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Biomedical subjects

M Da Prada

Publications and source records attributed to M Da Prada.

At least 91 records · Page 5Linked to original sources
PubMed1987

Uptake, release, and subcellular localization of 1-methyl-4-phenylpyridinium in blood platelets.

The neurotoxic compound 1-[methyl-3H]-4-phenylpyridinium ([3H]MPP+) was actively taken up by human, rabbit, and guinea pig platelets incubated in plasma. In human platelets, the apparent Km of this uptake (22.6 microM) was 50 times higher than that for serotonin [5-hydroxytryptamine (5-HT]). The uptake of [3H]MPP+ by human platelets was inhibited by selective 5-HT uptake blockers [cianopramine, (-)-paroxetine, and clomipramine], by metabolic inhibitors (KCN and ouabain), and by drugs that interfere with amine storage in the 5-HT organelles (reserpine, mepacrine, and Ro 4-1284). Impairment of the transmembrane proton gradient by ionophores (monensin and nigericin) induced a marked release of radioactivity from platelets preincubated with [3H]MPP+. Fractionation of homogenates of rabbit platelets preincubated with [3H]MPP+ showed that the drug was concentrated to a great extent in the 5-HT organelle fraction. MPP+ competitively inhibited [14C]5-HT uptake by human platelets and reduced the endogenous 5-HT content of human, rabbit, and guinea pig platelets. These investigations show that MPP+ is transported into the platelets via the 5-HT carrier and is accumulated predominantly in the subcellular organelles that store 5-HT and other monoamines. It is suggested that an accumulation of MPP+ in amine storage vesicles of neurons may be involved in the effects of the drug in the CNS, e.g., by protecting other subcellular compartments from exposure to high concentrations of MPP+, by sustaining a gradual release of the toxin, or both.

1-Methyl-4-phenylpyridinium↗
PubMed1987

Binding of [3H]Ro 16-6491, a reversible inhibitor of monoamine oxidase type B, to human brain mitochondria and platelet membranes.

The reversible inhibitor of monoamine oxidase type B (MAO-B) [3H]Ro 16-6491 binds specifically and with high affinity to a single population of binding sites in human frontal cortex crude mitochondria and platelet membranes. In both tissues binding equilibrium was reached after 1 h incubation at 20 degrees C. Dissociation of bound radioactivity was relatively fast at 20 degrees C (t1/2 = 90-120 min) whereas at 0 degrees C [3H]Ro 16-6491 showed the characteristics of a slowly dissociating ligand. Inhibitors and substrates of MAO-B inhibited binding of [3H]Ro 16-6491, whereas MAO-A blockers were much less potent. Ro 16-6491 was also a substrate for MAO-B and a stable unidentified intermediate of the oxidation of Ro 16-6491 possessing high affinity for the enzyme may account for the marked MAO-B inhibitory effect of the drug. According to this hypothesis Ro 16-6491 would behave as a mechanism-based reversible inhibitor. In conclusion, [3H]Ro 16-6491 binds selectively to MAO-B and represents an excellent new radioligand probe for studying the regional tissue distribution of this enzyme in normal and pathological conditions.

Benzamides↗
PubMed1987

Inhibition of decarboxylase and levels of dopa and 3-O-methyldopa: a comparative study of benserazide versus carbidopa in rodents and of Madopar standard versus Madopar HBS in volunteers.

The combinations of benserazide and levodopa (1:4, Madopar) and of carbidopa and levodopa (1:10 and 1:4, Sinemet) are currently the most effective treatment of Parkinson's disease. In the present comparative study some effects of the peripheral aromatic L-amino acid decarboxylase (AADC) inhibitors benserazide and carbidopa administered alone or in combination with levodopa by the oral route were investigated in two animal species (rat and mouse) and in healthy volunteers. Benserazide is about 10 times more potent than carbidopa as inhibitor of peripheral AADC both in animals and man. Even at relatively high doses (up to 60 mumol/kg p.o.) benserazide is shown in animals to inhibit the decarboxylation of levodopa only in the extracerebral tissues, thus permitting the formation of dopamine in the striatum and in the hypothalamus. As benserazide is the most potent peripheral AADC inhibitor presently available, is well tolerated and relatively nontoxic even when used chronically, it appears to be the peripheral AADC inhibitor of choice for the development of controlled-release formulations in which Dopa is combined with a peripheral AADC inhibitor. When administered to healthy subjects the pharmacokinetics of the new drug delivery system named Madopar HBS (hydrodynamically balanced system) was characterized by lower and delayed plasma peak concentrations but a longer-lasting concentration of Dopa than after Madopar standard. Therefore, this new controlled-release system may reduce the clinical fluctuations occurring in patients with 'wearing-off' and 'on-off' phenomena.

