PubMed Health⌕ Search

Biomedical subjects

A J Friedhoff

Publications and source records attributed to A J Friedhoff.

At least 19 recordsLinked to original sources
PubMed1992

Site-directed mutagenesis of tyrosine hydroxylase. Role of serine 40 in catalysis.

We have investigated the role of serine 40 (Ser-40) in tyrosine hydroxylase (TH) catalysis of basal and activated enzymes by protein kinase A (PKA)-mediated phosphorylation. Wild type and mutant TH were transiently and stably expressed in AtT-20 cells, and the enzymatic activities of the recombinant enzymes were analyzed. The specific enzymatic activity of transiently expressed TH mutants Ser-40-->leucine or-->tyrosine (Leu-40m or Tyr-40m) was higher than that of the wild type enzyme or of other mutants in which Ser-8, -19, and -31 were replaced by leucine. The kinetic studies carried out with the stably expressed TH show that the Km for the cofactor 6-methyltetrahydropterine is lower and the Ki for dopamine is higher when the enzymatic hydroxylation is catalyzed by the Leu-40m or Tyr-40m than by the wild type enzyme. The kinetic parameters and the pH profile of the enzymatic hydroxylation catalyzed by the Leu-40m or Tyr-40m are similar to the enzyme activated by PKA-mediated phosphorylation. We suggest that Ser-40 in TH exerts an inhibitory influence on the enzymatic activity, and its replacement with another amino acid by site-directed mutagenesis or its modification by phosphorylation leads to a change in conformation with an increased enzymatic activity. The importance of Ser-40 in the activation of TH by PKA-mediated phosphorylation was investigated by comparing the activation of the wild type enzyme with that of Leu-40m or Tyr-40m. The findings that the enzymatic activity is increased by PKA-mediated phosphorylation of the wild type enzyme, but not of the Leu-40m or Tyr-40m, demonstrate that phosphorylation at Ser-40 is essential for activation of TH by PKA. The findings that addition of ATP plus cAMP to homogenates from transfected AtT-20 cells stimulates the recombinant wild type TH activity indicate that these cells contain endogenous cAMP-dependent protein kinase.

Amino Acid Sequence↗
PubMed1992

Tonic inhibition of striatal dopamine transmission: effects of benzodiazepine and GABAA receptor antagonists on extracellular dopamine levels.

At present, it is unclear whether ligands which bind at the benzodiazepine/GABA receptor complex play a tonic modulatory role with regard to striatal dopamine (DA) transmission. The present study was designed to examine the effects of Ro15-1788, a benzodiazepine (BZ) receptor antagonist, and SR 95531, a GABAA receptor antagonist, on striatal extracellular DA (DA[e]) concentrations in anesthetized and awake rats using the technique of in vivo microdialysis. Local administration of Ro15-1788 resulted in a dose-dependent increase in DA[e] in both anesthetized and awake animals. The Ro15-1788-induced increase in DA[e] was blocked by coadministration of the BZ agonist diazepam, as well as GABA. Local administration of SR 95531 also resulted in a dose-dependent alteration in striatal DA levels in both anesthetized and awake animals. The SR 95531-induced increase in DA was blocked by coadministration of GABA. The results suggest that GABA may play a tonic inhibitory role with regard to striatal DA transmission.

Animals↗
PubMed1991

Receptor reserve for D2 dopaminergic inhibition of prolactin release in vivo and in vitro.

