, iron + folic acid, or iron + folic acid + vitamin A weekly for 12 wk. The supplements contained 2.42 mg vitamin A (retinol) as retinyl palmitate, 120 mg elemental Fe as ferrous sulfate, and 3.5 mg folic acid.

RESULTS

Hemoglobin concentrations increased significantly more after supplementation with iron + folic acid or iron + folic acid + vitamin A than after either the placebo or vitamin A alone. There was a significantly greater increase in hemoglobin after iron + folic acid + vitamin A than after iron + folic acid, but the additional effect disappeared after adjustment for baseline hemoglobin, serum vitamin A, and ferritin and the number of supplements taken. Those with the lowest baseline hemoglobin had the greatest increase in hemoglobin. Compared with the placebo, iron + folic acid + vitamin A reduced anemia by 92%, iron deficiency by 90%, and vitamin A deficiency by 76%.

CONCLUSION

There may be significant health benefits from a program that enhances the nutritional status of iron, folate, and vitamin A in poor urban young women before they become pregnant.

Relationship of maternal protein turnover and lean body mass during pregnancy and birth length

Epidemiological evidence shows that small size at birth is associated with an increased risk of developing cardiovascular and metabolic disease in adult life. We have examined the relationships between size at birth and maternal body composition and protein turnover in normal pregnant women. A group of 27 multiparous Caucasian women with singleton pregnancies were studied at around 18 and 28 weeks' gestation. Body composition was determined by anthropometry, and whole-body protein turnover was estimated by using a single oral dose of [(15)N]glycine and the end-product method. The baby's weight and length were measured within 48 h of birth. Mothers with a greater lean body mass had higher rates of protein turnover at 18 weeks' gestation. This association was largely accounted for by differences in the mother's visceral, rather than muscle, mass. Mothers who had higher protein turnover at 18 weeks' gestation had babies that were longer at birth. After adjustment for the duration of gestation and the baby's sex, 26% of the variation in length at birth was accounted for by maternal protein synthesis at 18 weeks' gestation. Maternal protein intake was not associated with the baby's birth length. Thus the mother's ability to nourish her fetus is influenced by her body composition and her rate of protein turnover. Dietary intake does not adequately characterize this ability.

Gastrointestinal handling and metabolic disposal of 13C-labelled tripalmitin during rehabilitation from childhood malnutrition

We investigated the gastrointestinal handling and post-absorptive metabolic handling of [1,1,1-13C]tripalmitin and [1-13C]glycocholate during recovery from severe childhood malnutrition. Eight children were studied on three occasions: at admission (phase 1), during rapid catch-up growth (phase 2) and when weight-for-height had reached 90 % of the reference (phase 3). Breath samples were obtained over a 24 h period and stools were collected over 3 d following the administration of each tracer. At admission, the lipid content of stool expressed as a percentage of ingested lipid was 6 (range 0.7-28.9) but less variation was shown between children at phase 2 (3.3 (range 0.9-4.1)) and phase 3 (1.4 (range 0.4-2.5)). The excretion of 13C in stool varied markedly between children at admission (11.1 (sd 5.4) % administered dose) and during rehabilitation (phase 2, 15.4 (sd 16.5) % administered dose; phase 3, 6.2 (sd 10.2) % administered dose). About 5 % of the absorbed label was recovered on breath at each stage (% absorbed dose; phase 1, 5.1 (sd 6.0); phase 2, 5.2 (sd 3.1); phase 3, 6.4 (sd 6.6)). None of the children exhibited significant bile salt malabsorption as a consequence of small intestinal overgrowth. Of the 13C measured in stool, more label was recovered in fatty acids than triacylglycerols during each of the three phases and this was interpreted to reflect a failure to absorb the products of digestion. The results show that not all the children had problems associated with the digestion and absorption of 13C-labelled tripalmitin in severe malnutrition and during recovery, which was not reflected in gross lipid balance across the gastrointestinal tract. Absorbed lipid was more likely to be deposited as adipose tissue than to satisfy the immediate needs for energy.

