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Biomedical subjects

J Bitman

Publications and source records attributed to J Bitman.

At least 37 records · Page 2Linked to original sources
PubMed1989

Gastric lipolysis and fat absorption in preterm infants: effect of medium-chain triglyceride or long-chain triglyceride-containing formulas.

The extent of gastric lipolysis, fat absorption, and infant weight gain was studied in 12 preterm infants (gestational age 28.75 +/- 0.50 weeks, postnatal age 6.08 +/- 0.81 weeks) fed medium-chain triglyceride or long-chain triglyceride formula for 1 week in a crossover design. The former formula contained 42% of 8:0 and 10:0 and 19% of 12:0, 14:0, and 16:0; the latter formula contained only 7% of 8:0 and 10:0 and 46% of 12:0, 14:0, and 16:0. Gastric aspirates were obtained on the second and third day of formula feeding for quantitation of lipase activity and of the extent of gastric lipolysis. Fat balance studies were conducted during the last three days of each feeding regimen. The study showed that (1) there was marked hydrolysis of formula fat in the stomach during feeding of either medium-chain triglyceride formula or long-chain triglyceride formula (20% and 16%, respectively); (2) lipase activity in the gastric aspirates was less during feeding of medium-chain triglyceride formula than before the meal, which suggested stimulation of lipase secretion by long-chain fatty acid released from long-chain triglyceride formula fat or more rapid binding of lipase to ingested lipid in the medium-chain triglyceride formula; (3) fatty acid distribution in glycerides and free fatty acids showed preferential release of medium-chain (8:0, 10:0) and long-chain unsaturated (18:1, 18:2) fatty acids in the stomach. The low content of 8:0 and 10:0 in gastric triglyceride and free fatty acids suggested that medium-chain fatty acids were absorbed directly in the stomach.(ABSTRACT TRUNCATED AT 250 WORDS)

Body Weight↗
PubMed1988

Lipid composition of bovine teat canal keratin.

Keratin was obtained by scraping the teat canals of excised teats from 12 lactating and 12 dry cows immediately after slaughter. Teats from four lactating and four dry cows were also stored at -20 degrees C for 2 wk to assess whether keratin composition was affected by frozen storage. Lipids were extracted from keratin of individual teats with 2:1 chloroform-methanol. Neutral lipid classes were determined by TLC and fatty acids by capillary GLC. Total lipid content of keratin was 4% of wet weight. Lipid composition of keratin from fresh and frozen teats was similar. Differences were observed in several lipid classes between keratin from lactating and dry cows. Triglycerides were higher in keratin from lactating cows, 58.4 vs. 28.1%, whereas cholesterol was lower in keratin from lactating cows, 18.5 vs. 37.5%. Short-chain and medium-chain fatty acids were 3x lower in keratin from dry than from lactating cows; 18:2 and polyunsaturated fatty acids were 2x higher in keratin from dry than from lactating cows. Results indicated that large differences exist between the detailed lipid composition of keratin from dry and lactating dairy cows.

Animals↗
PubMed1987

Serum concentrations of thyroid hormones and extrathyroidal thyroxine-5'-monodeiodinase activity during lactation in the rat.

Serum thyroxine (T4) and triiodothyronine (T3) concentrations and T4-5'-monodeiodinase activity in liver and kidney homogenates were studied in Sprague-Dawley rats during lactation. Blood and tissue samples were collected from nulliparous and pregnant rats 2 days before delivery and from lactating rats 0, 2, 7, 12, 19, and 26 days after delivery. Litters were removed from half of the mothers immediately after delivery to create a postpartum nonlactating group for study at the same times. Pregnant rats had lower serum T4 and T3 concentrations and higher liver T4-5'-monodeiodinase activity than nulliparous females. Low serum T4 persisted throughout lactation but further decrease in serum T3 was observed. Activity of T4-5'-monodeiodinase in liver and kidney homogenates was significantly reduced during lactation as compared to nonlactating rats. Serum concentration of T4 and T3 and T4-5'-monodeiodinase activity in liver and kidney returned toward control values 5 days after weaning (Postpartum Day 26). Our findings suggest that the relative hypothyroid state observed during lactation in rats is associated with a significant decrease in T4 to T3 conversion in the liver and kidneys.

Animals↗
PubMed1987

Lipid composition of milk from mothers with cystic fibrosis.

