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At least 973 records · Page 54Linked to original sources
PubMed1996

Fluorodopa positron emission tomography with an inhibitor of catechol-O-methyltransferase: effect of the plasma 3-O-methyldopa fraction on data analysis.

Flurodopa (FDOPA) is an analogue of L-di-hydroxyphenylalanine (L-dopa) used to assess the nigrostriatal dopamine system in vivo with positron emission tomography (PET). However, FDOPA/PET quantitation is complicated by the presence of the 3-O-methyl-FDOPA (3OMFD) fraction in brain and plasma. Pretreatment with entacapone (OR-611), a peripheral catechol O-methyl-transferase (COMT) inhibitor, greatly reduces the plasma 3OMFD fraction and provides an ideal situation to evaluate the contribution of the plasma 3OMFD fraction in several kinetic models of FDOPA uptake. We performed FDOPA/PET with and without the OR-611 preadministration in six Parkinson's disease (PD) patients. We measured the time-course of the plasma FDOPA and 3OMFD fractions using high-pressure liquid chromatography (HPLC). We calculated striato-occipital ratios (SOR), and estimated the striatal FDOPA uptake rate constant graphically using the plasma FDOPA and occipital tissue time activity curves (KiFD and KiOCC, respectively). We also estimated striatal dopa decarboxylase (DDC) activity (k3D) using a model incorporating independent measurements of 3OMFD transport kinetic rate constants. With the preadministration of OR-611, the pharmacological efficiency in plasma was prolonged significantly (21.1-37.7%; p < 0.01). We also observed significant mean elevations in SOR and KiOCC by 21.8 and 53.5%, respectively (p < 0.05). KiFD and k3D did not show significant change. We conclude that OR-611 prolongs the circulation time of FDOPA in the plasma but does not alter rate constants for striatal FDOPA uptake or decarboxylation.

Adult↗
PubMed2004

Crystallization and preliminary X-ray diffraction studies of a catechol-O-methyltransferase/inhibitor complex.

Inhibitors of the enzyme catechol-O-methyltransferase (COMT) are used as co-adjuvants in the therapy of Parkinson's disease. A recombinant form of the soluble cytosolic COMT from rat has been co-crystallized with a new potent inhibitor, BIA 8-176 [(3,4-dihydroxy-2-nitrophenyl)phenylmethanone], by the vapour-diffusion method using PEG 6K as precipitant. Crystals diffract to 1.6 A resolution on a synchrotron-radiation source and belong to the monoclinic space group P2(1), with unit-cell parameters a = 52.77, b = 79.63, c = 61.54 A, beta = 91.14 degrees.

Animals↗
PubMed1985

Relationship between catechol-O-methyltransferase and phenolsulfotransferase in the metabolism of dopamine in the rat brain.

The relationship between phenolsulfotransferase (PST) and catechol-O-methyltransferase (COMT) in the metabolism of free 3,4-dihydroxyphenylethylamine (DA, dopamine) in the rat brain was studied. In rats not pretreated with a monoamine oxidase (MAO) inhibitor a huge increase of free DA in the brain, following an intraperitoneal injection of L-3,4-dihydroxyphenylalanine (L-DOPA) or an intraventricular injection of free DA, did not lead to any noticeable change in DA sulfate or 3-methoxytyramine (3-MT), which remained undetectable by the present HPLC method. However, in rats previously treated with the MAO inhibitors pargyline or tranylcypromine, the same L-DOPA or free DA treatment resulted in significant increases in both 3-MT and DA sulfate in the hypothalamus, brainstem, and striatum. This response of COMT and PST was not affected by prior treatment of the rats with 6-hydroxydopamine, which suggests that O-methylation and sulfoconjugation occur outside adrenergic neurons not destroyed by the neurotoxin. Inhibition of COMT activity did not lead to any increase in DA sulfate, which showed that despite their common mode of action (both enzymes react preferentially at the same hydroxyl group in the DA molecule), the two enzymes are not competitive. After MAO inhibition there were strong correlations between an increase in DA sulfate and 3-MT on the one hand, and between free DA and 3-MT on the other. Because 3-MT is a marker of central DA release, these data suggest that inhibition of MAO activity not only affects DA metabolism by this enzyme but also influences DA release in the rat brain.