Human nutrition in medical practice: the training of doctors

Nutritional advice from doctors and other health workers is held in high regard by the general public. It is important, therefore, to ensure that the advice given is sound and safe. Historically, the training in nutrition for the health professions has been piecemeal and selective. As a first step in the development of national standards, a core curiculum on nutrition for health professionals was developed as part of the National Nutrition Task Force. Designed for undergraduates, the curriculum sought to provide a standard for training which would ensure safe practice. The curriculum, which has been accepted by all undergraduate medical schools, identifies eighteen bullet points covering: the principles of nutritional science; public health nutrition; clinical nutrition and nutritional support. Postgraduate training for doctors is the responsibility of the Royal Colleges, who have formed an Intercollegiate Group on nutrition. This group has developed an intercollegiate foundation course in nutrition which lasts for I week and is offered at different centres around the country. Using the Intercollegiate Course as a base, individual Colleges are exploring how they might best develop the next level of training by identifying the educational needs for nutrition in different sub-specialities. There is some discussion as to whether it is timely to develop a defined clinical speciality in human nutrition. Within these developments, nutritionists and dietitians are identified as a resource to be called upon by other health professionals, and therefore it is important that in their own training they are suitably equipped to take on this challenge.

Intake of micronutrient-rich foods in rural Indian mothers is associated with the size of their babies at birth: Pune Maternal Nutrition Study

One third of the Indian babies are of low birth weight (<2.5 kg), and this is attributed to maternal undernutrition. We therefore examined the relationship between maternal nutrition and birth size in a prospective study of 797 rural Indian women, focusing on macronutrient intakes, dietary quality and micronutrient status. Maternal intakes (24-h recall and food frequency questionnaire) and erythrocyte folate, serum ferritin and vitamin C concentrations were measured at 18 +/- 2 and 28 +/- 2 wk gestation. Mothers were short (151.9 +/- 5.1 cm) and underweight (41.7 +/- 5.1 kg) and had low energy and protein intakes at 18 wk (7.4 +/- 2.1 MJ and 45.4 +/- 14.1 g) and 28 wk (7.0 +/- 2.0 MJ and 43.5 +/- 13.5 g) of gestation. Mean birth weight and length of term babies were also low (2665 +/- 358 g and 47.8 +/- 2.0 cm, respectively). Energy and protein intakes were not associated with birth size, but higher fat intake at wk 18 was associated with neonatal length (P < 0.001), birth weight (P < 0.05) and triceps skinfold thickness (P < 0.05) when adjusted for sex, parity and gestation. However, birth size was strongly associated with the consumption of milk at wk 18 (P < 0.05) and of green leafy vegetables (P < 0.001) and fruits (P < 0.01) at wk 28 of gestation even after adjustment for potentially confounding variables. Erythrocyte folate at 28 wk gestation was positively associated with birth weight (P < 0.001). The lack of association between size at birth and maternal energy and protein intake but strong associations with folate status and with intakes of foods rich in micronutrients suggest that micronutrients may be important limiting factors for fetal growth in this undernourished community.

Dietary guidelines for pregnancy: a review of current evidence

In a successful pregnancy maternal health is maintained, a healthy baby is delivered and the mother is able to nurture her newborn adequately. Despite continued interest in the role and importance of maternal diet in this process, we do not have a clear understanding of how the nutritional status of the mother influences fetal growth and development. Recent epidemiological evidence of an association between poor fetal growth and adult disease highlights the need to reconsider the influences which act on the fetus, and the role maternal nutrition may play. Nutrient needs are increased in pregnancy. For the mother to be solely dependent upon her dietary intake to meet these demands, would represent a very high risk strategy. Hence adequate reserves are important for a successful outcome. Whilst there are numerous observational studies of diet during pregnancy, there are only limited data from well-controlled, randomised supplementation studies. A recent systematic review showed only dietary supplements balanced in energy and protein content to result consistently in improved fetal growth. There is no strong evidence that nutrient supplements confer benefit in women without overt deficiency. To interpret future dietary studies in pregnancy we need to consider metabolic differences between women which may influence their ability to meet fetal nutrient demand, to allow for nutrient-nutrient interactions, and to take account of differences in timing in gestation. Consideration of these factors in studies of pregnancy, will lead to a clearer understanding of the links between maternal diet and fetal growth and development. Until we have this understanding, it is reasonable to expect that women entering pregnancy are provided with a diet which is adequate, based upon our normal understanding of requirements, and it is not acceptable for women to be expected to carry a pregnancy with an obvious or overt nutritional deficiency.

