Maintenance of maternal diet-induced hypertension in the rat is dependent on glucocorticoids

Recent epidemiological evidence suggests that adult cardiovascular risk is determined by birth weight and factors that influence birth weight, such as maternal nutrition. Data from animal models suggest that an interaction between nutrition and glucocorticoid hormones "programs" increased risk of adult hypertension. Increased fetal exposure to maternal glucocorticoids that is proposed to occur from a reduction in the placental barrier to maternal glucocorticoid, 11beta-hydroxysteroid dehydrogenase, is suggested to program hypertension in the resultant offspring from both glucocorticoid-treated and maternally protein-restricted rats. The extent to which postnatal glucocorticoid stimulation may influence the progression of hypertension in the offspring from protein-restricted rat dams was assessed in 6-week-old male Wistar rats, prenatally exposed to either an 18% casein (control) or 9% casein (low protein) diet. Rats from each dietary group were sham operated, adrenalectomized or adrenalectomized, and treated with 20 mg corticosterone/kg body weight per day. Before surgery, systolic blood pressure was significantly higher in the low protein-exposed rats compared with controls (165+/-3.8 versus 142+/-3.3 mm Hg, P<.0001). Adrenalectomy of the low protein-exposed animals significantly reduced the blood pressure to control levels, while corticosterone replacement restored the hypertensive state. No effect of adrenalectomy on blood pressure was observed in 18% casein controls. In both dietary groups adrenalectomy decreased brain, but not hepatic, glucocorticoid-sensitive enzyme activities and corticosterone treatment elevated activities of all enzymes. The data suggest that maternal diet-induced hypertension is dependent on an intact adrenal gland postnatally and that glucocorticoids are key trophic agents in maintaining the high blood pressure.

Transbilayer movement of fully ionized taurine-conjugated bile salts depends upon bile salt concentration, hydrophobicity, and membrane cholesterol content

Taurine-conjugated bile salts mediate rapid transmembrane flux of divalent cations, irrespective of whether bile salts and divalent cations are initially on the same or opposite side of the membrane. We therefore hypothesized that ionized bile salts can equilibrate between membrane hemileaflets. We quantitated bile salt binding to large unilamellar egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) vesicles under conditions in which one or both hemileaflets were initially exposed to bile salts. At unbound taurodeoxycholate (TDC) concentrations >0.2 mM, the dependence of binding on TDC concentration after 30 min was indistinguishable for vesicles prepared by either method and did not change from 30 minutes to 24 h. At unbound TDC concentrations <0.1 mM, the ratio of bound/free TDC to EYPC vesicles doubled over a single exponential time course. Equilibration times were greater for the more hydrophilic bile salts taurocholate and tauroursodeoxycholate, for EYPC/Ch vesicles, and at lower temperatures. For glycine-conjugated bile salts, time-dependent changes in binding did not occur, consistent with more rapid equilibration of the small fraction of the protonated form. We conclude that fully ionized conjugated bile salts translocate between lipid bilayer hemileaflets, in contrast to previous observations that equilibration of fully ionized unconjugated bile salts occurs at a negligible rate in small unilamellar vesicles. The rate of "flip-flop" increases with increases in intramembrane bile salt concentration and hydrophobicity but decreases with cholesterol content and lower temperature. We speculate that physiologically, even in the absence of a specific membrane transporter, bile salts can gain access to intracellular compartments and mediate increases in divalent cation flux that may underlie cytotoxicity.

Enrichment in urinary ammonia and urea with hourly oral doses of [15N]glycine: evidence for a step function and a circadian rhythm in protein turnover

1. The present study sought to determine the possible existence of a pool of proteins which turn over with life-time kinetics. The pattern of enrichment of ammonia and urea in hourly samples of urine was determined in normal adults to whom oral doses of [15N]glycine were given hourly for 36 h. The subjects received hourly meals throughout, and in six the study commenced at 06.00 hours, in five at 12.00 hours and in two at 18.00 h. 2. A plateau level of enrichment was achieved in urinary ammonia within 4-6 h. Regardless of the time at which the study started this plateau was held until about midnight, at which time there was an increase in enrichment, with a second higher plateau 5-6 h later. The second plateau was held to the end of the study. For urinary urea the rate of rise in enrichment was slower and smoother, because of the slow turnover of the urea pool. 3. Protein synthesis, derived from the first ammonia plateau, 179 mg h-1 kg-1, was significantly higher than that derived from the second plateau, 118 mg h-1 kg-1. Using the plateau in urea towards the end of the 36 h, the estimate of protein synthesis was 153 mg h-1 kg-1. 4. The results are considered to provide evidence of a pool of proteins for which degradation takes place in harmony with a circadian rhythm.

