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Biomedical subjects

H Woelk

Publications and source records attributed to H Woelk.

At least 37 records · Page 2Linked to original sources
PubMed1979

[Effect of piracetam on neuronal and synaptosomal phospholipase A2 activity].

In search of the biochemical mechanism of the action of 2-oxopyrrolidine-1-acetamide (piracetam, Normabrain, Nootrop) the influence of the encephalotropic substance on the hydrolysis of different glycerophosphatides by the neuronal and synaptosomal phospholipase A2 was investigated. Pure synaptosomes and neurons were prepared by a new method. The synaptosomal and neuronal phospholipase A2 plays an important role during the process of synaptic transmission. The administration of piracetam enhanced both the neuronal and synaptosomal phospholipase A2-activity by about 50%. The piracetam-induced stimulation of the enzyme activity was in the same order of magnitude for all substrates investigated. Thus piracetam stimulates the synaptic transmission. The stimulation of the phospholipase A2-activity by piracetam appears to be mediated by a neurotransmitter.

Animals↗
PubMed1978

Membrane-bound base-exchange reactions in animal tissues.

The calcium-stimulated incorporation of ethanolamine, L-serine and choline into rabbit synaptosomal phospholipids in vitro has been investigated. The synaptosomal membranes were prelabelled in vitro in their choline-, ethanolamine- or serine-phosphoglycerides by base-exchange and then chasing experiments were performed by displacing the lipid-bound base by ethanolamine, choline or L-serine labelled with a different isotope. The results indicate that membrane phosphatidylcholine, phosphatidylethanolamine and phosphatidylserine are substrates for the exchange with all the three mentioned bases. A very small phospholipid pool (0.5-2% of the total available pool) is active in the calcium-dependent exchange between membrane phosphatidylcholine or phosphatidylethanolamine and free bases, whereas the pool of exchanging phosphatidylserine is sensibly larger (2-9%). In another series of experiments the effect of the base-exchange reaction upon the production of cyclic-AMP at the level of rat brain synaptic membranes has been examined. An exchange with ethanolamine produces a significant decrease of the NaF-stimulated production of the cyclic nucleotide, whereas it increases the noradrenaline-induced production. With some exceptions, the exchange with L-serine produces opposite effects. The possible physiological importance of phospholipid pool at the synaptosomal level is discussed.

Adenylyl Cyclases↗
PubMed1978

Enzymic studies on glial and neuronal cells during myelination.

The formation of ethanolamine plasmalogen from labelled 1-alkyl-2-acyl-sn-glycero-3-phosphorylethanolamine was studied in neurons and glial cells of the developing rat brain. It was found that the conversion of the ether to the enol-ether bond of the 1-alkyl moiety by the neuronal and glial desaturase system requires unsaturated fatty acids at the 2 position of the substrate. There is almost no difference between the activity of the neuronal and glial desaturase during the period of active myelination, whereas the neuronal cell fraction of the adult rats displays a threefold higher enzyme activity as compared to the glial cells. Evidence for the involvement of a microsomal electron transport system in the enzymic conversion of alkylacyl-glycero-3-phosphorylethanolamine to ethanolamine plasmalogen was obtained by using specific antibodies against NADH-cytochrome b5 reductase. Cytochrome b5 stimulated the biosynthesis of ethanolamine plasmalogen.

Animals↗
PubMed1978

The action of piracetam on the formation of ethanolamine-plasmalogen by neuronal microsomes of the developing rat brain.

In search of a common biochemical denominator of the action of the nootropic drug 2-oxo-pyrrolidine-1-acetamide (piracetam, Normabrain, Nootrop) the effects of the substance on the neuronal respiratory chain were investigated. The activity of the electron transport system of the respiratory chain was measured by the conversion of the ether to the enolether bond (plasmalogen) of ethanolamine containing glycerophosphatides. Piracetam enhances the formation of ethanolamine-plasmalogen from the corresponding ether lipid by neuronal microsomes and thus resembles the action of cytochrome b5. The addition of antibody against cytochrome b5 was able to inhibit the piracetam-dependent stimulation of the plasmalogen biosynthesis. Thus it appears that the stimulatory effect of piracetam on the formation of ethanolamine-plasmalogen is mediated by an increased synthesis or turnover of cytochrome b5.