Whole body protein turnover can be measured non-invasively in women using the end product method with [15N]glycine to show changes with the menstrual cycle and pregnancy

OBJECTIVES

To assess the effect of the menstrual cycle and pregnancy on whole body protein turnover.

DESIGN AND SUBJECTS

Whole body protein turnover was determined using oral [15N]glycine in normal women from enrichment measured in urine at days 7 and 14 of the menstrual cycle and in pregnant women at 17-20 weeks and 30-32 weeks gestation.

RESULTS

Nitrogen flux was 38.2 (5.8) mg N/kg/h using a single dose and 31.1+/-4.1 mg N/kg/h with prime-intermittent doses-the same as in men using the same methods. Nitrogen flux around the time of ovulation, 32.3 (8.2) mg N/kg/h, was greater than at day 7, 26.8 (3.0) mg N/kg/h (P<0.05). For women taking the contraceptive pill flux at day 7, 22.7 (0.2) mg N/kg/h, and day 14, 21.3 (2.1) mg N/kg/h, were similar, but were lower at day 14 than for women not taking the pill (P<0.05). Protein synthesis increased between mid and late pregnancy (1.7-2.0 g N/h; P=0.012), but not when expressed in relation to body weight

CONCLUSIONS

Protein turnover can be measured reproducibly in women using a non-invasive method, provided care is taken to standardize the conditions, and especially the duration over which urine is collected. There is an increase around the time of ovulation when hormonal levels are at their highest and during pregnancy the results obtained are similar to those reported using [13C]leucine.

SPONSORSHIP

University of Southampton and Medical Research Council.

Maternal pre-pregnancy weight and placental weight determine birth weight in normal Jamaican infants

Birth weight is related to neonatal health and long-term risk of chronic disease. Since animal studies have shown that birth outcome is related to placental function, the present project was designed to explore the relationship between birth weight and placental growth and composition with maternal factors during pregnancy among normal term pregnancies in 51 primiparous and 40 multiparous women delivering at the University Hospital of the West Indies. Both groups were followed from 15 weeks of gestation to term. The primiparous group was generally younger than the multiparous (mean age 22 +/- 4 versus 31 +/- 5 yr). They were significantly lighter (55 +/- 8 versus 61 +/- 9 kg) with a lower body mass index (21 +/- 3 versus 23 +/- 4 kg/m2) during early pregnancy, but gained more weight during pregnancy, 11 kg compared with 8 kg, respectively. The duration of pregnancy was similar for both groups. Although the size of the placenta was not significantly different between the two groups, the mean weight of the multiparous placentae was more than that of the primiparous placentae. Also, for all mothers both placental weight and initial maternal weight related directly to birth weight. Placental non collagen protein (NCP), sodium and potassium contents were significantly higher for multiparous women and were related to birth weight. The primiparous group had babies who were significantly lighter, 3.03 kg compared with 3.36 kg, for the multiparous and this could be attributed to differences in placental function and maternal weight. When account was taken of the difference in maternal weight at the start of pregnancy and the difference in placental weight, parity no longer explained any of the differences in birth weight. It is concluded that maternal body weight at the time of becoming pregnant and the early development of the placenta determine the efficiency with which nutrients might be delivered to the foetus and hence foetal growth. The difference in birth weight between primiparous and multiparous women can be explained by the differences in maternal weight at the time of becoming pregnant.