Urinary 5-L-oxoproline (pyroglutamic acid) excretion is greater in infants in Jamaica than in infants in England

OBJECTIVE

To determine the pattern of excretion in urine of 5-L-oxoproline, as a measure of glycine status, during the first six weeks of life in Jamaican infants.

DESIGN

Spot samples of urine were collected from term and preterm infants at birth and longitudinally to four weeks of age, or at six weeks of age. 5-L-oxoproline was isolated by column chromatography and hydrolysed to L-glutamic acid, which was measured enzymatically and the results expressed relative to creatinine excretion.

SETTING

Maternity wards and postnatal clinic of the University Hospital of the West Indies.

SUBJECTS

African-Caribbean infants, 19 term and 21 preterm, from birth to four weeks of age, and 79 term infants at six weeks of age.

RESULTS

There were no differences between term and preterm infants. Excretion of 5-L-oxoproline increased progressively from birth, 141 mumol/mmol creatinine, to 270 mumol/mmol creatinine at four weeks of age. At six weeks of age, excretion was significantly greater than at birth or four weeks of age, 525 mumol/mmol creatinine. Compared with infants born in England, the excretion of 5-L-oxoproline was not different at birth, but was significantly greater in Jamaican infants at six weeks of age.

CONCLUSIONS

Glycine status, indicated by increased excretion of 5-L-oxoproline, is marginal in Jamaican infants at six weeks of age, and this possibly reflects a limitation in the endogenous biosynthesis of glycine due to a dietary limitation of folate or vitamin B-12.

Urinary excretion of 5-L-oxoproline (pyroglutamic acid) during early life in term and preterm infants

Urinary 5-L-oxoproline was measured in term and preterm infants from shortly after birth until 6 weeks of postnatal age to determine their ability to synthesise glycine. In term infants the excretion was five to 10 times that seen in normal adults, increasing from 105 mumol/mmol creatinine in the first 72 hours after birth to 170 mumol/mmol creatinine at 6 weeks of age. There was a significant inverse linear correlation between the excretion of 5-L-oxoproline and length of gestation or birthweight. By 6 weeks of age there was no longer a significant difference in 5-L-oxoproline between term and preterm infants. There was no difference in the excretion of 5-L-oxoproline between boys and girls, or between infants fed on human milk or an artificial formula. If, in part, variability in the excretion of 5-L-oxoproline is determined by the extent to which the endogenous formation of glycine is adequate, then glycine formation may be marginal during early life, more so in preterm than in term infants, providing additional evidence that glycine is a conditionally essential amino acid in the neonate.

Stable-isotope method for determining the gastrointestinal handling of [1-13C]palmitic acid

The 13C enrichment in individual fatty acids extracted from human feces following the oral administration of [1-13C]palmitic acid has been determined using a novel approach based upon gas chromatography-isotope ratio mass spectrometry. The method was established and tested for precision and repeatability. Analytical precision was determined from 10 repeated injections of a sample containing 16:0 and 18:0 with levels of delta 13C abundance measured at -34.01 +/- 0.60 and -23.62 +/- 0.95 delta per mil (parts per thousand) (/1000), respectively (mean +/- SD). For the repeatability study, measurement of enrichment of the same mixture of unlabeled fatty acid methyl ester (FAME) standards (13:0, 14:0, 16:0, and 18:0) was found to have standard deviations (0.45, 0.56, 1.46 and 1.54/1000, respectively). When labeled [1-13C]palmitic acid was serially diluted with naturally enriched palmitic acid, a linear relationship was obtained to a dilution of 10% enriched compound (530/1000). FAME were prepared from two fecal samples from a normal healthy adult; the first, a baseline specimen, containing no added label and the second, followed a single oral dose of [1-13C]palmitic acid and was enriched. Enrichment in 13C was confined to the solvent-soluble fraction following lipid extraction, and was only identified with prior acidification. The enrichments were measured in triplicate, baseline sample -32.66 +/- 0.5/1000, enriched sample +268.61 +/- 8.0/1000. Enrichment was restricted to the labeled species consumed, 16:0. The methodology described here allows for the separation of compounds prior to the determination of enrichment and can be utilized to contribute to a more complete description of the gastrointestinal handling of labeled substrates than previously obtained.

