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F Martel

Publications and source records attributed to F Martel.

At least 37 records · Page 2Linked to original sources
PubMed2000

Effect of P-glycoprotein modulators on alkaline phosphatase activity in cultured rat hepatocytes.

Alkaline phosphatases (orthophosphoric-monoester phosphohydrolase, E. C. 3.1.3.1) are a group of nonspecific phosphomonoesterases located primarily in the plasma membrane of the cells in which they occur [1]. It was recently demonstrated that alkaline phosphatase (ALP) concentration in different tissues is positively correlated with the extent of exchange surface per unit volume of the tissue, suggesting an association between ALP and transport systems [2]. Moreover, several groups [3,4,5] obtained evidence of an involvement of ALP in the modulation of P-glycoprotein activity in hepatocytes. The aim of the present study was to determine the putative influence of compounds known to modulate P-glycoprotein-mediated transport on hepatic ALP activity, by using primary cultured rat hepatocytes. The K(m) and V(max) values of ALP were determined (657.2 microM (306.8-933.1) and 32.0+/-1.5 nmol mg protein(-1) min(-1), respectively). Vanadate and corticosterone concentration-dependently reduced ALP activity, producing maximal reductions of 79% (100 microM) and 71% (100 microM), respectively. The IC50's were found to be 7.9 microM (2.1-29.5 microM) and 2.4 microM (0.2-35.2 microM), respectively. Cyclosporin A, verapamil, octreotide, kaempferol, daunomycin and genistein produced a concentration-dependent increase in ALP activity. ALP activity was maximally increased to 253%, 390%, 180%, 487%, 449% and 193% of control in the presence of 100 microM cyclosporin A, 50 microM verapamil, 10 microM octreotide, 100 microM kaempferol, 100 microM daunomycin and 1 microM genistein, respectively. The results show that all P-glycoprotein modulators tested were able to significantly affect the activity of hepatic-ALP. These effects on ALP activity may contribute to the modulation of P-glycoprotein activity by these drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1999

Characterization of the efflux of the organic cation MPP+ in cultured rat hepatocytes.

The aim of this study was to characterize the efflux of organic cations from primary cultured rat hepatocytes, using 1-methyl-4-phenylpyridinium (MPP+) as a model compound. The efflux of [3H]MPP+ was temperature dependent, and pH and metabolic inhibition independent. It was either strongly reduced (verapamil, vinblastine and rhodamine123) or only moderately reduced (daunomycin) by other organic cations. The anti-P-glycoprotein antibody UIC2 (20 microg/ml) and the P-glycoprotein inhibitors vanadate and cyclosporine A had no effect on [3H]MPP+ efflux. Decynium22 and corticosterone, known inhibitors of rat Organic Cation Transporter 1 (rOCT1), markedly reduced [3H]MPP+ efflux. The uptake of [3H]MPP+ into hepatocytes, known to be mediated by rOCT1, was inhibited by verapamil and vinblastine (IC50s of 2.6 and 34.4 microM, respectively). In conclusion, [3H]MPP+ efflux from primary cultured rat hepatocytes appears to be mediated by rOCT1, a polyspecific organic cation transporter. Moreover, our results do not support the involvement of P-glycoprotein or of an organic cation/proton antiporter in the efflux of [3H]MPP+.

1-Methyl-4-phenylpyridinium↗
PubMed1999

Inhibition by levamisole of the organic cation transporter rOCT1 in cultured rat hepatocytes.

Levamisole is known to be subject to hepatic removal and metabolism and to biliary excretion. The aim of our work was to study the mechanism involved in the removal of this compound by the liver. For this purpose, we studied the influence of levamisole on the uptake and efflux of the model organic cation 1-methyl-4-phenylpyridinium (MPP(+)) by primary cultured rat hepatocytes. Levamisole (500 microm) was found to produce a strong inhibition (to 31+/-2% of control) of [(3)H]MPP(+)uptake. Moreover, efflux of [(3)H]MPP(+)was also potently reduced by levamisole (500 microm). Our results show that levamisole interferes with an hepatic organic cation transporter which accepts MPP(+)as a substrate. This mechanism most probably corresponds to rOCT1, and it might be responsible for the hepatic removal of levamisole from the blood circulation.