Administration, Oral↗
PubMed1987

Bioavailability of L-dopa after Madopar HBS administration in healthy volunteers.

Eight healthy male and fasted volunteers received alternatively either one HBS capsule of Madopar 125 or two HBS capsules of Madopar 125 or one standard capsule of Madopar 125 at weekly intervals with and without benserazide pretreatment (50 mg t.i.d. for 6 days). In this trial the Madopar formulations were administered 9.5 h after the last dose of benserazide. Serial blood samples were collected at various time intervals up to 12 h after Madopar dosing. Levodopa plasma concentrations were measured by high-performance liquid chromatography with electrochemical detection. After Madopar HBS without benserazide pretreatment the peak concentration (Cmax) of levodopa was lower and occurred at later times (tmax) than after standard Madopar. The mean values for tmax were 2.4, 2.8 and 0.8 h, whereas those for Cmax were 0.25, 0.56 and 1.38 micrograms/ml for one HBS capsule, two HBS capsules and standard Madopar, respectively. The mean relative bioavailability (versus standard Madopar) was 58 and 67% (value normalized to dose) for one and two HBS capsules, respectively. The parameter of half-value duration (= time span where plasma concentrations are equal to or higher than the half Cmax) was on average 3.5, 3.8 and 0.8 h for one HBS capsule, two HBS capsules and standard Madopar, respectively. Following benserazide pretreatment the mean tmax values for levodopa were 2.8, 2.3 and 0.8 h and the mean Cmax values were 0.35, 0.60 and 1.33 micrograms/ml, respectively, for one HBS capsule, two HBS capsules and standard Madopar. The relative bioavailability (versus standard Madopar) was 57 +/- 14 and 63 +/- 21% (value normalized to dose) for one and two HBS capsules, respectively. The mean values of the half-value duration were 3.6, 4.2 and 1.3 h for one HBS capsule, two HBS capsules and standard Madopar, respectively. For most of the parameters measured, the interindividual variability after Madopar HBS was less pronounced than after standard Madopar. In conclusion, according to these kinetic data, Madopar HBS shows the characteristics of a controlled-release formulation. The reduced bioavailability of the HBS form (60% of that of the standard form) suggests that a higher daily dose of Madopar HBS should be used for clinical practice.

Administration, Oral↗
PubMed1985

Evidence for the release of 1-methyl-4-phenylpyridinium (MPP+) from rat striatal neurons in vitro.

[3H]MPP+ (1-[methyl-3H]4-phenylpyridinium) is taken up into rat striatal slices in a temperature-, time- and Na+-dependent process blocked by dopamine (DA) uptake inhibitors. Once taken up, authentic [3H]MPP+ is released at 37 degrees C by 15 mM KCl. This release is inhibited by (-)N-propyl-norapomorphine and enhanced by (-)sulpiride, as observed under the same conditions for [3H]DA release. Thus, rat striatal DA-ergic nerve endings do not discriminate between DA and MPP+ for their active transport and DA autoreceptor-regulated release.

1-Methyl-4-phenylpyridinium↗
PubMed1985

Conversion of the neurotoxic precursor 1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine into its pyridinium metabolite by human platelet monoamine oxidase type B.

MPTP (1-methyl-4-phenyl-1,2,5,6-tetrahydropyridine) causes selective and irreversible degeneration of the substantia nigra of human and non-human primates. In the central nervous system, the oxidative metabolism of MPTP to 1-methyl-4-phenyl-pyridinium (MPP+) by monoamine oxidase type B (MAO-B) seems to be a critical feature in the neurotoxic process. We now report that [3H]MPTP is rapidly converted in vitro into [3H]MPP+ by human platelet MAO-B. The formation of [3H]MPP+ in human platelets is prevented by specific MAO-B but not by MAO-A or by 5-hydroxytryptamine uptake inhibitors.

1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine↗
PubMed1985

Simultaneous determination of histamine and N alpha-methylhistamine in biological samples by an improved enzymatic single isotope assay.

