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Biomedical subjects

A S Larsen

Publications and source records attributed to A S Larsen.

11 recordsLinked to original sources
PubMed1994

Volume-homeostatic mechanisms in humans during graded water immersion.

The purpose of this experiment was to investigate whether a graded increase in cardiac distension induced by graded water immersion (WI) could be related to endocrine responses and renal sodium excretion (UNaV). On 3 separate days, nine healthy males were investigated in the upright seated position before, during, and after 3 h of WI to the midchest (CI) or to the neck (NI) or during control. Central venous pressure increased twice as much during NI as during CI. UNaV increased to the same extent during NI compared with CI, whereas urine flow rate, solute-free water clearance, and osmotic excretion increased more during the 2nd h of NI than during CI. During NI, the plasma concentration of atrial natriuretic peptide (ANP) increased twice as much as during CI. The plasma concentrations of aldosterone and norepinephrine were decreased in a similar manner during NI compared with CI. In conclusion, graded cardiac distension induced by graded WI and accompanied by a graded release of ANP was not accompanied by a graded increase in UNaV. Thus either a cardiac distension pressure of approximately one-half of that during NI is enough to induce a maximum UNaV during WI or other stimuli are important. Furthermore, aldosterone and norepinephrine are probably more important mediators of the natriuresis of WI in humans than is ANP.

Adult↗
PubMed1993

Food intake adjustments of chicks: short term reactions of genetic stocks to deficiencies in lysine, methionine or tryptophan.

1. Growth, food intake, and food preference were measured in two experimental lines (White Rocks and White Leghorns) of chickens fed diets varying in content of lysine, methionine, or tryptophan. Diet A was balanced in all amino acids, while the remaining 6 diets were moderately (approximately 30%) or slightly (approximately 15%) deficient in either lysine, methionine, or tryptophan relative to NRC recommendations for broiler diets. 2. Body weight and food utilisation efficiency of White Leghorns at 10 d of age were not affected by diet, whereas the lower concentrations of lysine and methionine depressed these traits in White Rocks. 3. Tryptophan deficiency reduced food intake of White Leghorns, but not White Rocks. 4. With choice feeding of balanced and deficient diets from day 10 to 16, preferences between the diets were minimal for White Leghorns, whereas for White Rocks there was an almost immediate preference for the balanced diet, followed by lack of preference or preference for the deficient diet. 5. Apparently for some genetic stocks there is rapid adjustment to deficiencies in these amino acids with overconsumption, followed by compensation for preference of the balanced diet. The response, however, will vary depending on the deficient amino acid.

Animal Feed↗
PubMed1993

Research note: resistance of chickens to an outbreak of necrotic enteritis as influenced by major histocompatibility genotype and background genome.

An outbreak of necrotic enteritis occurred in chickens that were B13B13 or B21B21 at the MHC in sublines of lines selected for high (HA) and low (LA) antibody response to sheep erythrocytes. Percentage mortality and hen-day egg production, although similar for both background genomes, were different for MHC genotypes. Mortality was 6% for B21B21 and 15% for B13B13 types. Although hen-day egg production for both types declined from about 76 to 50%, the decrease occurred earlier but recovery of survivors was faster in B13B13 than in B21B21 pullets.

Animals↗
PubMed1993

Responses of dwarf and normal chickens to feed restriction, Eimeria tenella infection, and sheep red blood cell antigen.

Relationships among stress responses, habituation to feed restriction, resistance to Eimeria tenella, and antibody response to SRBC were studied in dwarf and normal White Plymouth Rocks. Transfer of chicks at 22 days of age from starter to developer batteries resulted in an increase within 24 h of heterophil:lymphocyte (H:L) ratios of chicks of both genotypes. Restriction of feed intake from ad libitum (AL) to 60% of ad libitum reduced body weight and increased size of the crop-esophagus. As measured by H:L ratios, the effect of adapting to the 60% feed restriction dissipated between 12 and 16 days after initiation. Release of 60% restricted chicks to 80% of ad libitum also elicited a stress response as measured by H:L. These effects were noted in both dwarf and normal chicks. Time required for chicks on restriction to consume their daily allotment was curvilinear with a plateau occurring at a smaller value for dwarf than for normal chicks. Neither feeding regimen nor genotype had an effect on antibody response to SRBC. Resistance to E. tenella was greater in normal than dwarf chicks and greater for restricted than ad libitum chicks.

Age Factors↗
PubMed1993

Self-selection among diets differing in methionine content by chickens of different lines.