Metabolism of lactose-[13C]ureide and lactose-[15N,15N]ureide in normal adults consuming a diet marginally adequate in protein

Oral lactose-ureide is resistant to human digestive enzymes, but is fermented by the colonic microflora. Nine normal adults consuming a diet which provided 36 g of protein/day were given oral doses of lactose-[(13)C]ureide and lactose-[(15)N,(15)N]ureide. The appearance on breath of (13)CO(2) derived from lactose-[(13)C]ureide was followed for 48 h. The fate of (15)N derived from lactose-[(15)N, (15)N]ureide was determined by measuring the recovery of (15)N in stools and urine in various forms. About 80% of the label given as lactose-[(13)C]ureide was recovered on the breath, and about 80% of label given as lactose-[(15)N,(15)N]ureide was not recovered in stool, indicating that 80% of the dose was completely fermented. At least 5% of the labelled urea was absorbed and excreted as the intact molecule. Of the (15)N derived from lactose-[(15)N, (15)N]ureide and available for further metabolic interaction, 67% was retained and 33% was excreted in urine. The time taken for [(15)N,(15)N]urea to appear in urine was similar for all subjects, but the appearance of either (13)CO(2) on the breath or [(15)N, (14)N]urea in urine varied. It is concluded that the hydrolysis of the sugar-urea bond may reflect oro-caecal transit time, but that other factors related to colonic bacterial metabolism determine the duration and extent of hydrolysis of urea by urease enzymes. Lactose-ureide can be used to probe the metabolic activity of the colonic microflora in normal individuals.

Long-term modification of the excretion of prostaglandin E(2) by fetal exposure to a maternal low protein diet in the rat

Prenatal exposure to maternal undernutrition in both humans and animals is associated with long-term changes in the structure, physiological functions and metabolism of key tissues and organs. This phenomenon, termed programming, is implicated in the aetiology of cardiovascular disease. Using an established rat model of hypertension programmed by prenatal protein restriction, assessment was made of the long-term influence of maternal diet upon prostaglandin metabolism. Pregnant rats were fed isoenergetic diets containing 18% casein (control) or 9% casein (low protein) from conception until littering. The offspring of these pregnancies were studied at day 20 of gestation, full-term gestation and at 4, 7 or 12 weeks postnatal age. Prostaglandin E(2) concentrations in plasma were similar in control and low-protein diet-exposed rats at 4 weeks of age. Urinary prostaglandin E(2) excretion was, however, significantly increased by prenatal undernutrition in rats at both 4 and 12 weeks postnatal age. The principal enzyme of prostaglandin E(2) degradation, 15-hydroxyprostaglandin dehydrogenase (PGDH) exhibited significantly lower activity in the kidneys of 4-week-old rats exposed to a maternal low-protein diet. This effect was transient and absent by 12 weeks postnatal age. There was also some evidence of an altered developmental profile of PGDH activity in the lungs of low-protein diet-exposed rats. These data are consistent with the long-term programming effects of the maternal diet upon renal prostaglandin metabolism. In the rat, increased local prostaglandin E(2) concentrations associated with impaired degradation may contribute to increased renovascular resistance and hypertension.

Dietary protein, growth and urea kinetics in severely malnourished children and during recovery