Urea kinetics in healthy women during normal pregnancy

Urea kinetics were measured in normal women aged 22-34 years at weeks 16, 24 and 32 on either their habitual protein intake (HABIT) or a controlled intake of 60 g protein/d (CONTROL), using primed-intermittent oral doses of [15N15N]urea and measurement of plateau enrichment in urinary urea over 18 h (ID) or a single oral dose of [15N15N]urea and measurement of enrichment of urea in urine over the following 48 h (SD). The intake of protein during HABIT-ID (80 g/d) was greater than that on HABIT-SD (71 g/d); urea production as a percentage of intake was significantly greater at week 16 for HABIT-ID than HABIT-SD, whereas urea hydrolysis at week 16 was greater for HABIT-SD than HABIT-ID and urea excretion at week 32 was greater for HABIT-ID than HABIT-SD. The combined results for HABIT-ID and HABIT-SD showed a significant reduction in urea production at week 32 compared with week 24. Urea excretion decreased significantly from week 16 to week 24 with no further decrease to week 32 and urea hydrolysis was significantly greater at week 24 than either week 16 or week 32. Compared with HABIT, on CONTROL there was a decrease in urea production at week 16, and urea excretion was significantly reduced at week 16. For all time periods urea production was closely related to the sum of intake plus hydrolysis. Hydrolysis was greatest at week 24 and closely related to urea production. There was a significant inverse linear relationship overall for hydrolysis as a proportion of production and excretion as a proportion of intake. The results show that on HABIT N is more effectively conserved in mid-pregnancy through an increase in urea hydrolysis and salvage, and during late pregnancy through a reduction in urea formation. Lowering protein intake at any stage of pregnancy increased the hydrolysis and salvage of urea. The staging of these changes was later than that in pregnancy in Jamaica.

Comparison of urinary 5-L-oxoproline (L-pyroglutamate) during normal pregnancy in women in England and Jamaica

Urinary 5-L-oxoproline was measured during normal pregnancies in Southampton, England and Kingston, Jamaica. The CV of 5-L-oxoproline excretion in urine, determined over 7 d in a non-pregnant woman and three pregnant women, was 10-36%. Compared with non-pregnant women, urinary 5-L-oxoproline increased three to four times from early pregnancy in women in Southampton, a highly significant difference, and remained elevated at similar levels during mid and late pregnancy. For women in Kingston, the excretion of 5-L-oxoproline was similar to that of Southampton women in the non-pregnant group and during early pregnancy. However, there was a progressive increase in the excretion of 5-L-oxoproline as pregnancy advanced and by late pregnancy excretion was from three to ten times greater than the average for the non-pregnant women. There was a significant difference between the women in Southampton and the women in Kingston during mid and late pregnancy, with women in Kingston excreting twice as much 5-L-oxoproline during late pregnancy. If the excretion of 5-L-oxoproline is a measure of glycine insufficiency, the results would indicate that in some pregnancies the ability of the mother to provide glycine for herself and the developing fetus is marginal or inadequate and the constraint appears more marked in Jamaica than in England.

Fetal exposure to low protein maternal diet alters the susceptibility of young adult rats to sulfur dioxide-induced lung injury

The maternal diet is an important determinant of glutathione-related metabolism in rats. Glutathione (GSH) may play a major role in the detoxification of sulfur dioxide (SO2) within the lungs. The effects of fetal exposure to a low protein maternal diet upon later susceptibility to pulmonary injury induced by chronic SO2 exposure were evaluated in young adult rats. Pregnant rats were fed purified diets containing 180 g casein/kg (control diet) or 120, 90 or 60 g casein/kg (experimental diets). After parturition, all dams were fed a standard non-purified diet (189 g protein/kg diet). The pups thus differed only in terms of protein nutrition during gestation. At seven wk of age the male pups were housed in either room air or 286 microg SO2/m3 for 5 h/d during a 28-d period. At the end of the final SO2 treatment period, the rats exposed to 90 or 60 g casein/kg diets in utero exhibited significantly greater pulmonary injury, as assessed by bronchoalveolar lavage, than did those exposed to control diet in utero. Significant maternal diet-induced differences in activities of enzymes of the gamma-glutamyl cycle were noted in the lungs and livers of rats which had not undergone SO2 treatment. Furthermore, the response of these enzyme activities to SO2 treatment was determined by prior exposure to the maternal diet. SO2-treated rats exposed to control diet (180 g casein/kg) and low protein diet (60 g casein/kg), but not those exposed to 120 or 90 g casein/kg diets, tended to augment the activities, relative to rats not treated with SO2, of enzymes which maintain tissue GSH status either through synthesis or recycling. Differences in susceptibility to SO2-induced tissue injury may be related to programming of GSH metabolism by the maternal diet. Alternatively, impaired immune and acute phase responses to an inflammatory insult may account for a failure to resolve initial SO2-induced injury in rats exposed to low protein maternal diets.