Animals↗
PubMed1993

Effects of catechol-O-methyltransferase inhibitors and L-3,4-dihydroxyphenylalanine with or without carbidopa on extracellular dopamine in rat striatum.

The effects of two new catechol-O-methyltransferase (COMT) inhibitors, OR-611 and Ro 40-7592, in combination with L-3,4-dihydroxyphenylalanine (L-dopa) with or without carbidopa on extracellular levels of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), 3-O-methyldopa (3-OMD), and 5-hydroxyindoleacetic acid in rat striatum were studied. A dose of 10 mg/kg i.p. of Ro 40-7592 alone, in contrast to the same dose of OR-611, decreased the dialysate level of HVA and increased that of DOPAC; this dose was thus used to differentiate between the effects of central and peripheral COMT inhibition. L-Dopa (50 mg/kg i.p.) alone slightly increased extracellular levels of DA, DOPAC, and HVA. The effects of L-dopa were potentiated by carbidopa (50 mg/kg i.p.), and even 3-OMD levels in dialysate samples became detectable. Both OR-611 and Ro 40-7592 significantly further increased the DA and DOPAC efflux from striatum produced by L-dopa. This increase was more pronounced when carbidopa was added to the treatment. OR-611 did not modify the effect of L-dopa or carbidopa/L-dopa on dialysate HVA levels, whereas Ro 40-7592 markedly reduced those levels. Both OR-611 and Ro 40-7592 very clearly suppressed dialysate 3-OMD levels produced by carbidopa/L-dopa. Ro 40-7592 was more effective than OR-611 in potentiating the effects of L-dopa or carbidopa/L-dopa. These in vivo data show that the new COMT inhibitors markedly inhibit the O-methylation of L-dopa and increase its availability to brain, which is reflected as increased DA formation.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Different in vivo properties of three new inhibitors of catechol O-methyltransferase in the rat.

1. We compared three new catechol O-methyltransferase (COMT) inhibitors (OR-611, Ro 40-7592 and CGP 28014; 10 and 30 mg kg-1, i.p.) in male rats given levodopa (L-DOPA, 50 mg kg-1, i.p.) and carbidopa ((-)-L-alpha-methyl dopa, 50 mg kg-1, i.p.). In some studies pretreatment with pargyline (80 mg kg-1, i.p.) was used to block the function of monoamine oxidase (MAO). 2. Decreases of hypothalamic and striatal 3-O-methyl-dopa (3-OMD) levels were used as measures of the inhibition of peripheral COMT. The inhibition of brain COMT activity was estimated by decreases of hypothalamic and striatal homovanillic acid (HVA) and 3-methoxytyramine (3-MT; after pargyline) levels. 3. The three COMT inhibitors studied had different individual characteristics. OR-611 was primarily a peripherally acting COMT inhibitor, decreasing 3-OMD levels in the striatum (to 31-52%) and in the hypothalamus (to 16-27%) both in the control and pargyline-treated animals at 1 and 3 h. It did not have any effect on brain HVA and 3-MT. 3. Ro 40-7592 was a broad spectrum COMT inhibitor decreasing striatal and hypothalamic 3-OMD (always to less than 30%), HVA (to less than 50%) and 3-MT levels (to less than 23%) significantly both at 1 and 3 h. It was more potent than OR-611. 4. CGP 28014 functioned as a weak COMT inhibitor in the periphery inhibiting 3-OMD formation only at 3 h. In contrast, it was fairly potent in decreasing the brain HVA and 3-MT levels at 1 h (to 37-22% and 42-35% in the striatum, and to 57-33% and 64-35% in the hypothalamus, respectively) but not at 3 h. Since CGP 28014, unlike OR-611 and Ro 40-7592, did not generally increase the brain DOPA, dopamine or DOPAC levels, it was not a typical COMT inhibitor.

Amidines↗
PubMed2000

Catechol-O-methyltransferase (COMT) inhibitors in Parkinson's disease.

Catechol-O-methyltransferase (COMT) inhibitors are a new therapeutic option in the treatment of patients with Parkinson's disease. COMT inhibitors act by extending the duration of action of levodopa, thus improving the amount of time a patient can experience benefit from levodopa. COMT inhibitors are only used in conjunction with levodopa. They do have a propensity to augment dopaminergic effects, such that levodopa doses might need to be adjusted downward. Other side effects of COMT inhibitors include diarrhea and liver function abnormalities. Due to the latter, recent guidelines have been developed to monitor patients on tolcapone for this rare side effect, and these guidelines will be discussed. This article also provides representative case histories for the appropriate use of COMT inhibitors that illustrate how these drugs can be used to manage patients with a fluctuating response to levodopa.

