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Biomedical subjects

D G Taylor

Publications and source records attributed to D G Taylor.

At least 91 records · Page 5Linked to original sources
PubMed1977

Reduction in blood pressure, sympathetic nerve discharge and centrally evoked pressor responses by methysergide in anesthetized cats.

Methysergide (1 and 3 mg/kg i.v.) caused dose-dependent reductions in blood pressure and heart rate of anesthetized cats. In addition, sympathetic nerve discharges of the postganglionic renal nerve were also markedly reduced by the same doses of drug. Pressor responses to electrical stimulation of the diencephalon were inhibited by 3 mg/kg but not 1 mg/kg of methysergide. These results suggest that methysergide acts to decrease blood pressure by a centrally mediated reduction in sympathetic nervous outflow and, at higher doses, can additionally prevent pressor changes caused by electrical activation of suprabulbar central structures. These results are in agreement with previous reports that methysergide has little or no peripheral effects on the cardiovascular system.

Action Potentials↗
PubMed1977

Bis-(4-methylumbelliferyl) phosphate as a substrate for the surface membrane-associated phosphodiesterase activity of pig platelets.

It was found that the newly-available compound, bis-(4-methylumbelliferyl) phosphate, could be used as a substrate for the pig platelet surface membrane-associated phosphodiesterase activity, usually assayed with bis-(p-nitrophenyl) phosphate. This enzyme activity is distinct from the phosphodiesterase activity towards 5'-dTMP-P-nitrophenyl ester, which is probably associated with intracellular membrane structures in platelets. Consequently, the use of the 4-methylumbelliferyl derivative as substrate for the phosphodiesterase activity provides a sensitive, fluorimetric assay for this marker enzyme of the platelet surface membrane.

Animals↗
PubMed1977

Localization in platelets of sodium 51Cr-chromate, 125I-antibody to whole membrane, and 3H-diisopropylfluorophosphate using electron microscopic autoradiography.

Platelets from the rabbit and rat, respectively, were incubated with sodium 51Cr-chromate and 3H-diisopropylfluorophosphate (3H-DFP) in the same manner as for platelet survival studies. A third isotope, 125I, was incorporated into a labeled antibody raised against a partially purified pig platelet membrane fraction. The 51Cr label was found to be concentrated predominantly in the cytoplasm, with a marked degree of association with mitochondria, whereas the tritium label appeared to be largely confined to the periphery of the platelet, particularly in association with the open canalicular system. The 125I-labeled antibody showed a very marked association with the plasma membrane and the open canalicular system, suggesting a membrane-bound affinity.

Animals↗
PubMed1976

Enzymatic and chemical analyses of pig platelet membrane subfractions isolated by zonal centrifugation.

1. A mixed membrane fraction prepared from pig platelets was subfractionated, using the "B 14" zonal rotor, into two distinct subpopulations of membrane vesicles, each associated with a different phosphodiesterase activity. 2. The lighter subfraction (MI) was enriched 7-8 fold with bis-(p-nitrophenyl) phosphate phosphodiesterase activity and the denser subfraction (MII) showed a similar degree of enrichment of 5'dTMP-p-nitrophenyl ester phosphodiesterase activity. 3. Assays for other enzyme activities revealed slight enrichement (approx. 2 fold) of acid phosphatase, 3'-dTMP-p-nitrophenyl ester phosphodiesterase and beta-glucuronidase activities in MI, and beta-galactosidase in MII. Cyclic AMP phosphodiesterase, lactate dehydrogenase and N-acetyl-beta-glucosaminidase showed negligible activity in both MI and MII, and succinate dehydrogenase activity could not be detected in either subfraction. 4. Chemical analyses of the membrane subfractions demonstrated that MI contained approx. twice as much cholesterol, phospholipid, sialic acid and hexosamine per unit weight of protein than MII. These results are consistent with our previously reported observations from surface-labelling experiments, which indicated that MI was derived principally from the platelet surface-exposed membranes and that MII was probably intracellular in origin. 5. Analysis of the membrane polypeptides by sodium dodecyl sulphate-polyacrylamide gel electrophoresis revealed the presence of 12-15 components, in each subfraction, in the mol. wt. range 12000-200000, including a prominent band of approx. mol. wt. 46000, which has beeen identified to be actin. Qualitative as well as possible quantitative differences were apparent in that MII contained three components in addition to those present in MI. 6. Analysis of the periodate-Schiff staining components by sodium dodecyl sulphate-polyacrylamide gel electrophoresis demonstrated the presence of 4 major glycoproteins in both subfractions with apparent mol. wt. ranging from approx. 95000 to 150000; in addition two minor components were also present. Further, a very fast-migrating band, which did not stain with Coomassie blue, was observed in both MI and MII and probably represents lipid material.

Amino Acids↗
PubMed1976

Spinal adrenergic mechanisms regulating sympathetic outflow to blood vessels.

