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M C Boadle-Biber

Publications and source records attributed to M C Boadle-Biber.

31 records · Page 2Linked to original sources
PubMed1982

Blockade by haloperidol of the increase in tryptophan hydroxylase activity induced by incubation of slices of brain stem with dibutyryl cyclic AMP.

Pretreatment of rat brain stem slices with dibutyryl cyclic AMP, caffeine, theophylline and 3-isobutyl-1-methylxanthine increased the activity of tryptophan hydroxylase in supernatant preparations of enzyme made from the slices. This effect does not appear to be mediated by a cyclic AMP sensitive mechanism since it was not reproduced by exposure of the slices to 8-bromo cyclic AMP, to papaverine, a nonxanthine phosphodiesterase inhibitor, or to other treatments known to raise tissue cyclic AMP levels. The ability of haloperidol to block this increase in enzyme activity is consistent with a role for calmodulin and calcium as mediators of the enzyme activation, particularly when this observation is considered in conjunction with the evidence that supernatant preparations of this enzyme was activated under phosphorylating conditions by a calcium-calmodulin dependent process [5]. Nevertheless, in view of the high concentrations of haloperidol employed in the present experiments, the possibility that this drug may produce its effects in the brain stem slices through some other action, unrelated to its ability to bind to calmodulin, should be kept in mind.

1-Methyl-3-isobutylxanthine↗
PubMed1982

A critical evaluation of LC-EC for the simultaneous determination of 5-hydroxytryptophan, 5-HT, 5-HIAA and HVA in biological samples using GC-MS for validation.

A method has been developed for LC-EC quantitation of 5-hydroxyindoles (5-HT, 5-HTP, 5-HIAA and N-acetyl-5-HT) and the catecholamine metabolite HVA from brain tissue and biological fluids such as CSF. It involves tissue homogenization in chromatographic buffer containing a non-biological internal standard, 5-hydroxyindole, that can be used to quantitate all the indoles of interest as well as HVA. Comparable chromatographic separations were obtained with conventional C18 stainless steel columns (5 and 10 um) and with the Waters C18 radial compression module with a 5 or 10 um C18 cartridge. The LC-EC quantitation of 5-HT, in brain tissue and of 5-HIAA and HVA in CSF has been validated by GC-MS-SIM. The LC-EC method is sensitive in the high pg range on a routine basis.

5-Hydroxytryptophan↗
PubMed1975

Formation of dopamine and noradrenaline in rat vas deferens: comparison with guinea-pig vas deferens.

1 The formation of [14C]-3,4-dihydroxyphenylalanine (DOPA) from [14C]-tyrosine, in the presence of the amino acid decarboxylase inhibitor, brocresine (3-hydroxy-4-bromobenzyloxyamine dihydrogen phosphate), was greatly enhanced in rat vasa deferentia depolarized by a KCl-enriched Krebs-Henseleit solution (52 mM KCl) compared with tissues maintained in unmodified Krebs-Henseleit solution. 2 When the conversion of tyrosine was allowed to proceed as far as catecholamine (brocresine absent) no significant difference was observed between the accumulation of [14C]-catecholamines (CA) in depolarized rat vasa deferentia and the accumulation in control (non-depolarized) tissues. 3 Endogenous CA levels in the depolarized rat vasa deferentia fell to 67% of the controls after a 1 h incubation period and to 53% at the end of 2 hours. 4 Chromatographic separation on Amberlite CG-120 columns of the newly synthesized CA and catechol metabolites from the rat vas deferens revealed that a very high proportion was present as dopamine. The percentage distribution after 1 h incubation in control Krebs-Henseleit was: noradrenaline (NA): 30.6 +/- 5.2; dopamine 56.9 +/- 5.9; acid metabolites: 12.8 +/- 1.1; and in KCl-rich Krebs-Henseleit, NA: 32; dopamine: 44.7 and acid metabolites 23.3. In contrast to the newly synthesized (14C-labelled) CA, endogenous dopamine comprises only 10% of the endogenous CA stores in rat vas deferens. 5 The distribution of newly synthesized NA and dopamine in rat vas deferens is strikingly different from that of guinea-pig vas deferens where more than 80% of newly formed amine is present as NA. In the latter tissue depolarization with K+ causes a striking increase in CA biosynthesis.

Animals↗
PubMed1972

Acceleration of catecholamine biosynthesis in sympathetically innervated tissues by angiotensin-II-amide..

1. The effect of angiotensin-II-amide on the biosynthesis of catecholamines (CA) has been studied in a number of isolated tissues in vitro.2. Angiotensin increased the synthesis of CA from (14)C-tyrosine in guinea-pig atria and portal vein, in rat vasa deferentia and the rabbit portal vein.3. Angiotensin had no effect on synthesis of CA from (14)C-labelled DL-DOPA.4. The conditions required to demonstrate an increased synthesis were critical with respect to incubation time and angiotensin concentration. Effects were most readily apparent after incubation for 1 h with concentrations of angiotensin ranging from 10(-9) to 10(-7)M. Higher concentrations caused a significant reduction in synthesis.5. An increased release of newly synthesized CA into the incubation medium was sometimes seen in the presence of angiotensin. However, there was no correlation between increased synthesis and release of CA.6. Angiotensin was rapidly destroyed when incubated with guinea-pig or rat tissues in Krebs solution. The increase in CA synthesis was only apparent at a time when the incubation medium could have contained only a fraction of the original angiotensin activity.7. It is concluded that the effect of angiotensin is not due to increased release of noradrenaline (NA) or to inhibition of NA uptake into nerves. It is possible that angiotensin may influence the activity of tyrosine hydroxylase or its cofactors by an as yet unknown mechanism.