Antiparkinson Agents↗
PubMed2003

Enzymology of methylation of tea catechins and inhibition of catechol-O-methyltransferase by (-)-epigallocatechin gallate.

(-)-Epigallocatechin gallate (EGCG) and (-)-epigallocatechin (EGC) are the major polyphenolic constituents in green tea. In this study, we characterized the enzymology of cytosolic catechol-O-methyltransferase (COMT)-catalyzed methylation of EGCG and EGC in humans, mice, and rats. At 1 microM, EGCG was readily methylated by liver cytosolic COMT to 4"-O-methyl-EGCG and then to 4',4"-di-O-methyl-EGCG; EGC was methylated to 4'-O-methyl-EGC. The K(m) and V(max) values for EGC methylation were higher than EGCG; for example, with human liver cytosol, the K(m) were 4.0 versus 0.16 microM and V(max) were 1.28 versus 0.16 nmol/mg/min. Rat liver cytosol had higher COMT activity than that of humans or mice. The small intestine had lower specific activity than the liver in the methylation of EGCG and EGC. Glucuronidation on the B-ring or the D-ring of EGCG greatly inhibited the methylation on the same ring, but glucuronidation on the A-ring of EGCG or EGC did not affect their methylation. Using EGC and 3,4-dihydroxy-L-phenylalanine as substrates, EGCG, 4"-O-methyl-EGCG, and 4',4"-di-O-methyl-EGCG were all potent inhibitors (IC(50) approximately 0.2 microM) of COMT. The COMT-inhibiting activity of (-)-EGCG-3'-O-glucuronide was similar to EGCG, but (-)-EGCG-4"-O-glucuronide was less potent. The present work provides basic information on the methylation of EGCG and suggests that EGCG may inhibit COMT-catalyzed methylation of endogenous and exogenous compounds.

Animals↗
PubMed2002

Kinetic interactions of dopamine and dobutamine with human catechol-O-methyltransferase and monoamine oxidase in vitro.

Dopamine and dobutamine are often infused together into acutely ill patients requiring temporary support of cardiac and renal function, but whether these catecholamines affect the metabolic clearance of each other is not established. We determined the kinetics of dopamine and dobutamine as substrates and inhibitors of each other, i.e., apparent V(max), K(m), and K(i), with crude preparations of human blood mononuclear cell catechol-O-methyltransferase (COMT) and platelet monoamine oxidase (MAO) at pH 7.4 and 37 degrees C. Values of V(max) for dopamine and dobutamine as substrates for COMT were 0.45 and 0.59 nmol of 3-O-methyl product formed per milligram of protein per minute, whereas those for K(m) were 0.44 and 0.05 mM, respectively. Dopamine and dobutamine were competitive inhibitors of each other in this reaction. The K(i) for dopamine as an inhibitor of dobutamine methylation was 1.5 mM, whereas that for dobutamine as an inhibitor of dopamine methylation was 0.015 mM. Dopamine but not dobutamine was a substrate for MAO. The V(max) for dihydroxyphenylacetaldehyde formation from dopamine was 0.29 nmol/mg protein/min and the K(m) for dopamine was 0.38 mM. Dobutamine was a noncompetitive inhibitor of dopamine oxidation in this reaction (K(i) congruent with 1.19 mM). The high apparent K(m) and K(i) values derived for dopamine and dobutamine when tested with these two human enzymes in vitro suggest that these catecholamines do not interfere with the metabolism of each other when both are infused together at therapeutic concentrations.

Adult↗
PubMed1996

Catechol dioxygenases from Escherichia coli (MhpB) and Alcaligenes eutrophus (MpcI): sequence analysis and biochemical properties of a third family of extradiol dioxygenases.

