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Biomedical subjects

S Knapp

Publications and source records attributed to S Knapp.

161 records · Page 9Linked to original sources
PubMed1973

Short- and long-term lithium administration: effects on the brain's serotonergic biosynthetic systems.

Short-term treatment with lithium chloride stimulates the uptake of tryptophan and its conversion to serotonin by striate synaptosomes. Preincubation of striate synaptosomes with L-tryptophan and in vivo administration of L-tryptophan appear to act in a similar manner. Midbrain tryptophan hydroxylase activity is reduced in temporal continuity with the lithium-induced activation of tryptophan uptake and conversion. By 10 days, conversion of tryptophan to serotonin in nerve endings becomes a joint function of the maintained increased uptake of tryptophan and a decreased level of tryptophan hydroxylase activity in nerve endings. The occurrence of this delayed alteration corresponds in time to the previously described axoplasmic flow rate for tryptophan hydroxylase.

Animals↗
PubMed1972

Narcotic drugs: effects on the serotonin biosynthetic systems of the brain.

The effects of short- and long-term administration of morphine on the activity of two measurable forms of rat brain tryptophan hydroxylase were studied. Morphine administration produced an immediate decrease and a longterm increase in the nerve ending (particulate) enzyme activity but did not change the cell body (soluble) enzyme activity. Cocaine administration demnonstrated a short-term decrcease in measurable nerve eniding enzyme activity that was due to the inhibition of the high affinity uptake (the Michaelis constant, K(m) is 10-(5) molar) of trytophan, the serotonin precursor. Cocaine did not aflect the low affinity uptake K(m) = 10-(5) molar) of tryptophan. Both the uptake of the precursor and the enizymiie activity appeared to be drug-sensitive regullatory processes in the biosynthlesis of serotonin.

Animals↗
PubMedDate not supplied

New insights into hepatitis C.

Hepatitis C infection is characterised by three key features, which are the consequence of a complex interaction between genetic determinants of immune and other host factors and viral characteristics: 1. A high rate of viral persistence after acute infection resulting from a combination of weak T cell responsiveness and specific viral mechanisms of immune escape. 2. Marked interindividual variability in end-organ damage (fibrosis and cirrhosis), probably due to host genetic polymorphisms in genes governing the immune response and fibrosis pathways in addition to viral pathogenicity factors. 3. Significant resistance to antiviral therapies. Viral mechanisms of antiviral resistance parallel those of viral persistence, and include the intriguing possibility that hepatitis C may infect immunologically privileged sites such as the central nervous system.

Antiviral Agents↗
PubMedDate not supplied

Correlation between plasma physostigmine concentrations and percentage of acetylcholinesterase inhibition over time after controlled release of physostigmine in volunteer subjects.

Five to six subjects ingested doses of controlled-release physostigmine salicylate tablets (9, 12, and 15 mg) followed by sequential blood drawing for measurement of plasma physostigmine concentrations and percentage of acetylcholinesterase (AChE) inhibition. Both plasma physostigmine concentrations and percentage of AChE inhibition demonstrated dose proportionality to three doses of ingested drug. Plasma physostigmine concentrations correlated with percentage of AChE inhibition across time by dose and across all doses and subjects tested. These data should be helpful to physicians in adjusting physostigmine dosing, enabling them to use the relatively simple and widely available AChE assay to approximate plasma physostigmine concentrations.

Adult↗