PubMed Health⌕ Search

Biomedical subjects

F W Heaton

Publications and source records attributed to F W Heaton.

At least 19 recordsLinked to original sources
PubMed1989

Mechanism of increased erythrocyte membrane fluidity during magnesium deficiency in weanling rats.

The erythrocyte membrane was investigated in weanling male rats pair fed with magnesium-deficient and control diets for 8 days. Fluorescence polarization studies revealed a 15% increase in the fluidity of membranes from deficient rats. A similar increase in the fluidity of liposomes indicated that protein was not involved. The change was associated with decreased osmotic fragility of intact erythrocytes; the cells lost their biconcavity and had a flattened appearance with surface irregularities. Analysis of the membranes showed decreased amounts of magnesium, cholesterol, and sphingomyelin in the deficient group. The reduced ratios of cholesterol to phospholipid and sphingomyelin to phosphatidylcholine were consistent with the increased fluidity. Addition of physiological amounts of magnesium to the medium rigidified membranes incubated in tris(hydroxymethyl)-aminomethane buffer, and this was prevented by the presence of EDTA. Cross-incubation experiments with erythrocyte ghosts and plasma from the two groups of rats showed that magnesium-deficient plasma increased the fluidity of control ghosts and control plasma rigidified ghosts from magnesium-deficient rats. Addition of sufficient magnesium chloride to raise the magnesium content of deficient plasma to normal had no significant effect. These results show that the increased fluidity of the erythrocyte membrane in magnesium deficiency is due to physicochemical exchange with the plasma. Although magnesium can directly influence membrane fluidity, the change during its deficiency in vivo is mainly mediated indirectly via disturbances in lipid metabolism.

Animals↗
PubMed1987

Zinc transfer among proteins in rat duodenum mucosa.

Duodenums from freshly killed stock colony rats were incubated in Krebs buffer containing carrier-free 65ZnCl2 for periods of time between 5 and 60 s. Mucosa cytosol was separated and fractionated by gel filtration on Sephadex G-75. 65Zn was present in two main bands of protein with molecular weights of about 45,000 and 6,500, but the ratio between them rose progressively with time of exposure to the isotope. Addition of metabolic inhibitors greatly lowered the 45,000/6,500 ratio for 65Zn. It is concluded that when zinc enters the mucosal cytoplasm during absorption, it rapidly binds to the 6,500 protein in a passive way and is then transferred to the protein of molecular weight 45,000 by an active process.

Animals↗
PubMed1985

Effect of dietary picolinic acid on the metabolism of exogenous and endogenous zinc in the rat.

The excretion of 65Zn was compared by metabolic balance studies in adult male rats fed purified diets containing 0.8 mmol Zn/kg diet, with and without 40 mmol picolinic acid per kilogram diet, after single intragastric (i.g.) and intraperitoneal (i.p.) doses of the isotope. In a third experiment picolinic acid was introduced for 3 d into the diet of rats prelabeled with 65Zn. The urinary excretion of total zinc was increased by the ingestion of picolinic acid in all three experiments. The urinary and fecal outputs of 65Zn were both consistently greater in picolinic acid-fed rats than in the corresponding control animals. This was particularly marked after i.p. injection of the tracer, and the specific activities of urine and feces from the treated rats were both increased. When picolinic acid was introduced into the diet of prelabeled rats there was a delay of 24 h in the urinary response and 48 h in the fecal response. The residual 65Zn levels were reduced in several tissues from the picolinic acid-fed rats, especially after i.p. administration of the isotope. These observations indicate that dietary picolinic acid increases the turnover of endogenous zinc in addition to enhancing the absorption and excretion of ingested metal, and this has implications for its use in cases of zinc deficiency.

Absorption↗
PubMed1984

Metabolic activity of liver mitochondria from magnesium-deficient rats.