A modified highly sensitive and specific radioenzymatic assay for the simultaneous determination of histamine (HA) and N alpha-methylhistamine (N alpha-MH) in tissues and body fluids is described. In the presence of the enzyme histamine-N-methyltransferase and of the methyl donor [3H]-S-adenosylmethionine, the transmethylation process was about seven times more effective for HA than for N alpha-MH. In the same conditions only very low amounts of N alpha, N alpha-dimethylhistamine (N alpha, N alpha-DMH) were converted into its 1-methylated derivative. The high degree of specificity attained by this method is due to the rapid quantitative extraction of the biological fluids, to the partially purified enzyme preparation and to the thin-layer chromatography system used which allows an excellent separation of the 3H-1-methyl products of HA, N alpha-MH and N alpha, N alpha-DMH. This method is highly sensitive for the assay of HA and N alpha-MH (detection limit 10 and 50 picograms, respectively), but due to lack in sensitivity, it cannot be extended to the measurement of N alpha, N alpha-DMH. The HA content of 20-30 samples can be determined in duplicate by one person in a working day. The concentrations of HA measured by this method in different biological samples (human whole blood, plasma, urine, gastric juice and skin biopsies) were in good agreement with the values reported in the literature. The presence of minute amounts of N alpha-MH in the human gastric juice was established by rigorous checking.

Body Fluids↗
PubMed1985

Serotonin involvement in lisuride-induced mounting and in sleep.

Mounting behavior of rats induced by several drugs, such as e.g. p-CPA, 5,7-dihydroxytryptamine, L-DOPA or lisuride, appears to result from a combined decrease of 5-hydroxytryptamine (5-HT) and increase of dopamine (DA) neurotransmission. In this paper, lisuride-induced mounting is proposed as a behavioral model for detecting pharmacologically active drugs that interact with monoaminergic mechanisms, e.g. 5-HT reuptake blockers and type A monoamine oxidase inhibitors. With regard to sleep, 5-HT appears to sustain a relevant part in controlling the sleep-wakefulness cycle. However, other transmitters or neuromodulators (catecholamines, oligopeptides etc.) may also be involved in sleep mechanisms.

Animals↗
PubMed1984

The pharmacology of Parkinson's disease: basic aspects and recent advances.

Basic aspects and recent advances in the understanding of the pharmacological mechanism of action of the clinically most used antiparkinson drugs are reviewed. Recent human and animal biochemical investigations clearly confirm and extend previous findings indicating that benserazide is much more potent than carbidopa as peripheral decarboxylase inhibitor. L-DOPA in combination with benserazide or carbidopa constitutes the best available therapy for Parkinson's disease (PD). To reduce peaks and rapid fluctuations of L-DOPA plasma levels (possibly responsible for peak-dose dyskinesias and end-of-dose deterioration) a slow-release formulation of L-DOPA in combination with benserazide or with benserazide plus catechol-O-methyltransferase inhibitors should be developed. In parkinsonian patients under long-term L-DOPA therapy monoamine oxidase inhibitors type B (MAO-B) e.g. (-)deprenyl and direct dopamine receptor agonists (bromocriptine, lisuride, pergolide etc.), due to their L-DOPA-sparing effects, alleviate in some cases L-DOPA-induced side-effects e.g. dyskinesias and on-off phenomena. However, since (-)deprenyl, due to its metabolism to (-)methamphetamine and (-)amphetamine, seem to have indirect sympathomimetic activity, new selective MAO-B inhibitors devoid of indirect sympathomimetic effects should be tested clinically to assess the functional role of pure MAO-B inhibition in the therapy of PD. The auxiliary therapy with direct dopamine receptor agonists of the D-2 subtype represents another valid approach which should be further investigated in order to find novel dopamine agonists, less expensive than bromocriptine, and strictly selective for D-2 receptor sites.

Animals↗
PubMed1984

Circadian rhythm in rat retinal dopamine.

Rat retinal dopamine concentration and synthetic rate exhibit a circadian rhythm that persists in the absence of time cues. Although the population of retinal amacrine cells containing dopamine is small, retinal dopamine neurones may lie on the pathway mediating light information to the circadian system.

Animals↗
PubMed1984

[Levels of free and conjugated catecholamines in amniotic fluid and in umbilical and maternal blood in patients undergoing cesarean section].