1-Methyl-4-phenylpyridinium↗
PubMed1999

Comparison between uptake2 and rOCT1: effects of catecholamines, metanephrines and corticosterone.

Active and specialized transmembrane transport systems are responsible for the functional inactivation of catecholamines. Uptake2, the classical extraneuronal uptake system, and rOCT1, a recently cloned organic cation transporter, share a number of properties. The present study was undertaken to investigate putative differences between these two transporters that might clarify their relative physiological roles. Uptake of [3H]MPP+ ([3H]1-methyl-4-phenylpyridinium) by Caki-1 cells (to study uptake2) and by primary cultured rat hepatocytes (to study rOCT1) was kinetically and pharmacologically characterized. In both cell types, [3H]MPP+ was avidly taken up and accumulated. All compounds tested (catecholamines, metanephrines and corticosterone) inhibited [3H]MPP+ uptake, albeit with different potencies. In Caki-1 cells, the ranking order of inhibitory potency was: (-)isoprenaline > (-)adrenaline >> (-)noradrenaline > dopamine. Metanephrine and normetanephrine were equipotent. Corticosterone had an IC50 of 102 nM. In cultured hepatocytes, the ranking order of inhibitory potency was: (-)isoprenaline > dopamine > (-)adrenaline >> (-)noradrenaline. Metanephrine was about seven times more potent than normetanephrine. Corticosterone had an IC50 of 72 microM, being about 700-fold less potent in inhibiting rOCT1 than uptake2. The results showed that uptake2 and rOCT1 can be clearly distinguished on a functional basis. On the one hand, uptake2 prefers adrenaline among the endogenous catecholamines, whereas rOCT1 has similar affinity for adrenaline and dopamine. On the other hand, corticosterone and normetanephrine are significantly more potent in inhibiting uptake2 than rOCT1. The results are compatible with a possible physiological role of corticosteroids in the modulation of adrenaline effects in tissues equipped with uptake2, without significant interference with the hepatic and renal excretion of catecholamines.

1-Methyl-4-phenylpyridinium↗
PubMed1998

Molecular cloning and characterization of two novel transport proteins from rat kidney.

The recent cloning of renal transport systems for organic anions and cations (OAT1, OCT1, and OCT2) opened the possibility to search, via polymerase chain reaction (PCR) homology screening, for novel transport proteins. Two integral membrane proteins, UST1 and UST2, were cloned from rat kidney. RT-PCR revealed that UST1 is confined to the kidney whereas UST2 mRNA was detected in all tested tissues. Sequence analyses suggest that UST1 and UST2, together with four related transporters, comprise, within the major facilitator superfamily, a so far unrecognized transporter family, termed amphiphilic solute facilitator (ASF) family. Characteristic signatures for the ASF family were identified.

Amino Acid Sequence↗
PubMed1998

Postnatal development of organic cation transport in the rat liver.

Previous studies have demonstrated that the small permanently charged organic cation 1-methyl-4-phenylpyridinium (MPP+) is avidly taken up by rat hepatocytes. The aim of this study was to characterise the postnatal development of hepatic uptake of organic cations, using the model compound MPP+. Accumulation of [3H]MPP+ by liver slices obtained from rats ranging from 1 day to 7 weeks was measured, and the effect of a series of compounds on [3H]MPP+ uptake was examined. The accumulation of [3H]MPP+ by liver slices was similar in adult (87.5 +/- 19.9 pmol g-1; n = 7) and neonatal rats (110.6 +/- 11.5 pmol g-1; n = 15). Verapamil, quinidine (100 microM) and progesterone (200 microM) produced very marked reductions on [3H]MPP+ uptake at all ages, and the inhibitory effect of verapamil and quinidine was maximum in livers from 1-day-old rats. Bilirubin (200 microM) significantly reduced [3H]MPP+ uptake by liver slices from 1 day, 1 week and 7-week-old rats. However, [3H]MPP+ accumulation was reduced by cimetidine, vinblastine and daunomycin (100 microM) in 1-day-old rats, but the effect of these drugs disappeared as the animals age increased. These findings demonstrate that hepatic organic cation uptake capacity is remarkably high shortly after birth and suggest that at least two distinct uptake mechanisms are involved in this process. These uptake systems are the type I hepatic transporter of organic cations, active from birth to adulthood, and P-glycoprotein, active only in very young rats.

