Biomedical subjects

D Sklan

Publications and source records attributed to D Sklan.

At least 91 records · Page 5Linked to original sources

PubMed1995

Posthatch changes in morphology and function of the small intestines in heavy- and light-strain chicks.

The morphology of the small intestines of heavy (Arbor Acres) and light (Lohman) chicks was determined posthatch in parallel with digestion, enzyme secretion, and passage time. Villus height and volume increased from 4 to 10 d, particularly in the jejunum and ileum. The number of enterocytes per villus increased with age, but enterocyte density was greater in jejunum than ileum. Villus volume and enterocyte density was greater in Arbor Acres than Lohman chicks from hatching and the rate of change with age was similar in both strains. Enzyme secretion to the duodenum was higher per gram of feed intake in heavy-strain birds on Day 4 after hatching but thereafter no differences were apparent. Passage time was 50% shorter in light-strain chicks on Day 4 but the difference between the strains was not significant from Day 10. No differences in fatty acid digestion were observed with age or between strains. Nitrogen digestion increased in both strains from approximately 70% on Day 4 to close to 90% on Day 14. Starch digestion was 90 to 95% from 4 to 14 d in Arbor Acres birds, but increased from approximately 80% on Day 4 in Lohman chicks to 93% on Day 14. Feed intake may determine the amount of uptake in posthatch chicks.

Animals↗

PubMed1994

A fluorimetric assay for hydrogen peroxide, suitable for NAD(P)H-dependent superoxide generating redox systems.

We report a simple and sensitive fluorimetric method for quantitative assay of the production rate of hydrogen peroxide, and indirectly of superoxide, during electron transfer reactions. The assay requires the inclusion of superoxide dismutase, catalase, and 6% methanol in the tested reaction system, to stochiometrically produce formaldehyde per molecule of H2O2 generated. The reaction is terminated by adding 2 vol of Nash reagent and heating at 60 degrees C for 10 min, to convert accumulated formaldehyde to diacetyldihydrolutidine (DDL). The standard curve for formaldehyde, based on the fluorescence of DDL, is highly reproducible and allows measurement of 1 microM amounts in the reaction sample (coefficient of variation < 15%). The excitation and emission wavelengths of DDL at 412 and 505 nm are distant from those of NAD(P)H. Thus, the method can be used in NAD(P)H-dependent enzymatic systems to measure both NAD(P)H oxidation and superoxide production in the same sample. We validated the assay in a mitochondrial P450 system determining the fraction of total electron flow that is channeled to oxy-radical formation. The assay should be useful in the study of this and other superoxide/H2O2 generating systems.

Catalase↗

PubMed1994

Retinoic acid receptor-alpha gene expression is modulated by dietary vitamin A and by retinoic acid in chicken T lymphocytes.

The effects of dietary vitamin A and retinoic acid in vitro on the proliferative response and gene expression of retinoic acid receptor-alpha (RAR-alpha) in chicken T lymphocytes were studied. Antigen-specific proliferative responses of T lymphocytes increased with dietary vitamin A intake from 0 to 6.6 mg/kg diet; however, at high dietary vitamin A (13.2 mg/kg diet), the proliferative response declined. RAR-alpha mRNA expression in T lymphocytes peaked in chicks fed low levels of vitamin A (830 and 1500 micrograms/kg diet) and declined at higher intakes. In vitro effects of retinoic acid on the modulation of RAR-alpha mRNA were studied in stimulated T lymphocytes. Retinoic acid (0.01 mumol/L) increased RAR-alpha mRNA levels within 2 or 16 h of incubation with concanavalin A- or beta-casein-stimulated T cells, respectively. This effect was transient. Expression of RAR-alpha mRNA in concanavalin A-stimulated T lymphocytes was up-regulated by retinoic acid in a dose-dependent manner, and maximal expression occurred in response to 1 mumol/L retinoic acid. The proliferative response of these cells was also modulated by retinoic acid in a dose-dependent manner, and highest effects were observed at 0.01 mumol/L retinoic acid. Our results indicate that RAR-alpha mRNA expression and antigen-specific proliferative responses of T lymphocytes are influenced by vitamin A status in vivo, and directly modulated by retinoic acid.

