Biomedical subjects

S Macaione

Publications and source records attributed to S Macaione.

At least 37 records · Page 2Linked to original sources

PubMed1984

Phenolic and tyrosyl ring deiodination in thyroxine from rat retina during postnatal development.

To elucidate tetraiodothyronine (T4) metabolism in developing rat retina 5-monodeiodinating and 5'-monodeiodinating activities were studied. T4 was incubated with aliquots of homogenate or crude primary subcellular fractions, and the 3,3',5'-triiodothyronine (rT3) or 3,5,3'-triiodothyronine (T3) produced were measured by radioimmunoassay. Reaction rates were dependent on incubation time, tissue amount, temperature and pH. The optimum pH values were 7.8 and 7.2 respectively for rT3-forming and T3-forming systems. Conversion of T4 to either T3 or rT3 was dependent on dithiothreitol concentration, and the T4-5'-deiodinating activity was inhibited by propylthiouracil. Deiodinase activities were mainly found in the crude microsomes. The retinal 5'-monodeiodination rate of T4 was immeasurably low by the 2nd day and the highest values were reached on 15th day of postnatal development. On the other hand deiodination of the T4 tyrosyl ring shows a progressive decline from birth, and adult values were reached on the 15th day. Data support the hypothesis that, in developing rat thyroxine, phenolic and tyrosyl-ring deiodinase activities are present in the retina and their reciprocal changes may regulate morphological and biochemical cell maturation.

Animals↗

PubMed1984

Retina maturation following administration of thyroxine in developing rats: effects on polyamine metabolism and glutamate decarboxylase.

The effects of subcutaneous daily treatment with thyroxine on cell proliferation, differentiation, polyamines, and gamma-aminobutyric acid metabolism in the rat retina were studied during the first 20 postnatal days. The retinal layers of the treated rats displayed an enhanced cell differentiation which reached its maximum 9-12 days from birth; but this effect stopped very quickly and was finished by the 20th postnatal day. Primarily there was an increase in ornithine decarboxylase activity which was accompanied by an increase in putrescine, spermidine, and spermine levels. S-Adenosylmethionine decarboxylase was induced later than ODC; corresponding with the enhanced synaptogenesis, glutamate decarboxylase increased 15-fold between the fourth and 15th days. Our data are consistent with the hypothesis that thyroxine may exert some of its effects by inducing the enzymes which regulate polyamine metabolism and synaptogenesis.

Adenosylmethionine Decarboxylase↗

PubMed1983

Effects of thyroxine on methionine adenosyltransferase activity in rat cerebral cortex and cerebellum during postnatal development.

Methionine adenosyltransferase (MAT) activity was evaluated in cerebral cortex and cerebellum in controls and in rats treated with thyroxine. In controls the enzyme showed a different pattern in cerebral cortex and cerebellum during neonatal and late suckling periods. Hyperthyroid rats showed a significant increase of the enzyme in cerebral cortex only at the 2nd day of the neonatal period; in cerebellum the developmental pattern of MAT in neonatal period was anticipated temporally by 2-4 days. During the late suckling period thyroxine treatment produced in cerebellum a significant decrease in MAT activity at the 15th day after birth. From these data, we propose that hyperthyroidism may cause precocious induction of MAT both in cerebral cortex and in cerebellum and that the increased availability of S-adenosyl-L-methionine during the neonatal period could be related to its utilization also in polyamine biosynthesis.

Animals↗

PubMed1982

S-adenosylmethionine decarboxylase levels in rat retina during postnatal development.

S-Adenosylmethionine decarboxylase from rat retina is similar to that isolated from other rat tissues with regard to kinetic parameters, pH optimum, putrescine requirement, and sensitivity to spermine. The enzymic activity increases during the first 7 days of postnatal life but decreases until the 20th day. After this period AdoMet decarboxylase activity increases, to reach the highest values at the 90th day. This behavior suggests that such enzymic activity is responsible for spermidine and spermine levels in rat retina and that a high content of retinal spermine might have a role in the photoreceptor outer segment renewal.

Adenosylmethionine Decarboxylase↗

PubMed1980

Effects of intraventricular gamma-acetylenic-GABA on GABA concentrations, GABA-T and GAD in several areas of the chick brain.

The great interest in new compounds able to increase GABA concentration in the brain as potential antiepileptic drugs has led to the synthesis of powerful inhibitors of GABA transaminase (GABA-T) e.g. gamma-acetylenic GABA (GAG) and gamma-vinyl-GABA. Present experiments were aimed to study behavioral, electrocortical and biochemical effects of GAG after its intraventricular injection. It has been shown that in chicks the microinjection of GAG into the third cerebral ventricle produced a biphasic behavioral and electrocortical syndrome : an initial phase of behavioral and electrocortical sleep followed by a paradoxycal increase in motor activity and a very intense behavioral and ECoG arousal pattern. In addition intraventricular GAG (0.8 mumol) produced a significant increase 1 and 2 h later in GABA concentration in the diencephalon and brain-stem whereas no changes occurred in other brain areas e.g. cerebral hemispheres, optic lobes. Higher doses (1.6 mumol), produced after 1 h, concomitantly to the increased GABA concentration, a significant GABA-T inhibition and a profound inhibition of glutamate-decarboxylase in the diencephalon and brain-stem. Present experiments may explain the paradoxical behavioral, motor and electrocortical stimulation observed at the time of GABA increase concentration and suggest that a small functional neuronal pool of GABA, more than the whole absolute levels of GABA in a given area of the brain, seems to be involved in the control of GABAergic mediated inhibitory mechanisms.

4-Aminobutyrate Transaminase↗

PubMed1979