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Biomedical subjects

R G Jensen

Publications and source records attributed to R G Jensen.

At least 55 records · Page 3Linked to original sources
PubMed1991

The composition of milk fat.

Bovine milk contains about 3.5 to 5% total lipid, existing as emulsified globules 2 to 4 microns in diameter and coated with a membrane derived from the secreting cell. In homogenized milk, the coat is mostly casein. About 98% or more of the lipid is triacylglycerol, which is found in the globule. Phospholipids are about .5 to 1% of total lipids, and sterols are .2 to .5%. These are mostly located in the globule membrane. Cholesterol is the major sterol at 10 to 20 mg/dl. Data are presented on the membrane and the emulsion. Bovine milk contains substantial quantities of C4:0 to C10:0, about 2% each of C18:2 and trans-C18:1, and almost no other long-chain polyunsaturated fatty acids. The fatty acid composition is not altered by ordinary changes in diet. The triacylglycerol structure is unique, with much of the C4:0 to C10:0 at sn-3. The effects of milk cholesterol and fatty acids on human blood cholesterol levels and nonnutritive roles of some microlipids are discussed.

Animals↗
PubMed1990

Carotenoids of human colostrum.

Colostrum, the initial postpartum secretion of the breast, ordinarily has a distinct yellow color due to carotenoids of its fat globules. This pigmentation progressively diminishes as milk production increases during the first week of lactation. Identity of these carotenoids was investigated by means of thin-layer chromatography, high performance liquid chromatography and spectral analysis. Alpha- and beta-carotene, lycopene and beta-cryptoxanthin were revealed as major chromogens. A component corresponding to lutein and/or zeaxanthin was also detected by both chromatographic techniques. Extracts of 23 saponified colostrum samples from 10 donors revealed considerable variation in total carotenoid concentration (0.34-7.57 micrograms/ml of colostrum). Multiparous mothers had greater mean colostrum carotenoid concentrations than did the primiparae, 2.18 +/- 1.94 vs 1.14 +/- 1.32 micrograms/ml, respectively. Seven of the eight primiparous donors' samples had little or no yellow color. These findings imply a difference in carotenoid transport by breasts that have lactated as compared to those that have not. The interrelation of carotenoids, lactation and breast cancer is discussed.

Carotenoids↗
PubMed1990

Changes in human milk at 0600, 1000, 1400, 1800, and 2200 h.

Milk from six mothers was collected every 4 h from 0600 to 2200 h. Total lipid and cholesterol, lactose, glucose, protein N, indicator acids 12:0, 14:0, and 18:2, and alpha- and gamma-tocopherols were analyzed. Total calories were calculated. Although considerable variation was seen in the lipid content, this was not significant and was apparently due to individuality. Differences in the other lipid components were not significant and were generally related to the total lipid content. Except for protein N (p less than 0.05), none of the other components varied significantly. Based upon these data and the results of others, the time of sampling of human milk should be matched to the population being studied to obtain consistent results, at least with lipids.

Cholesterol↗
PubMed1990

Status of the substrate binding sites of ribulose bisphosphate carboxylase as determined with 2-C-carboxyarabinitol 1,5-bisphosphate.