Administration, Oral↗

PubMed1994

Effect of dietary calcium soaps on milk yield, body weight, reproductive hormones, and fertility in first parity and older cows.

The effects were determined of dietary Ca soaps of fatty acids fed to cows to 120 DIM on milk yield, BW, peripheral concentrations of reproductive hormones, and fertility in primiparous and multiparous cows. Milk yield was increased in primiparous and multiparous cows fed Ca soaps, and milk fat and protein yields were enhanced. Body weight losses were greater for all cows fed Ca soaps, and this trend was greater and longer lasting in primiparous cows than in multiparous cows. Plasma triglyceride concentrations were elevated in multiparous cows, but FFA tended to be higher in primiparous cows fed Ca soaps. Conception rate at first AI was lower for primiparous cows fed Ca soaps (33%) than for controls (74%), but differences were not significant for later AI or between multiparous groups. No differences were apparent for plasma progesterone or estradiol in the luteal or follicular phases preceding the first AI, and differences in mean luteinizing hormone concentrations were small in a 6-h window in the follicular phase. The differences in conception rate at first AI in primiparous cows could not be explained on the basis of changes in peripheral hormone concentrations. The enhanced negative energy balance in primiparous cows fed Ca soaps apparently was related to the decrease in their conception rate.

Animals↗

PubMed1994

The effect of varying levels of dietary vitamin A on immune response in the chick.

The effect of dietary vitamin A on antibody production and T cell proliferative response was determined in broilers from 21 to 39 d old. Chicks were fed soybean meal-sorghum diets with levels of supplemented vitamin A from 0 to 13,200 micrograms/kg retinol equivalents from hatching and were immunized with beta-casein at 21 d of age. T cell proliferation response to beta-casein or an acetone precipitate of antigen to Mycobacterium tuberculosis was determined in vitro at 34 to 37 d old. Antibodies to beta-casein in serum were determined every 5 d from 21 d of age. In chicks with no added dietary vitamin A, antibody production and proliferative response were depressed in comparison with chicks receiving vitamin A. Addition of small amounts of vitamin A enhanced the responses; both antibody production and proliferative responses increased with dietary vitamin A until the diet contained 6,660 micrograms/kg, above which the responses decreased. This suggests that maximal immune responses in the chick may be achieved at dietary intakes considerably higher than NRC recommendations.

Animal Feed↗

PubMed1993

The interaction between beta-carotene and lipoxygenase in plant and animal systems.

The effect of beta-carotene (BC) on the activity of lipoxygenase (LOX) from plant and animal sources has been examined. Soybean lipoxygenase L-2 activity towards linoleate was inhibited by BC by a maximum of 70% at pH 6.5, whereas L-1 activity was little affected at pH 9.0. Lineweaver-Burk plots indicated that BC inhibited LOX activity by mixed competitive/non-competitive mechanisms. Other hydrophobic compounds also inhibited LOX activity; oleic acid and retinol were competitive inhibitors whereas tocopherol acetate and 5,8,11,14-eicosatetraynoic acid (ETYA) were non-competitive inhibitors. Binding studies with L-2 LOX bound to Sepharose indicated BC-binding and inhibition with the immobilized LOX. Activity of LOX from animal sources was also inhibited by BC both towards linoleate and arachidonate.

Animals↗

PubMed1993

Electron leakage from the mitochondrial NADPH-adrenodoxin reductase-adrenodoxin-P450scc (cholesterol side chain cleavage) system.

In electron (e-) transfer systems some e- may "leak," reducing O2 to a superoxide radical. This study examined the sites and kinetics of e-leakage from the mitochondrial P450scc system. Adrenodoxin reductase alone oxidized NADPH, reducing O2 to a superoxide radical at a very low rate. However, the reductase-adrenodoxin system reduced O2 at a rapid steady-state rate with Michaelis-Menten dependence on [adrenodoxin](Vmax = 3.5 micro M e-/min). After depletion of NADPH, reduced adrenodoxin was oxidized (autooxidation) with pseudo first order kinetics and the rate of e- transfer decreased 10-fold. Ca2+ (< 1 mM) stimulated e- leakage in both phases. The reductase-adrenodoxin-P450scc system exhibited the highest rate of leakage (Vmax = 7.8 microM e-/min). At low [adrenodoxin] the majority of e-leaked through P450scc and not through adrenodoxin. In the presence of the substrate, cholesterol, leakage drastically decreased to <0.5 microM e-/min. These results indicate that the mitochondrial P450 systems can leak e-, producing O2 derived free radicals. Reduction of leakage during P450scc conversion of cholesterol to pregnenolone provides a clue to understanding physiological mechanisms that control e-leakage. These may include coregulation of NADPH and cholesterol availability to the P450scc system and a system of antioxidants for quenching the oxygen radicals.