The case mortality for severe malnutrition in childhood remains high, but established best approaches to treatment are not used in practice. The energy and protein content of the diet at different stages of treatment appears important, but remains controversial. The effect on growth, urea kinetics and the urinary excretion of 5-L-oxoproline was compared between a standard infant formula (HP group) provided in different quantities at each stage of treatment and a recommended dietary regimen, which differentiates the requirements of protein and energy during the acute phase of resuscitation (maintenance intake of energy and protein, relatively low protein to energy ratio, LP group) from those during the restoration of a weight deficit (energy and nutrient dense). The energy required to maintain weight was less in the HP than the LP group, but the HP group was not able to achieve as high an energy intake during repletion of wasting because of the high volume which would have had to be consumed. Compared to the LP group, in the HP group during catch-up growth there was significantly greater deposition of lean tissue and higher rates of urea production, hydrolysis and salvage of urea-nitrogen. These, together with higher rates of 5-L-oxoprolinuria, suggest a greater constraint of the formation of adequate amounts of nonessential amino acids, especially glycine, in the face of enhanced demands. Although more effective rehabilitation might be achieved using a standard formula, there is the need to determine the extent to which it might impose metabolic stress compared with the modified formulation.

Fetal exposure to a maternal low protein diet impairs nephrogenesis and promotes hypertension in the rat

Epidemiological evidence suggests that hypertension and coronary heart disease are programmed by exposure to a poor diet during intrauterine life. It has been proposed that the prenatal environment may exert an adverse effect on the development of the kidney and hence later control of blood pressure. These assertions are supported by animal experiments. In the rat, fetal exposure to a maternal low protein diet is associated with disproportionate patterns of fetal growth and later elevation of blood pressure. Pregnant female rats were fed control (18% casein) or low protein diets throughout pregnancy, or during specific periods. Nephron number was determined at day 20 gestation, full term and 4 weeks of age. Exposure to low protein throughout gestation, or in mid-late gestation increased total nephron number at day 20. By term nephron number was reduced, relative to controls, in rats that were undernourished between days 8-14 or 15-22 gestation. At 4 weeks postnatally rats exposed to low protein throughout fetal life had a reduced (13%) nephron complement and blood pressures 13 mmHg above control animals. Lower renal size and elevated blood pressure persisted to 19 weeks of age, at which time glomerular filtration rate was normal. The data are consistent with the hypothesis that maternal undernutrition may programme the renal nephron number and hence impact upon adult blood pressure and the development of renal disease.

Limits of adaptation to high dietary protein intakes

Ingested protein is made available to the body following digestion and absorption as amino acids and contributes to the body's demand for amino acids for protein synthesis and other metabolic pathways. As the pattern of amino acids required for metabolism is substantially different from that ingested, extensive metabolic interchange serves to improve the match. As a matter of course oxidation of amino acids contributes to satisfying the energy needs of the body. Amino acids in excess of immediate requirements follow degradative pathways and if the capacity of these pathways is exceeded adverse consequences ensue. In pathological states, such as inborn errors of metabolism, there is an obvious constraint on metabolic flow with serious sequelae. Pathways may be constrained to a lesser extent due to genetic polymorphisms, metabolic programming, limitation of cofactors or lack of associated substrates. Any of these can result in metabolic derangements, which do not manifest as overt disease, but limit normal function. There is the need to determine the dose response to increases in dietary protein and amino acid availability, using critical metabolic intermediates as outcome indices in order to clarify the upper limit of intake with which the body can cope under a range of physiological and pathological states.

Intrauterine programming of hypertension: the role of the renin-angiotensin system

From experiments with prenatal undernutrition in the rat, it is clear that fetal exposure to glucocorticoids of maternal origin is a key first step in the programming of hypertension and perhaps coronary heart disease. The chain of events leading from glucocorticoid action in the fetal tissues to hypertension in adulthood involves the development of hypersensitivity to glucocorticoids in adult life (Scheme 1). This has the effect of activating the RAS through induction of key genes such as ACE, which, in turn, may increase sensitivity of the blood vessels to the actions of ANGII. Another consequence of prenatal undernutrition, which may or may not involve glucocorticoids, is the abnormal development of the kidney [35]. Impaired nephrogenesis must surely have an impact upon lifelong renal function and cardiovascular control. Progress has been made in demonstrating that hypertension can be prenatally programmed through maternal dietary manipulation and some of the putative mechanisms involved have been identified. The priorities in this field of research must now be to clarify the role of maternal diet as a programming stimulus in order to generate an effective series of public health guidelines for pregnant women. Although the identification of metabolic mechanisms might suggest possible pharmacological interventions in early life as a means of reducing cardiovascular risk in adult life [49], it will always be more desirable to optimize maternal diet.