The properties of the tight and specific binding of 2-C-carboxy-d-arabinitol 1,5-bisphosphate (CABP), which occurs only to reaction sites of ribulose 1,5-bisphosphate carboxylase (Rubisco) that are activated by CO(2) and Mg(2+), were studied. With fully active purified spinach (Spinacia oleracea) Rubisco the rate of tight binding of [(14)C]CABP fit a multiple exponential rate equation with half of the sites binding with a rate constant of 40 per minute and the second half of the sites binding at 3.2 per minute. This suggests that after CABP binds to one site of a dimer of Rubisco large subunits, binding to the second site is considerably slower, indicating negative cooperativity as previously reported (S Johal, BE Partridge, R Chollet [1985] J Biol Chem 260: 9894-9904). The rate of CABP binding to partially activated Rubisco was complete within 2 to 5 minutes, with slower binding to inactive sites as they formed the carbamate and bound Mg(2+). Addition of [(14)C]CABP and EDTA stopped binding of Mg(2+) and allowed tight binding of the radiolabel only to sites which were CO(2)/Mg(2+)-activated at that moment. This approach estimated the amount of CO(2)/Mg(2+)-activated sites in the presence of inactive sites and carbamylated sites lacking Mg(2+). The rate of CO(2) fixation was proportional to the CO(2)/Mg(2+)-activated sites. During light-dependent CO(2) fixation with isolated spinach chloroplasts, the amount of carbamylation was proportional to Rubisco activity either initially upon lysis of the plastids or following total activation with Mg(2+) and CO(2). Lysis of chloroplasts in media with [(14)C]CABP plus EDTA estimated those carbamylated sites having Mg(2+). The loss of Rubisco activation during illumination was partially due to the lack of Mg(2+) to stabilize the carbamylated sites.

Journal Article↗
PubMed1990

Lipids of bovine and human milks: a comparison.

Human and bovine milks contain about 3 to 5% total lipid, existing as emulsified globules 2 to 4 microns in diameter and coated with a membrane derived from the secreting cell. About 98% or more of the lipid is triacylglycerol, which is found in the globule. Phospholipids are about .5 to 1% of total lipids and sterols are .2 to .5%; these are mostly located in the globule membrane. Cholesterol is the major sterol. The major differences are in fatty acid composition, triacylglycerol structure, and the response of fatty acids in human milk to changes in diet. Bovine milk contains substantial quantities of 4:0 to 10:0, about 2% 18:2, and almost no other long-chain polyunsaturated fatty acids. The fatty acid composition is not altered by ordinary changes in diet. Human milk contains very little 4:0 to 10:0, 10 to 14% 18:2, and small quantities of other polyunsaturates. The triacylglycerol structure differs, with much of the sn-2 position occupied by 16:0 in human milk and 4:0 to 10:0 at sn-3 in bovine milk. The effects of milk cholesterol and fatty acids on human blood cholesterol levels are discussed.

Animals↗
PubMed1990

Utilization of outpatient health services by Army retirees and spouses.

To determine the sources and volumes of outpatient care used by one group of military beneficiaries, a data collection tool entitled the Outpatient Health Care Survey was developed and mailed to 496 Army retirees in southern Texas. This article details the results of that survey based on responses from 262 Army retirees and spouses.

Adult↗
PubMed1989

The simultaneous separation and quantitation of human milk lipids.

A protocol using a dry column method was modified for the extraction of total lipids and the simultaneous separation and quantitation of neutral and polar lipids in human milk. The triacylglycerol, cholesterol, phospholipid and vitamin E contents of the lipid extracts were determined and compared with lipids extracted using a modified Folch procedure. Good precision for the extraction of neutral, polar and total lipids, as well as the different lipid classes, was demonstrated. No significant differences were found between the two methods with respect to the amount of cholesterol, phospholipid, total lipid or vitamin E extracted, thus validating the method as an extraction technique. We discuss the relationship between vitamin E and the three major milk lipids as an indicator of the vitamin's place of origin in the mammary gland. Our findings do not support the idea that vitamin E in mature milk has its original location in the apical membrane.

Cholesterol↗
PubMed1989

Contracting out military health care.

The military health care system is currently facing a critical provider supply versus patient demand imbalance. Contracting out health care through the Civilian Health and Medical Program of the Uniformed Services and the Primary Medical Care for the Uniformed Services programs is one approach that Army Medical Department leaders have taken to correct the problem. This article critically analyzes the success of this approach using data from an Army hospital in the eastern United States. The article concludes with three suggestions aimed at improving the current situation.

Contract Services↗
PubMed1988

HPLC separation and indirect ultraviolet detection of phosphorylated sugars.