Adrenal Cortex↗

PubMed1993

Retinoic acid promotes proliferation and induces expression of retinoic acid receptor-alpha gene in murine T lymphocytes.

We have studied the direct effect of retinoic acid on the antigen-specific proliferative response of a T lymphocyte clone and have investigated the related expression of the retinoic acid receptor-alpha gene (RAR-alpha). Retinoic acid provided direct growth support, in a dose-dependent manner, for hen egg white lysozyme (HEL)-activated T lymphocytes in serum-free medium. The increase of T lymphocyte proliferation supported by retinoic acid was dose dependent, and best effects were achieved at physiological concentrations (10(-9)-10(-7) mol/liter). Expression of RAR-alpha mRNA in antigen-stimulated T lymphocyte cultures was upregulated by retinoic acid in a dose-dependent manner; maximal expression occurred within 6 hr of culture and in response to 10(-9)-10(-7) mol/liter retinoic acid. Lower expression of RAR-alpha was attained by antigen or mitogen (concanavalin A) in the absence of externally added retinoic acid. The inclusion of retinoic acid at the time of HEL processing led to increased T lymphocyte proliferation, provided antigen presenting cell cultures had been maintained for 16 hr. Our results indicate that retinoic acid and RAR-alpha might function in T lymphocytes in a manner similar to that described in other cell systems, namely as ligand-inducible transcriptional enhancer factors.

Animals↗

PubMed1993

Diet planning for humans using mixed-integer linear programming.

Human diet planning is generally carried out by selecting the food items or groups of food items to be used in the diet and then calculating the composition. If nutrient quantities do not reach the desired nutritional requirements, foods are exchanged or quantities altered and the composition recalculated. Iterations are repeated until a suitable diet is obtained. This procedure is cumbersome and slow and often leads to compromises in composition of the final diets. A computerized model, planning diets for humans at minimum cost while supplying all nutritional requirements, maintaining nutrient relationships and preserving eating practices is presented. This is based on a mixed-integer linear-programming algorithm. Linear equations were prepared for each nutritional requirement. To produce linear equations for relationships between nutrients, linear transformations were performed. Logical definitions for interactions such as the frequency of use of foods, relationships between exchange groups and the energy content of different meals were defined, and linear equations for these associations were written. Food items generally eaten in whole units were defined as integers. The use of this program is demonstrated for planning diets using a large selection of basic foods and for clinical situations where nutritional intervention is desirable. The system presented begins from a definition of the nutritional requirements and then plans the foods accordingly, and at minimum cost. This provides an accurate, efficient and versatile method of diet formulation.

Algorithms↗

PubMed1993

Escherichia coli produces linoleic acid during late stationary phase.

Escherichia coli produces linoleic acid in the late stationary phase. This was the case whether the cultures were grown aerobically or anaerobically on a supplemented glucose-salts medium. The linoleic acid was detected by thin-layer chromatography and was measured as the methyl ester by gas chromatography. The linoleic acid methyl ester was identified by its mass spectrum. Lipids extracted from late-stationary-phase cells generated thiobarbituric acid-reactive carbonyl products when incubated with a free radical initiator. In contrast, extracts from log-phase or early-stationary-phase cells failed to do so, in accordance with the presence of polyunsaturated fatty acid only in the stationary-phase cells.

Aerobiosis↗

PubMed1993

Production and reproduction responses by dairy cows fed varying undegradable protein coated with rumen bypass fat.

