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Biomedical subjects

S A Atkinson

Publications and source records attributed to S A Atkinson.

At least 73 records · Page 4Linked to original sources
PubMed1989

Partition of nitrogen intake and excretion in low-birth-weight infants.

Although nitrogen balance studies have been carried out in low-birth-weight infants, few have partitioned the nitrogen into its components. In this study, 72-hour balance studies were conducted in 24 low-birth-weight infants (gestational age, 30.7 +/- 1.6 weeks; birth weight 1.36 +/- 0.25 kg) fed their mothers' milk (preterm milk) or 50% preterm milk and 50% formula. Total nitrogen, nonprotein nitrogen, and whey protein intake and excretion were measured. Total nitrogen intake (preterm milk group, 452 +/- 138 mg/kg per day; preterm + formula group, 406 +/- 93 mg/kg per day), absorption (85%), and retention (71%) were not significantly different between groups. Intact and fragments of secretory IgA and lactoferrin were detected in soluble fecal extracts, and represented 25% and 9% of intake, respectively. Feeding preterm milk allows for nitrogen accretion similar to intrauterine growth rates for 5 weeks postnatally, and provides potentially functional proteins for the low-birth-weight infant.

Birth Weight↗
PubMed1989

Mineral homeostasis and bone mass in children treated for acute lymphoblastic leukemia.

Clinical observations of bone pain, abnormal gait, and unusual fractures during remission of leukemia led us to assess mineral status in a cohort of 16 children with acute lymphoblastic leukemia treated with intensive chemotherapy. During maintenance and 6 months after the completion of therapy, blood and urine were analyzed for calcium and magnesium and blood for osteocalcin, vitamin D, and parathyroid hormone. Bone mineral content and bone width of the distal one third of the radius of the nondominant arm was measured by single-photon absorptiometry. During therapy, mild ionic hypocalcemia (less than 1.19 mmol/L) and hypomagnesemia (less than 0.77 mmol/L) were demonstrated in 9 and 8 of 16 children, respectively; hypercalciuria (8/16) and hypomagnesiuria (12/16) were also observed. Plasma osteocalcin values correlated with plasma magnesium levels (r = 0.54; p less than 0.05). Oral magnesium supplements normalized plasma magnesium, calcium, and osteocalcin levels, all of which were normal at the postchemotherapy study. Plasma 1,25-dihydroxyvitamin D levels were nondetectable (less than 8 ng/ml) in 12 of 13 patients receiving therapy and in 7 of 14 patients not receiving therapy; alkaline phosphatase activity increased significantly after therapy (179 +/- 86 to 340 +/- 101 units/L), and parathyroid hormone levels were normal in both studies. Bone mineral content/bone width ratio was less than 1 SD below the mean for age- and sex-related population standards in 70% of patients. These data indicate that alterations in magnesium, calcium, and vitamin D metabolism in children treated for acute lymphoblastic leukemia may be instrumental in inducing or sustaining altered bone turnover during chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1989

In vitro solubility of calcium glycerophosphate versus conventional mineral salts in pediatric parenteral nutrition solutions.

Low-birth-weight infants requiring total parenteral nutrition receive inadequate intakes of calcium (Ca) and phosphorus (P) due to poor solubility of available mineral salts. To optimize Ca/P delivery, we tested the effects on in vitro solubility of mineral salt:calcium glycerophosphate (CaGP) versus calcium gluconate and K2HPO4 (CG + P); Ca:P ratios of 1:1 (at 12.5 and 25 mmol/L of Ca and P) and 2:1 (25:12.5 mmol/L); amino acid (AA) formulation: Aminosyn (A), Aminosyn-PF (A-PF), TrophAmine (T) or Vaminolac (V); and AA concentration (25 versus 8.3 g/L). Parenteral nutrition solutions contained 10% dextrose and vitamins and minerals typical of a neonatal prescription. Solutions were sampled at preparation, after 24 h in the neonatal unit (25 degrees C), and from before and after a 0.22-micron filter in extension tubing through which solutions were pumped at 5 ml/h within an incubator at 37 degrees C. Samples were analyzed for Ca and pH, and precipitation by spectrophotometry at 600 nm and light microscopy at x 100 magnification. The Ca concentration was unaffected by filtration. While spectrophotometry detected only gross precipitation, with light microscopy crystal formation was evident with 25 mmol/L of Ca and P as CG + P in A and T at 25 g of AA/L and in A, V, T, and A-PF at 8.3 g of AA/L. Precipitation did not occur with CaGP or CG + P at 12.5 mmol/L of Ca and P. Under in vitro conditions mimicking the neonatal unit, CaGP versus CG + P resulted in greater mineral solubility even at low AA concentrations.