The full dopamine agonist R-(-)-N-n-propylnorapomorphine (NPA) completely suppressed (ED50 0.12 micrograms/kg) serum prolactin (PRL) levels elevated by pretreatment with gamma-butyrolactone (750 mg/kg). Pretreatment with the receptor-inactivating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (1 and 2 x 6 mg/kg) progressively shifted the dose-response curve for NPA to the right, but PRL secretion was still maximally inhibited. Receptor inactivation elicited smaller (2-fold) dextral shifts in the ED50 for the partial agonists (+)- and (-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine. These results are consistent with the presence of a sizable receptor reserve at the D2 receptor regulating PRL release in the anterior pituitary. Analogous results were obtained in vitro utilizing primary cultures of anterior pituitary cells. NPA potently inhibited basal PRL release in culture (ED50 0.06 nM, maximal inhibition 83%). Receptor alkylation with phenoxybenzamine (1 microM, 1 hr) did not affect basal PRL release but right-shifted the ED50 for NPA more than 6-fold and attenuated maximal inhibition (to 68%); both effects were significant (P less than .01). The extracellular accumulation of cyclic AMP (cAMP) stimulated by a combination of forskolin (1 microM) and 3-isobutyl-1-methyl xanthine (100 microM) required higher concentrations of NPA (ED50 0.36 nM), and the maximal effect was much smaller (46%). Phenoxybenzamine treatment did not alter either basal or forskolin-stimulated cAMP accumulation, but it reduced the maximal inhibitory response to NPA (to 13%) without shifting the ED50. Plots of receptor occupancy vs. response demonstrated a 60% receptor reserve for NPA inhibition of PRL release, but none for inhibition of cAMP production.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Antagonists↗
PubMed1990

Interleukin-1 stimulates the beta-amyloid precursor protein promoter.

1. Amyloid plaques found in the brains of Alzheimer's diseased patients are composed of the 42 amino acid beta-amyloid peptide (BAP) which is processed out of the larger amyloid precursor protein (APP). 2. To study the regulation of the APP gene expression, we have isolated the promoter region of this angle of this single-copy gene and produced a reporter gene system to determine if the promoter is responsive to agents that may cause the overproduction of APP leading to the abnormal accumulation of plaques in AD. 3. The promoter contains sequences homologous to heat shock elements, AP-1 binding sites, and phorbol ester-inducible sequences as well as GG-rich regions found in other constitutively expressed genes. 4. We show here that this promoter is inducible in cultured cells by interleukin-1 (IL-1) in a transient assay system and that the HSE and AP-1 binding site are required for this inducibility. 5. This induction of transcription from the APP promoter implies that this gene is responsive to tropic and/or trophic agents which may be present in the diseased brain.

Alzheimer Disease↗
PubMed1979

Enduring changes in dopamine receptor cells of pups from drug administration to pregnant and nursing rats.

A decrease in specific [3H]spiroperidol binding to rat caudate tissue and a parallel decrease in sensitivity to apomorphine in eliciting stereotyped behavior was observed in the offspring of rat mothers treated with either haloperidol or alpha-methyl-p-tyrosine-methyl ester during pregnancy. In contrast, evidence of increased dopamine-receptor sensitivity was observed in the pups if haloperidol was administered to their mothers postpartum during nursing rather than during pregnancy.

Animals↗
PubMed1979

Multiple molecular forms of catechol-O-methyltransferase. Evidence for two distinct forms, and their purification and physical characterization.

Catechol-O-methyltransferase (COMT: EC 2.1.1.6) has been shown to exist in the soluble fraction of rat liver as two distinct molecular forms, designated COMT I and COMT II, which are separable by gel filtration, ion exchange chromatography, and sedimentation. The predominant form, COMT I, has a smaller Mr of about 24,000, as determined by gel filtration and sedimentation, and less negative charge, whereas the minor form, COMT II, has a larger Mr of about 47,500 and more negative charge. The COMT I and COMT II have been purified 450- and 205-fold, respectively, from rat liver by a newly developed procedure which gives homogeneous enzyme preparations with respect to catechol-methylating activities. The molecular properties of the predominant form, COMT I, were: s20,w, 2.7; D20,W, 10.5; Stokes radius, 20.1 A; f/fo, 1.08; and pI, 4.9. For the minor form, COMT II, the values were s20,w, 3.8; D20,w, 7.3; Stokes radius, 28.7 A; f/fo, 1.23; and pI, 4.8. Catechol-O-methyltransferase was found to exhibit tissue-specific isozymic patterns in the distribution of its two variant forms. In the rat tissues, the liver and kidney exhibited the presence of the two physically separable forms. Catechol-O-methyltransferase was also found as two distinct molecular forms in human tissues, including liver, brain, and placenta. The two forms of human catechol-O-methyltransferase were not distinguishable by the criteria of gel filtration from their counterparts in rat liver, indicating that the two molecular forms of human and rat liver catechol-O-methyltransferase are homologous. No interconversion of one molecular form of catechol-O-methyltransferase into the other was observed under experimental conditions employed. Available evidence indicates that the two molecular forms of catechol-O-methyltransferase are genetically dissimilar proteins.

