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Biomedical subjects

D J Morton

Publications and source records attributed to D J Morton.

At least 91 records · Page 5Linked to original sources
PubMed1985

Effect of magnesium ions on rat pineal N-acetyltransferase (EC 2.3.1.5) activity.

N-Acetyltransferase (NAT) activity at night and following isoproterenol treatment in intact animals was higher in rats pretreated with magnesium than in controls. This effect was probably due to enhancement of agonist binding and/or adenylate cyclase activation caused by magnesium ions. A similar effect was observed in vitro, where magnesium increased norepinephrine-stimulated NAT activity in organ-cultured pineal glands, suggesting that magnesium acts primarily on the pineal gland as opposed to some other peripheral or central site. This enhancement of NAT activity by magnesium would presumably lead to increased melatonin production; and as melatonin has been shown to decrease serum magnesium levels, a negative feedback mechanism may exist.

Acetyltransferases↗
PubMed1984

Metabolic dependence of glycolytic enzyme binding in rat and sheep heart.

Perfused rat hearts show a markedly increased binding of phosphofructokinase and fructose-bisphosphate aldolase as a consequence of ischaemia, but little change in binding of pyruvate kinase, lactate dehydrogenase or glyceraldehyde-3-phosphate dehydrogenase. After 10 min ischaemia over one quarter of the phosphofructokinase and three quarters of the aldolase are bound. The effect of anoxia is less well marked in its influence on binding with only aldolase showing a significant increase in binding. These results suggest that one factor involved in the increased binding during ischaemia is the fall in pH of the heart. Binding studies with isolated myofibrils confirm that the affinity and stoichiometry of aldolase binding are considerably increased as the pH is lowered over a range comparable to that which occurs in ischaemic heart. The low level of binding of glyceraldehyde-3-phosphate dehydrogenase in perfused rat hearts correlates with the relatively low affinity of this enzyme for binding to rat or rabbit cardiac myofibrils. There are species differences in the enzyme binding response to ischaemia. Sheep hearts show rapid and large increases in the binding of glyceraldehyde-3-phosphate dehydrogenase in addition to changes in aldolase and phosphofructokinase binding. The greater binding of glyceraldehyde-3-phosphate dehydrogenase reflects the greater affinity of sheep cardiac myofibrils. It is suggested that the altered metabolic demands of ischaemia are satisfied by changes in glycolytic enzyme organisation as the enzymes shift from the soluble to the particulate phase of cardiac muscle.

Animals↗
PubMed1984

Effect of derivatization of the bioavailability of ophthalmic steroids. Development of an in vitro method of evaluation.

An in vitro method for evaluating efficacy of ophthalmic steroid preparations was developed using bovine eyes. The method was tested using three derivatives of dexamethasone (alcohol, acetate, and sodium phosphate) and the results obtained were similar to those obtained in studies using live rabbits, although differences were noted. Bioavailability of the acetate was greatest; that of the sodium phosphate was the lowest. On the basis of this study, bovine eyes could be used as an alternative method for assessing ophthalmic steroid efficacy.

Animals↗
PubMed1984

Pharmacokinetics of twelve anticonvulsant drugs in the rat.

The pharmacokinetic data for 12 anticonvulsant drugs was evaluated after administration to laboratory rats. In all cases the half-life and elimination rate constants were significantly different from clinically-determinant values which suggests that pharmacokinetic parameters should be treated as species specific.

Animals↗
PubMed1983

The appearance and characteristics of early pregnancy factor in the pig.

The occurrence of early pregnancy factor in the pig has been established by the rosette inhibition test and by the criteria that gel filtration of serum resulted in a number of peaks of activity similar to those observed in other species. In the pig EPF is present virtually to the end of pregnancy, with a biphasic production in which the titres of EPF decline markedly in mid-pregnancy. Free EPF-A appears concurrently with EPF in the first 3 weeks of pregnancy in some but not all pigs. The presence of excess EPF-A has an inhibitory effect in the rosette inhibition test and modifications, including an initial serum dialysis step, have been introduced into the test to take account of this inhibitory effect.

Animals↗
PubMed1981

The reversible binding of glycolytic enzymes in ovine skeletal muscle in response to tetanic stimulation.

The extent of binding of glycolytic enzymes to the particulate fraction of homogenates was measured in sheep hind muscles after electrical stimulation. As compared to the control muscles, stimulation led to significant increases in the amount of phosphofructokinase, aldolase and glyceraldehyde-3-phosphate dehydrogenase bound to the particulate fraction. The binding of other glycolytic enzymes was not significantly altered. A servey of different hind limb muscles at variable rates of stimulation revealed that each muscle exhibited its own characteristic response pattern in terms of the level of increased enzyme binding. Generally, an increased stimulation rate led to greater enzyme adsorption. The increase in enzyme binding was rapidly reversible for it was shown that the amount of enzyme bound quickly returned to control values when the muscles were allowed to recover in the live anaesthetised animal following cessation of stimulation. Those muscles which exhibited increased enzyme binding were characterised by a marked loss of glycogen and accumulation of lactate suggesting that accelerated glycolytic flux was a necessary condition for the observation of increased enzyme binding. In support of this, enzyme adsorption was observed to the greatest on stimulation of ischemic muscles, whereas in trained muscles, or muscles with depleted glycogen stores induced by prior adrenalin treatment, the increased enzyme binding response was greatly diminished. It is concluded that the variable binding of key glycolytic enzymes has a role to play in the regulation of glycolytic behaviour in skeletal muscle.

Animals↗
PubMed1980

Binding of aldolase to actin-containing filaments. Evidence of interaction with the regulatory proteins of skeletal muscle.

The interactions of aldolase with regulatory proteins of rabbit skeletal muscle were investigated by moving-boundary electrophoresis. A salt-dependent interaction of troponin, tropomyosin and the tropomyosin-troponin complex with aldolase was detected, the tropomyosin-troponin complex displaying a greater affinity for the enzyme than did either regulatory protein alone. The results indicate that aldolase possesses multiple binding sites (three or more) for these muscle proteins. Quantitative studies of the binding of aldolase to actin-containing filaments showed the interaction to be influenced markedly by the presence of these muscle regulatory proteins on the filaments. In imidazole/HCl buffer, I 0.088, pH 6.8, aldolase binds to F-actin with an affinity constant of 2 x 10(5) M-1 and a stoicheiometry of one tetrameric aldolase molecule per 14 monomeric actin units. Use of F-actin-tropomyosin as adsorbent results in a doubling of the stoicheiometry without significant change in the intrinsic association constant. With F-actin-tropomyosin-troponin a lower binding constant (6 x 10(4) M-1) but even greater stoicheiometry (4:14 actin units) are observed. The presence of Ca2+ (0.1 mM) decreases this stoicheiometry to 3:14 without affecting significantly the magnitude of the intrinsic binding constant.

Actins↗