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G Breves

Publications and source records attributed to G Breves.

At least 55 records · Page 3Linked to original sources
PubMed1996

Mechanisms of phosphate uptake into brush-border membrane vesicles from goat jejunum.

This study concerns the uptake of inorganic phosphate into brush-border membrane vesicles prepared from jejunal tissues of either control or Ca- and/or P-depleted goats. The brush-border membrane vesicles showed a time-dependent accumulation of inorganic phosphate with a typical overshoot phenomenon in the presence of an inwardly direct Na+ gradient. The Na+-dependent inorganic phosphate uptake was completely inhibited by application of 5 mmol.1(-1) sodium arsenate. Half-maximal stimulation of inorganic phosphate uptake into brush-border membrane vesicles was found with Na+ concentrations in the order of 5 mmol.1(-1). Inorganic phosphate accumulation was not affected by a K+ diffusion potential (inside negative), suggesting an electroneutral transport process. Stoichiometry suggested an interaction of two or more Na ions with one inorganic phosphate ion at pH 7.4 Na+-dependent inorganic phosphate uptake into jejunal brush-border membrane vesicles from normal goats as a function of inorganic phosphate concentration showed typical Michaelis-Menten kinetic with Vmax = 0.42 +/- 0.08 nmol.mg-1 protein per 15S-1 and Km = 0.03 +/- 0.01 mmol.1(-1) (n = 4, mean +/- SEM). Long-term P depletion had no effect on these kinetic parameters. Increased plasma calcitriol concentrations in Ca-depleted goats, however, were associated with significant increases of Vmax by 35-80%, irrespective of the level of P intake. In the presence of an inwardly directed Na+ gradient inorganic phosphate uptake was significantly stimulated by almost 60% when the external pH was decreased to 5.4 (pHout/pHin = 5.4/7.4). The proton gradient had no effect on inorganic phosphate uptake in absence of Na+. In summary, in goats Na+ and calcitriol-dependent mechanisms are involved in inorganic phosphate transport into jejunal brush-border membrane vesicles which can be stimulated by protons.

Animals↗
PubMed1996

Effects of varying dietary calcium and phosphorus on growth and on composition of empty bodies and isolated bones of male kids.

Two experiments, each following a two-factorial design (2 x 2), were carried out using 12 and 13 male kids initially weighing about 10 kg. Concentrations per kg dietary dry matter were 10 vs. 4 g Ca and 4.5 vs. 2.0 g P in experiment 1 as compared to 10 vs. 17 g Ca and 4.2 vs. 2.5 g P in experiment 2, respectively. In experiment 1, low Ca intake significantly reduced empty body concentrations of ash, Ca and P with no negative effect on performance traits, whereas low P intake negatively affected feed intake, growth rate and feed conversion ratio, and reduced empty body concentrations of ash, Ca, P and Mg. Low intake of either one or both of these elements increased lipid concentrations of femora, pelvis and vertebrae. In these three bones, the respective ratios Ca/P, Ca/Mg and P/Mg were decreased by low Ca intake and, to greater extents, increased by low P intake. Low intake of both elements caused less pronounced changes than low intake of P alone. In experiment 2, lowering dietary P concentration to 2.5 g/kg dry matter significantly reduced growth rates without affecting empty body concentrations of ash, Ca, P or Mg. Almost doubling Ca intake significantly increased body concentrations of ash, Ca and P at both levels of P intake without influencing growth rates.

Animals↗
PubMed1996

[Prospects and limits of animal breeding from the physiological aspects].

Livestock breeding is characterized by substantial increases in performance in recent years. However, pathophysiological changes have to be considered when increased production levels will exceed maximal physiological capacities. Gastrointestinal adaptation processes of ruminants kept under aride grazing conditions are discussed in comparison with european sheep breeds. The high stress susceptibility in pigs which is genetically determined is taken as a further example to explain the onset of diseases on the basis of pathophysiological mechanisms being induced by breeding techniques. From this the necessity for a close cooperation between animal breeding and physiology has to be concluded.

Animal Husbandry↗
PubMed1996

Mechanisms of intestinal phosphorus absorption and availability of dietary phosphorus in pigs.