Milk lipids from six mothers with cystic fibrosis were compared with milk lipids from six mothers without cystic fibrosis. Mean neutral lipids (in g/dL) were colostrum, 2.4; transitional, 2.9; mature milk, 2.9, suggesting that milk fat content was sufficient to support energy needs of the infant. Lipid class composition was normal, 98% being present as triglyceride. Cholesterol and cholesteryl ester concentrations were similar in the milk of both groups of lactating women. Phospholipid class distribution of cystic fibrosis milk was different from that in control milk. Approximately 85% of the lipids were present in six major fatty acids from 12:0 to 18:2 in both groups, indicating that the profile of most of the lipid was similar. The linoleic acid content of cystic fibrosis milk was decreased significantly to 75% of normal values. Other polyunsaturated fatty acids were elevated in cystic fibrosis milk. Concentrations of 16:2, 18:3, and several longer chain polyunsaturated fatty acids were twice that in the milk of the control women, suggesting increased delta 6-desaturation. Elevated proportions of several other polyunsaturated fatty acid metabolites suggested increased chain elongation to C20 and C22 polyunsaturated fatty acids. These differences in fatty acid patterns in cystic fibrosis milk were similar to differences found in blood lipid patterns of children with cystic fibrosis. These results suggest abnormal polyunsaturated fatty acid nutrition or metabolism in cystic fibrosis.

Cholesterol↗
PubMed1986

Radiotelemetry system for continuously monitoring temperature in cows.

Deep body temperature is an important index of the physiological status of an animal. A radiotelemetry system was developed to monitor continuously udder and body temperatures in cows under normal housing conditions. Radiotransmitters were crystal controlled blocking oscillators operating in the 27 MHz band. Functionally, the transmitters turned on and off in a pulsatile fashion with temperature encoded as the time interval between two pulses (nominally .5 s at 38 degrees C). Transmitters were powered by lithium batteries (6-mo lifespan) and were encapsulated in paraffin/Elvax (cylinder 6 cm X 3 cm diameter). Signals were detected using a radio receiver in the AM mode. Reception frequency was selected by computer. Each audio pulse was electronically converted to a digital pulse. A PDP 11/23 computer converted intervals between digital pulses to temperature values. As finally configured, the computer collected data from 12 transmitters every 1.4 min (1024 readings/transmitter/d). Temperatures were graphed continuously and stored on magnetic media for future analyses.

Animals↗
PubMed1985

Gastric lipolysis of milk lipids in suckling rats.

Fatty acid composition of the major lipid classes in stomach contents of suckling rats at 1, 5, 10, 17 and 20 days of lactation was compared to that of milk lipids. In milk, 98% of fatty acids were in triacylglycerols at all lactation times. Medium-chain fatty acid concentrations increased from 8% in colostrum to 26% at day 5. Fatty acid composition of stomach acylglycerols at all lactation times was different from that of milk triacylglycerols, containing less medium-chain fatty acids, 8:0 and 10:0. This preferential hydrolysis was also shown by higher concentrations of medium-chain fatty acids in the free fatty acid fraction. The lipolysis of medium-chain fatty acids from triacylglycerols resulted in the appearance of di- and monoacylglycerols with 50-100% higher amounts of 14:0 and 16:0. The similar fatty acid composition of products suggests that considerable lipolysis occurred in stomachs of suckling rats even at 1 day of age. Although there was a 10-fold increase in milk consumption, the extent of lipolysis was similar throughout the suckling period because of a parallel rise in lingual lipase levels.

Animal Population Groups↗
PubMed1985

Changes in plasma concentrations of thyroxine and triiodothyronine in beef steers fed different levels of propylthiouracil.

Three Latin-square trials were conducted to determine the effects of feeding the thyroid depressant propylthiouracil (PTU) on plasma concentrations of thyroxine (T4) and triiodothyronine (T3) in feedlot steers. In trial 1, four steers were fed 0, 1, 2 or 4 mg PTU/kg body weight daily during five 35-d experimental periods. In trial 2, eight steers were fed 0, .5, 1 or 2 mg PTU/kg body weight daily during five 28-d periods. In trial 3, three steers were fed 0, 1 or 4 mg PTU/kg body weight daily during the first 3 d in each of three 28-d periods. In general, feeding PTU caused increases in plasma T4 concentrations that peaked 5 to 7 d after feeding started. Concurrently, T3 concentrations tended to decrease when PTU was fed. The effects of PTU on hormone concentrations were apparent within approximately 1 to 4 h after PTU feeding started. Furthermore, when PTU was not fed, T4 and T3 concentrations appeared to have rhythmic cycles of 90 and 111 min, respectively, and PTU treatment appeared to interrupt this cyclical pattern. After the initial PTU response, the dose response relationship between PTU level and plasma hormone concentration was not linear. Both 4 and 2 mg PTU appeared to depress both T4 and T3 concentrations, suggesting direct inhibition of the thyroid gland and, for the 1-mg PTU treatment, T4 tended to stabilize at concentrations significantly greater than for 0 mg PTU, while T3 concentrations for 1 mg PTU were slightly lower than for 0 mg PTU.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

In vitro studies of the effect of propylthiouracil and ronnel on thyroxine-5'-monodeiodinase activity in steers.