Amino Acids↗
PubMed1989

Physiological responses to caffeine during endurance running in habitual caffeine users.

Several studies have found that caffeine improved endurance exercise performance, but the factors which are responsible for this are not fully understood. Possibilities include an increased free fatty acid (FFA) oxidation and a resultant sparing of muscle glycogen as well as an enhancement of neuromuscular function during exercise. In order to further examine these factors, six varsity level runners (VO2max = 63.3 ml.kg-1.min-1) were studied over 90 min of treadmill running (70% VO2max) in a thermoneutral environment in order to determine the metabolic and neuromuscular effects of caffeine (6 mg.kg-1) administered in a randomized, crossover, double-blind manner. Subjects were habitual caffeine consumers (200 mg.d-1) and were given identical diets during each 3-d testing period. Caffeine administration, 60 min prior to exercise, significantly (P less than 0.05) increased plasma FFA levels both prior to and during exercise. Caffeine administration did not alter any of the other variables examined: VO2, HR, RER, rating of perceived exertion; plasma levels of glucose, lactate, epinephrine, and norepinephrine; or neuromuscular function (maximal voluntary strength, peak twitch torque, and motor unit activation). We conclude that caffeine administration (6 mg.kg-1) in athletic, habitual caffeine consumers increased plasma FFA levels but had neither metabolic nor neuromuscular effects that would be of potential ergogenic benefit in endurance running.

Adult↗
PubMed1988

Mineral excretion in premature infants receiving various diuretic therapies.

The association of various diuretic therapies with the renal handling of minerals, important factors in the development of nephrocalcinosis and osteopenia, was studied in low birth weight infants. Twenty-four-hour urine specimens (n = 65) were collected from 30 patients who were treated with (1) furosemide with or without spironolactone and hydrochlorothiazide (2) spironolactone with hydrochlorothiazide, (3) spironolactone alone, or (4) no diuretic (control; i.e., after diuretic). Hypercalciuria (urinary calcium greater than or equal to 0.15 mmol/kg/day) was observed in all but the control group. Covariate analysis demonstrated a significant effect of sodium, calcium, and vitamin D intakes (p less than 0.01) and sodium excretion (p less than 0.05) on urinary calcium excretion. Treatment with any of these diuretics in neonates may be associated with abnormal renal losses of calcium, sodium, chloride, and potassium. From a nutritional perspective, neonates requiring long-term diuretic therapy thereby require special consideration, including monitoring of mineral excretion and renal ultrasonography.

Birth Weight↗
PubMed1988

Influence of protein intake and training status on nitrogen balance and lean body mass.

The present study examined the effects of training status (endurance exercise or body building) on nitrogen balance, body composition, and urea excretion during periods of habitual and altered protein intakes. Experiments were performed on six elite bodybuilders, six elite endurance athletes, and six sedentary controls during a 10-day period of normal protein intake followed by a 10-day period of altered protein intake. The nitrogen balance data revealed that bodybuilders required 1.12 times and endurance athletes required 1.67 times more daily protein than sedentary controls. Lean body mass (density) was maintained in bodybuilders consuming 1.05 g protein.kg-1.day-1. Endurance athletes excreted more total daily urea than either bodybuilders or controls. We conclude that bodybuilders during habitual training require a daily protein intake only slightly greater than that for sedentary individuals in the maintenance of lean body mass and that endurance athletes require daily protein intakes greater than either bodybuilders or sedentary individuals to meet the needs of protein catabolism during exercise.

