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Biomedical subjects

G Breves

Publications and source records attributed to G Breves.

At least 73 records · Page 4Linked to original sources
PubMed1988

Flux of inorganic phosphate across the sheep rumen wall in vivo and in vitro.

Experiments were done in vivo and in vitro to study the flux of inorganic phosphate (P1) across the rumen wall in sheep. The technique of the temporarily isolated and washed reticulo-rumen was applied to measure P1 net flux at nine different P1 concentrations in the buffer solutions introduced into the reticulo-rumen for 1 h. Six sheep were either P replete (4.25 g P d-1) or in a P-depleted state (1.05 g P d-1). Under both dietary treatments P1 net secretion into the reticulorumen was found at P1 concentrations between 0.1 and 2.2 mmol l-1 whereas P1 net absorption was observed at P1 concentrations between 4.1 and 15.8 mmol l-1. There were positive linear relationships between P1 concentration and P1 net flux for the whole concentration range studied in repleted and in depleted sheep. There were no indications of active transport components or saturation phenomena. Unidirectional P1 fluxes were then measured in Ussing chambers with 32P using a total of 100 rumen wall epithelia obtained from eighteen sheep of different ages. No P1 net flux was found under short-circuit conditions. Experiments with changed potential differences (+25 or -25 mV at serosal side) showed that P1 flux was influenced by the electrical gradient indicating electrogenic phosphate ion diffusion without involvement of active transport processes. Critical evaluation of the obtained unidirectional flux ratios suggests that part of the P1 flux was electroneutral, e.g. by ion exchange or cotransport. The results from these studies show that the reticulo-rumen substantially contributes to phosphate absorption from the sheep gastrointestinal tract.

Aging↗
PubMed1988

Flux of calcium across the sheep rumen wall in vivo and in vitro.

Experiments were carried out in vivo and in vitro to study the flux of Ca2+ across the sheep rumen wall. Buffer solutions with five different Ca2+ concentrations in the range 0.2-3.6 mmol l-1 were introduced into the isolated, emptied and washed reticulo-rumen for 1 h to determine Ca2+ net flux. Phosphate concentrations were either kept constant at 8 mmol l-1, or varied so as to maintain a constant phosphate/Ca2+ ratio of 2:1. Under both conditions there was a Ca2+ net secretion into the rumen at Ca2+ concentrations below approximately 1 mmol l-1 whereas Ca2+ net absorption occurred at higher Ca2+ concentrations and linearly increased with increasing Ca2+ concentrations. When phosphate concentrations were reduced to 4.3 and 0.6 mmol l-1 (Ca2+, 3 mmol l-1) Ca2+ net absorption was reduced by about 50% and completely abolished, respectively. The unidirectional (mucosal-to-serosal or serosal-to-mucosal) Ca fluxes in vitro, JCams and JCasm, were measured in Ussing chambers with computer-controlled voltage clamp. Under short-circuit current conditions (Ca2+ and phosphate, 2 mmol l-1) there was a significant net flux of Ca2+ from the mucosal to the serosal side. This net flux of Ca2+ was abolished when ouabain was added to the serosal solution, indicating that the unidirectional Ca2+ flux JCams and, hence, the net flux of Ca2+ was dependent upon active Na+ transport accomplished by the Na, K-ATPase system. Under voltage clamp conditions, the net flux of Ca2+ was greatly increased at a potential difference PD = -25 mV (serosa negative) but disappeared at PD = +25 mV (serosa positive). Analysis of the unidirectional Ca2+ fluxes JCams and JCasm under varying potential differences indicated that both Ca2+ fluxes consisted of a PD-dependent and a PD-independent component. The results show that the reticulo-rumen participates in Ca2+ absorption in sheep.

Animals↗
PubMed1986

The passage of protozoa from the reticulo-rumen through the omasum of sheep.

1. Protozoa in rumen contents and omasal effluent of growing wethers were counted. The wethers were equipped with rumen and abomasal cannulas, and omasal sleeves attached to the omasal-abomasal orifice. Rumen fluid dilution rates were elevated by continuous infusions of hypertonic mineral solutions (3-4 litres/d) for 24 d. Rumen contents and omasal effluent were sampled between 9 and 21 h during the last 10 d of each experiment. 2. Protozoal concentrations in omasal effluent were only 0.2-0.3 those found in the rumen under normal conditions. The ratio of protozoal concentrations in rumen: those in omasal effluent was for small Diplodinium spp. 4.6 (SD 0.9), for Ophryoscolex spp. 4.3 (SD 1.0), for Dasytricha ruminantium 4.0 (SD 0.5), for Isotricha spp. 3.8 (SD 0.8), for Entodinium spp. 3.6 (SD 0.9) and for Polyplastron multivesiculatum 2.6 (SD 0.5). 3. Elevation of rumen fluid dilution rate by 20 and 55% respectively, increased protozoal concentrations in omasal effluents from 22 to 33% and from 31 to 47% those in rumen contents. The apparent residence times of protozoa in the rumen were decreased 50% by the infusion of a mineral-salt solution. The increase in rumen fluid dilution rate had no significant effect on concentrations of protozoa in the rumen or on the differences of the apparent residence times between different species. The apparent residence time of holotrichs remained the same before and after infusion of the mineral-salt solution. 4. Apparent residence times of individual species of protozoa in the rumen were, under normal feeding conditions, 2.55 d, and were four to six times longer than the mean residence time of CrEDTA in the rumen.

