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Biomedical subjects

C J Fowler

Publications and source records attributed to C J Fowler.

At least 307 records · Page 17Linked to original sources
PubMed1978

The inhibition by clorgyline of 5-hydroxytryptamine deamination by the rat liver.

The inhibition of the monoamine oxidase activity in the rat liver by the substrate selective inhibitor clorgyline has been investigated with 5-hydroxytryptamine as substrate. The results obtained are consistent with a theoretical model whereby the inhibition of enzyme activity by clorgyline follows a reversible association phase leading to an irreversible 'suicide' reaction. The relative concentrations of enzyme and inhibitor are of the same order, and can account both for the failure of the reaction to go to completion, and for the differences in the apparent sensitivity of enzyme preparations to inhibition by clorgyline. The possible value of this type of inhibition as a means of assay for monoamine oxidase active centres is discussed.

Animals↗
PubMed1977

The effect of tris buffers on rat liver mitochondrial monoamine oxidase.

The effect of tris buffers upon the monoamine oxidase (MAO) activity in rat liver mitochondria has been investigated. Tris buffer was shown to inhibit MAO in a non-competitive manner with a Ki of 15-25 mM. Tyramine, 5-hydroxytryptamine and beta-phenethylamine but not benzylamine oxidations were all inhibited by tris buffer. All inhibitions, except that of 5-HT, were completely reversible. It is suggested that these effects are produced by conformational changes in the structure of the MAO. The significance of these results is discussed with respect to the use of tris buffers in the extraction and estimation of the activity of MAO.

Animals↗
PubMed1977

The effect of age and thyroid hormones upon the ability of the chick heart to deaminate monoamines.

The effect of age and thyroid hormones upon the ability of chick heart homogenates to metabolize monoamines has been investigated. 5-Hydroxytryptamine is entirely metabolized by a monoamine oxidase (MAO) with the characteristics of MAO-A, whereas some of the tyramine and all of the benzylamine are oxidatively deaminated by a clorgyline-resistant, but semicarbazide-sensitive enzyme, with a similar subcellular distribution to that of MAO. The remainder of the tyramine deamination is brought about by MAO-A and MAO-B. The specific activities of both clorgyline-sensitive and resistant enzymes are increased by the same proportion by increase in age or by treatment with (--)-thyroxine, and decreased by 2-thiouracil. The significance of these results is discussed.

Animals↗
PubMedDate not supplied

Disturbances in signal transduction mechanisms in Alzheimer's disease.

Many of the treatments directed towards alleviation of symptoms in Alzheimer's disease assume that target receptor systems are functionally intact. However, there is now considerable evidence that this is not the case. In human post-mortem brain tissue samples, the function of the GTP-binding protein Gs in regulating adenylyl cyclase is severely disabled, whereas that of Gi is intact. This difference in the function of the two G-protein types is also found in G-protein regulation of high- and low-affinity receptor recognition site populations. Measurement of G-protein densities using selective antibodies has indicated that the dysfunction in Gs-stimulation of cAMP production correlates with the ratio of the large to small molecular weight isoforms of the Gs alpha subunit. With respect to intracellular second messenger effects, there is a dramatic decrease in the density of brain receptor recognition sites for Ins(1,4,5)P3 that is not accompanied by a corresponding change in the Ins(1,3,4,5)P4 recognition site density. Protein kinase C function is also altered in Alzheimer's disease, a finding that may be of importance for the control of beta-amyloid production. These studies indicate that signal transduction processes are severely compromised in Alzheimer's disease. Some of these disturbances are also seen in cultured fibroblasts from Alzheimer's disease patients, indicating that they are neither restricted to areas of histopathological change, nor non-specific changes found late in the course of the disease. Cellular models to investigate the relation between amyloid production and deficits in signal transduction are also discussed.

Alzheimer Disease↗
PubMedDate not supplied

Estimation of the elimination half-life of the monoamine oxidase inhibitor cimoxatone in rat brain on the basis of ex vivo inhibition data.

Cimoxatone is a reversible mixed-type selective inhibitor of monoamine oxidase-A. For a mixed-type inhibitor, it can be shown that (vo-vi)/Vi is proportional to the inhibitor concentration. This relationship has been used to estimate the t 1/2 of the elimination of cimoxatone in rat brain after a single dose of inhibitor. t 1/2 values, estimated with three monoamine oxidase substrates, were in the range 3.9-4.8 h, in reasonable agreement with t 1/2 values determined from the plasma and brain concentration/time curves of cimoxatone.

Animals↗
PubMedDate not supplied

Conduction velocity and conduction block after experimental ischaemic nerve injury.

The effect of ischaemic nerve injury on conduction in the tibial branch of the sciatic nerve has been studied in rabbits. Ischaemic nerve damage wa produced in 40 animals by ligation of the common and external or the internal and external iliac arteries. Conduction in the motor fibres to the small foot muscles was examined at internals after operation, with nerve stimulation in the thigh and at the ankle. Ascending nerve action potentials in the tibial nerve were also studied. In 8 animals there was evidence o widespread degeneration of myelinated fibres; muscle action potentials could not be activated by nerve stimulation nerve action potentials were absent. In contrast there were 14 animals in which arterial ligation appeared to produce little, if any, nerve degeneration; in this group there was no significant change in motor or afferent velocity. The remaining 18 animals showed changes of intermediate severity. While nerve degeneration was extensive, it was never complete, and in 9 nerves examined 5 - 11 days after surgery, conduction block between the thigh and ankle could be demonstrated in surviving fibres. In the other 9 nerves there was no block in surviving fibres but maximal motor velocity was significantly reduced. In no case did the conduction block affect more than a minority of the motor fibres, the remainder undergoing complete degeneration. This was in keeping with the histological appearances which showed a relatively small amount of paranodal and segmental demyelination compared with the amount of Wallerian degeneration.