The nucleotide sequence of the Escherichia coli mhpB gene, encoding 2,3-dihydroxyphenylpropionate 1,2-dioxygenase, was determined by sequencing of a 3.1-kb fragment of DNA from Kohara phage 139. The inferred amino acid sequence showed 58% sequence identity with the sequence of an extradiol dioxygenase, MpcI, from Alcaligenes eutrophus and 10 to 20% sequence identity with protocatechuate 4,5-dioxygenase from Pseudomonas paucimobilis, with 3,4-dihydroxyphenylacetate 2,3-dioxygenase from E. coli, and with human 3-hydroxyanthranilate dioxygenase. Sequence similarity between the N- and C-terminal halves of this new family of dioxygenases was detected, with conserved histidine residues in the N-terminal domain. A model is proposed to account for the relationship between this family of enzymes and other extradiol dioxygenases. The A. eutrophus MpcI enzyme was expressed in E. coli, purified, and characterized as a protein with a subunit size of 33.8 kDa. Purified MhpB and MpcI showed similar substrate specificities for a range of 3-substituted catechols, and evidence for essential histidine and cysteine residues in both enzymes was obtained.

Alcaligenes↗
PubMed1994

Effect of entacapone, a peripherally acting catechol-O-methyltransferase inhibitor, on the motor response to acute treatment with levodopa in patients with Parkinson's disease.

Catechol-O-methyltransferase (COMT) inhibitors may be useful in the treatment of Parkinson's disease by improving the bioavailability of levodopa and by prolonging its effects. Entacapone (OR-611), a novel COMT inhibitor, which does not cross the blood brain barrier, was assessed in 12 patients with Parkinson's disease and motor fluctuations in a randomised, double-blind, cross-over, single dose study. The magnitude and duration of the therapeutic response to a single dose of 200 mg levodopa/50 mg carbidopa was evaluated after concomitant placebo, or 200 or 800 mg entacapone. A significant increase in the duration of the motor response to levodopa was seen when 200 mg entacapone was given with levodopa/carbidopa. Plasma levodopa concentrations were increased with both doses of the COMT inhibitor. The latency to onset of motor response did not differ significantly between active drug and placebo. Entacapone may prove useful in prolonging the duration of the benefit obtained from individual doses of levodopa.

Aged↗
PubMed2000

The catechol-O-methyltransferase (COMT) inhibitor entacapone enhances the pharmacokinetic and clinical response to Sinemet CR in Parkinson's disease.

OBJECTIVES: Entacapone is a specific, potent, peripherally acting catechol-O-methyltransferase (COMT) inhibitor. It has been shown to improve the bioavailability of plasma levodopa and extend its clinical effect when used as an adjunct to standard levodopa preparations, but there is little experience of the effect of entacapone on controlled release levodopa preparations. METHODS: A double blind, placebo controlled, single dose, randomised, cross over trial was performed in 14 patients with Parkinson's disease with motor fluctuations to investigate the clinical effect of a single dose of entacapone (200 mg) when administered with either standard levodopa-carbidopa (Sinemet) or controlled release levodopa-carbidopa preparations (Sinemet CR). RESULTS: When entacapone was administered with standard Sinemet the duration of the clinical response to standard Sinemet was longer in comparison with the response after placebo (p=0.02). Moreover, in the same patients, entacapone significantly increased the duration of the clinical response to Sinemet CR (p=0.05) without prolonging the latency of response or enhancing dyskinesias. CONCLUSIONS: These data confirm the clinical efficacy of entacapone-standard Sinemet combination. They also indicate that adding entacapone to controlled release levodopa preparations might provide a useful treatment option in patients with Parkinson's disease with motor fluctuations. A double blind clinical trial with a chronically administered entacapone-Sinemet CR combination is, however, required to verify this viewpoint.

Adult↗
PubMed2003

BIA 3-202, a novel catechol-O-methyltransferase inhibitor, reduces the peripheral O-methylation of L-DOPA and enhances its availability to the brain.

The present study aims at determining the effects of the catechol-O-methyltransferase (COMT) inhibitor BIA 3-202 [1-(3,4-dihydroxy-5-nitrophenyl)-2-phenyl-ethanone] upon levels of L-3,4-dihydroxyphenylalanine (L-DOPA) and metabolites in peripheral circulation (jugular vein), whole brain, and striatal microdialysates in rats orally treated with L-DOPA plus benserazide. A low dose (3 mg/kg) of BIA 3-202 was relatively selective to inhibit liver COMT, being devoid of major significant inhibitory effects upon brain COMT. By contrast, a high dose (30 mg/kg) of BIA 3-202 markedly inhibited liver and brain COMT. BIA 3-202 (3 and 30 mg/kg) reduced the L-DOPA-induced rise of 3-O-methyl-L-DOPA in the peripheral circulation (jugular vein), brain tissue, and striatal dialysate, but failed to increase the levels of dopamine in striatal dialysates despite the increase in dopamine brain levels. However, the changes in brain levels of L-DOPA, 3-O-methyl-L-DOPA, and dopamine and in striatal dialysate levels of L-DOPA and 3-O-methyl-L-DOPA, obtained with 3 mg/kg BIA 3-202, were not different from those obtained with 30 mg/kg BIA 3-202. In conclusion, inhibition of peripheral COMT by BIA 3-202 may suffice to improve the availability of L-DOPA to the brain.

