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R Timmermans

Publications and source records attributed to R Timmermans.

14 recordsLinked to original sources
PubMed2000

Coherent bremsstrahlung in the alpha + p system at 50 MeV/nucleon

Photons originating from coherent bremsstrahlung have been measured over a large dynamic range for the reaction of 200 MeV alpha particles with protons. At low photon energies the bremsstrahlung spectrum exhibits the classical behavior with an approximate 1/E(gamma) shape. At higher photon energies there is a pronounced contribution from capture into the unbound ground state and first excited state of 5Li. These results allow one, for the first time, to test theoretical models for a consistent description of bremsstrahlung and radiative capture in a complex system. Calculations predict both features qualitatively but fail to account for their relative importance.

Journal Article↗
PubMed1984

The effect of X irradiation on cardiac beta-adrenergic receptors in the rabbit.

Cardiac beta receptors in rabbits were studied at different times following lethal (5 Gy) or supralethal (10 Gy) whole-body X irradiation. Using the radioactive ligand [125I]iodocyanopindolol, it was found that the maximal binding capacity, as determined from the Scatchard plot, decreased from 298.2 +/- 13.2 fmole/mg protein in controls to 142.4 +/- 5.5 fmole/mg 3 days after 10 Gy whole-body X irradiation, whereas the dissociation constant was only little affected. Three days after an exposure to 5 Gy, maximal binding capacity was reduced slightly and tended toward control values at Day 7. Local irradiation of the cardiac region with 10 Gy reduced cardiac beta receptors to 218 +/- 7 fmole/mg (73% of control) after 3 days. The latter observation suggests that about half the effect of radiation on cardiac beta receptors originates from a direct action of radiation on the heart tissue, the rest being due to abscopal systemic reactions.

Animals↗
PubMed1984

Reaction of blood pressure and mesenteric blood flow to an infusion of biogenic amines in rats: influence of irradiation and alpha blockers.

The reaction of systemic blood pressure and mesenteric blood flow to an infusion of different biogenic amines was determined in controls and in lethally (8 Gy) X-irradiated rats. The influence of the alpha blocker phenoxybenzamine on these reactions was also investigated. Changes in blood pressure and flow response similar to, but less marked than, those seen earlier after a supralethal (20 Gy) exposure were detected 3 and 7 days after irradiation. These observations as well as the consequences of alpha blockade suggest that the reactivity of alpha receptors in blood vessels is reduced after irradiation, and that the function of the heart is impaired.

Acetylcholine↗
PubMed1984

[Effect of age on the chromosomal radiosensitivity of bone marrow erythrocytes in the mouse].

The frequency of cells with micronuclei has been determined in bone marrow polychromatic erythrocytes of 7 days, 12 weeks or 15 months old mice. This was also carried out in mice exposed to different doses of whole-body X-irradiation 30 hours before. Significantly more micronuclei were found in old control mice. The increase in micronuclei induced by irradiation, was not influenced by age.

Age Factors↗
PubMed1981

The effect of beta blockade on the reaction of pressure and mesenteric flow to biogenic amines in normal and X-irradiated rats.

A beta-blocker, propranolol, was infused to control and irradiated rats the 1st and 3rd day after 2-kR X-ray irradiation. Blood pressure and mesenteric blood flow were recorded during infusion of biogenic amines (noradrenaline, dopamine, serotonin, acetylcholine and histamine). After beta-blockade, there was intensified increase in pressure and decrease in flow with increased overshoot after infusion of noradrenaline, no effect on the increase in pressure and flow after dopamine, but an enhanced increase in pressure and decrease in flow after serotonin. No effect on the decrease in pressure and flow was seen after acetylcholine, and a greater decrease in pressure and flow, after histamine. Irradiation altered the vascular reactivity, mainly for noradrenaline, serotonin and histamine.

Acetylcholine↗
PubMed1980

[Effect of phenoxybenzamine on mesenteric blood flow in irradiated rats].

Reactivity of the superior mesenteric artery has been studied in rat Wistar by infusion of biogenic amines (noradrénaline, dopamine, serotonin, acetylcholine and histamine) in presence of phenoxybenzamine. A decrease in reactivity of the post-synaptic alpha receptor located on the mesenteric vascular smooth muscle cell was seen three days after irradiation by 2 Kr.

Animals↗
PubMed1978

[Blood pressure and mesenteric blood flow in rats during the infusion of biogenic amines. Effect of supralethal irradiation].

The action of biogenic amines (noradrenaline, dopamine), infused at different concentration into the aorta of the urethane anesthetized control and irradiated rats for 2 min., was followed on the basis of systemic blood pressure and mesenteric blood flow. The mesenteric blood flow was measured by means of an electromagnetic flow meter. The changes observed i.e. after dopamine an increase in pressure and flow, after noradrenaline an increase in pressure and a decrease in flow with an increase after infusion had been stopped, correspond to those obtained in larger animals. In many, but not in all cases, the response is proportional to the log of the concentration of the amine infused. Irradiation with 2 kR, i.e. a dose which causes the animals to die from the gastrointestinal syndrome after 3 days, modified the response to dopamine and noradrenaline. The changes are, for noradrenaline, a greater pressure and a lower flow responses and for dopamine a greater pressure response at low and middle doses.

Animals↗
PubMed1977

Absorption of different amino acids by an intestinal preparation from normal rats and from rats exposed to supralethal X-irradiation.

Absorption of different amino acids [lysine, alpha-amino isobutyrate (AIB), methionine, alanine, glycine] was studied in an intestinal in vivo preparation from normal and X-irradiated rats (1 and 3 days after 2000 R). Absorption of amino acids under loading and in presence of other amino acids was also followed. Lysine and AIB absorption follow a saturation kinetics with a maximal velocity of 35 and 85.6 micronmoles/min and a Kt of 10 and 67 micronmoles for lysine and AIB respectively. Interference in absorption exists not only between amino acids of the same class, but also by lysine on neutral amino acids. One day after irradiation, absorption is normal or even enhanced, although active transport appears impaired as indicated by the increase in Kt. Three days after exposure absorption, particularly the active one, is severely depressed. This is indicated by the low Vm and high Kt as well as by the fact that loading has little influence on absorption.

Alanine↗