The role of descending spinal catecholamine (CA)-containing fibers in cardiovascular regulation was examined. Monoamine-containing fibers were visualized by fluorescence histochemical methods at the cervical, thoracic, and lumbar spinal segments. Two major groups of descending CA-containing axons were located in the lateral funiculus at the midcervical spinal level. At the thoracolumbar spinal segments CA-containing terminals were concentrated mostly around cells of the intermediolateral nucleus. In addition a distinct CA-containing fasciculus was observed at the level of the sympathetic nucleus which appeared to course toward the opposite site of the cord. To evaluate the role of the efferent CA-containing fibers, changes in heart rate, arterial pressure, femoral blood flow, and calculated peak vascular resistance were elicited by electrical stimulation of selected sites in the midcervical spinal cord. Although changes in femoral flow and arterial pressure were evoked from many midcervical sites, there was a distinct correlation between the magnitude of peak femoral resistance elevation and density of CA-containing axons activated. Furthermore, efferent spinal vasoconstrictor outflow to the hindlimbs crosses below the cervical level. This observation is in good agreement with fluorescence microscopy studies revealing CA-containing fibers which appear to decussate. Pharmacological studies also were undertaken to evaluate transmission in spinal vasopressor pathways. In these studies alpha-adrenergic receptor antagonists and agonists were perfused into the spinal subarachnoid space. Heart rate, arterial pressure, femoral flow, and femoral resistance responses elicited from efferent spinal pathways were significantly attenuated following superfusion of the spinal cord with the alpha-antagonists BE-2254 (HEAT) and phentolamine. It was shown that inhibition of the centrally evoked responses was due to actions of the alpha-antagonists at a spinal locus and not due to peripheral vascular alpha-receptor blockade. Spinal perfusion with the alpha-receptor agonist norepinephrine potentiated cardiovascular responses. Likewise, loading with the norepinephrine precursor 3,4-dihydroxy-L-phenylalanine (L-dopa) enhanced vasoconstrictor responses evoked in the cross-perfused hindlimb of p-chlorophenylalanine-pretreated cats. These observations support the idea that bulbospinal CA-containing fibers relay excitatory impulses to preganglionic vasoconstrictor neurons and that spinal alpha-adrenergic receptor activation is necessary for transmission of this information.

Adrenergic alpha-Agonists↗
PubMed1975

Pathways for the degradation of m-cresol and p-cresol by Pseudomonas putida.

A comparison of the oxidation rates of various compounds by whole cells of Pseudomonas putida 3, 5 indicated that m-cresol is metabolized by oxidation to 3-hydroxybenzoate followed by hydroxylation to gentisate, the ring-fission substrate, when grown with 3, 5-xylenol. However, when m-cresol was the growth substrate, similar experiments suggested a different pathway involving a methyl-substituted catechol, and ring-fission by meta cleavage. Assays of ring-fission enzymes in cell-free extracts confirmed that different pathways are induced by the two growth substrates. 3, 5-Xylenol-grown cells contained high levels of gentisate oxygenase and only very small amounts of catechol oxygenase, whereas gentisate ocygenase could not be detected in m-cresol-grown cells, but levels of catechol oxygenase were greatly increased. Extracts of m-cresol-grown cells also contained 2-hydroxymuconic semialdehyde dehydrogenase and hydrolase, whose specificities enable them to metabolize the ring-fission products from catechol, 3-methylcatechol, and 4-methylcatechol. This catechol pathway is also used by m-cresol-grown cells for p-cresol metabolism. In contrast, the results for cells grown with p-cresol point to an alternative pathway involving oxidation to 4-hydroxybenzoate and hydrosylation to protocatechuate as ring-fission substrate. Extracts of these cells contained high levels of protocatechuate oxygenase and only small amounts of catechol oxygenase.

Adipates↗
PubMed1975

Baroreceptor mechanisms controlling sympathetic nervous rhythms of central origin.

A study was made in the anesthetized cat of the slow wave of sympathetic nervous discharge (SND) locked in a 1:1 relation to the cardiac cycle (3 cycle/s periodicity). SND was recorded from the preganglionic splanchnic and postganglionic renal nerves. The data contradict the generally accepted view that the slow wave occurs as the direct result of a waxing and waning of baroreceptor nervous discharge. Although baroreceptor denervation unlocked the phase relations between SND and the cardiac cycle, the slow wave persisted and its duration was not changed. Furthermore, the slow wave was aborted by stimuli delivered to the baroreceptor nerves or paramedian reticular nucleus during a time span which accounted for less than 1 percent of the cardiac cycle. It is concluded that the 3 cycle/s periodicity of SND is representative of a vasomotor rhythm of central origin which is entrained to the cardiac cycle by the baroreceptor reflexes. The sympathoinhibitory effect leading to the entrainment of the slow wave is mediated in the brainstem. ta spinal component of baroreceptor-induced sympathoinhibition also was demonstrated.

Animals↗