Angiotensin II↗
PubMed1972

Effect of drugs on the synthesis of noradrenaline in guinea-pig vas deferens.

1. Reserpine in vitro (10(-5)M) caused a profound inhibition (>85%) of the formation of both (14)C-catecholamine ((14)C-CA) and (14)C-dihydroxyphenylalanine ((14)C-DOPA) (in the presence of the amino acid decarboxylase inhibitor brocresine) from (14)C-tyrosine in guinea-pig vas deferens. The magnitude of the inhibition was similar for both (14)C-CA and (14)C-DOPA suggesting that the inhibition occurred primarily at the tyrosine hydroxylase step.2. One hour after in vivo treatment with reserpine (1 mg/kg) when tissue stores of noradrenaline (NA) were depleted by 50%, there was a significant inhibition of the formation of (14)C-DOPA. Twenty-four hours after such treatment, when endogenous NA could no longer be detected, synthesis of (14)C-DOPA was indistinguishable from untreated controls. However a 45% inhibition of (14)C-DOPA synthesis from (14)C-tyrosine could be produced in tissues which had been depleted of NA for 24 h or 48 h by the addition of reserpine, 10(-5)M, to the incubation medium.3. Addition of pteridine cofactor, 2-amino-6,7,-dimethyl-4-hydroxy-5,6,7,8-tetrahydropteridine, to the incubation medium in a concentration of 5 x 10(-3)M enhanced the formation of both (14)C-CA and (14)C-DOPA from (14)C-tyrosine in guinea-pig vas deferens. In 52 mM KCl Krebs-Henseleit medium (14)C-CA formation increased from 2.58+/-0.20 (nmol/g)/h to 6.35+/-0.47 (nmol/g)/h whilst (14)C-DOPA formation increased from 5.04+/-0.88 (nmol/g)/h to 11.29+/-0.59 (nmol/g)/h.4. Pteridine cofactor (5 x 10(-3)M) did not reverse the inhibition of (14)C-DOPA formation seen with reserpine (10(-5)M) in previously untreated tissues or in vasa deferentia from animals pretreated with reserpine 1 mg/kg for 24 hours. However, the inhibition did disappear in the presence of pteridine cofactor when treatment with reserpine was prolonged to 48 h and included two doses of reserpine of 2 mg/kg.5. Tyramine (5.8 x 10(-5)M) and bretylium (10(-5)M) in vitro inhibited the formation of (14)C-CA and (14)C-DOPA from (14)C-tyrosine to the same extent in guinea-pig vas deferens again indicating that their major site of action is on tyrosine hydroxylase. The inhibitory effects were reversed by pteridine cofactor.6. Synthesis of (14)C-NA from (14)C-tyrosine in calf splenic nerve was not increased by incubating the tissue in 52 mM KCl-Krebs-Henseleit solution.

Animals↗
PubMed1970

Acceleration of noradrenaline biosynthesis in the guinea-pig vas deferens by potassium.

1. Increasing the concentration of KCl in Krebs-Henseleit bicarbonate solution enhanced the formation of (14)C-noradrenaline ((14)C-NA) from (14)C-tyrosine in the guinea-pig vas deferens. In 52 mM KCl Krebs-Henseleit solution the specific activity of the newly formed (14)C-NA was double that of controls.2. The rate of synthesis of (14)C-NA from (14)C-tyrosine was constant for up to 2 h in 52 mM KCl Krebs-Henseleit solution and for 4 h in unmodified Krebs-Henseleit solution.3. There was no increase in NA formation in the presence of KCl rich Krebs-Henseleit solution if (14)C-DOPA was used as the starting substrate instead of (14)C-tyrosine.4. The specific activity of (14)C-tyrosine in the high KCl treated vas deferens was 80% of that of control tissues. Thus the enhanced synthesis of (14)C-NA in high KCl Krebs-Henseleit solution did not arise from an increase in the specific activity of precursor.5. The effect of K(+) on NA synthesis was not mimicked by ganglionic stimulants nor blocked by tetrodotoxin.6. Removal of Ca(2+) ions or increasing the concentration of Mg(2+) ions abolished the increase in synthesis of NA seen in high KCl Krebs-Henseleit solution but left the basal rate of NA synthesis in unmodified Krebs-Henseleit solution unaltered.7. The spontaneous release of newly synthesized catecholamines ((14)C-labelled) or tritiated noradrenaline ((3)H-NA) from vasa deferentia was increased in 52 mM KCl Krebs-Henseleit solution. Removal of Ca(2+) ions reduced the increased efflux of newly synthesized amine in high KCl media to that seen in unmodified Krebs-Henseleit solution. The efflux of (3)H-NA was reduced to one-third of its former rate in the absence of Ca(2+).8. High KCl Krebs-Henseleit solution caused a substantial contraction of the vas deferens which was not abolished by tetrodotoxin. Release of (3)H-NA paralleled the contractile response, and was likewise unaffected by tetrodotoxin.9. No evidence was obtained for any alterations in the activity of tyrosine hydroxylase, the rate limiting enzyme in the formation of NA from tyrosine, in homogenates of vas deferens which had been treated with 52 mM KCl Krebs-Henseleit solution.10. These results support the hypothesis that acceleration of NA synthesis occurs when tyrosine hydroxylase is freed from end-product inhibition by the release of noradrenaline, brought about in this case, by high concentrations of KCl.

Animals↗