1-Methyl-4-phenylpyridinium↗
PubMed1998

Effect of bile duct obstruction on hepatic uptake of 1-methyl-4-phenylpyridinium in the rat.

Previous studies have demonstrated that the organic cation 1-methyl-4-phenylpyridinium (MPP+) is avidly taken up by rat freshly isolated hepatocytes through at least two distinct transport mechanisms: the type I hepatic transporter of organic cations and P-glycoprotein. In this study, the effects of extrahepatic cholestasis induced by bile duct ligation for 4 days on the uptake of [3H]MPP+ by rat freshly isolated hepatocytes and liver slices were determined. Bile duct ligation produced no significant alterations in the characteristics of [3H]MPP+ uptake by freshly isolated hepatocytes. The strong correlation found between the effect of various drugs on [3H]MPP+ uptake by hepatocytes from control and treated rats (r = 0.958; P < 0.0001; n = 15) suggests that neither the type I hepatic transporter of organic cations nor P-glycoprotein were affected by bile duct ligation. On the contrary, uptake of [3H]MPP+ by liver slices was markedly changed after bile duct ligation: (1) there was a significant increase (approximately equal to 40%) in the amount of [3H]MPP+ taken up by liver slices from bile duct-ligated rats; (2) there was no correlation between the effect of various drugs on [3H]MPP+ uptake by liver slices from control and treated rats (r = 0.772; P= 0.072; n = 6). On the basis of (1) the lack of effect of bile duct ligation on [3H]MPP+ uptake by isolated hepatocytes; and (2) the profound morphological alterations of liver tissue observed 4 days after bile duct ligation (increase in volume density of bile ductules, ductular cells and infiltration of inflammatory cells), we suggest that non-parenchymal liver cells have an important participation in the hepatic uptake of [3H]MPP+ after bile duct ligation in the rat.

1-Methyl-4-phenylpyridinium↗
PubMed1998

Uptake of [3H]-adrenaline by freshly isolated rat hepatocytes: putative involvement of P-glycoprotein.

1. The liver has an important role in the elimination of circulating catecholamines. Adrenaline and noradrenaline are avidly taken up and metabolized by rat hepatocytes, but the nature of the mechanism(s) involved remains partially unknown. 2. The aim of this work was to further characterize the uptake of catecholamines by isolated rat hepatocytes. For that purpose, the effects of a series of chemically unrelated compounds, including substrates/inhibitors of P-glycoprotein, on [3H]-adrenaline removal was investigated. 3. Freshly isolated rat hepatocytes were incubated in Krebs-Henseleit solution at 37 degrees C with 50 nM [3H]-adrenaline for 5 min. Removal of [3H]-adrenaline was calculated as the sum of [3H]-adrenaline present in cells, and its [3H]-metabolites present both in cells and in the incubation medium. Radioactivity was determined by liquid scintillation counting. 4. Verapamil, quinidine, 1-methyl-4-phenylpyridinium, cimetidine, tetraethylammonium, d-tubocurarine, taurocholate, daunomycin and vinblastine (100 microM), progesterone, bilirubin (200 microM), vecuronium (45 microM), and amiloride (1 mM) significantly reduced [3H]-adrenaline removal. On the other hand, cyclosporine A (100 microM) apparently had no effect. The O-methylated metabolite of adrenaline, metanephrine (30 microM), produced a 40% reduction of [3H]-adrenaline removal. 5. Vinblastine and corticosterone produced concentration-dependent decreases of [3H]-adrenaline removal, with IC50 values of 23.3 and 116.0 microM, respectively. 6. In the presence of verapamil (100 microM), desipramine (1 microM) was devoid of significant effect on [3H]-adrenaline removal. Corticosterone (40 microM) produced a further decrease (+/- 50%) on removal of the [3H]-amine. 7. Removal of [3H]-adrenaline by isolated cells did not show pH-dependence since an increase or a decrease in the pH of incubation medium (to 8.2 or 6.2, respectively) caused no alteration of that parameter. 8. In conclusion, [3H]-adrenaline is efficiently removed and subsequently metabolized by isolated rat hepatocytes. The results are compatible with the involvement of multiple mechanisms in the hepatic uptake of this amine including the type I and the type II hepatic transporters for organic cations, uptake2 and P-glycoprotein.