Urea kinetics varies in Jamaican women and men in relation to adiposity, lean body mass and protein intake

OBJECTIVE

We have measured urea kinetics in normal adult men and women of different body composition to determine whether adiposity is associated with differences in the rate of urea production or endogenous urea hydrolysis.

DESIGN

Urea kinetics were determined from the excretion of [15N15N]urea in urine over a period of 48 h following a single oral dose of [15N15N]urea, in nine lean and nine obese women and in seven light and seven heavy males while they were consuming their habitual diets. Urinary 5-L-oxoproline was measured as an index of glycine metabolic status.

SETTING

The studies were carried out in the research ward of the Tropical Metabolism Research Unit, University of the West Indies.

RESULTS

Successful studies were completed in eight obese and five lean women and in six heavy and five light men. When compared with lean women, in obese women the rate of urea production and hydrolysis was significantly greater and this difference could not be accounted for by the greater fat-free mass alone, and was in part associated directly with the increase in fat mass. The rate of urea production and hydrolysis was greater in heavy men than in light men, a difference which was attributed to an increase in dietary protein. In obese women and heavy men there was a significantly higher rate of excretion of 5-L-oxoproline in urine when compared with lean women and lean men respectively.

CONCLUSION

This paper highlights the difficulty in identifying an appropriate reference with which to express results in people of different body composition. In obese women urea production and the hydrolysis of urea are increased, in part related to the increased fat-free mass, but also related to the increased fat mass itself. In obese women and men on high protein diets the greater rate of hydrolysis urea may be a reflection of an increased demand for the synthesis of non-essential amino acids, especially glycine.

Weanling rats exposed to maternal low-protein diets during discrete periods of gestation exhibit differing severity of hypertension

1. In the rat, hypertension is induced by fetal exposure to maternal low-protein diets. The effect on blood pressure of undernutrition before conception and during discrete periods in early, mid or late pregnancy was assessed using an 18% casein (control) diet and a 9% casein to apply mild protein restriction. 2. The offspring of rats fed 9% casein developed raised blood pressure by weaning age. Feeding a low-protein diet before conception was not a prerequisite for programming of hypertension. 3. Hypertension was observed in rats exposed to low protein during the following gestational periods: days 0-7, days 8-14 and days 15-22. Blood pressure increases elicited by these discrete periods of undernutrition were lower than those induced by feeding a low-protein diet throughout pregnancy. The effect in early gestation was significant only in male animals. Post-natal growth of male rats exposed to low-protein diets was accelerated, but kidneys were small in relation to body weight. 4. Biochemical indices of glucocorticoid action in liver, hippocampus, hypothalamus and lung were elevated in rats exposed to low-protein diets in utero. The apparent hypersensitivity to glucocorticoids was primarily associated with undernutrition in mid to late gestation. 5. Plasma renin activity was elevated in rats exposed to 9% casein over days 15-55 of gestation. Animals undernourished over days 0-7 and 8-14 produced pups with lower plasma angiotensin II concentrations at weaning. 6. Fetal exposure to maternal low-protein diets for any period in gestation may programme hypertension in the rat. Alterations to renal structure, renal hormone action or the hypothalamic-pituitary-adrenal axis may all play a role in the programming phenomenon, either independently or in concert.

Urinary excretion of 5-L-oxoproline (pyroglutamic acid) is increased during recovery from severe childhood malnutrition and responds to supplemental glycine

We hypothesized that a limitation in the endogenous formation of glycine might constrain catch-up growth during recovery from severe childhood malnutrition. The urinary excretion of 5-L-oxoproline is increased when the glycine available for glutathione synthesis is limited. Urinary excretion of 5-L-oxoproline was measured throughout recovery in 12 children (aged 16 +/- 6 mo) with severe malnutrition. Urinary 5-L-oxoproline was similar at admission and after recovery, but was increased significantly during rapid catch-up growth. There was a significant relationship between the rate of weight gain and 5-L-oxoproline excretion in urine. In nine children (aged 15 +/- 5 mo), the effect of oral supplementation with glycine, [1.7 mmol/(kg x d) for 48 h] during rapid catch-up growth on 5-L-oxoprolinuria and blood glutathione concentration was determined. In seven of the nine children weight gain was less than 17 g/(kg x d) and following oral glycine supplements 5-L-oxoproline excretion was reduced up to 64% and blood glutathione concentration increased up to 100%. In the two children who were gaining weight at a rate > 17 g/(kg x d), glycine supplementation was associated with a further increase in 5-L-oxoproline excretion and a decrease in blood glutathione. If 5-L-oxoproline is an index of the relative availability of glycine, then the data indicate that glycine may be limiting during rapid catch-up growth. This would have important implications for repletion of muscle and gain in height.