Phosphorus (P) is an essential component of many organic and inorganic compounds in vertebrates such as pigs. Therefore, adequate dietary P supply is important to meet daily requirements in order to maintain P homeostasis. Under normal circumstances regulation of P homeostasis occurrs by controlling the absorption rate of inorganic phosphate (Pi) in the upper small intestines and by renal Pi excretion. These processes are mainly mediated by parathyroid hormone (PTH) and calcitriol (1,25-dihydroxycholecalciferol, 1,25-(OH)2D3). If, for example, the Pi level in plasma decreases, renal calcitriol production is stimulated and higher amounts of the hormone are released into the circulation. Calcitriol increases Pi absorption from the intestinal tract by stimulation of a secondary active, sodium-coupled Pi-cotransport system in the upper small intestines. In addition, calcitriol is involved in the mobilization of bone and soft tissue P. Simultaneously, hypercalcemia develops, which can be induced by either increased intestinal Ca absorption and/or Ca mobilization from bone. Hypophosphatemia and hypercalcemia suppress PTH release from the parathyroid glands and thus minimize urinary Pi losses. The concerted action of increased/decreased circulating calcitriol/PTH on the intestinal tract, bone and kidneys normalizes Pi levels in plasma. With respect to adequate P supply in animal nutrition, it must be considered that utilization of dietary P not only depends on absorption capacity of the pig intestinal tract but also on differences in availability of dietary P between ingredients. In feedstuffs of plant origin most of the P is bound as phytate-P and can only be absorbed after enzymatic breakdown of phytic acid by phytases. Intrinsic phytase activity differs between plant materials such as wheat, wheat bran, barley and triticale with higher activities than found in maize and legume seeds subjected to thermal treatments. Supplementation of microbial phytase increased P digestibility more pronounced in those feedstuffs which showed very limited intrinsic phytase activity. At present, a digestibility of about 70% seems to be the upper level for digestibility of P from plant material. From the environmental point of view, an increased digestibility resulting from phytase supplementation offers the possibility to reduce the supplementation of phosphates and the concentration of total P in the diet. Therefore, the amount of P being excreted by the pig can be remarkably reduced. However, the first step for minimizing faecal P excretion should be to supply P in accordance with the animal's requirement.

Animals↗
PubMed1995

Mechanisms of intestinal phosphate transport in small ruminants.

In order to study the localization and mechanisms of intestinal phosphate transport in sheep and goats, unidirectional inorganic phosphate (Pi) flux rates across isolated stripped epithelial tissues were measured in vitro by applying the Ussing-chamber technique. In the first experiment the tissues were obtained from animals which had been kept on an adequate dietary P supply. In the second experiment the animals had either been kept on an adequate Ca and P supply or were Ca- and/or P-depleted. Significant net Pi absorption was measured in all segments of the small intestine and in the proximal colon of sheep and in the duodenum and jejunum of goats. Since the experiments were carried out in the absence of any electrochemical gradient, this clearly indicates the presence of active mechanisms for Pi transport in the intestinal tract of small ruminants. In sheep jejunum, reduction of mucosal Na concentration to 1.8 mM or serosal application of ouabain (0.1 mM) resulted in significant decreases of net Pi absorption of the same order of magnitude, indicating that about 65% of active Pi transport in sheep jejunum is mediated by a Na-dependent active transport mechanism. The mechanism for the remaining Na(+)-independent active Pi transport has not yet been identified. Dietary P depletion caused hypophosphataemia and induced a significant stimulation of net Pi absorption in goat duodenum and jejunum. This increase was independent of dietary Ca supply and was not associated with increased plasma calcitriol concentrations. This suggests substantial differences in hormonal regulation of Pi transport in small ruminants in comparison with single-stomached species.

Animals↗
PubMed1995

Binding properties of goat intestinal vitamin D receptors as affected by dietary calcium and/or phosphorus depletion.