Comparisons were made between the metabolic activities of whole mitochondria and intact mitochondrial inner membrane preparations from magnesium-deficient and control rats in a basic medium without exogenous magnesium. Magnesium deficiency partially uncoupled oxidative phosphorylation in whole mitochondria and completely uncoupled it with inner membrane preparations. Addition of 1 mM MgCl2 to the medium prevented the total uncoupling of inner membranes and gave ADP:O values similar to those obtained with whole mitochondria from magnesium-deficient rats. No impairment in proton extrusion by intact inner membranes or in ATPase activity by either intact or fragmented inner membranes was detected during magnesium deficiency, but there was evidence of increased membrane permeability to the inward movement of protons. It is concluded that magnesium deficiency probably increases the permeability of the mitochondrial inner membrane and this weakens the coupling between oxidation and phosphorylation.

Adenosine Triphosphatases↗
PubMed1983

Chemical factors affecting the intestinal absorption of zinc in vitro and in vivo.

Everted sacs of rat duodenum and ileum were used to study the effect of anions and organic ligands on the absorption of zinc. The uptake per unit weight of tissue was greater in duodenum than ileum, and it was influenced by the Zn concentration and pH of the incubation medium. The Zn uptake from inorganic salts in simple buffered medium varied in the order zinc sulphate greater than zinc chloride greater than zinc phosphate. Zinc acetate was more effective and zinc citrate less effective than ZnCl2. Addition of aspartic acid or histidine to ZnCl2 increased the uptake but galactose or lactose decreased it. 2-Picolinic acid greatly increased the Zn uptake but 4-picolinic acid reduced it. When incubated with intestinal sacs after incorporation into a synthetic rat diet, only ZnSO4 and 2-picolinic acid increased Zn uptake compared with ZnCl2, but zinc citrate and 4-picolinic acid still tended to decrease it. Metabolic balance studies showed no significant differences in the faecal excretion, total excretion or retention of Zn between rats receiving diets containing different forms of Zn. ZnSO4, zinc citrate and particularly 2-picolinic acid increased the urinary excretion of Zn. The significance of these results is discussed in relation to the suitability of methods for investigating Zn absorption and the importance of Zn-binding ligands.

Animals↗
PubMed1982

Changes in cellular and subcellular composition during potassium deficiency.

1. A specific dietary deficiency of potassium in young rats reduced the potassium concentration in thigh muscle by 48%, and in heart and kidney by 18%, but did not significantly affect the concentration in liver or brain. Conversely the sodium concentration rose in liver, heart and thigh muscle, and thigh muscle also accumulated increased amounts of magnesium. Apart from an increase in the water content of many tissues, no consistent changes in the composition of major cell constituents were observed. 2. The loss of potassium and accumulation of sodium and magnesium occurred predominantly in the supernatant fraction of the cell. The supernatant of all tissues studied contained about 80% of the total cellular potassium and sodium, and the potassium was present entirely in the ionic form. 3. Potassium and magnesium are the two most abundant intracellular metals, but their deficiencies have very different effects on the cell. The relationship between them is more complex than the inverse relationship between potassium and sodium.

Animals↗
PubMed1982

Heterogeneous nature of alkaline phosphatase from rat liver.

1. Alkaline phosphatase from rat liver was separated into tow components by gel filtration. 2. Both components had the same temperature and pH optima, were inhibited by high concentrations of urea and had the same activity towards hydrolysis of phenyl disodium phosphate and p-nitrophenyl phosphate. 3. They differed in electrophoretic mobility, sensitivity to inactivation by heat and digestion by neuraminidase, response to low concentrations of urea, and catalytic activity with sodium pyrophosphate and sodium phytate.

Alkaline Phosphatase↗
PubMed1980

Distribution of copper and zinc among protein fractions in the cytoplasm of rat tissues.

Supernatant preparations from the liver, small intestine, and skeletal muscle of normal rats were separated on Sephadex G-150 into six Cu and Zn containing protein fractions with molecular weights of about 250,000, 153,000, 73,000, 41,000, 22,000, and 10,000. Small differences in molecular weight and metal binding were observed between tissues, but the corresponding fractions from all three tissues were generally very similar. Age affected the distribution of both metals, particularly in liver; growth from the weanling to adult stage was accompanied by the transfer of considerable amounts of Cu and Zn from the 10,000 to the 22,000 fraction. A small influence of sex on the distribution was found in skeletal muscle. After injection of 65Zn radioactivity initially entered the 10,000 fraction in liver; it was then transferred to the region of the 73,000 fraction and entered the 22,000 fraction most slowly. The metabolic importance and probable nature of the various fractions is discussed.