Urinary excretion of 5-L-oxoproline (pyroglutamic acid) is increased in normal adults consuming vegetarian or low protein diets

A method for measuring 5-L-oxoproline in urine, which involves isolation by short-column chromatography, acid hydrolysis to glutamic acid and enzymic assay of glutamic acid, was used to measure the rate of excretion in normal adults, aged 20 to 45 y. There was no difference in the daily excretion between omnivorous males (217 micromol/d) and females (195 micromol/d). In vegetarian males, urinary 5-L-oxoproline (404 micromol/d) was significantly greater than in vegetarian females (267 micromol/d, P = 0.013). Compared with omnivorous males or females, excretion of 5-L-oxoproline was significantly greater in vegetarian males (P < 0.0001) and females (P= 0.005). When normal adults consumed a diet in which the protein content was controlled at either 4.0 or 6.2 g N/d for 5 d, there was a significant increase in urinary 5-L-oxoproline on d 5, compared with either d 1 or 4. There was a significant inverse linear relationship between the increased urinary 5-L-oxoproline on the fifth dietary day and the nitrogen content of the diet. On the basis of this relationship, when the urinary excretion of 5-L-oxoproline (320 micromol/d) for vegetarians was predicted from an estimate of their dietary intake of nitrogen, the estimate was, on average, close to the measured value (345 micromol/d). As a matter of course, vegetarians excrete more 5-L-oxoproline in urine than do omnivores, and we speculated that this difference might be accounted for by differences in dietary nitrogen and the endogenous capacity for de novo synthesis of glycine.

The effect of splenectomy for hypersplenism on whole body protein turnover, resting metabolic rate and growth in sickle cell disease

OBJECTIVE

To determine whether, in the same individual, an observed fall in whole body protein turnover following splenectomy in children with hypersplenism and homozygous sickle cell (SS) disease is associated with a measurable fall in resting metabolic rate (RMR) and an increase in rate of growth.

SUBJECTS

Six children (5 SS disease, 1 S beta degree thalassaemia), aged 68 to 126 months, were studied before and after splenectomy for hypersplenism.

DESIGN

Protein turnover was measured by the end product method using prime/intermittent oral doses of 15N-glycine and RMR by indirect calorimetry before preoperative transfusion and repeated at least eight weeks after splenectomy. Height and weight velocities were measured over six month periods before and after splenectomy.

SETTING

University Hospital of the West Indies in Jamaica and the Medical Research Laboratories (Jamaica).

RESULTS

After splenectomy protein turnover fell significantly by 30% and RMR by 34 kJ/kg/d. Mean weight velocity which was below normal before surgery, z = -2.3, improved significantly after surgery, z = 0.7, (P = 0.03). Height velocity increased in two children but the mean height velocity did not change following splenectomy. The reduction in protein turnover was estimated to account for 62% of the fall in RMR.

CONCLUSION

This study confirms that there is a significant reduction in energy expenditure following splenectomy for hypersplenism in SS disease. A reduction in protein turnover was a major contributor to the saving in energy, although it is not clear whether it accounted for all. In the present group of children the energy saved was associated with an improvement in the wasting present before splenectomy.

Influence of dietary fats upon systolic blood pressure in the rat

Studies were performed to determine whether feeding diets with differing fatty acid content and composition had an influence on systolic blood pressure in the rat. Weanling male rats were fed standard laboratory chow (2.9% fat in total), or synthetic diets (10% fat in total) containing fish oil, butter, coconut oil or corn oil, for 5 weeks. Coconut oil and butter diets were rich in saturated fatty acids, whilst fish oil and corn oil were rich in the n-3 and n-6 unsaturated fatty acids respectively. Systolic blood pressure was measured using an indirect tail-cuff method at the end of the feeding period, and compared to a group of weanling rats. Feeding the different diets did not alter the growth of the rats, so all animals were of similar weights at the time of blood pressure determination. Control (chow fed) animals, at nine weeks of age, had higher systolic blood pressures than the weanling, baseline control group. Fish oil fed rats had similar pressures to the chow fed rats. Corn oil fed rats had significantly lower systolic pressures than the controls. The rats led the diets rich in saturated fatty acids (butter and coconut oil) had significantly higher blood pressures than all other groups. Systolic blood pressure was found to be significantly related to the dietary intakes of saturated and unsaturated fatty acids. The dietary intake of linoleic acid was significantly higher in corn oil fed rats than in other groups. Systolic blood pressure was inversely related to linoleic acid intake. Feeding a diet rich in saturated fatty acids significantly increases blood pressure in the rat. A high intake of n-6 fatty acids, and in particular linoleic acid, appears to have a hypotensive effect. Prenatal exposure of the rats to a maternal low protein diet, abolished the hypertensive effects of the coconut oil diet and the hypotensive effect of the corn oil diet upon young adult females. The intrauterine environment may, therefore, be an important determinant of the effects of these fatty acids on blood pressure in later life.