Action Potentials↗
PubMedDate not supplied

Intracellular inositol (1,4,5)-trisphosphate receptor levels are preserved in Alzheimer's disease platelets.

An increasing number of signal transduction disturbances have been reported in Alzheimer's disease. These changes are not restricted to histopathologically changed brain areas but are seen also in peripheral tissues. One of the most severe disturbances is a loss of calcium-mobilizing intracellular inositol(1,4,5)-trisphosphate receptors in Alzheimer cerebellar and cortical tissues. In the present study, the binding of [3H]inositol(1,4,5)trisphosphate ([3H]Ins(1,4,5)P3) to the calcium-mobilizing inositol(1,4,5)trisphosphate receptors in platelet membranes from eight Alzheimer's disease patients and eight control subjects were investigated to determine its possible role as a biological marker in Alzheimer's disease. It was found that there were no significant difference in [3H]Ins(1,4,5)P3 binding with respect to the number of sites measured at different protein concentrations or to the sensitivity of the binding to inhibition by nonradioactive Ins(1,4,5)P3 between Alzheimer disease platelets and controls. It is concluded that inositol(1,4,5)trisphosphate receptor levels are preserved in platelets from patients with Alzheimer's disease.

Aged↗
PubMedDate not supplied

Cellular transport of anandamide, 2-arachidonoylglycerol and palmitoylethanolamide--targets for drug development?

The endogenous cannabinoid anandamide (AEA) is transported into cells by a temperature-sensitive process of facilitated diffusion. This uptake process has been characterised both biochemically and pharmacologically, and shown to be regulated at least in part by the intracellular metabolism of the accumulated AEA by fatty acid amide hydrolase. In this review, the properties of this transport process are briefly reviewed together with the corresponding transport mechanisms for the related endogenous compounds 2-arachidonoylglycerol and palmitoylethanolamide. In addition, the possibility that these transport mechanisms can be targets for therapeutic strategies aimed at prolonging the effects of the endocannabinoids is discussed.

Amides↗
PubMedDate not supplied

Substance P enhances forskolin-stimulated cyclic AMP production in human UC11MG astrocytoma cells.

The effects of substance P (SP) upon basal and forskolin-stimulated cAMP production have been investigated in UC11MG cells. The cells expressed 40,000 NK1 receptors/cell, the stimulation of which led to enhanced phosphoinositide breakdown. Forskolin (10 and 100 mcM) stimulated cAMP production, whereas SP (3 and 300 nM) produced no significant increase in cAMP production. However, SP enhanced the response to forskolin, with an EC50 value of about 10 nM. The response to forskolin was also enhanced by physalaemin and eledoisin, and was sensitive to inhibition by (+/-)CP96345. It is concluded that in the UC11MG cell line, SP not only stimulates phosphoinositide breakdown but also enhances the cAMP response to forskolin, possibly via stimulation of NK1 receptors.

Adenylyl Cyclases↗
PubMedDate not supplied

The effects of two inositol (1,4,5)-trisphosphate 5-phosphatase inhibitors on thyrotropin releasing hormone stimulated inositol (1,4,5)-trisphosphate production in GH3 cells.

The effects of FLA99 and EWP840, two disulfiram analogs which potently inhibit Ins(1,4,5)P3 5-phosphatase, upon basal and thyrotropin-releasing hormone (TRH)-stimulated inositol (1,4,5)-trisphosphate (Ins(1,4,5)P3) levels were investigated. Neither test compound affected the characteristics of the [3H]Ins(1,4,5)P3 binding site used in the competitive protein binding assay of Ins(1,4,5)P3 levels. In rat GH3 pituitary cell suspensions, TRH (100 nM) produced a large and time-dependent increase in Ins(1,4,5)P3 concentration, the maximum response being obtained within 5 seconds of stimulation in these cells. Neither FLA99 (100, 300 and 1000 microM) nor EWP840 (100 microM) produced obvious effects on the Ins(1,4,5)P3 response to TRH stimulation. Higher concentrations of EWP840 (300 and 1000 microM) abolished the Ins(1,4,5)P3 response to TRH stimulation. The lack of effect of the 5-phosphatase inhibition in the cells may indicate that 5-phosphatase is not the major metabolic pathway of this second messenger in this cell line under the assay conditions used.

Adenoma↗
PubMedDate not supplied

"Specific" binding of [3H]-[Sar9,Met(O2)11]-substance P to tissue culture plates is found when substance P is used to define non-specific binding.

Following incubation at 4 degrees C, [3H]-[Sar9,Met(O2)11]-substance P bound to tissue culture plates in a manner displaceable by substance P (SP). The IC50 for SP was about 100 nM. Although the total binding to the wells could be reduced by increasing the assay bovine serum albumin concentration, by the presence of divalent ions and by gelatin-precoating of the wells, the remaining binding could be inhibited by about 70% by SP, and would thus appear as "specific" binding in assays. The non-peptide antagonist (+/-)CP-96345 also inhibited the binding to the wells at high concentrations (IC50 about 2 mcM), whereas physalaemin did not. Physalaemin is thus a better agent to define non-specific binding. The consequences of the "specific" binding to the culture wells observed with SP to define non-specific binding are demonstrated in two cell systems: in cultured human umbilical vein endothelial cells, an apparent receptor density of about 100,000/cell is shown to be due mainly to binding to the wells, rather than the cells. In UC11MG cells, which express 40,000-60,000 NK-1 recognition sites/cell, the use of SP to define binding gives artifactually high KD and Bmax values, and an artifactually low potency (and Hill slope) of (+/-)CP-96345 when compared with data obtained using physalaemin to define the non-specific binding.

Astrocytoma↗