Calcium soaps of fatty acids were used to coat proteins, thus reducing rumen degradability. This material was used to determine the effects of either increasing undegradable intake protein with constant CP or varying degradable protein with constant undegradable protein intake. Increased undegradable intake protein and Ca soaps fed for 120 DIM enhanced milk fat and FCM production during 140 and 305 DIM. Reproductive performance also was improved. Feed efficiency and partial efficiency of milk production were enhanced. Varying degradable protein intake at constant undegradable protein intake using proteins coated with Ca soap resulted in decreased production when degradable protein intake was .4 kg/d lower than NRC recommendations, but no differences were significant when intakes were close to or .5 kg/d above NRC recommendations. Use of Ca soaps to coat proteins appears to be useful to optimize protein supply to dairy cows while increasing ration energy density.

Animal Feed↗

PubMed1992

Short-chain fatty acid absorption in patients with cystic fibrosis.

Patients with cystic fibrosis (CF) often exhibit malabsorption despite the use of supplemental pancreatic enzymes. Unabsorbed carbohydrates and amino acids can serve as substrates for large intestine anaerobic fermentation, thus increasing excretion of short-chain fatty acids (SCFA) in the feces. Nine patients with CF on regular pancreatic enzyme supplementations in the age range of 5-11 years and one older patient were studied. Three-day stool samples were collected, as were 72-h food records. Stools were analyzed for gross energy, total nitrogen, fat content, and SCFA concentration. A significant difference was found between CF and normal controls in total caloric excretion due to fat malabsorption. No significant difference was found between CF and normal controls in protein or SCFA excretion. Fat excretion as percentage of fat intake was significantly increased in CF patients: 35.3 +/- 10.2% versus 8.0 +/- 3.0%, respectively. These data suggest that carbohydrate supplementation could be more widely used to increase caloric intake in CF patients without causing secondary osmotic diarrhea.

Adolescent↗

PubMed1992

Fatty acids, calcium soaps of fatty acids, and cottonseeds fed to high yielding cows.

We examined the effects of dietary fat as cottonseed, fatty acids, or calcium soaps of fatty acids in the rations of high yielding lactating cows receiving low forage. Experiments were with isoenergetic, isonitrogenous diets containing equal amounts of forage. Inclusion of up to 510 g/d of fatty acids in the ration enhanced FCM yield. With cottonseed, increased FCM was mainly due to increased fat yield. Dietary fatty acids tended to increase milk in mid and late lactation and to decrease fat percentage. Calcium soaps of fatty acids enhanced FCM, particularly in early lactation. Feeding cottonseed and fatty acids together did not enhance yield. Effects described may be attributed in part to changes in ruminal fermentation in which cottonseed increased acetate concentrations and fatty acids decreased the ratio of acetate and butyrate to propionate and in part to enhanced efficiency of milk yield when fat was included in the ration.

Acetates↗

PubMed1992

Vitamin A metabolism in plasma of normal and anorectic women.

Plasma retinol and retinyl ester kinetics were determined following an oral bolus of vitamin A in normal women and in women suffering from anorexia nervosa. Circulating levels of vitamin A and alpha-tocopherol were lower in anorectics than in normals with alpha-tocopherol levels close to minimal adequate levels. This suggests the possibility of deficiencies of other dietary factors. Following an oral bolus, plasma retinol increased more in anorectics than in normals, but transport values were not changed. Retinyl ester levels increased sevenfold more in anorectics than normals with a parallel enhancement in transport. Retinyl esters in plasma of normals and anorectics were present mainly in low-density lipoprotein with lesser amounts in very-low-density and high-density lipoprotein, but only minor amounts were found in chylomicrons. These data were used to calculate a relative dose response and indicated that anorectics had higher values than normals. Anorectics appear to have a lower status of vitamins A and E than normals but no defect in vitamin A metabolism was observed.

Administration, Oral↗

PubMed1991

Decreased resistance and immune response to Escherichia coli infection in chicks with low or high intakes of vitamin A.

The effects of vitamin A excess of insufficiency on resistance to Escherichia coli infection and subsequent anti-E. coli immune response were examined in chicks. Chicks receiving depleted (0 microgram/kg), sufficient (0.85 mg/kg) or excess (1000 mg/kg) levels of vitamin A in their feed were inoculated by a subcutaneous injection of pathogenic E. coli (1 x 10(9) and 2 x 10(9) cfu per chick). Susceptibility to E. coli was determined by mortality, morbidity and immune responses (antibody production and T lymphocyte proliferation). Excess of insufficient vitamin A led to increased susceptibility of chicks of E. coli infection; this was accompanied by depressed immune responses. Chicks receiving excess vitamin A were more sensitive to E. coli than vitamin A-depleted chicks. This was reflected in higher mortality and morbidity rates and in severely depressed immune responses. In contrast to chicks receiving excess vitamin A, T lymphocyte responses (though not antibody responses) of vitamin A-depleted chicks achieved levels similar to those of vitamin A-sufficient birds with a lag period of 6 to 10 d. Therefore, reduction in resistance to E. coli infection, resulting from vitamin A excess or deficiency, probably was compounded by a delayed immune response.