Infants in Trinidad excrete more 5-L-oxoproline (L-pyroglutamic acid) in urine than infants in England: an environmental not ethnic difference

The demand for glycine to satisfy normal growth during early life is considerable and most has to be made endogenously. The extent to which adequate glycine is available can be assessed by measuring the urinary excretion of 5-L-oxoproline. The excretion of 5-L-oxoproline at 6 weeks of age for infants in Trinidad of African, Indian or mixed parentage (398 mumol/mmol creatinine) was significantly greater than for infants born in England of Caucasian parentage (194 mumol/mmol creatinine). There was no relationship between 5-L-oxoproline excretion and either sex or pattern of feeding. There were significant inverse relationships between 5-L-oxoproline/creatinine and birth weight, and head circumference either at birth or 6 weeks of age, suggesting that limited availability of glycine is associated with poorer growth before and after birth. For a group of infants born in England of Indian parentage, excretion of 5-L-oxoproline (155 mumol/mmol creatinine) was not different to infants of Caucasian parentage, but significantly less than infants born in Trinidad. The demonstration that 5-L-oxoproline/creatinine was similar in infants born in England, regardless of parentage, shows that the differences between England and Trinidad are related to environment and are unlikely to be accounted for by genetic differences or ethnicity.

Dietary pattern, nutrient intake and growth of adolescent school girls in urban Bangladesh

OBJECTIVE

To investigate the dietary pattern and nutritional status of adolescent girls attending schools in Dhaka city and to examine the association with various social factors.

DESIGN

Cross-sectional study.

SETTING

Girls high schools in Dhaka city.

SUBJECTS

A total of 384 girls, aged from 10 to 16 years, who were students of classes VI to IX of 12 girls high schools in Dhaka city were selected by systematic random sampling. Nutrient intake was assessed using the 24-h recall method and the usual pattern of food intake was examined using a 7-day food frequency questionnaire.

RESULTS

The prevalence of undernutrition among the participants assessed as stunting was 10% overall with younger girls being less stunted (2%) than older girls (16%), whereas 16% were thin with relatively more of the younger girls (21%) being thin than of the older girls (12%). Based on the usual pattern of food intake, a substantial proportion of the girls did not consume eggs (26%), milk (35%) or dark green leafy vegetables (20%). By comparison, larger proportions consumed meat (50%) and fish (65%) at least four times a week. For the intake of energy and protein, only 9 and 17% of the girls, respectively, met the recommended daily allowance (RDA). For nearly 77% of the girls, the intake of fat was less than the recommendation. Intakes less than the RDA were found for iron (77% of the girls), calcium (79%), vitamin A (62%), vitamin C (67%), and riboflavin (96%). Based on the food consumption data, cereals were the major source of energy (57%), thiamin (67%), niacin (63%) and iron (37%). Animal sources supplied 50% of dietary protein. Cooking fats were the principal source of fat (67%) in the diet. Milk was the major contributor for riboflavin and preformed vitamin A (retinol). Leafy vegetables and fruits were the main sources of provitamin A (carotenes). The girls from families with less educated parents were more likely to be thin and short for their age. Those girls from families with lower incomes and less educated parents had a dietary pattern which tended to be poor with regard to egg, milk, meat and fruit, with lower intakes of protein, fat and riboflavin.

CONCLUSION

The findings indicate that the diets of these girls tended to be inadequate both for macronutrients and micronutrients, with significant health implications. There was also a relationship between the family income and the education of the parents with the nutritional status of the girls.

