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Biomedical subjects

A A Jackson

Publications and source records attributed to A A Jackson.

At least 73 records · Page 4Linked to original sources
PubMed1996

Salvage of exogenous urea nitrogen enhances nitrogen balance in normal men consuming marginally inadequate protein diets.

1. Urea kinetics were measured in six healthy men using prime/intermittent oral doses of [15N15N] urea, after five days consuming one of four diets which varied in their nitrogen content: a reference diet (REF, 70 g of protein and 11.2 g of N); a low-protein diet (LP, 30 g of protein and 4.8 g of N); a low-protein diet with 6.9 g of urea added (LP-U1, 30 g of protein and 8 g of N); a low-protein diet with 13.7 g of urea added (LP-U2, 30 g of protein and 11.2 g of N). 2. Apparent nitrogen balance on the REF diet was significantly better than on the LP or the LP-U1 diets. The addition of the higher level of urea in the LP-U2 diet enhanced apparent nitrogen balance compared with the LP or LP-U1 diets, and was not different to apparent nitrogen balance on the REF diet. 3. On the LP, LP-U1 and LP-U2 diets, the rate of endogenous urea production was not different, and was about 60% of that on the REF diet, a statistically significant difference. The addition of a dietary supplement of urea increased the rate of urea appearance in the urea pool in direct relation to the dose of urea taken. There was no difference in the rate of appearance between the REF and LP-U2 diets, for both of which the rate of appearance was significantly greater than on the LP diet. 4. The excretion of urea in urine on the LP diet was 62% of that on the REF diet, a significant difference. There was no significant difference in the rate of urea excretion between the REF, LP-U1 and LP-U2 diets. 5. The rate of urea hydrolysis by the colonic microflora on the REF diet was more than twice that on the LP or LP-U1 diets. Supplementation with urea at the higher level, LP-U2, significantly increased hydrolysis to the same level as on the REF diet. Most of the nitrogen derived from urea hydrolysis was retained in the metabolic pool (> 80%), with no difference in the rate of retention between the REF and LP-U2 diets, both greater than the LP or LP-U1 diets. 6. The dietary supplements of urea increased the size of the body urea pool significantly. Renal clearance of urea was highest on the REF diet and decreased 13-29% on the low-protein diets. Bowel clearance was highest on the REF diet and decreased 46-55% on the low-protein diets. Neither urinary excretion of urea nor urea hydrolysis in the bowel were related simply to the concentration of urea in blood. Urea hydrolysis related most closely to the rate of appearance of urea in the urea pool. 7. The salvage of urea nitrogen was increased on the highest level of supplementation, but the overall sensitivity of the system was low, suggesting that other factors might be limiting for effective urea hydrolysis and the salvage of urea nitrogen.

Adult↗
PubMed1996

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.

Animals↗
PubMed1996

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.

Adult↗
PubMed1996

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.

Adult↗
PubMed1996

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.

Adult↗
PubMed1996

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.

Aging↗
PubMed1996

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.

Adrenal Glands↗
PubMed1996

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.

Administration, Oral↗
PubMed1996

Rats with hypertension induced by in utero exposure to maternal low-protein diets fail to increase blood pressure in response to a high salt intake.

Hypertension in the rat has been demonstrated to be determined in utero by exposure to maternal low-protein diets. Assessment was made of the response of rats with maternal diet-induced hypertension to a chronic high intake of sodium chloride. Normotensive and hypertensive animals were provided with either drinking water (control) or 1.5% sodium chloride over a 7-day period. Normotensive rats significantly increased blood pressure in response to the increased salt intake. 5-7 days after the start of the study systolic blood pressure was 30-41 mm Hg higher than in controls. 7 days of salt drinking did not alter blood pressure in maternal low-protein diet-exposed, hypertensive rats. In both normotensive and hypertensive groups provision of 1.5% sodium chloride significantly increased fluid intake. In hypertensive rats in the increased fluid intake appeared to be an immediate response, whilst normotensive rats increased intake only after the first day. Urinary volume was increased in both groups of animals receiving salt, within 1 day, and Na+ excretion similarly increased by between 3.5- and 4.5-fold in both groups. K+ excretion initially decreased significantly in both normotensive and hypertensive rats drinking 1.5% sodium chloride, but returned to pre-salt drinking levels by day 5 of the experiment. Rats with maternal-diet-induced hypertension appear to be insensitive to the hypertensive effects of sodium chloride. This insensitivity does not appear to stem from a more rapid clearance of excess sodium, and may relate to other aspects of kidney function and metabolism.

Animals↗
PubMed1996

Association of disproportionate growth of fetal rats in late gestation with raised systolic blood pressure in later life.

In human populations, patterns of disproportionate fetal growth are associated with cardiovascular disease in later life. Protein restriction of pregnant rats is known to impair fetal growth and is also associated with increased systolic blood pressure in later life. Growth of fetuses exposed to maternal low protein diets was found to be accelerated between day 14 and day 20 of gestation, but this growth appeared to falter in late gestation, resulting in low or normal birthweights. Placental growth was also accelerated by protein restriction. Day 20 fetuses from rats fed low protein diets were heavier but had proportionally smaller brains than did control fetuses. These animals were also longer in proportion to body mass. Between day 20 and full term (day 22), growth of the brain was spared at the expense of the trunk and at birth, pups exposed to low protein were short in relation to body mass. At weaning, rats exposed to low protein diets in utero had significantly higher systolic blood pressure relative to control animals. These data indicate that increased blood pressure in rats is linked to disproportionate patterns of growth in middle and late gestation.