The binding capacity (Bmax) and the affinity (Kd) of the intestinal vitamin D receptor (VDR) have been studied using mucosa preparations from the duodenum, jejunum and proximal colon of male growing goats which had been kept in a two-factorial (2 x 2) trial on Ca and/or P deficient diets for 9 weeks. This treatment resulted in significant changes of different parameters of Ca and P homeostasis. Irrespective from the level of Ca intake, P depletion caused significant hypophosphatemia with corresponding hypercalcemia. In both Ca depleted groups the calcitriol concentrations in plasma significantly increased by more than 100% in comparison with normal Ca supply. No changes were recorded for plasma calcitriol concentrations in response to P depletion with an adequate Ca supply. Plasma PTH levels were only increased significantly in Ca depletion with adequate P supply. Irrespective of different feeding regimens, the highest Bmax values were found in the jejunum. In all intestinal segments tested, the Bmax values were significantly decreased by P depletion as compared with an adequate P supply. No effects on the Bmax of VDR were observed in response to changes of Ca supply. The Kd values of the VDR were neither affected by different intestinal localizations nor by Ca and/or P depletion. From the present results, it has to be concluded that the physiological relevance of VDR down-regulation may not be related to P homeostasis rather than to Ca homeostasis by minimizing the hypercalcemia induced by P depletion.

Animals↗
PubMed1995

Transepithelial transport of short chain fatty acids and their metabolism in pig hindgut.

In vitro experiments in Ussing chambers were performed in order to study the transport as well as the intraepithelial metabolism of short chain fatty acids in the caecum, proximal and distal colon. Stripped epithelial tissues were incubated in isotonic buffer solutions. SCFA were only present in the mucosal solutions at a concentration of 60 mmol/l consisting of 60% acetate, 25% propionate and 15% butyrate at the beginning of each flux rate measurement. For osmotic reasons SCFA were completely replaced by gluconate in serosal buffer solutions. The tissues were incubated under short-circuit current conditions for 1 h. In addition, with epithelia from the proximal colon flux rate measurements were also performed after setting the transepithelial potential difference (PD) to 25 mV with the serosa being positive. At the end of each 1h flux period samples were taken from the mucosal and serosal solutions for HPLC analysis of SCFA concentrations. SCFA transport and rate of intraepithelial metabolism were calculated from mucosal uptake and serosal release during the experimental periods. In the presence of 2 cm2 serosal area of the tissues, mucosal SCFA uptake ranged between 53 and 75 mumol with no change of molar SCFA proportions irrespective of hindgut segment. Voltage clamp condition did not influence mucosal SCFA uptake indicating the presence of electroneutral transport mechanisms. Serosal SCFA release ranged between 105 and 126 mumol thus exceeding mucosal loss. In serosal solutions molar butyrate proportions were significantly lower in comparison with mucosal solutions. This was accompanied by slight increases of molar acetate proportions indicating intraepithelial butyrate cleavage.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

The application of a semi-continuous colon simulation technique (Cositec) for studying the effects of clindamycin on microbial hindgut metabolism.

The semi-continuous colon simulation technique was used as an experimental in vitro model to study potential effects of clindamycin application on basic parameters of microbial hindgut metabolism. Hindgut contents from fistulated pigs kept on conventional diets were used as substrates for incubation. Measurements on reproducibility demonstrated the colon simulation technique as a suitable in vitro method to characterize microbial hindgut metabolism and those factors potentially influencing microbial fermentation. Application of clindamycin resulted in disturbances of microbial steady state metabolism and time- and dose-dependent decreases of SCFA production rates with significant reductions of molar butyrate proportions to almost zero. These effects can be related to the onset of functional disturbances of hindgut function under in vivo conditions since butyrate is an essential trophic factor for colonocytes. In addition, clindamycin induced increases in lactate production with a shift towards D-lactate. The relevance of these changes for hindgut function have to be elucidated in further experiments.

Animals↗
PubMed1994

Colonic absorption and bioavailability of the pentapeptide metkephamid in the rat.

The concept of delivering systemically active peptide drugs to the colon in order to improve their oral absorption requires reasonable peptide permeability of the large intestinal wall and stability against the activity of the colonic microflora. In addition, the role of hepatic extraction needs to be addressed. In this study the absorption of the pentapeptide metkephamid following single pass perfusion of rat ascending colon was investigated by monitoring its disappearance from the large intestine and simultaneous appearance in the portal vein, the hepatic vein and the aorta. In addition its stability against colonic microflora was tested in vitro using pig caecal contents. Metkephamid was absorbed from the large intestine and appeared in the blood circulation; peptide concentrations in the portal vein increased over-proportionally with increasing perfusate concentrations (0.1-4.6 mmol/L) from 0.19 microgram/mL +/- 0.12 (SD, n = 7) to 31.6 micrograms/mL + 20.65 (SD, n = 4), respectively, and thus suggesting a saturable transport or metabolism. Concentrations in the hepatic vein were significantly lower than in the portal vein, hepatic extraction ratios were 0.35 +/- 0.14, 0.61 +/- 0.18 and 0.62 +/- 0.28 (SD, n = 4) for 0.1, 0.5 and 1.0 mM metkephamid perfusate concentrations, respectively. In the anaerobic colon metabolism model the degradation half-life of the peptide was 14.9 hours, thus, indicating relative stability in the bacterial environment of the colon. The results of the present study encourage further investigations on colonic delivery of peptide drugs.