Urea kinetics in healthy young women: minimal effect of stage of menstrual cycle, contraceptive pill and protein intake

Urea kinetics were measured using prime/intermittent oral doses of [15N15N]urea, on five separate protocols in thirteen normal young women. Each woman underwent either two or three study protocols. Measurements were made at day 12 and day 22 of the menstrual cycle, whilst consuming their habitual protein intake in seven women not taking the contraceptive pill and in six women taking the contraceptive pill. In three women taking the pill, and three not taking the pill, urea kinetics were measured whilst taking a diet in which the intake was restricted to 55 g protein/d. There was no difference in the rate of urea production, urea excretion or urea hydrolysis between the women taking the pill and those not taking the pill at day 22. In the women not taking the pill there was no difference in any measure between day 12 and day 22. In the women taking the pill there was a significant difference in the disposal of urea N to excretion or hydrolysis on day 12 compared with day 22, with a relative decrease in excretion and enhancement of hydrolysis at day 12 compared with day 22. On the restricted diet, an intake of 55 g protein/d represented 77% of the habitual intake and urea production, excretion and hydrolysis were reduced to about 84% of the rate found on the habitual intake. In paired studies the reduction in urea production was statistically significant, and there was a statistically significant linear relationship between urea production and either intake or the sum of intake plus hydrolysis. The within-individual variability for urea production was about 10%, for excretion 15% and for hydrolysis 44%. The between-individual variability for intake was about 17% on the habitual intake. The variability for production, excretion and hydrolysis (14, 13, 36%) was less in the women not taking the contraceptive pill than in those taking the pill 23, 32, 42% respectively). The variability was reduced on the controlled low intake of 55 g protein compared with the habitual intake. These results confirm the wide variability in aspects of urea kinetics between individuals. In women this variability is not, to any large extent, accounted for by changes associated with the menstrual cycle.

Protein turnover rates of two human subjects during an unassisted crossing of Antarctica

During the Austral summer of 1992-3, two men, MS and RF, walked 2300 km across Antarctica in 96 d, unassisted by other men, animals or machines. During the journey they ate freeze-dried rations, towed on sledges, that contained an average of 21.3 MJ/d of which 56.7% was fat, 35.5% carbohydrate and 7.8% protein (98.8 g). Despite this high energy intake both men lost more than 20 kg in body weight due to their extremely high energy expenditures. Studies of protein turnover using [15N]glycine by the single-dose end-product method were made before, during and after the journey, and these demonstrated considerable differences in the metabolic responses of the two men to the combined stresses of exercise, cold and undernutrition. However, both men maintained high and relatively stable levels of protein synthesis during the expedition despite the great exertion and the onset of considerable debilitation. This stability indicates the vital physiological function of protein synthesis.

Effects of submicellar bile salt concentrations on biological membrane permeability to low molecular weight non-ionic solutes

Bile salts have been hypothesized to mediate cytotoxicity by increasing membrane permeability to aqueous solutes. We examined whether submicellar bile salt concentrations affect model and native membrane permeability to small uncharged molecules such as water, urea, and ammonia. Osmotic water permeability (Pf) and urea permeability were measured in large unilamellar vesicles composed with egg yolk phosphatidylcholine (EYPC) +/- cholesterol (Ch) or rat liver microsomal membranes by monitoring self-quenching of entrapped carboxyfluorescein (CF). Ammonia permeability was determined utilizing the pH dependence of CF fluorescence. Submicellar bile salt concentrations did not significantly alter Pf of EYPC +/- Ch or rat liver microsomal membranes. At taurodeoxycholate (TDC) or tauroursodeoxycholate concentrations approaching those that solubilized membrane lipids, CF leakage occurred from vesicles, but Pf remained unchanged. Higher bile salt concentrations (0.5-2 mM TDC) did not alter Pf of equimolar EYPC/Ch membranes. The activation energy for transmembrane water flux was unchanged (12.1 +/- 1.2 kcal/mol for EYPC) despite the presence of bile salts in one or both membrane hemileaflets, suggesting strongly that bile salts do not form transmembrane pores that facilitate water flux. Furthermore, submicellar bile salt concentrations did not increase membrane permeability to urea or ammonia. We conclude that at submicellar concentrations, bile salts do not form nonselective convective channels that facilitate transmembrane transport of small uncharged molecules. These results suggest that bile salt-mediated transport of specific substrates, rather than nonselective enhancement of membrane permeability, underlies bile salt cytotoxicity for enterocytes and hepatocytes.