Two trials were conducted to compare the ability of chickens from different genetic lines to select among diets differing in methionine. In Trial 1, chicks from White Plymouth Rock (HW) and White Leghorn (HA) lines were offered a choice of diets containing .85, .58, or .44% methionine from 1 through 7 days of age. In Trial 2, a slow-growing line of White Plymouth Rocks (LW) was used in addition to the same lines used in Trial 1. A choice of the three diets was offered from 1 through 13 and from 20 through 23 days of age. During the period from 14 through 19 days of age, all chicks were fed the .44% methionine diet. In both trials, Line HW chicks first exhibited a dietary preference at 5 days of age. Line HA chicks did not discriminate among diets in either trial when given a choice from 1 day posthatch. They did, however, exhibit a preference starting on Day 20 in Trial 2 (after being fed the deficient diet). No dietary preferences were exhibited by chicks from Line LW. Results of these trials showed that selection among diets varying in methionine content was influenced by genotype, age, nutritional state of the chick, and their interactions.

Age Factors↗
PubMed1992

Correlated responses in lines of chickens divergently selected for fifty-six-day body weight. 2. Organ growth, deoxyribonucleic acid, ribonucleic acid, and protein content.

Growth of organs relative to body weight and cellular protein, RNA, DNA, and cell unit size of breast muscle, liver, and small intestinal tissue were measured in females from four lines of chickens. Two lines had undergone 32 generations of divergent selection for 56-day body weight, and the other two lines were derived by sampling the first two lines at Generation 28 and relaxing selection for the next five generations. The diet used in the present experiment was the same diet under which selection was practiced (20% crude protein and 2,685 kcal of ME/kg). Comparisons at common chronological ages and a common body weight revealed that supply organ weights, especially that of the small intestine, were associated with subsequent growth of demand organs. Although the upper gastrointestinal tract was also important in this respect, it was more susceptible to influences such as feed intake. Selection for juvenile body weight resulted in correlated changes in cell size of breast muscle but not liver and small intestine. Muscle increased posthatch as cells underwent hypertrophy but liver and small intestine grew chiefly by hyperplasia.

Animals↗
PubMed1992

Correlated responses in lines of chickens divergently selected for fifty-six-day body weight. 3. Digestive enzymes.

Levels of amylase, trypsin, chymotrypsin, and lipase in the pancreas and small intestinal chyme were measured in females from four lines of chickens. Two of the lines had undergone 32 generations of divergent selection for 56-day body weight, and in the other two lines selection for high or low weight had been relaxed for 5 generations. The diet used in the present experiment was that under which selection had been practiced (20% crude protein and 2,685 kcal of ME/kg). Comparisons between divergently selected lines at common ages revealed higher enzyme levels for high- than low-weight lines. When comparisons were made at a common body weight (80 +/- 5 g) there were no differences between lines. These results suggested that correlated responses in feed intake were mediating the regulation of digestive enzyme levels in the pancreas and in intestinal chyme of growth-selected lines of chickens. Chicks from high-weight lines had elevated enzyme levels after a mild feed restriction compared with those provided ad libitum access to feed. It was hypothesized that hyperphagia associated with the high-weight lines in combination with a mild feed restriction and the associated meal feeding stimulated synthesis and secretion of digestive enzymes.

Age Factors↗
PubMed1987

A tissue-specific transcriptional enhancer is found in the body of the HLA-DR alpha gene.

We mapped cis-acting regulatory elements in the HLA-DR alpha gene, which encodes the monomorphic subunit of the HLA-DR heterodimer. Genomic fragments of HLA-DR alpha were placed 5' or 3' to the chloramphenicol acetyltransferase reporter gene, the transcription of which was initiated from the Herpes simplex thymidine kinase promoter. In transient expression assays, fragments from the body of the HLA-DR alpha gene were able to increase chloramphenicol acetyltransferase activity in a position-, orientation-, and promoter-independent yet tissue-specific fashion. These HLA-DR alpha cis-acting regulatory elements contain previously identified DNase I-hypersensitive sites and DNA sequences homologous to those found in other eukaryotic transcriptional enhancers.

Acetyltransferases↗
PubMed1987

Chromatin structure of the HLA-DR alpha gene in different functional states of major histocompatibility complex class II gene expression.

We utilized DNase I hypersensitivity mapping to study chromatin structure within the HLA-DR alpha gene. We found a single DNase I-hypersensitive site coinciding with the HLA-DR alpha gene promoter in all cells studied. Moreover, in cells that constitutively express HLA-DR, two additional DNase I-hypersensitive sites were observed. These lie within the first intron of the HLA-DR alpha gene and encompass DNA sequences that share homologies with regulatory loci of the immunoglobulin and immune response genes, as well as with core enhancer consensus sequences.

Base Sequence↗