Glycine is not formed through the amino transferase reaction in human or rat placenta

The fetus has a substantial demand for glycine, which is satisfied in part by placental formation. The ability to form glycine through the activity of alanine:glyoxylate aminotransferase enzyme was measured in placentae from normal term human pregnancies and placentae from rats at day 20 of gestation. There was no detectable enzyme activity in either human or rat placentae, although activity was measured in rat liver. It is concluded that in the placenta glycine is only formed from serine through the activity of serine hydroxymethyl transferase enzyme, which uses folate as a cofactor, because there are no other known metabolic pathways for endogenous glycine production.

Dietary supplementation with L-methionine impairs the utilization of urea-nitrogen and increases 5-L-oxoprolinuria in normal women consuming a low protein diet

Urea kinetics were measured in normal women after 5 d consuming a low protein diet [LP, 67 mg N/(kg.d), 0.42 g protein/(kg.d)]. To determine whether the availability of methionine limits the utilization of nonessential nitrogen from low protein diets, the study was repeated on four further occasions with the addition of dietary supplements of L-methionine, 9 mg N/(kg.d) (LP-M); urea, 52 mg N/(kg.d) (LP-U); urea and methionine (LP-UM); or urea, 26 mg N/(kg.d), and glycine, 26 mg N/(kg.d), (LP-UG). Urea kinetics were derived after prime and intermittent oral doses of [15N15N]urea from the measurements of enrichment by isotope ratio mass spectrometry in urea isolated from urine. Nitrogen balance was significantly improved when the women consumed LP-U and LP-UG, but not LP-M or LP-UM. The urinary excretion of 5-L-oxoproline was measured as a marker of glycine availability and was significantly lower when women consumed LP-U and LP-UG compared with either LP or LP-M and LP-UM. There was a significant correlation between urinary 5-L-oxoproline and urinary sulfate excretion (r = 0.68, P = 0.00003). The availability of methionine was not limiting for nitrogen metabolism when women consumed these diets, whereas the response to supplementation with urea alone or urea with glycine showed that the availability of nonessential nitrogen was limiting. Glycine is consumed in the detoxification of excess methionine, and supplementation with methionine appeared to place a competitive demand on the availability of glycine for other metabolic processes.

Accurate separation of biliary lipid aggregates requires the correct intermixed micellar/intervesicular bile salt concentration

The intermixed micellar/intervesicular bile salt (BS) concentration (IMC), composed of BS monomers and simple micelles, is in dynamic equilibrium with mixed micelles and vesicles. Accurate separation of biliary lipid aggregates is believed to depend on accurately measuring the IMC. Using centrifugal ultrafiltration, we measured the IMC of cholesterol-supersaturated model biles that were physiologically composed. Gel chromatography was performed using eluants containing the following: 1) the IMC; 2) the same BS composition as the IMC but higher or lower BS concentrations; 3) the same BS concentration as the IMC, but with more hydrophilic or hydrophobic BS; and 4) 10 mmol/L cholate. Compared with an eluant containing the same BS composition as the IMC, an eluant containing the same relative BS composition but 75% of the IMC increased the proportion of cholesterol in vesicles and decreased the vesicular cholesterol/egg yolk phosphatidylcholine (EYPC) ratio. In contrast, an eluant containing 150% of the IMC entirely transformed vesicles to micelles. Eluants containing slightly more hydrophobic or more hydrophilic BS eliminated or increased vesicular cholesterol content, respectively. An eluant of 10 mmol/L cholate overestimated vesicular cholesterol and in concentrated biles reproducibly produced an incompletely separated intermediate peak, possibly because of re-equilibration between mixed micelles and vesicles. Further, in concentrated biles, fractions eluting at volumes corresponding to mixed micelles were visibly turbid, irrespective of the eluant used. The correct IMC allows accurate separation of biliary lipid aggregates, but differences in BS concentration or composition substantially alter the vesicular percentage of cholesterol as well as the cholesterol/EYPC ratio. Elution with 10 mmol/L cholate may introduce artifactual gel-filtration peaks and inadequate separation of particles with widely differing molecular weights, both of which have confused previous analyses of biliary lipid aggregates.