Acetophenones↗
PubMed1987

Immunocytochemical evidence for the coexistence of catecholestrogen and catechol-O-methyltransferase in the rat parotid gland.

Catechol-O-methyltransferase (COMT) (EC 2.1.1.6) and catecholestrogen were localized in the parotid gland of the rat by immunocytochemical methods. Specific immunoreactive deposits for COMT and catecholestrogen were found in the cytoplasm of duct cells, but only those for COMT in myo-epithelial cells. The pattern of localization of COMT and catecholestrogen in the parotid gland suggests a functional relationship between COMT and catecholestrogen.

Animals↗
PubMed1994

Effect of peripheral catechol-O-methyltransferase inhibition on the pharmacokinetics and pharmacodynamics of levodopa in parkinsonian patients.

Catechol-O-methyltransferase (COMT) metabolizes a portion of administered levodopa and thus makes it unavailable for conversion to dopamine in the brain. In an open-label trail, we examined the effects of entacapone, a peripheral inhibitor of COMT, administered acutely or for 8 weeks, on the pharmacokinetics and pharmacodynamics of levodopa in 15 parkinsonian subjects with a fluctuating response to levodopa. Acutely and chronically administered entacapone similarly decreased the plasma elimination of orally and intravenously administered levodopa. Absorption of levodopa was minimally affected. During chronic entacapone treatment, daily levodopa dosages were reduced by 27% yet mean plasma levodopa concentrations were increased by 23%. Plasma 3-O-methyldopa concentrations were decreased by 60%. Entacapone increased the duration of action of single doses of levodopa by a mean of 56%. The percent of the day "on" after 8 weeks of entacapone treatment was 77%; it dropped to 44% upon withdrawal of entacapone. We conclude that inhibition of COMT by entacapone increases the plasma half-life of levodopa and augments the antiparkinsonian effects of single and repeated doses of levodopa.

Aged↗
PubMed1989

A chemical model of catechol-O-methyltransferase. Methylation of 3,4-dihydroxybenzaldehyde in aqueous solution.

The reaction of 3,4-dihydroxybenzaldehyde (LH2) and dimethylsulfate (DMS) to form the m- and p-O-methylated products (vanillin and isovanillin, respectively) in aqueous 2-(N-morpholino)ethane sulfonate buffer was studied kinetically. The products were determined by means of high-performance liquid chromatography. The O-methylation occurred principally at the p-hydroxyl group in the absence of divalent metal ions. In the presence of Cu(II), the m-methylation was promoted and became predominant. Zn(II) showed a similar but less pronounced effect. The effects were explained in terms of the complex formation of LH2. The second order rate constants for the m- and p-methylation of the species, LH2, CuL and CuL2-2 by DMS were calculated. The values and their ratio for the m-/p-reactions increased in the order of LH2 less than CuL less than CuL2-2. The reaction may serve as a chemical model for catechol-O-methyltransferase, which requires divalent metals and catalyzes the m-methylation.

Benzaldehydes↗
PubMed2003

Hepatotoxic profile of catechol-O-methyltransferase inhibitors in Parkinson's disease.

Entacapone and tolcapone are selective catechol-O-methyltransferase (COMT) inhibitors developed recently as adjuncts to levodopa for the treatment of Parkinson's disease (PD). They extend the duration of action of levodopa. As a result, they increase 'on' time, decrease 'off' time and improve motor scores in patients with motor fluctuations. Both benefits and main side effects are related to increased dopaminergic activity. This paper reviews the use of those COMT inhibitors in PD with particular focus on the issue of hepatotoxicity. Neither tolcapone nor entacapone caused hepatotoxicity in preclinical studies. However, in 1998, four patients who were using tolcapone presented with serious liver dysfunction; three of them died due to acute liver failure. Tolcapone is now known to have the potential to cause hepatotoxicity in clinical use and experimental studies. It is now recommended that tolcapone be administered only in patients with motor fluctuations who are no longer satisfactorily treated with other medications for PD. Routine liver monitoring is now mandatory with this agent. Entacapone has been described as a well-tolerated and safe drug in recent experimental studies, human clinical trials and postmarketing surveillance. It can be offered to any patient with motor fluctuations and routine liver monitoring is not required.