Age Factors↗
PubMed1980

The effect of zinc deficiency on alkaline phosphatase (EC 3.1.3.1) and its isoenzymes.

1. Zinc deficiency in young rats reduced both the total alkaline phosphatase (EC 3.1.3.1) activity and Zn concentration in serum, kidney, small intestine and femur. 2. Addition of 0.01 mM-exogenous Zn had no greater activating effect with extracts of kidney, small intestine and femur from Zn-deficient than control rats, indicating that the main effect of the deficiency was on the amount of enzyme present rather than the efficiency of its operation. Exogenous Zn increased the activity of enzyme in serum Zn-deficient rats, but it was still lower than in the serum of control animals. 3. Electrophoresis on polyacrylamide gel separated the alkaline phosphatase activity from all tissues into two bands. The bands had similar electrophoretic mobilities and appeared to be qualitatively identical in corresponding tissues from Zn-deficient and control rats. 4. Zn deficiency eliminated the first band found in serum from control rats and it had selective effects on the activity of individual bands in other tissues. The major inhibitory effect was on the first bands of enzyme activity in kidney and femur, but in small intestine only the second band was affected. In liver the activity of the first band was increased and that of the second band decreased by similar amounts.

Alkaline Phosphatase↗
PubMed1979

The differential effect of magnesium deficiency on isoenzymes of alkaline phosphatase (EC 3.1.3.1) in rat tissues.

1. Alkaline phosphatase (EC 3.1.3.1) from many rat tissues was separated into two or three bands by electrophoresis on polyacrylamide gel. Ten of the bands had different electrophoretic mobilities, but some were present in more than one tissue. 2. Bands from the corresponding tissues of magnesium-deficient and control rats were qualitatively similar, but there were quantitative differences in the distribution of enzyme activity between them. 3. Mg deficiency had differential effects on the absolute activity of individual bands, but two main types of response were observed. There was an increase in the activity of the first bands from liver and kidney, the second band from femur and both bands from spleen, whereas the first band from femur, the first and second bands from intestinal mucosa and the second bands of serum, liver and kidney all decreased in activity during the deficiency. 4. The change in total alkaline phosphatase activity of a tissue during Mg deficiency depended on the ratio between the enzyme components within it.

Alkaline Phosphatase↗
PubMed1978

Changes in organ growth with feeding pattern. The influence of feeding frequency on the circadian rhythm of protein synthesis in the rat.

The effect of eating one large meal rather than several small meals per day on protein metabolism and the growth of individual organs was investigated in young male rats. Meal-eating did not affect the rate of protein catabolism in liver, kidney, small intestine, or spleen in vivo compared with continously fed control animals that consumed the same total amount of food. A circadian rhythm of protein synthesis was found in liver and kidney slices taken from normal rats killed at various times; starvation reduced the magnitude of protein synthesis but did not alter its cyclical nature. Consumption of the daily food all in one meal distorted the circadian rhythm, particularly when it was taken in the morning, and a morning meal increased the total 24 hour synthesis of protein in liver whereas an evening meal did not. Meal-feeding in the morning increased the weights of the liver, small intestine and tibia compared with continuously fed rats, but meal-feeding in the evening did not.

Animals↗
PubMed1976

The effect of feeding frequency on the growth on composition of individual organs in the rat.

1. The effect of consuming the same total amount of food in either one large meal or several small meals per d was studied using weanling male rats. 2. The increase in total body-weight was the same in both instances, but the weights of the liver, kidneys, femur, small intestine and stomach were greater, and those of the spleen and residual carcass were smaller, in meal-eating rats than in continuously fed control animals. These differences persisted into the adult state. 3. No differences in gross chemical compositions were found between the corresponding organs of the two groups of rats, and the differences in weight appeared to be the result of changes in the general growth rate of individual organs. 4. The hypertrophy of the kidneys in meal-eaters was due to an increase in mean cell size, but the increased weight of the liver and reduced weight of the spleen appeared to be largely the result of changes in the number of cells present.

Animals↗