Animals↗
PubMed1978

Paradoxical reaction to L-dopa in schizophrenic patients.

The authors administered 6 g of L-dopa to 8 schizophrenic patients and 750 mg of chlorpromazine to 7 schizophrenic patients. Chlorpromazine showed only a modest advantage over L-dopa and only on some Brief Psychiatric Rating Scale factor scores, and at maximum dosage the thought disturbance factor score in the L-dopa-treated group was not worse than at baseline. The results suggest that L-dopa is associated more with toxic than with schizophreniform symptoms and that there is adaptation to its effects. The authors discuss implications of these findings for the dopamine hypothesis of schizophrenia.

Adult↗
PubMed1978

Human platelet MAO in drug-free and medicated schizophrenic patients.

The authors compared platelet monoamine oxidase activity in drug-free chronic and acute schizophrenic patients, medicated chronic schizophrenic patients, and normal controls. A significant decrement in MAO activity was found only in medicated chronic schizophrenic patients. The possible mechanism for this finding is discussed.

Acute Disease↗
PubMed1978

The neuroleptic hypothesis: study of the covariation of extrapyramidal and therapeutic drug effects.

A therapeutic trial with chlorpromazine was conducted with a homogeneous (for age and sex) group of recently admitted schizophrenic patients. Extrapyramidal effects were measured through quantitative analysis of digital tremor, after four days of fixed-dose treatment. Assessment of treatment efficacy was based on Brief Psychiatric Rating Scale ratings, done at the end of four weeks' treatment. Those patients whose tremor was least affected by drug were most likely to benefit from the treatment. Implications of this negative correlation for our understanding of the neuroleptic hypothesis and the closely associated dopamine hypothesis of schizophrenia are discussed.

Adolescent↗
PubMed1978

In vivo formation of dopamine from 3,4-methylenedioxyphenethylamine in the rat.

Administered 1-C14-3,4-methylenedioxyphenethylamine led to the excretion of about 2% of the urinary C14 as conjugated dopamine and 3-methoxytyramine metabolites, in tranylcypromine treated rats. The amine was not excreted unchanged. The major metabolites were identified as conjugates of methylenedioxyphenylacetic acid, homovanilic acid and dihydroxyphenylacetic acid. The latter are derived by the further metabolism of conjugated methylenedioxyphenylacetic acid. Administered tranylcypromine doubled the excretion of conjugates of labeled dopamine and3-methoxytyramine. NADPH served as a cofactor for the microsomal demethylenation of the amine.

3,4-Methylenedioxyamphetamine↗
PubMed1978

A comparison of the onset of action and therapeutic efficacy of amoxapine and amitriptyline.

A total of 61 moderately to severely depressed outpatients were treated for four weeks with either amoxapine (a dibenzoxapine tricyclic) or amitriptyline. This double blind study showed that amoxapine was as effective as amitriptyline and had an earlier onset of action. Maximum doses used were 300 mg of amoxapine and 150 mg of amitriptyline. Side effects were similar for the two drugs, except for impotence or loss of libido in eight male amoxapine, as against three amitriptyline patients. Laboratory, EKG, and vital signs findings showed no pathological trends.

Adolescent↗