Serum retinol and biochemical measures of iron status in adolescent schoolgirls in urban Bangladesh

OBJECTIVE

To examine the relationship between serum retinol and biochemical indices of iron nutritional status amongst adolescent girls in urban Bangladesh.

DESIGN

A cross-sectional study.

SETTING

Girls' high schools in Dhaka City, Bangladesh.

SUBJECTS

Adolescent girls, n = 225, aged between 12 and 15 years, from four urban schools participated in the study. Information on socio-economic conditions were obtained using a questionnaire. The height and weight of each girl were measured and a sample of blood was taken for biochemical analyses.

RESULTS

Twenty-two per cent of the participants were found to be anaemic (Hb < 120 g/l), 15% had subnormal serum iron ( < 7.16 mumol/l) and about 25% were iron deficient judged by serum transferrin saturation (TS < 15%). Eleven per cent of the participants had low levels of serum retinol ( < 1.05 mumol/l). Anaemic girls (n = 51) were found to have significantly lower serum retinol as well as lower packed cell volume (PCV), mean corpuscular haemoglobin concentration (MCHC), serum iron, TS, and higher serum total iron binding capacity (TIBC) compared with those with normal haemoglobin levels. When the girls were classified by serum retinol, the third with the highest serum retinol had significantly higher levels of haemoglobin, PCV, MCHC and serum iron levels. When age, family size, family income, expenditure on food, education of the parents, supplementation with vitamin A or iron and menstruation at the time of study were accounted for by multiple regression analysis, a strong relationship was found for serum retinol concentration with PCV, MCHC, haemoglobin, serum iron and TS. For 1 mumol/l change in serum retinol concentration there was a 10.1 g/l change in haemoglobin whilst taking other factors into account.

CONCLUSION

The data indicate that there is an interaction between serum retinol and biochemical indices of iron nutriture in adolescent girls who do not display any clinical signs of overt deficiency.

Urea production in normal breast-fed infants measured with primed/intermittent oral doses of [15N, 15N]urea

Urea kinetics were measured on 11 occasions in six normal, breast-fed infants aged 29-88 days. Prime and intermittent oral doses of [15N, 15N]urea with measurement of enrichment of urea in urine were used. The rate at which urea appeared in the urea pool was 265 mgN/kg per hour, 85% of which derived from endogenous production and 15% from the diet. Urinary excretion of urea was 87 mgN/kg per hour. Therefore, 60% of the urea entering the pool each day was hydrolysed by the metabolic activity of the colonic microflora and the nitrogen was made available for further metabolic interaction. The rate of urea appearance and the extent to which urea nitrogen was salvaged were greater in infants under 6 weeks than in those over 6 weeks, indicating that urea kinetics is a more active process at an early age, and slows with time. With respect to factors influencing urea kinetics, the apparently conflicting results which have appeared in the literature may be explained. The results may help explain the growth of breast-fed infants on low protein intakes.

Maternal protein restriction influences the programming of the rat hypothalamic-pituitary-adrenal axis

The role of glucocorticoids in the intrauterine programming of hypertension was assessed in the progeny of rats fed either 18 g casein/100 g diet (control diet) or 9 g casein/100 g diet (low protein diet), before conception and throughout pregnancy. Rats exposed to the low protein diet had significantly (P < 0.05) higher systolic blood pressures than control animals, when weaned. These rats had elevated brain and liver activities of specific glucocorticoid-inducible marker enzymes, relative to controls. Glycerol 3-phosphate dehydrogenase activity was also higher (377%) in whole brains of newborn rats exposed to low protein diet in utero, but no similar effect of corticosteroids was noted in brains of d 20 fetuses. Weanling rats of the low protein group exhibited a blunted diurnal pattern of adrenocorticotrophin (ACTH) concentrations in plasma. Plasma corticosterone concentrations were unaltered by prenatal dietary experience and exhibited a normal pattern of diurnal variation. Brain regional 11beta-hydroxysteroid dehydrogenase activities were unaltered by prenatal dietary experience, as was binding of 3H-corticosterone to type I glucocorticoid receptors in hippocampus, hypothalamus and liver. Type II glucocorticoid receptor binding capacity and receptor numbers in male rats were apparently elevated in hippocampus of low protein-exposed rats and were significantly lower in liver (P < 0.05), relative to control rats. Programming of the hypothalamic-pituitary-adrenal axis is inferred, and the observation that binding of steroid to type II receptor sites in vascular tissue is increased in low protein exposed rats may provide a direct mechanism for modulation of blood pressure by glucocorticoids in this model.