Adolescent↗
PubMed1987

Changing osteocalcin concentrations during pregnancy and lactation: implications for maternal mineral metabolism.

We measured serum osteocalcin concentrations in 82 pregnant and 21 nonpregnant women. Osteocalcin values declined in the second trimester, but returned to nonpregnant levels late in the third trimester. The mean serum osteocalcin concentration in 36 women during pregnancy (mean gestation, 26 weeks) of 2.8 ng/mL was significantly lower than that in nonpregnant women (6.4 ng/mL; P less than 0.001) or term pregnant women at delivery (6.1 ng/mL; n = 46). Serum immunoreactive PTH (iPTH) levels were significantly higher during pregnancy than in nonpregnant women [97 +/- 5 vs. 56 +/- 4 ng/L (mean +/- SE); P less than 0.001]. No significant correlations were found between maternal osteocalcin concentrations and serum phosphorus, alkaline phosphatase, or iPTH, but significant negative correlations were found between osteocalcin and total calcium or total protein. Osteocalcin concentrations in midtrimester amniotic fluid were very low (mean, 0.3 +/- 0.1 ng/mL; n = 11). In 29 lactating mothers, the mean serum osteocalcin level was 9.5 +/- 1.5 ng/mL, significantly higher than in any of the other groups (P less than 0.05), but their serum calcium and iPTH levels were normal. There was no correlation between serum osteocalcin and calcium or iPTH concentrations in lactating women. These changes are compatible with a sequence in which bone turnover is reduced during early pregnancy, rebounds in the third trimester, and increases in postpartum lactating women.

Adolescent↗
PubMed1983

Macromineral balances in premature infants fed their own mothers' milk or formula.

The premature infant's own mother's milk (preterm milk) and modified infant formula (SMA, 67 and 80 kcal/dl) were fed to paired groups of seven infants, all of whom were of very low birth weight (VLBW) (less than 1.3 kg) and were studied during the first month of life. Sodium, potassium, magnesium, calcium, and phosphorus status was compared. The apparent retention of sodium from their mother's milk paralleled intrauterine retention rates and was greater than retention from SMA formula (P less than 0.01) during the first two weeks of life. However, when the formula was supplemented with NaHCO3 to intakes of 2.7 mmol Na/kg/24 hr after week 2, the infants retained adequate amounts of sodium. Potassium retention was similar to intrauterine retention rates in both groups throughout the four postnatal weeks. Magnesium intake, but not retention, was consistently higher in the group fed SMA (P less than 0.01), and intrauterine retention rates were achieved only in the group given formula. Calcium and phosphorus intakes from SMA were also higher (P less than 0.01) than from human milk. However, retention of calcium and phosphorus in both groups did not meet intrauterine retention rates, and hypophosphatemia developed in infants who received their mothers' milk. Growth in length and head circumference in both groups approximated intrauterine growth rates. If it is assumed that body composition of the growing VLBW infants should be similar to the composition of the fetus at corresponding gestational ages, then their nutrient requirements should be based on knowledge of intrauterine nutrient accretion rates. Based on this premise, we conclude that, for the growing VLBW infant, early maternal milk provided for sufficient retention of sodium, chloride, and potassium during the first four postnatal weeks. Neither human preterm milk nor SMA supplied adequate calcium and phosphorus for the growing VLBW infant.

Body Composition↗
PubMed1981

Human milk feeding in premature infants: protein, fat, and carbohydrate balances in the first two weeks of life.

The nutritional adequacy of the premature infant's own mother's milk was assessed during the first two weeks of life. Studies were carried out in three groups (n = 8) of infants of less than 1,300 gm birth weight, matched for gestational age and weight, and fed either pooled breast milk, their mothers own milk, or infant formula (SMA20 or SMA24). Macronutrient balances at the end of the first and second postnatal weeks demonstrated differences in nitrogen and lipid absorption and retention between groups. Nitrogen retentions (mg/kg/day) were similar to normal fetal accretion rates only in the PT and SMA24 groups. Fat absorption was poorest from the heat-sterilized PBM (average of 64.0% of intake) when compared to PT (88.2%) and SMA groups (83.3%). Average gross and metabolizable energy intakes were similar among groups. Nutritional status as measured by plasma total protein and albumin concentrations and weight gain tended to be poorest in the PBM-fed infants. It was concluded that either PT milk or infant formula of a composition similar to SMA24 are more appropriate than pooled banked milk for feeding the premature infant during the first two weeks of life.