This study compares in vitro effects of propylthiouracil (PTU) and ronnel on the conversion of thyroxine (T4) to triiodothyronine (T3) in liver and kidney from Angus steers. Tissues were homogenized and incubated with T4 (1.3 microM) in the presence of 0 to 59 microM PTU or 0 to 49.7 microM ronnel. The T3 generated during a 30-min incubation was measured by radioimmunoassay. It was found that 1.47, 5.9 and 59 microM PTU decreased T4 to T3 conversion in liver and kidney by 62 and 88, 71 and 100, and 81 and 100%, respectively. The inhibition caused by 1.47 and 5.9 microM PTU was overcome by addition of 2 mM dithiothreitol (DTT). Ronnel in concentrations of 1.24, 6.22, 49.7 microM decreased T4 to T3 conversion in liver and kidney 46 and 45, 51 and 72, and 78 and 95%, respectively. However, with ronnel, the addition of DTT caused further inhibition. A Lineweaver-Burk plot of the data obtained using .32 to 6.43 microM T4 with 1.47 and 5.9 microM PTU or 6.22 and 12.44 microM ronnel indicated that PTU is an uncompetitive inhibitor (Ki = 1.67 microM) and ronnel is a noncompetitive (Ki = 15.5 microM) inhibitor of T4-5'-monodeiodination. The data suggest that decreased conversion of T4 to T3 by PTU or ronnel may be responsible for the increased plasma concentrations of T4 and slightly decreased plasma concentrations of T3 reported in steers treated with levels of both PTU and ronnel that are associated with growth stimulation.

Animals↗
PubMed1985

Method for automatic, continuous blood sampling with remote alarm for clogged catheters.

An inexpensive blood sampling system is described that includes a remote alarm triggered by a decrease in rate of blood withdrawal. Additional modifications include design of a reliable sampling catheter and of a method for quickly and atraumatically replacing clogged catheters. This system has been used to collect continuous, integrated blood samples every 15 min for up to 72 h from cows. The alarm system is also useful for monitoring any flow in which minimum rate is critical, e.g., for column chromatography.

Animals↗
PubMed1985

Effect of dose of bovine growth hormone on milk composition: alpha-lactalbumin, fatty acids, and mineral elements.

Tissue-specific effects of bovine growth hormone on lactating dairy cows were examined by analysis of milk composition. Milk samples were from 6 cows that received subcutaneous injections of 0, 5, 10, 25, 50, and 100 IU/d of growth hormone in a Latin-square design. Samples from the last 5 d of each 10-d treatment period were pooled for analyses of milk components. Concentration of alpha-lactalbumin in milk increased progressively across the treatment range up to 32% above controls (1.30 mg/nl) at the 100 IU dose. Specific alpha-lactalbumin synthesis (expressed as a percent of total milk protein) was also increased. Secretion of de novo synthesized fatty acids (short and medium chain length) in milk was increased, but response plateaued between the 50 and 100 IU/d. Secretion of preformed (long-chain) fatty acids progressively increased across the entire dose range. Thus, the percentage of long-chain fatty acids in milk increased at the highest doses of hormone. Changes in fatty acid composition of milk were apparently related to energy status; the milk response to 50 and 100 IU/d of growth hormone caused cows to be in or near negative energy balance. Exogenous growth hormone did not affect the concentration of calcium, phosphorus, sodium, iron, copper, and manganese in milk. Results are consistent with growth hormone functioning in homeorhesis to coordinate the partitioning of all nutrients to support the increased secretion of milk and milk components.

Animals↗
PubMed1985

Lipids in milk and the first steps in their digestion.

Human milk contains 3.0% to 4.5% fat. The fat is contained within membrane-enclosed milk fat globules. The core of the globules consists of triglycerides (98% to 99% of total milk fat) whereas the globule membrane (which originates from the mammary secretory cell's Golgi and cell membranes) is composed mainly of phospholipids, cholesterol, and proteins. Milk fat content and composition change during lactation. Whereas the triglyceride level rises, the phospholipid and cholesterol concentrations decrease during the transition from colostrum to mature milk, resulting in an increase in the size of the milk fat globules. Digestion of milk fat depends on the consecutive action of several lipases. The first step is the partial hydrolysis of the milk fat globule core by lingual and gastric lipases in the stomach. Hydrolysis continues in the duodenum, where the bile salt-stimulated lipase of human milk and pancreatic lipase complete the process initiated in the stomach.

Animals↗
PubMed1984

Comparison of the phospholipid composition of breast milk from mothers of term and preterm infants during lactation.