Animals↗
PubMed1982

Thiamin compartment models in healthy sheep.

Adult sheep received a single intravenous injection of 35S-thiamin. Blood and urine samples were taken at short intervals for the following 180 minutes and analyzed for 35S-radioactivity. Tracer disappearance from blood followed three-exponential functions. It was shown by computer simulation of different compartment models that a serial as well as a parallel three-compartment model would adequately describe 35S-thiamin disappearance from blood whereas a cyclic arrangement of the three compartments can be excluded. Total tracer excretion rates exceeding experimentally determined urinary excretion suggest the existence of a fourth compartment with nor or extremely small tracer return during the experimental period.

Animals↗
PubMed1981

Effects of increased blood ammonia concentrations on the concentrations of some metabolites in rat tissues.

Rats were given ammonium chloride intravenously (5 and 10 mg per 100 g body weight) and sacrificed 30 sec, 5 min and 30 min after injection. Ammonia concentrations were determined in brain, liver, skeletal muscle and epididymial fat, and glycogen, glucose, pyruvate, lactate, ATP and cyclic AMP were assayed in brain, liver and muscle. In control animals, muscle and fat showed a high capacity for ammonia accumulation. After injection of NH4Cl the ammonia concentration increased in all tissues analysed, particularly in muscle and fat, where ammonia concentrations remained elevated for 30 min. In brain, glycogen was reduced whereas glucose, pyruvate, lactate and cyclic AMP levels were raised. In liver, glycogen was lower and glucose higher than in controls. ATP concentrations were unchanged in both tissues. In muscle samples taken 30 sec and 5 min after dosing, glycogen concentrations were not affected but glucose, pyruvate and lactate concentrations were reduced and ATP concentrations were increased. In muscle samples taken after 30 min metabolite concentrations were normal again but glycogen concentrations had dropped.

Adenosine Triphosphate↗
PubMed1980

Glucocorticoid levels in blood plasma of normal and preketotic cows.

Twenty pregnant cows were kept in two feeding groups. Feeding regimens were designed to induce high milk production (16 kg milk/day) in group I and low production (2 kg/day) in group II. Milk weights were corrected for fat content. After onset of lactation, each cow was fed according to actual production level. Four cows from group I and two from group II developed clinical ketosis during the first few weeks of lactation. Blood taken weekly from all animals from about 2 weeks before until an average of 7 weeks after parturition was assayed for glucocorticoids, glucose and ketone bodies. Average plasma cortisol concentration for both groups was 4.5 +/- 2.6 ng/ml (range from 0 to 13 ng/ml). Plasma cortisol levels in cows which later developed clinical ketosis were not different from those in cows that remained healthy. There was, however, a positive correlation between blood glucose and plasma cortisol, and a negative correlation between blood ketone bodies and plasma cortisol. The findings suggest that adrenal cortical activity is interrelated with onset of ketosis although plasma cortisol levels appear unsuitable for identifying ketotic cows prior to clinical manifestation of the disorder.

Acidosis↗
PubMed1980

Thiamin balance in the gastrointestinal tract of sheep.

Six 5- to 6-month-old sheep fitted with rumen fistulas and reentrant cannulas in the duodenum and in the ileum were adapted to two dies low in thiamin and containing different percentages of urea nitrogen. The sheep were subjected to seven thiamin balance experiments, with continuous feeding and total collection of duodenal and ideal contents and feces for periods of 6 day each. Thiamin and dry matter were determined in aliquots of collected digesta and feces. Daily thiamin intake was always less than .3 mg, but average daily flow of thiamin into the duodenum was between 1.53 and 3.46 milligrams. Microbial net synthesis of thiamin in the forestomach system was between 1.44 and 3.23 mg/day, so 90 to 96% of thiamin entering the duodenum was of microbial origin. Disappearance of thiamin from the small intestines approximately equaled thiamin net synthesis in the forestomachs, indicating high absorption of microbially produced thiamin. In five experiments, thiamin balance in the large intestines was positive, but no measurements were made of thiamin breakdown within, and absorption from, the large intestines.

Animals↗
PubMed1979

The effect of ammonium ion concentration on the activity of adenylate cyclase in various rat tissues in vitro.

The effects of three different ammonium ion concentrations (0.143; 1.43; 14.3 mmol .1(-1)) on adenylate cyclase activities in liver, muscle, fat and brain tissue in vitro were studied in the rat. At physiological levels, ammonium ions reduced adenylate cyclase activity in liver and fat by about 30%, did not affect enzyme activity in muscle tissue but increased adenylate cyclase activity in brain by 40%. Similar effects were observed at higher ammonium ion concentrations though there were no statistically significant correlations between ammonium ion concentration and the degree of change of enzyme activity.

Adenylyl Cyclases↗
PubMed1979

Disappearance from blood and urinary excretion of 35S-thiamin in sheep. A kinetic study.

In seven experiments with two adult sheep a single dose of 35S-thiamin was injected intravenously. Blood and urine samples were taken at short intervals after dosing and analyzed for 35S-radioactivity. The data obtained were subjected to a curve fitting computer program. The disappearance of 35S-thiamin from blood followed a three-exponential function; the average half-times of the three components were 0.4, 3.7 and 93.7 minutes. Urinary excretion of the tracer was also three-exponential and amounted to 19--32% of the injected dose over 150 minutes.

Animals↗