1-Methyl-4-phenylpyridinium↗
PubMed1997

Primary structure and functional expression of the apical organic cation transporter from kidney epithelial LLC-PK1 cells.

Renal secretion of organic cations involves at least two distinct transporters, located in the basolateral and apical membranes of proximal tubule cells. Whereas the basolateral transporter has recently been cloned, sequence information about the apical type was not yet available. An organic cation transporter, OCT2p, was cloned from LLC-PK1 cells, a porcine cell line with properties of proximal tubular epithelial cells. OCT2p was heterologously expressed and characterized in human embryonic kidney 293 cells. OCT2p-mediated uptake of the prototypical organic cation [14C]tetraethylammonium ([14C]TEA) into 293 cells was saturable. There was a highly significant correlation between the Ki values for the inhibition of apical [14C]TEA uptake into LLC-PK1 cells and 293 cells transfected with OCT2p (r = 0.995; p < 0.001; n = 6). Although OCT2p is structurally related to OCT1r, the basolateral organic cation transporter from rat kidney, the transporters could be clearly discriminated pharmacologically with corticosterone, decynium22, and O-methylisoprenaline. The findings at hand suggest that OCT2 corresponds to the apical type of organic cation transporter. Reverse transcriptase-polymerase chain reaction indicates that mRNA of OCT1r is limited to non-neuronal tissue, whereas OCT2r, the OCT2p homologue from rat, was found in both the kidney and central nervous regions known to be rich in the monoamine transmitter dopamine.

Amino Acid Sequence↗
PubMed1997

Prevention by a somatostatin analogue of the hypertensive and cardiovascular structural changes induced by blockade of adenosine receptors.

1. Long-term administration of the adenosine receptor antagonist, 1,3-dipropyl-8-sulfophenylxanthine (DPSPX), causes arterial hypertension and cardiovascular hypertrophic and hyperplastic changes (Matias, Albino-Teixeira, Polónia & Azevedo, 1991). As somatostatin is a repressor of cell growth, and adenosine is a potent inducer of the somatostatin gene, we investigated the putative involvement of somatostatin in the cardiovascular effects of DPSPX. 2. DPSPX (90 micrograms kg-1 h-1, i.p.) or saline and the somatostatin analogue, octreotide (75 micrograms kg-1 day-1, s.c.), or saline were infused through Alzet minipumps to Wistar rats. Blood pressure was measured with the tail-cuff technique. Seven days after implantation of the minipumps the rats were killed and the tissues prepared for microscopy. 3. DPSPX induced arterial hypertension and cardiovascular hypertrophic and hyperplastic changes as previously described (Matias et al., 1991). Treatment of the rats with octreotide alone had no effect either on blood pressure or in blood vessel morphology. However, octreotide prevented both the hypertensive and the cardiovascular morphologic effects of DPSPX. 4. The results are compatible with the involvement of somatostatin in the long-term cardiovascular effects of adenosine.

Animals↗
PubMed1996

The extraneuronal transporter for monoamine transmitters exists in cells derived from human central nervous system glia.