Animals↗

PubMed1991

Effect of feeding calcium soaps of fatty acids on production and reproductive responses in high producing lactating cows.

The effect of feeding Ca soaps of fatty acids for 120 d from parturition on productive and reproductive performance of dairy cows was examined, together with changes in blood lipids and progesterone. Cows fed Ca soaps received 1.5 Mcal NE1 d more than controls fed isonitrogenous and equi-forage rations. Cows fed Ca soaps produced more milk and fat for 60 d, and more FCM for 90 d after calving. In these cows, BW decreased more, and reached a minimum later than controls. Plasma free fatty acids were higher until 50 d postpartum, when phospholipid, and later triglyceride, concentrations were elevated. Cows fed soaps commenced ovarian cyclicity later than controls as shown by frequency distribution of the time required to reach cyclic plasma progesterone concentrations, 2 ng/ml progesterone in plasma, or behavioral estrus. However, once cyclicity commenced, more fat-fed cows had normal cycle length (18 to 26 d) than controls. Progesterone concentrations were higher in Ca soap-fed cows in the luteal phase before AI and were higher 9 and 24 d after AI in percent that conceived. Conception rate was higher in cows fed Ca soaps for 2nd to 4th AI, a higher proportion of cows were pregnant at 150 d after calving and number of open days was reduced. Feeding Ca soaps of fatty acids resulted in higher production at the expense of body reserves close to calving, and subsequently enhanced lipid concentrations in plasma. Higher progesterone production was accompanied by increased pregnancy rate and reduced open days.

Animal Feed↗

PubMed1990

Inhibition of the activity of human leukocyte elastase by lipids particularly oleic acid and retinoic acid.

The effect of various natural hydrophobic lipids on the in vitro and in vivo activity of human leukocyte elastase has been examined. In vitro studies using 2 different substrates indicated that fatty acids inhibit human leukocyte elastase activity, with maximum inhibition observed with oleic acid. Triolein, cholesterol, and beta-carotene caused little inhibition. The presence of a carboxyl group appears important since retinoic acid but not retinol also inhibited activity. In vivo studies of an emphysema model in mice indicated that intrapulmonary instillation of oleic or retinoic acid reduced lung injury caused by human leukocyte elastase. The possibility of using these compounds to diminish elastolytic damage in emphysema is raised.

Animals↗

PubMed1990

Responses of dairy cows in early lactation to bovine somatotropin and ruminally inert fat.

Bovine somatotropin (0 or 41.2 mg/d bST) and calcium salts of long-chain fatty acids (0 or .77 kg/d Ca-LCFA) were administered to 16 Holstein cows in early lactation. Cows remained on 0 or 41.2 mg/d bST for the entire 10 wk and received 0 or .77 kg/d Ca-LCFA in one of two 5-wk periods. Production data were recorded daily, milk fatty acids, and blood metabolites were determined once each period. Treatments did not affect feed intake. Fat-corrected milk (kg/d) and percentage of milk fat for cows receiving no supplementation, fatty acids alone, bST alone, and fatty acids and bST together were 33.8, 3.2; 33.5, 3.1; 37.4, 3.4; and 40.8, 3.5. Milk fatty acids below C16 were reduced with either bST or dietary fatty acids; C16 fatty acids were lower with bST but higher with dietary fatty acids; C18:0 fatty acids were reduced with dietary fatty acids; and C18:1 fatty acids were higher with either bST or dietary fatty acids. Blood acetoacetate concentrations were higher with both bST and dietary fatty acids, beta-hydroxybutyrate was not different, and FFA and insulin concentrations increased with bST. In this experiment, the energy supplied by Ca-LCFA acids enhanced the lactogenic effect of bST.

3-Hydroxybutyric Acid↗