Phospholipids were determined in milk on postpartum day 3 (colostrum) and days 7, 21, 42, and 84 from mothers of 18 very premature (26 to 30 wk gestation age), 28 premature (31 to 36 wk), and 6 term (37 to 40 wk) infants. Lipids were analyzed by thin-layer and gas-liquid chromatography. Total fat content increased during lactation whereas phospholipids and cholesterol declined. Phospholipids were separated from neutral lipids by column chromatography and distributed by preparative thin-layer chromatography into classes, sphingomyelin, phosphatidyl choline, serine, inositol, and ethanolamine for fatty acid analysis. Phospholipids exhibited a remarkable constancy in class percentages in milks from mothers giving birth prematurely or at term. Changes were observed in fatty acid composition within each of the phospholipid classes as secretion progressed from colostrum (3d) to transitional (7d) to mature milk (21, 42, 84d). These changes in phospholipid fatty acid composition occurred only during the first 3 wk of lactation. Mature milk was found to be relatively constant in phospholipid composition.

Colostrum↗
PubMed1984

Lipases and lipids in human milk: effect of freeze-thawing and storage.

Frozen storage is often used by milk banks to preserve expressed human milk for later use. Optimal storage and handling conditions which ensure minimum alteration of lipid composition have not been well defined. Therefore we investigated the effect of rapid freeze-thawing and storage conditions (-20 and -70 degrees C) on the free fatty acid (FFA) levels and on the activities of lipoprotein lipase (LPL) and bile salt-stimulated lipase (BSSL) in human milk. Since during mechanical expression leakage of serum components into milk may occur, we also investigated the effect of the presence of serum on human milk LPL during storage. Lipase activity levels were unaffected by rapid freeze-thawing (x3) followed by storage for 1 month at -20 or -70 degrees C. LPL activity (nmol FFA released/ml milk/min) was 414 +/- 128, 451 +/- 37, and 351 +/- 20 and BSSL activity (mumol FFA/ml milk/min) was 5.7 +/- 0.7, 5.5 +/- 0.8, and 5.7 +/- 0.2 in fresh, freeze-thawed, and stored milk, respectively. FFA levels (% of total lipid) were 3.01 +/- 1.05 and 10.3 +/- 1.6 in fresh-frozen milk stored at -70 and -20 degrees C for 5 months, and 3.78 +/- 1.08 and 13.60 +/- 1.25 in specimens of freeze-thawed (x3) before storage at -70 or -20 degrees C. Addition of serum had no effect on milk LPL at either temperature. We conclude that LPL and BSSL remain fully active during frozen storage of human milk and that milk fat is hydrolyzed at -20 degrees C but not at -70 degrees C. We suggest that banked human milk be stored routinely at -70 degrees C.

Bile Acids and Salts↗
PubMed1984

Circadian and ultradian temperature rhythms of lactating dairy cows.

Thermistors were implanted in the right front quarter of udder and peritoneal cavity of six lactating Holstein cows to investigate whether udder temperature is regulated independently of deep body temperature. Sequential measurements of udder, body, chamber, and outdoor temperatures were every 1.4 min (1024 readings/probe per 24 h) by digital computer. Cows were housed (except for short exercise periods) in a chamber at 16.7 +/- .3 degrees C, lights on 0730 to 1630 and 2100 to 0200 h. Temperature was monitored continuously for 5 days in three cows in early lactation and in three cows in late lactation. Udder temperature was closely correlated with body temperature (body and udder temperatures were 38.8 +/- .1 degree C). Five of six cows showed two patterns of temperature variation: a 24-h pattern with two troughs each day--minimum at 0930 to 1100 h, increase 1.0 degree C by 1200 to 1300 h, decline 1 degree C from 2000 to 2200 h, second minimum by 2100 to 2200 h, and constant elevation from 2300 to 0800 h (peak to trough, 1.23 +/- .09 degrees C); and superimposed upon the 24-h rhythm was an ultradian rhythm with an approximate 90 min period (peak to trough, .5 +/- .03 degrees C). Rhythmicity of udder and body temperatures should be considered in research on the chronobiology of milk secretion and mastitis.

Animals↗
PubMed1984

Triiodothyronine and thyroxine during gestation in dairy cattle selected for high and low milk production.

Circulating thyroxine, triiodothyronine, and prolactin were analyzed by radioimmunoassay from two groups of pregnant heifers representing genetic populations that differed by 685 kg milk in their first lactation. At 100 days of gestation, blood samples were taken every 15 min for prolactin assay and every 2 h to determine variations of thyroid hormone serum concentration from 0800 to 2000. Basal serum prolactin concentrations in the two genetic groups were not significantly different. A pattern was consistent for both triiodothyronine and thyroxine; concentrations were lower in the morning and higher during the afternoon. Serum triiodothyronine means were not different in the high-producing (1.84 ng/ml) and low-producing heifers (1.86 ng/ml). Serum thyroxine concentrations were significantly higher in the low-producing heifers (67.84 ng/ml) than in high-producing heifers (59.18 ng/ml). The higher thyroxine concentration in pregnant heifers with lower producing ability suggests a negative relationship of thyroxine to milk yield potential.

Animals↗