Antiparkinson Agents↗
PubMed1980

Effect of catechol oestrogens on induced ovulation in the immature rat.

The 'positive feedback' effect of exogenous oestradiol-17 beta in advancing ovulation induced by pregnant mare serum gonadotrophin (PMSG) has been used in the present study as a model in which to test the possible oestrogenic or antioestrogenic effects of the catechol oestrogens, 2-hydroxyoestradiol (2-OHE2) and 4-OHE2. Sprague-Dawley rats of 26 days of age were injected with 20 i.u. PMSG together with either vehicle alone or test steroids. The animals were killed 72 h later and the Fallopian tubes were examined for the presence of ova. Advancement of induced ovulation by treatment with oestradiol was confirmed; 2-OHE2, in doses of up to 100 micrograms, influenced neither the time of ovulation nor the number of ova present but 4-OHE2 was equipotent with oestradiol in doses varying from 0.5 micrograms (the minimum effective dose for both steroids) to 10 micrograms. The possible antioestrogenic effect of 2-OHE2 was tested by giving a 100 micrograms dose either at the same time or 2 h before PMSG plus 2 micrograms oestradiol or 4-OHE2. The effects of oestradiol and 4-OHE2 were not altered by this treatment. These data show that, in this model of 'positive feedback', 2-OHE2 has neither an oestrogenic nor an antioestrogenic action but that 4-OHE2 has a potent oestrogenic action, thus raising the question of a physiological role for 4-OHE2 in the regulation of ovulation.

Animals↗
PubMed2001

Periovulatory changes in catfish ovarian oestradiol-17beta, oestrogen-2-hydroxylase and catechol-O-methyltransferase during GnRH analogue-induced ovulation and in vitro induction of oocyte maturation by catecholoestrogens.

In the catfish Heteropneustes fossilis and Clarias batrachus, ovarian oestrogen-2-hydroxylase (OE-2-H) activity increased significantly at 8 h after the injection of an ovulatory dose (0.15 microg/g body weight) of a mammalian GnRH analogue ([d -Ala(6)-Pro(9)]-LHRH ethylamide) and was restored to the 0 h (control) level after egg-stripping at 16 h. On the other hand, ovarian oestradiol-17beta (OE2) level and catechol-O-methyltransferase (COMT) activity decreased significantly at 8 h. While the OE2 level was restored to the 0 h level, COMT activity increased significantly at 16 h. Changes in ovarian OE2 level and enzymes indicate higher synthesis of 2-hydroxylated catecholoestrogens and their degradation during the periovulatory period. Under in vitro conditions, the synthetic catecholoestrogens (CEs, 2- and 4-hydroxylated oestradiol17beta and oestrone (OE1)) induced germinal vesicle break down (GVBD) in a dose- (0.01-10 microg/ml) and duration- (1-36 h) dependent manner, the mean values of the responses being in the order 2-OH OE2>4-OH OE2> 2-OH OE1>4-OH OE1. The CE-induced GVBD response (8 h induction) was not blocked by prior and subsequent incubations with steroid synthesis inhibitors (cyanoketone, epostane and aminoglutethimide) up to 36 h, suggesting that de novo steroidogenesis is not essential for the response. The percentage of GVBD response to 2-h induction by CEs was significantly inhibited by actinomycin D (a transcriptional inhibitor) and cycloheximide (a translational inhibitor), indicating the involvement of both RNA and protein synthesis. The CE-induced 8-h stimulation of GVBD was mildly blocked by propranolol, the beta-adrenergic inhibitor, suggesting the response was partly mediated through a beta-adrenergic receptor mechanism. Incubations with phentolamine, an alpha-adrenergic inhibitor, did not interfere with the CE-induced GVBD response. The results demonstrate CE-related enzymatic changes in teleost (catfish) ovaries and maturation-inducing substance activity of CEs.

Animals↗