Animals↗
PubMed1996

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.

Animals↗
PubMed1996

Protein quality and urea kinetics in prepubertal Chilean schoolboys.

Urea kinetics were measured non-invasively in 12 Chilean schoolboys aged 8-10 years who were receiving one of two diets, either predominantly animal protein or predominantly vegetable protein. Both the diets provided an equivalent level of gross protein, 1.2 g/kg/day. The study diets were given for 10 days to enable adaptation to take place. On the eighth day a single oral dose of 15N15N-urea, 100 mg, was given and the amount of label excreted as 15N15-urea in urine over the subsequent 48 hours was measured. There was little difference in any aspect of urea kinetics between the two diets with urea production (animal, 173 +/- 50 mgN/kg/day; vegetable 179 +/- 53 mgN/kg/day), urea excretion (animal, 86 +/- 19 mgN/kg/day; vegetable, 105 +/- 13 mgN/kg/day), urea nitrogen hydrolysis (animal, 87 +/- 49 mgN/kg/day; vegetable, 74 +/- 42 mgN/kg/day), and the salvaged urea-nitrogen derived from hydrolysis which returned to urea formation (animal, 12 +/- 5 mgN/kg/day; vegetable, 17 +/- 9 mgN/kg/day) all being similar. A very high proportion of the salvage nitrogen derived from urea hydrolysis was maintained within the metabolic pool, about 80%, which was equivalent to 0.4 g protein/kg/day. This is the first time urea kinetics have been measured in children of this age and shows that 57% of the ura produced is excreted in urine on average with about 43% of the urea-nitrogen being salvaged for further metabolic interaction. It is concluded that the vegetable based protein diet taken habitually by Chilean children is metabolically equivalent in terms of urea kinetics to a diet based upon animal protein at this level of intake, but that high rates of salvage of urea nitrogen are found on both diets.

Aging↗
PubMed1996

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.

Adolescent↗
PubMed1996

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.

Adolescent↗
PubMed1996

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.

Anemia, Sickle Cell↗
PubMed1995

Captopril normalises systolic blood pressure in rats with hypertension induced by fetal exposure to maternal low protein diets.

Recent studies have demonstrated that the feeding of low protein diets to rats during pregnancy induces hypertension in their offspring. Maternal-diet-induced hypertension has been previously associated with elevated pulmonary angiotensin converting enzyme (ACE) activity. In the present study, the importance of the renin angiotensin system, and in particular ACE, in the maintenance of the hypertensive state, is investigated. Pulmonary and plasma ACE activity were determined in rats of different ages, following in utero exposure to 18 (control) or 9% (deficient) casein diets. No maternal diet induced changes in pulmonary ACE were noted, but at 4 and 13 weeks of age, plasma ACE activity was increased by 34 and 134%, respectively in 9% casein exposed rats relative to controls (P < 0.001). Thirteen-week-old rats had significantly raised systolic blood pressure (28 mmHg, P < 0.05), and tended to have higher diastolic blood pressure (not significant). These hypertensive animals had slightly raised plasma angiotensin II concentrations (30% higher, not significant), but similar renin activities, when compared with normotensive controls. Treatment of normotensive and hypertensive rats with the ACE inhibitor captopril demonstrated that higher plasma ACE activity may play a major role in the maintenance of maternal-diet-induced hypertension. Whilst normotensive rats showed no significant response to drug treatment, systolic blood pressure in the hypertensive rats fell rapidly to the level observed in the normotensive control group. Blood pressure remained at this lower level until treatment was withdrawn, at which time pressure began to increase slowly, but steadily. A period of 7-8 weeks was required following cessation of captopril administration for the restoration of hypertension.(ABSTRACT TRUNCATED AT 250 WORDS)

Analysis of Variance↗
PubMed1995

Urea kinetics: effect of severely restricted dietary intakes on urea hydrolysis.

Urea kinetics (urea-N production-P, excretion-E, hydrolysis-H, recycling-R and retention-S) were measured in 7 healthy adults consuming a standard diet compared with 4 fasted for 24 and/or 96 h, using primed/intermittent doses of [(15)N (15)N]-urea and mass spectrometry. Standard values were P = 196, E = 132, H = 65, R = 13 and S = 51, mgN/kg/day. After 24 h fasting all urea kinetics were reduced, and P and H were significantly reduced compared with the standard diet (p < 0.01 and < 0.05 respectively). After 96 h fasting, urea kinetics returned to standard values (P = 187, E = 136, H = 51, R =13 and S = 38, mgN/kg/day), although nitrogen intake was significantly lower (p < 0.001). Relative urea excretion (E/P) was 67%, standard diet, and 75% after fasting. Consequently H/P was slightly reduced from 33 to 25%. S/P was 26%, standard diet, 15% after 24 h and 20% after 96 h fasting, suggesting increased urea-N retention with prolonged fasting. These results imply a slight temporary shift towards increased nitrogen excretion at 24 h and subsequent return to the kinetics of the fed state after 96 h. Urea-N retention increases with prolonged fasting.

Journal Article↗