From studies on sympathetically innervated peripheral tissues it is well known that both neuronal and non-neuronal transport systems contribute to the inactivation of released monoamine transmitters. The close proximity between synapses and glia cell processes in the CNS leads to the so far unresolved question whether non-neuronal transporters are involved in the inactivation of centrally released monamine transmitters such as noradrenaline, dopamine and 5-hydroxytryptamine. 1-Methyl-4-phenylpyridinium (MPP+) is a prototypical substrate of the extraneuronal monoamine transporter (uptake2). [3H]MPP+ was found to accumulate in various human glioma cell lines. [3H]MPP+ transport was characterized in more detail in HTZ146 human glioma cells. The Ki values of various compounds for the inhibition of initial rates of [3H]MPP+ transport into HTZ146 cells were closely correlated with known Ki values for the inhibition of the extraneuronal monoamine transporter (P < 0.01, r = 0.991, n = 7). The rank order of inhibitory potencies was decynium 22 > corticosterone > cyanine 863 > O-methylisoprenaline > quinine > clonidine > quinidine. [3H]MPP+ accumulation was investigated not only in various CNS tumour cell lines but also in primary cultures of human astrocytes and rat cerebral cortex slices. In all tested experimental systems, accumulation was sensitive to cyanine-related inhibitors of the extraneuronal monamine transporter. These findings suggest that the extraneuronal monamine transporter exists in glia cells. Furthermore, it was shown that MPP+ is able to make use of the extraneuronal monoamine transporter not only to enter but also to leave glia cells. This finding suggests that the extraneuronal monoamine transporter may play a key role in the mechanism of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) neurotoxicity.

Animals↗
PubMed1996

Inward transport of [3H]-1-methyl-4-phenylpyridinium in rat isolated hepatocytes: putative involvement of a P-glycoprotein transporter.

1. The liver has an important role in the detoxification of organic cations from the circulation. [3H]-1-methyl-4-phenylpyridinium ([3H]-MPP+), a low molecular weight organic cation, is efficiently taken up and accumulated by rat hepatocytes through mechanisms partially unknown. 2. The aim of the present work was to characterize further the uptake of MPP+ by rat isolated hepatocytes. The putative interactions of a wide range of drugs, including inhibitors/substrates of P-glycoprotein, were studied. 3. The uptake of MPP+ was investigated in rat freshly isolated hepatocytes (incubated in Krebs-Henseleit medium with 200 nM [3H]-MPP+ for 5 min) and in the rat liver in situ (perfused with Krebs-Henseleit/BSA medium with 200 nM [3H]-MPP+ for 30 min). [3H]-MPP+ accumulation in the cells and in tissue was determined by liquid scintillation counting. 4. Verapamil (100 microM), quinidine (100 microM), amiloride (1 mM), (+)-tubocurarine (100 microM), vecuronium (45 microM), bilirubin (200 microM), progesterone (200 microM), daunomycin (100 microM), vinblastine (100 microM), cyclosporin A (100 microM) and cimetidine (100 microM) had a significant inhibitory effect on the accumulation of [3H]-MPP+ in isolated hepatocytes. Tetraethylammonium (100 microM) had no effect. 5. In the rat perfused liver, both cyclosporin A (100 microM) and verapamil (100 microM) had much less marked inhibitory effects as compared to their effects on isolated hepatocytes (0% against 35% and 45% against 96% of inhibition, respectively). 6. Inhibition of alkaline phosphatase activity by increasing or decreasing the pH of the incubation medium or by the presence of vanadate (1 mM) or homoarginine (500 microM) led to a significant increase in the accumulation of [3H]-MPP+ in isolated hepatocytes. 7. It was concluded that, in addition to the type I organic cation hepatic transporter, [3H]-MPP+ is taken up by rat hepatocytes through P-glycoprotein, a canalicular transport system that usually excretes endobiotics and xenobiotics. We proposed that the reversal of transport through P-glycoprotein may be related to the loss of efficacy of alkaline in isolated hepatocytes.

1-Methyl-4-phenylpyridinium↗
PubMed1995

The fate of [3H]-(-)-noradrenaline in the perfused rat liver.