Adenine Nucleotides↗
PubMed1977

Biosynthesis of rat brain phosphatidylethanolamines from intracerebrally injected ethanolamine.

[2-3H]Ethanolamine was injected intracerebrally into male rats and the brains of the animals immediately removed by particular procedures at regular intervals over the first 1200 sec. The incorporation of radioactivity into brain phosphorylethanolamine, cytidine-5'-diphosphate (CDP) ethanolamine and phosphatidylethanolamines was examined and quantitated. The nature of phosphatidylethanolamine molecular subspecies, which became labelled, was also investigated after isotope administration. Phosphorylethanolamine, CDP-ethanolamine and phosphatidylethanolamines were all labelled already 5 sec after the administration of labelled ethanolamine. The specific radioactivities of different phosphatidylethanolamine molecular subspecies varied according to the time elapsed from the injection to the sacrifice of the animals. This last result, together with the data on time course of labelling of ethanolamine phosphoglycerides and their precursors, provides indications that this base may be incorporated into lipids not only by net synthesis pathway, but also by base-exchange reaction.

Animals↗
PubMed1976

Relationships between base-exchange reaction and the microsomal phospholipid pool in the rat brain in vitro.

The calcium-stimulated incorporation of ethanolamine, choline and L-serine into rat brain microsomal phospholipids has been investigated. The membranes were prelabeled in vitro in their choline or serine phosphoglycerides by base-exchange and then chasing experiments were done by displacing the lipid-bound base by ethanolamine, choline, or L-serine labeled with a different isotope. The results indicate that membrane phosphatidylcholine is presumably a substrate for the exchange with all the three bases, whereas phosphatidylserine exchanges only with ethanolamine and L-serine but not with choline. A small phospholipid pool (3-7% of the total available pool) is active in the calcium-dependent exchange with choline, ethanolamine, and L-serine. When the microsomal membranes are prelabeled in vitro in their phosphatidylcholine moiety through the cytidine-dependent pathway and then chasing experiments are performed with the three nitrogenous bases, as above, the small phospholipid pool is hardly detectable. In view of these and other results (Gaiti et al., FEBS Letters 49:361 1975), it is suggested that at least two different pools of phosphatidylethanolamine, phosphatidylserine, and phosphatidylcholine might exist in rat brain microsomes.

Animals↗
PubMed1975

On the activity of brain phospholipase A2 towards specifically labelled glycerophospholipids during subacute sclerosing panencephalitis.

1,2-Diacyl-sn-glycero-3-phosphorylcholine, -ethanolamine and -serine, specifically labelled with different fatty acids at either the 1- or 2-position, were prepared enzymatically using the acyltransferase system of rat liver microsomes. The substrates were subjected to hydrolysis by phospholipase A2 obtained from brain tissue of a normal and a case of subacute sclerosing panencephalitis (SSPE). In the pathological tissue and increase of approx. 50% in phospholipase A2 activity could be observed in comparison to that from the control brain for all investigated substrates. Experiments with phosphatidylethanolamines, specifically labelled with different fatty acids in the 2-position, revealed that the phospholipase A2 activity of the SSPE brain tissue was enhanced by about 50% when compared to the control brain regardless of the fatty acid constituent at the 2-position of the substrates.

Adolescent↗
PubMed1975

On the effect of brain phospholipase A1 on specifically labelled glycerophospholipids in the course of subacute sclerosing panencephalitis.

The effect of phospholipase A1 of human brain on 1,2-diacyl-sn-glycero-3-phosphorylcholine, -ethanolamine and -serine, specifically labelled with different fatty acids at either the 1 or 2 position, was determined in subacute sclerosing panencephalitis. An increase of approximately 40% in the specific activity of phospholipase A1 could be observed for all substrates investigated during the demyelinating disorder. On investigating the specific activity of the enzyme with various molecular species of phosphatidylcholine and -ethanolamine, labelled at the 1 position with different radioactive fatty acids, we found that the phospholipase A1 preferentially removed those fatty acids from the 1 position of phosphatidylcholines that have the fewest double bonds, while oleic and linoleic acid were released at almost similar rates from phosphatidylethanolamine.

Adolescent↗