An HPLC method for the separation and analysis of phosphorylated sugars is presented. Ion-exchange chromatography coupled to indirect ultraviolet detection has produced good resolution and sensitivity. Fructose 6-P, glucose 6-P, ribose 5-P, 3-phosphoglyceric acid, ribulose 1,5-P(2), fructose 1,6-P(2), and sedoheptulose 1,7-P(2) can be separated at a sensitivity down to 10 nanomoles. The system resolves 2-carboxy-D-arabinitol 1,5-P(2) from 2-carboxy-D-ribitol 1,5-P(2). The natural inhibitor of ribulose bisphosphate carboxylase, 2-carboxy-D-arabinitol 1-P, has been separated from its 5-P isomer and most other phosphorylated compounds. This method is applied to identification of the products obtained upon ion-exchange purification of synthetic 2-carboxyarabinitol 1-P.

Journal Article↗
PubMed1988

Lactation outcome in insulin-dependent diabetic women.

To document the incidence and management of breast feeding among women with insulin-dependent diabetes mellitus (IDDM), 30 IDDM mothers and 30 controls were followed from birth of their infants to 6 weeks postpartum. The researchers interviewed the mothers in the hospital and by telephone at 1, 2, and 6 weeks postpartum. Fifty-three percent of the IDDM women and 57% of the general hospital population intended to breast feed. Because of the need for neonatal observation for hypoglycemia, most IDDM mothers were separated from their infants for the first 2 days. After 1 week, as many IDDM mothers as controls nursed. Initially, no differences in breast-feeding problems were found between the groups, but between 2 and 6 weeks postpartum, two IDDM nursing mothers but none of the controls experienced clinically diagnosed mastitis. A daily diet prescription of 31 kcal per kilogram of maternal body weight was associated with IDDM mothers' ability to sustain lactation, in contrast with 25 kcal per kilogram of maternal weight for IDDM mothers who stopped nursing. Six-week postpartum fasting plasma glucose levels of IDDM mothers who exclusively breast fed were significantly lower (4.6 +/- 2.2 mmol/L [82 +/- 40 mg/dl]) than the glucose levels of the women who stopped nursing (8.1 +/- 2.1 mmol/L [145 +/- 37 mg/dl]) or the glucose levels of the IDDM mothers who chose to bottle feed (6.7 +/- 1.7 mmol/L [120 +/- 30 mg/dl]). It appears that adequate maternal calories, blood sugar control, early breast stimulation, and mastitis monitoring are necessary for optimal lactation outcome in insulin-dependent diabetic women.

Blood Glucose↗
PubMed1988

Macronutrients in human milk at 2, 12, and 16 weeks postpartum.

This study evaluated changes in human milk composition from 2 to 16 weeks postpartum. Milk from 12 mothers was analyzed for lipid (utilizing a modified Folch), lactose (enzymatic hydrolysis), and nitrogen (semi-micro Kjeldahl). Energy was calculated by fractional analysis and bomb calorimetry. All samples were from well-defined subjects, and uniform collection procedures were used. Milk lipid, total nitrogen, and energy content differed significantly from one woman to another. Lipid and energy content increased from 3.98 +/- 1.0 to 5.50 +/- 1.1 gm/100 ml and 68.5 +/- 9.8 to 83.0 +/- 11.1 kcal/100 ml, respectively, and nitrogen content decreased significantly from 0.24 +/- 0.05 to 0.16 +/- 0.02 gm/100 ml from 2 to 16 weeks postpartum. Lactose remained statistically stable, increasing from 6.3 +/- 0.7 to 7.0 +/- 0.7 gm/100 ml. Estimates of energy from fractional analysis of macronutrients produced lower caloric estimates, especially at 2 weeks postpartum. Statistical differences over time and between and among mothers were found at all periods studied; therefore, on the basis of these data, we caution against reliance on single sample values as representative of mature milk either for individuals or for groups.

Energy Intake↗
PubMed1987

Photosynthesis and Activity of Ribulose Bisphosphate Carboxylase of Wheat and Maize Seedlings during and following Exposure to O(2)-Low, CO(2)-Free N(2).