1. Hepatic removal and metabolism as well as biliary excretion of noradrenaline were studied. Rat livers were perfused in situ for 60 min with Krebs-Henseleit buffer at 37 degrees C containing 2 nM [3H]-(-)-noradrenaline. [3H]-noradrenaline and its [3H]-metabolites were determined in liver, venous effluent and bile. 2. Removal of [3H]-noradrenaline by the liver, calculated as the sum of total radioactivity in the liver at the end of perfusion plus total radioactivity in the bile formed during perfusion plus [3H]-metabolites in the venous effluent formed during perfusion, was 40.2 +/- 6.9 pmol g-1 h-1. This removal corresponded to about 25% of the amount of [3H]-noradrenaline offered to the liver. 3. A proportion of the [3H]-noradrenaline (86.8%) taken up by the liver was metabolized, 13.2% remained unmetabolized in the liver and 0.019% was excreted unmetabolized into the bile. The most abundant metabolites were those present in the [3H]-OMDA fraction (72.5%), followed by [3H]-NMN (15.8%), [3H]-DOPEG (6.1%) and [3H]-DOMA (5.6%). Some of these metabolites (66.6%) were recovered from the venous effluent, 32.7% from the liver and only 1.3% from the bile. The amount of [3H]-noradrenaline present in the liver at the end of the perfusion produced a tissue:perfusion medium ratio of 2.6. 4. Simultaneous inhibition of monoamine oxidase and catechol-O-methyl transferase with pargyline (75 mg kg-1, i.p., 3 h before) and tolcapone (1 microM), respectively, markedly reduced the formation of [3H]-NMN, [3H]-DOPEG and [3H]-DOMA, but did not affect the hepatic removal of [3H]-noradrenaline, the content of [3H]-noradrenaline in the liver, the formation of [3H]-OMDA or the excretion of [3H]-noradrenaline and its [3H]-metabolites into the bile. 5. Treatment with an uptake2 blocker, corticosterone (40 microM), did not change the hepatic removal and metabolism of [3H]-noradrenaline or the biliary excretion of [3H]-noradrenaline and its [3H]-metabolites. 6. These findings indicate that the perfused rat liver efficiently removed and metabolized [3H]-noradrenaline, both monoamine oxidase and catechol-O-methyl transferase being involved in the metabolism of this amine. The apparent lack of effect of monoamine oxidase and catechol-O-methyl transferase inhibition on the formation of [3H]-OMDA may be due to the presence, especially in the liver, of conjugated metabolites of [3H]-noradrenaline in the [3H]-OMDA fraction. These results also show that uptake2 does not seem to be involved in the hepatic uptake of [3H]-noradrenaline, confirming previous findings. Finally, the results indicate that the rat liver perfused with Krebs-Henseleit buffer is not a suitable experimental model for studies on the biliary excretion of catecholamines.

Adrenergic Uptake Inhibitors↗
PubMed1994

Uptake of 3H-catecholamines by rat liver cells occurs mainly through a system which is distinct from uptake1 or uptake2.

Isolated rat hepatocytes were incubated with 200 nmol/l 3H-(-)-noradrenaline or 50 nmol/l 3H-(-)-adrenaline for 15 min, in Krebs-Henseleit solution at 37 degrees C, gassed with 95% O2 5% CO2. Monoamine oxidase and catechol-O-methyl transferase were inhibited with pargyline (500 mumol/l) and Ro 01-2812 (3,5-dinitropyrocatechol; 2 mumol/l), respectively. Total radioactivity present in the cells, which corresponded mostly to intact 3H-amine, was measured. The content of 3H-noradrenaline increased with time of incubation, a plateau having been reached after 15 min of incubation. After 15 min of incubation, the cell: medium ratio for 3H-noradrenaline and 3H-adrenaline was 0.6-0.7. Desipramine (an inhibitor of the neuronal uptake of catecholamines-uptake1; 1 mumol/l) did not affect the uptake of either 3H-noradrenaline or 3H-adrenaline into hepatocytes. Corticosterone (an inhibitor of the extraneuronal uptake of catecholamines-uptake2; 40 mumol/l) slightly inhibited (by 28%) the uptake of 3H-adrenaline, and did not significantly reduce 3H-noradrenaline uptake. Probenecid (an inhibitor of the renal transport of organic anions; 100 mumol/l) did not influence the amount of either 3H-noradrenaline or 3H-adrenaline in hepatocytes. Cyanine 863 (an inhibitor of the renal transport of organic cations; 10 mumol/l) decreased by 62% the uptake of 3H-adrenaline into cells but did not significantly affect 3H-noradrenaline uptake. Bilirubin (a substrate of a hepatic transport for organic anions; 200 mumol/l) produced a significant increase (50%) in the amount of 3H-noradrenaline and 3H-adrenaline present in the cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Extraneuronal uptake and O-methylation of 3H-adrenaline in the rabbit aorta.