Anthropometry↗
PubMed1981

Energy and macronutrient content of human milk during early lactation from mothers giving birth prematurely and at term.

The lactose, lipid, protein, and total energy content of milk produced during the first 4 wk of lactation was determined in milk from mothers giving birth prematurely and at term. Milk samples analyzed were representative of complete 24-h expressions. Over the first 4 wk of lactation lactose concentration increased, but nitrogen concentration decreased by an average of 25%. Lipid and total energy concentration increased by 25% from the 1st to 2nd wk and then remained stable in both groups. Although these changes with duration of lactation were similar in both groups, premature compared to full term milk was consistently 20 to 30% higher in total energy and lipid concentration, 15 to 20% higher in total protein and, after the 1st wk, approximately 10% lower in lactose. By comparing predicted nutrient intakes to estimated requirements of premature infants fed 150 to 200 ml/kg/day of their own mothers' milk, we predict that the quantities of protein and energy provided would be adequate to meet the needs of the infant during the early weeks of life.

Adult↗
PubMed1981

Net acid excretion during first week of life.

Metabolic acidosis occurs frequently in newborns. Net acid excretion (NAE) in 34 preterm and 12 term infants was measured during the first week of life. Twenty preterm infants received breast milk or formula; the remaining infants received total parenteral nutrition (TPN) -- synthetic amino acids or casein hydrolysate solution. NAE for breast milk vs formula fed infants was 5.4 +/- 0.4 and 7.8 +/- 0.6 muEq/min/m2 (mean +/- SEM). The corresponding values for the two TPN solutions in preterm infants were significantly higher at 12.5 +/- 1.4 and 19.4 +/- 3.5 muEq/min/m2. Term infants produced even greater amount of net acid, 20.6 +/- 2.9 and 35 +/- 3.7 muEq/min/m2 respectively for the two TPN solutions. Milk fed infants are less prone to acidosis because of base generated from milk consumption. Due to its inherent acidogenic effect, TPN solutions induce acidosis more readily. Infants receiving TPN are therefore required to generate a higher NAE rate to maintain acid-base homeostasis compared to milk fed infants.

Acid-Base Equilibrium↗
PubMed1980

Macro-mineral content of milk obtained during early lactation from mothers of premature infants.

Milk from mothers giving birth prematurely was analyzed for Na, Cl, K, Mg, Ca and P concentrations. The data presented are from analyses of milk samples representative of complete 24-hour expressions and collected serially over the first 29 days of lactation from mothers giving birth at term (FT) and mothers giving birth prematurely (PT). Mineral composition of FT and PT milks was similar during the first month lactation. With the exceptions of Mg and P, the concentrations of the minerals studied were higher initially than at the end of the fourth week of lactation. From these data, intakes of premature infants fed their own mothers' milk can be estimated and compared to predicted mineral requirements for the premature infant. On the basis of this comparison, we suggest that the quantities provided of Na, Cl, K and Mg, but not Ca and P, would be adequate to meet requirements of premature infants during the early weeks of life.

Adult↗
PubMed1980

Human milk: comparison of the nitrogen composition in milk from mothers of premature and full-term infants.

Total nitrogen concentration of human milk during the first 4 weeks of lactation is higher in milk obtained from mothers giving birth prematurely than in milk from mothers giving birth at term. In the present study, the relative composition of total nitrogen was found to be similar in premature and full-term milk except for some minor differences in small molecule components. Total nitrogen is comprised of an average of 82% protein, 8% of the nonprotein nitrogen components--urea, free amino acids, uric acid, and ammonia--and the remaining 10% is predicted to be peptide nitrogen.

Female↗