Sulphur dioxide: a potent glutathione depleting agent

Sulphur dioxide (SO2) is an air pollutant implicated in the initiation of asthmatic symptoms. Glutathione (GSH) has been proposed to play a role in detoxification of SO2 through the sulfitolysis of glutathione disulphide (GSSG) to S-sulphoglutathione (GSSO3-). Rats were exposed to concentrations of SO2 between 5 and 100 ppm for 5 hr a day between 7 and 28 days. Lung injury as assessed by bronchoalveolar lavage and tissue GSH status were evaluated. SO2 5 ppm failed to elicit any lung injury or inflammatory response but did deplete GSH pools in lung, liver, heart and kidney. Activities of gamma-glutamylcysteine synthetase (GCS), glutathione peroxidase (GPx), glutathione S-transferase (GST) and glutathione reductase (GRed) in lung were lowered relative to those in control animals. In liver, GRed activity was decreased. SO2 50 ppm exposure also failed to elicit injury or inflammation but did lower inflammatory cell numbers in the circulation. Rats exposed to 50 ppm SO2 maintained tissue GSH status, but activities of GCS, GPx, GRed and gamma-glutamyltranspeptidase in lung and hepatic GRed and GPx were significantly lower than in control rats. Unaltered GST activity in lung and liver was suggestive of an impairment of the sulfitolysis reaction in these animals, perhaps through lower substrate flux through the GPx reaction, as GSSO3- is a known inhibitor of GST in the rat. Rats exposed to 100 ppm SO2 exhibited evidence of inflammation (120-fold increase in neutrophil numbers recovered in lavage fluid) and like the 5 ppm exposed rats had lower tissue GSH concentrations and GSH-related enzyme activities in lung. We conclude that sulfitolysis of GSSG does occur in vivo during SO2 exposure and that SO2, even in the absence of pulmonary injury, is a potent glutathione depleting agent.

The determinants of plasma beta-carotene: interaction between smoking and other lifestyle factors

OBJECTIVE

To assess the effect of cigarette smoking on the relationship between dietary intake and circulating levels of beta-carotene.

DESIGN

A secondary analysis of data collected for the Diet and Nutritional Survey of British Adults by The Department of Health and The Ministry of Agriculture, Fisheries and Food; the study was a cross-sectional survey of a representative sample of the British population.

SETTING

The study was conducted on a free living adult (16-64 years of age) population resident in Great Britain.

SUBJECTS

1483 subjects completed a seven day weighed inventory and provided a blood sample.

RESULTS

Smokers had statistically significantly lower dietary intakes and circulating levels of beta-carotene than non-smokers. At the same level of dietary intake, smokers were more likely to have lower circulating levels than non-smokers. For every 1000 micrograms change in dietary intake, there was a 0.01 mumol/l change in plasma beta-carotene in smokers and a 0.04 mumol/l change in non-smokers. The effect of smoking on circulating levels of beta-carotene persisted after adjusting for other factors.

CONCLUSIONS

The results suggest that smoking places extra demands on the host; the higher risk of heart disease for smokers may be due to a combination of an increased inflammatory response, reduced host defences, and increased levels of circulating LDL. Failure to take account of the interaction between risk factors may distort the estimates of the relative importance of each factor when considered in isolation.

Protein intake in pregnancy, placental glucocorticoid metabolism and the programming of hypertension in the rat

Hypertension is strongly predicted by a low birthweight:placental weight ratio. Two independent models have been described to explain this association; less than optimal maternal protein nutrition leading to fetal undernutrition, or glucocorticoid excess. Pregnant rats were fed diets containing 18 per cent casein (control) or 9 per cent casein, balanced for energy. On day 20 of gestation the pregnancies were terminated and placentae collected for determination of 11 beta-hydroxysteroid dehydrogenase (11 beta HSD) activity. Placental 11 beta HSD normally protects the fetus from the effects of maternal glucocorticoids. Activity was specifically attenuated by mild protein restriction (33 per cent in activity), whilst activities of glucocorticoid-insensitive control enzymes were unchanged and glucocorticoid-inducible glutamine synthetase activity was increased (27 per cent), relative to activity in placentae from control animals. The nutritional manipulation during pregnancy significantly increased systolic blood pressure (17 mmHg) in the resulting offspring in early adulthood. A possible common pathway whereby maternal environmental factors may influence fetal and placental growth and programme disease is inferred.