The influence of uptake2 inhibitors on the O-methylation and accumulation of 3H-adrenaline by the isolated rabbit aorta was studied. Strips were incubated with 0.05 mumol/l 3H-(-)-adrenaline during 15 min. Monoamine oxidase and uptake1 were inhibited and the 3H-adrenaline present in the tissue was measured as well as the metabolites found in the tissue and in the incubation fluid. In another series of experiments, monoamine oxidase, uptake1 and catechol-O-methyl transferase (COMT) were inhibited, and tritium accumulation was measured in the tissue. When COMT was inhibited, inhibitors of uptake2 produced a maximal reduction of 3H-adrenaline accumulation that did not exceed 50%. When COMT was intact, inhibitors of uptake2 diminished total 3H-removal and, more markedly, O-methylation and concomitantly increased the tissue content of 3H-adrenaline. Mineralocorticoids (corticosterone and deoxycorticosterone acetate) inhibited 3H-adrenaline uptake (when COMT was inhibited) and 3H-metanephrine formation (when COMT was functional) as effectively as did sexual steroids (17-beta-oestradiol, progesterone and testosterone); hydrocortisone (hemisuccinate or phosphate) had no effect (for concentrations up to 120 mumol/l). At the end of the incubation some strips were washed out with amine-free solution. Compartmental analysis of the efflux showed that the amine had distributed into three extraneuronal compartments (compartment I, II and III, with half times of 0.4, 4 and 15 min, respectively). Corticosterone (120 mumol/l) decreased the amount of 3H-adrenaline in compartment III and simultaneously increased the amount of the amine in compartment I (extracellular space).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1993

Uptake and metabolism of 3H-adrenaline and 3H-noradrenaline by isolated hepatocytes and liver slices of the rat.

Isolated rat hepatocytes were incubated with 0.05 mumol/l or 0.2 mumol/l 3H-(-)-noradrenaline or 0.05 mumol/l 3H-(-)-adrenaline for 15 min and the content of amines as well as the formation of metabolites was measured. The removal of both amines from the incubation medium was quantitatively similar, and mainly due to metabolism (which represented 96% of the removal of 3H-adrenaline and 98% of the removal of 3H-noradenaline). O-methylation predominated for 3H-adrenaline: O-methylated and deaminated metabolites (3H-OMDA) and 3H-metanephrine (3H-MN) were the most abundant metabolites, accounting for 63% and 34% of total metabolite formation, respectively. Deamination predominated for 3H-noradrenaline: 3H-OMDA and 3H-dihydroxymandelic acid (3H-DOMA) were the most abundant metabolites, representing respectively 56% and 36% of total metabolite formation. The following activities of monoamine oxidase and catechol-O-methyl transferase were determined for 3H-noradrenaline: kCOMT 0.70 +/- 0.15 min-1 and kMAO 2.27 +/- 0.14 min-1. In experiments with 3H-noradrenaline, inhibition of monoamine oxidase reduced the formation of 3H-OMDA and deaminated metabolites [3H-dihydroxphenylglycol (3H-DOPEG) and 3H-DOMA] and increased the formation of 3H-normetanephrine (3H-NMN). Inhibition of catechol-O-methyl transferase, on the other hand, decreased 3H-NMN and increased 3H-DOPEG formation. When both enzymes were inhibited, the formation of all metabolites was strongly reduced but surprisingly there was no accumulation of 3H-amines in the cells, as the cell: medium ratio for 3H-noradrenaline or 3H-adrenaline was about unity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