Seven day old wheat and maize seedlings were exposed to 1300 or 2000 microeinsteins per square meter per second photosynthetically active radiation in CO(2)-free air for 3 hours with either 1% O(2) in N(2) or N(2)-only and then returned to normal air of 340 microliters per liter CO(2), 21% O(2) in N(2). Activity of the ribulose bisphosphate carboxylase and amount of the substrate, ribulose 1,5-bisphosphate, were measured during and following the CO(2)-free treatments as was photosynthetic CO(2) fixation. Photoinhibition of photosynthesis was observed only with wheat seedlings following the N(2) only treatment. During the CO(2)-free treatments, the levels of RuBP rose during all experiments except when wheat was photoinhibited. The activity of the ribulose bisphophate carboxylase, measured directly upon grinding the leaves, declined during the CO(2)-free conditions. The carboxylase total activity increased in minutes in the leaf during and following the CO(2)-free treatments. The specific activities of the wheat carboxylase went from 0.16 to 1.06 micromoles CO(2) fixed per milligram protein per minute while the maize carboxylase varied from 0.05 to 0.36 micromole CO(2) fixed per millogram protein per minute. This suggests that in these seedlings considerable inactive carboxylase must be stored in a form not activatable in extracts by CO(2) and Mg(2+). Possible mechanisms of regulation of photosynthesis by the ribulose bisphosphate carboxylase must consider not only the amount of active enzyme, but the amount of enzyme which the plant can make activatable upon demand.

Journal Article↗
PubMed1986

Measurement of the Enzyme-CO(2)-Mg Form of Spinach Ribulose 1,5-Bisphosphate Carboxylase/Oxygenase.

When the amount of activation of ribulose 1,5-bisphosphate carboxylase has been measured, two forms of the enzyme, not one, are actually determined experimentally. Only the enzyme-activator CO(2)-Mg(2+) form can bind ribulose bisphosphate for reaction with substrate CO(2) or O(2). A method is presented which measures only this catalytically active form by stabilizing it with ribulose bisphosphate just before dilution and assay in Mg(2+)-free reaction medium.

Journal Article↗
PubMed1986

Causes for the Disappearance of Photosynthetic CO(2) Fixation with Isolated Spinach Chloroplasts.

When isolated spinach chloroplasts are illuminated, photosynthesis and CO(2) fixation die off within 30 to 90 minutes. Even when air levels of CO(2) are used which maintain high and rate-saturating amounts of ribulose 1,5-bisphosphate inside the plastids, CO(2) fixation declines. The decline begins with a drop in activity of the ribulose 1,5-bishosphate carboxylase/oxygenase, specifically loss of the enzyme-activator CO(2)-Mg(2+) form. Next, the light reactions cause gradual leakage of the carboxylase and other stromal proteins to the suspending medium. The chloroplast outer envelope appears to reseal and protect the thylakoids since there is little change in the ferricyanide-dependent Hill reaction. In the dark, under otherwise identical conditions, leakage of carboxylase does not occur.

Journal Article↗
PubMed1985

Total phospholipid analysis in human milk without acid digestion.

A colorimetric method for measuring the organic phosphorus in human milk without acid digestion was studied. Human milk samples were assayed and compared to phosphatidylcholine, phosphatidylethanolamine, and sphingomyelin standards. Spectral and calibration curves prepared from phospholipid standards were equivalent. Absorption maxima occurred between 720 and 740 nm. A reproducibility study of twenty total lipid samples had a coefficient of variation of 3.8%. Phosphorus ranged from 4.7 to 5.5 micrograms with a mean +/- SD of 5.2 +/- 0.2 micrograms P. The recovery of phosphatidylcholines added to 10 mg samples of human milk triacylglycerols ranged from 99.0 to 102.1%. The results from the new method were comparable to those obtained by a modified Fiske and Subbarow method for measuring inorganic phosphorus after sulfuric acid digestion of the milk lipids. We concluded that the new method provides a satisfactory alternative for the determination of organic phosphorus in human milk.

Acids↗