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Biomedical subjects

N S Sharpless

Publications and source records attributed to N S Sharpless.

At least 55 records · Page 3Linked to original sources
PubMed1978

Demethylation in erythrocytes: a reaction involving hemoglobin.

A reaction is described in erythrocytes of rat and of man whereby O-methylated metabolites of the catecholamines are demethylated to the corresponding catechols. The reaction was studied by incubating aliquots of erythrocyte lysates with radiolabeled O-methylated compounds and isolating the catechol product by alumina adsorption chromatography. The demethylating activity was located in the cytosol of the erythrocytes. Evidence was strong that oxyhemoglobin was responsible for the reaction: the demethylase activity was inseparable from oxyhemoglobin in several chromatographic separations. In addition, although commercially available hemoglobins were inactive in the reactions, after their conversion to oxyhemoglobin and purification, they did effect demethylation. Methemoglobin did not demethylate guaiacols and in fact inhibited demethylation by oxyhemoglobin. The reaction was inhibited by the addition of reduced pyridine nucleotides and of the methyl acceptor tetrahydrofolic acid.

Animals↗
PubMed1978

Ventricular fluid homovanillic acid and 5-hydroxyindoleacetic acid concentrations in patients with movement disorders.

Ventricular fluid concentrations of homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), the respective metabolites of dopamine and serotonin, were measured in 57 patients undergoing thalamotomy for relief of movement disorders. The diseases included were Parkinson disease, dystonia, cerebral palsy, multiple sclerosis, and posttraumatic or posthypoxic encephalopathy. Untreated parkinsonian patients had the lowest mean HVA level (119 ng per milliliter). Patients with multiple sclerosis or with posttraumatic or posthypoxic encephalopathy with both intellectual impairment and bilateral motor involvement had lower mean HVA levels (197 and 177 ng per milliliter, respectively) than cerebral palsy patients with bilateral motor disease (233 ng per milliliter), dystonia patients (246 ng per milliliter), or multiple sclerosis patients with normal intellect (376 ng per milliliter). The data suggest that diffuse cerebral disease may lead to diminished dopaminergic activity. Ventricular fluid 5-HIAA levels were similar in all groups of patients. Chronic cerebellar stimulation markedly increased ventricular fluid HVA and 5-HIAA levels, indicating that cerebellar stimulation affected cerebral dopaminergic and serotonergic systems.

Adult↗
PubMed1978

Diminished ventricular fluid dopamine metabolites in adult-onset dystonia.

Homovanillic acid (HVA) and 5-hydroxyindoleacetic acid (5-HIAA), the respective metabolites of dopamine and serotonin, were measured in ventricular fluid obtained from 20 patients with torsion dystonia at the time of ventriculography prior to thalamic surgery. The patients could be divided into two distinct types of dystonia--childhood-onset and adult-onset--which were identifiable on clinical and biochemical grounds. In the 14 patients with childhood-onset dystonia, the first symptom appeared in one limb in early childhood and the disease usually progressed rapidly. In the six patients with adult-onset dystonia, the first symptom usually appeared in axial muscles after adolescence and the disease progressed slowly. Ventricular fluid HVA levels were significantly lower in the patients with adult-onset dystonia than in those with childhood-onset dystonia. The differences suggest diminished dopaminergic activity, possibly secondary to nigrostriatal dysfunction, in adult-onset dystonia.

Adolescent↗
PubMed1977

Determination of 3-methoxy-4-hydroxyphenylglycol in urine and the effect of diet on its excretion.

A modified method is described for determination of 3-methoxy-4-hydroxyphenylglycol (MHPG) in urine by gas chromatography with electron capture detection. The method is reproducible and mean (+/- SD) recoveries of MHPG from urine were 78.5 +/- 12.7% and 76.5 +/- 15.0% in two separate series of analyses. Mean 24-hour MHPG excretion was 1884 +/- 591 microgram in 11 normal subjects and 1688 +/- 593 microgram in 20 patients with various types of depression. Males excreted more MHPG than females but this difference could be eliminated by expressing the values relative to the creatinine in urine. Variations in diet did not appear to influence urinary MHPG excretion.

Chromatography, Gas↗
PubMed1977

Patterns of dystonia ("I-D-I" and "D-I-D-") in response to l-dopa therapy for Parkinson's disease.

The clinical, biochemical, and pharmacologic responses to L-dopa were studied in 87 patients with Parkinson's disease. Eleven of the 87 patients had a long-duration response, 39 had a short-duration response, and 37 had a combination of both. Thirty-four of the 39 patients with short-duration response to L-dopa experienced a consistent and reproducible sequence of clinical and biochemical events after each dose, characterized by improvement of parkinsonism and a single phase of dystonia occurring during or shortly after the peak of dopa concentration in plasma and during maximal clinical improvement. We have called this the I-D-I- response, for Parkinsonism-Improvement-Dystonia-Improvement-Parkinsonism. The remaining five patients all had the onset of the disease at an unusually young age and showed a distinctly different response pattern consisting of a first phase of dystonia, before there was any improvement, followed by a phase of improvement without dystonia and then by a second phase of dystonia before the abrupt return of parkinsonism. We have called this the D-I-D response, for Parkinsonism-Dystonia-Improvement-Dystonia-Parkinsonsim. Dystonia occurs in the D-I-D- response when the concentration of dopa in plasma passes through a critical but relatively low level, whereas it remains absent as long as the concentration of dopa remains above that level. In the I-D-I- response, dystonia is avoided by keeping the plasma concentration of dopa low, in the D-I-D- response by keeping it high. It is postulated that in the D-I-D response postsynaptic depolarization blockade due to supramaximal stimulation of the neuronal system mediating dystonia occurs, whereas in the I-D-I response the postsynaptic members of the same neuronal population respond with excitation but not with depolarization blockade.

Dose-Response Relationship, Drug↗
PubMed1975

Effect of L-DOPA on endogenous histamine metabolism.

To estimate the effect of long-term administration of L-3,4-dihydroxyphenylalanine (L-Dopa) on methylation of compounds not formed from it, the urinary excretion of histamine and its methylated metabolites was studied in rats and guinea pigs fed L-Dopa in their diets and in patients with Parkinson's disease being treated with L-Dopa. In the guinea pigs, but not in the rats, L-Dopa administration decreases excretion of histamine and of its methylated metabolites, methylhistamine and 1-methylimidazole-4-acetic acid. Because excretion of 1-methylimidazole-5-acetic acid, which comes from the diet and is not a metabolite of histamine, was unaffected by the L-Dopa treatment, the decreases were due to a specific effect of L-Dopa on histamine metabolism. When compared to normal control subjects, patients with Parkinson's disease excreted less histamine and methylhistamine, both before and during treatment with L-Dopa. Administration of the peripheral aromatic L-amino acid decarboxylase inhibitor, L-alpha-methyldopa hydrazine (MK 486), decreased urinary excretion of histamine markedly. Neither L-Dopa nor MK 486 appeared to influence excretion of the imidazoleacetic acids in the patients. The results suggest that L-Dopa may decrease histamine formation or release in some species but that it does not influence histamine methylation.

Acetates↗