Animals↗
PubMed1993

Evidence for vitamin D-independent active calcium absorption in newborn piglets.

The role of 1,25-dihydroxycholecalciferol (calcitriol) for intestinal calcium (Ca2+) absorption was studied in newborn (< 1 week old) and weaned piglets (> 6 weeks old). In both groups, normal piglets and piglets suffering from inherited pseudo vitamin D-deficiency rickets, type I (PVDRI) were used. In this inherited disorder, renal production of calcitriol is absent. Plasma samples were assayed for calcitriol and total Ca, and dissociation constants (Kd) and maximum binding capacities (Bmax) of intestinal calcitriol receptors were determined under equilibrium conditions at 4 degrees C. Unidirectional Ca(2+)-flux rates were measured across stripped duodenal mucosae in Ussing chambers in the absence of electrochemical gradients. The plasma calcitriol concentrations of neonatal (26.5 +/- 7.1 pg/ml, n = 11; mean +/- SEM) and weaned PVDRI piglets (18.8 +/- 5.7 pg/ml, n = 8) were unphysiologically low and differed significantly from control animals (83.6 +/- 14.8 pg/ml, n = 8, and 86.9 +/- 9.6 pg/ml, n = 11, respectively). However, newborn PVDRI piglets had normal plasma Ca levels at least during the first days of life. They became hypocalcemic and developed clinical symptoms of rickets during the following weeks. In newborn PVDRI and control piglets, Bmax was significantly lower (84 +/- 28 fmol/mg protein and 127 +/- 55 fmol/mg protein, n = 9, respectively) than in weaned piglets (741 +/- 82 fmol/mg protein, n = 9, and 778 +/- 121 fmol/mg protein, n = 8, respectively). Significant net Ca(2+)-fluxes were found in both newborn PVDRI and control piglets (88.8 +/- 25.1 nmol.cm-2 x h-1, n = 6, and 86.5 +/- 10.5 nmol.cm-2 x h-1, n = 9, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

25-Hydroxyvitamin D3 1-alpha-Hydroxylase↗
PubMed1993

The application of 13C-labelled short chain fatty acids to measure acetate and propionate production rates in the large intestines. Studies in a pig model.

The production rates of acetate and propionate were measured in the large intestine of pigs by applying the single injection technique of (1-13C)acetate and (1-13C)propionate. Both acids were injected individually through the caecal cannula and for both acids the experiments were performed during two diets with different crude fibre contents. For acetate the increase of dietary crude fibre from 5.1 to 18.3% of dry matter resulted in an increase of mean production rate from 27.4 to 56.2 mmol/h. The mean propionate production rate was raised from 3.6 to 7.0 mmol/h when the dietary crude fibre was increased from 4.4 to 24.3%. From both experimental series the contribution of hindgut fermentation to energy maintenance requirement were estimated to be in a range between 7 and 40% depending on the body weight of the animals and the percentage of dietary crude fibre.

Acetates↗
PubMed1992

Effect of energy metabolism on 13C/12C-ratios in milk fat and lactose of cows.

1. The ratios of stable carbon isotopes 13C/12C in milk constituents of Holstein dairy cattle were investigated by mass spectrometry. 2. Under physiological feeding conditions the natural abundance of 13C in lactose was greater than in milk fat. 3. Reduction of energy intake diminished the abundance of 13C in lactose resulting in values similar to those of fat. 4. It is suggested that by comparing the 13C/12C ratios in milk fat and lactose the metabolic energy state of cows may be rated.

Animals↗
PubMed1992

Effect of niacin supplementation on the concentration of niacin in rumen and duodenal digesta and in whole blood of sheep.

