A non-radiometric method to measure the catechol-O-methyltransferase (COMT) activity in erythrocytes was modified to increase its sensitivity four-fold as well as its reproducibility and applicability. The method is based on the COMT-mediated O-methylation of 4-(naphtho [1,2-d] thiazol-2-yl) pyrocatechol, the product of which was determined fluorometrically. COMT activities down to less than 1% of those present at baseline could be measured precisely and accurately. The intra- and inter-assay coefficients were below 3 and 5.3%, respectively. Basal COMT activity and the distribution between soluble and membrane-bound COMT was shown to be variable among different species (ten species tested). The applicability of the method was demonstrated by the characterization of COMT activity-time courses in human erythrocytes after oral administration of the COMT inhibitor tolcapone. The assay developed will be useful in the rapid screening and clinical development of new COMT inhibitors.

Animals↗

PubMedDate not supplied

Effects of L-dopa on plasma levels of parathyroid hormone in calves.

After oral administration of l-dihydroxyphenylalanine (L-dopa) to calves, plasma concentrations of L-dopa, dopamine, norepinephrine and parathyroid hormone increased whereas prolactin and calcium decreased while epinephrine remained unchanged. The decrease of prolactin presumably occurred as a consequence of the conversion of L-dopa to dopamine (in the hypothalamus), whereas the increase in parathyroid hormone was caused by hypocalcemia, by elevated dopamine and possibly by norepinephrine.

Administration, Oral↗

PubMedDate not supplied

Accumulation of basic drugs in 5-hydroxytryptamine storage organelles of rabbit blood platelets.

The subcellular distribution of basic substances such as mepacrine, chloroquine, chlorpromazine and imipramine was studied in rabbit blood platelets exposed to these compounds in vitro and to some in vivo. All the drugs showed a preferential concentration in the 5-hydroxytryptamine (5HT) storage organelles (5HT vesicles). Chloroquine and mepacrine accumulated more specifically in the organelles than did chlorpromazine and imipramine. After osmotic shock of the 5HT vesicles chlorpromazine sedimented mostly with the vesicular membranes, whereas the other compounds preferentially went into the supernatant. It is concluded that (a) fluorescent basic compounds such as mepacrine are rather specific markers for the 5HT storage organelles in live platelets and (b) drugs such as chlorpromazine and imipramine also have a considerable affinity for these organelles.

Animals↗

PubMedDate not supplied

Catecholamine and serotonin depletion from rat spinal cord: effects on morphine and footshock induced analgesia.

Using a methodology that causes a selective degeneration of spinal cord catecholaminergic or serotoninergic pathways but not those of the brain, it has been possible to study more precisely the role played by the spinal cord monoaminergic systems that underly the mechanism through which morphine and endogenous opioids modulate nociceptive inputs. Both noradrenaline (NA) and serotonin (5-HT) appear to be involved: first, the noradrenergic and only subsequently, with higher doses of the opiate, the serotoninergic pathways.

5,7-Dihydroxytryptamine↗

PubMedDate not supplied

[Pharmacological changes in metabolism of blood platelet 5-hydroxytryptamine].

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Animals↗