A new radioenzymatic assay was used to evaluate free and conjugate catecholamines in six pregnant women who underwent cesarean section at term, in their newborns and in the amniotic fluid. Free adrenaline in maternal plasma was higher while noradrenaline and dopamine were lower at the moment of surgery than 24 hours before the operation. In umbilical plasma adrenaline and noradrenaline are higher than in maternal plasma while only traces of free dopamine and salsolinol are present. In the amniotic fluid high levels of free and conjugated salsolinol are found. The high level of free and conjugated catecholamines found in the umbilical plasma demonstrates that fetal sympathetic nervous system is strongly activated at delivery. Furthermore the presence of sulfoconjugating activity similar to that of the adult is confirmed.

Amniotic Fluid↗
PubMed1983

Effects of neurochemical lesions restricted to spinal cord monoaminergic neurons on blood pressure and sympathetic activity of spontaneously hypertensive rats.

Intraspinal (i.s.) injection of 6-hydroxydopamine or 5,7-dihydroxytryptamine in newborn spontaneously hypertensive rats (SHR) resulted, in the adult animal (30-week-old), in a marked decrease of spinal cord noradrenaline (NA) or 5-hydroxytryptamine (5-HT) levels, respectively. Since both neurotoxin- and vehicle-injected rats developed full hypertension and had similar plasma catecholamine concentrations, it is concluded that in SHR neither spinal cord NA nor 5-HT play a major role in development and maintenance of hypertension.

Animals↗
PubMed1983

The immune response evokes changes in brain noradrenergic neurons.

A decreased noradrenaline turnover in the hypothalami of rats was observed at the peak of the immune response to sheep red blood cells. The decrease in noradrenergic neuronal activity was mimicked by injection of soluble r mediators released by immunological cells activated in vitro. Noradrenaline also tended to decrease in the brainstem but not in the residual brain. It is suggested that products released from activated immunological cells during the immune response may induce the previously described autonomic and endocrine mechanisms that contribute to immunoregulation.

Animals↗
PubMed1983

Effects of clonidine on the rate of noradrenaline turnover in discrete areas of the rat central nervous system.

Turnover of noradrenaline in various regions of the rat brain was estimated by the decrease in noradrenaline content and/or formaldehyde-induced catecholamine fluorescence after inhibition of noradrenaline biosynthesis with alpha-methyl-p-tyrosine. Clonidine (0.1 and 0.3 mg/kg p.o.) decelerated the decrease in noradrenaline content of the locus coeruleus, the nucleus of the solitary tract, the intermediolateral cell column and the ventral horn of the thoracic spinal cord, as measured in tissue punches of the respective regions with a sensitive radioenzymatic method. In all these central regions the clonidine-induced decrease in noradrenaline turnover was antagonized by yohimbine, but not by phenoxybenzamine, indicating mediation through central alpha 2-adrenoceptors, similar to the cardiovascular effects of clonidine. When given alone, both yohimbine and phenoxybenzamine accelerated the disappearance of noradrenaline after inhibition of its biosynthesis. The combined results of radioenzymatic assay and fluorescence histochemistry determinations demonstrated that clonidine markedly reduced noradrenaline turnover in central noradrenaline-containing nerve terminals, but had no effect on the cell bodies of the A1 and A2 cell groups. Noradrenaline turnover was, however, decreased in projection areas of the A1 and A2 cell groups, namely the intermediolateral cell column of the spinal cord and nucleus of the solitary tract, respectively. This observation argues against the existence of a neuronal feedback loop running from the projection areas to the cell bodies of the A1 and A2 cell groups and mediating inhibition of noradrenaline turnover. The effect of clonidine on noradrenaline turnover is, therefore, most likely the result of a local feedback inhibition through presynaptic alpha-adrenoceptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1983

Intestinal absorption of levodopa in man.

In four healthy subjects the intestinal absorption of levodopa (l-dopa) was investigated by measuring the plasma concentration of the amino acid following the administration of l-dopa at three different sites in the small intestine. In order to minimize presystemic clearance of l-dopa, the subjects were pretreated with the peripheral decarboxylase inhibitor benserazide 3 X 50 mg every 8 h on the previous day and 1 X 50 mg 2 h prior to administration of the l-dopa. L-dopa 100 mg dissolved in 0.05 N HCl and 50 mg benserazide dissolved in 0.05 N HCl were coadministered. Under these conditions no difference in tmax, cmax or AUC of l-dopa was observed between administration of the drug into the proximal or the distal part of duodenum, or into the upper part of jejunum. The results indicate that in healthy subjects, during inhibition of peripheral decarboxylase, the rate and extent of l-dopa absorption does not differ at any site in the upper small intestine.

Adult↗