1. Niacin concentrations in rumen liquor, duodenal digesta and blood, and daily duodenal flow of niacin were measured in four wethers which were fed an oatstraw grain concentrate diet (with normal niacin content) or an oatstraw maize diet (with low niacin content). The effect of an intraruminal supplementation of 2 mmoles nicotinic acid (NIA) or nicotinamide (NAM) on concentrations of NIA and NAM in gastrointestinal contents and blood and on daily duodenal flow of NIA and NAM was studied. The animals were equipped with rumen fistula and duodenal re-entrant cannulae. 2. NIA concentration in strained rumen liquor was 384 and 264 nmol/ml and daily duodenal flow of niacin was 616 and 528 mumoles/d in animals fed normal or low niacin diet, respectively. Intraruminal administrations of 2 mmoles of NIA or NAM raised NIA concentration in strained rumen liquor for approximately 6 h. About 20% of the administered dose of NIA or NAM passed out of the rumen and resulted in a 41% increase in daily duodenal flow of niacin. The remaining 80% of the administered dose of NIA or NAM disappeared from rumen liquor without being washed out. 3. Supplemented NAM was rapidly hydrolyzed to NIA and ammonia when administered into the rumen. 4. NAM concentration in blood appeared to be unaffected by the dietary content of NIA or by niacin supplementation. 5. The NIA concentration in strained rumen liquor was positively related with niacin content of the diet. Increases in duodenal flow of niacin had no marked effect on concentration of NAM in blood. It appeared that feeding diets with different NIA content affected apparent niacin synthesis in the rumen.

Animal Feed↗
PubMed1990

Binding properties of duodenal 1,25-dihydroxyvitamin D3 receptors as affected by phosphorus depletion in lactating goats.

1. Capacity and affinity of duodenal 1,25(OH)2D3 receptors were measured in P depleted goats and in control animals kept on an adequate P supply. Plasma concentrations of Pi, Ca and vitamin D3 metabolites and activity of plasma alkaline phosphatase were measured to characterize the effects of P depletion. 2. During P depletion plasma Pi concentrations decreased significantly whereas plasma Ca and alkaline phosphatase activity increased. No changes were recorded for plasma vitamin D3, 25OHD3 and 1,25(OH)2D3 concentrations. 3. P depletion resulted in a significant decrease of the equilibrium dissociation constant Kd of duodenal 1,25(OH)2D3 receptors without affecting the maximum binding capacity.

Alkaline Phosphatase↗
PubMed1989

Concentrations of volatile fatty acids and acetate production rates in the forestomachs of grazing camels.

1. Concentration profiles of volatile fatty acids (VFA), fluid volumes and turnover rates, and acetate production rates were measured in two different seasons in the forestomachs of four fistulated dromedary camels grazing in the Kenyan thornbush savannah. 2. VFA profiles and average concentrations were similar under both feeding conditions but, due to a smaller fluid turnover, VFA outflow to lower gastric sections in the dry season was reduced by almost 50%. 3. The mean acetate production rate fell from 2234 mmol/hr in the green season to 816 mmol/hr in the dry season, i.e. by approximately 64%.

Acetates↗
PubMed1989

Role of 1,25-(OH)2D3 during pregnancy; studies with pigs suffering from pseudo-vitamin D-deficiency rickets, type I.

Biochemical parameters of Ca homeostasis in fetal and maternal plasma and placental transfer of Ca, Pi and vitamin D metabolites were measured during pregnancy and at parturition. Control pigs and pigs with inherited pseudo-vitamin D-deficiency rickets, type I (PVDR), which are devoid of renal calcitriol production, were used. Although sows with PVDR normally require treatment with massive doses of vitamin D at intervals of 4 weeks to stabilize Ca and Pi concentrations in plasma, these plasma parameters tended to normalize during the first 3 months of pregnancy when the vitamin D treatment was discontinued about 4 weeks before conception. In homozygote sows plasma calcitriol concentrations remained unphysiologically low and the 25OHD3 concentrations increased steadily during pregnancy reaching higher levels than those found in control sows. Despite hypocalcaemia and hypophosphataemia of the homozygote sows at term, fetal Ca and Pi concentrations were normal. This demonstrated a higher feto-maternal concentration gradient in PVDR pigs than in control pigs. It is concluded that maintenance of Ca and Pi homeostasis of the feto-maternal system, including active transplacental transport in pigs, is at least partly independant from calcitriol.

Alkaline Phosphatase↗