Search PubMed⌕ Search

Biomedical subjects

C H Cheng

Publications and source records attributed to C H Cheng.

At least 199 records · Page 11Linked to original sources
PubMed1984

The cerebral metabolism of L-dihydroxyphenylalanine. An autoradiographic and biochemical study.

The regional cerebral distribution of carbon-14 activity was studied using autoradiography following the intravenous administration of L-3,4-dihydroxyphenyl-(3-14C)-alanine (14C-L-dopa) to rats pretreated with carbidopa. 5 min after 14C-L-dopa administration, the regional cerebral distribution of carbon-14 varied with regional cerebral blood flow. From 45 min to 4 h after 14C-L-dopa administration, however, carbon-14 activity accumulated in a regionally selective manner which correlated (p less than 0.001) with the total endogenous catecholamine content of each region (n = 26). A prior unilateral lesion of the substantia nigra pars compacta markedly reduced the accumulation of carbon-14 in the ipsilateral, but not the contralateral, striatum at all times from 45 min to 4 h after 14C-L-dopa administration. Similarly, reserpine pretreatment selectively reduced the accumulation of carbon-14 in only those regions in which a marked accumulation occurred in controls after intravenous injections of 14C-L-dopa. Liquid chromatography with electrochemical detection was utilized to determine the tritium content of L-dopa and its metabolites in the striatum and cerebellum from 1 min to 4 h after the intravenous administration of 3H-L-dopa. 3H-dopamine, and subsequently 3H-dihydroxyphenylacetic acid and 3H-homovanillic acid, appeared only in the striatum. 3H-3-O-methyldopa levels rose simultaneously in the cerebellum and striatum. These results demonstrate a feasible approach for imaging dopamine neurons in man in vivo by positron emission tomography provided that L-dopa can be labeled with a positron-emitting isotope with sufficient specific activity. Furthermore, these results suggest that quantitative interpretation of the images is possible.

Animals↗
PubMed1984

Pubertal gonadal hormones in modulating the testosterone dependency of hepatic aryl hydrocarbon hydroxylase in female rats.

The responsiveness of the hepatic microsomal aryl hydrocarbon hydroxylase (AHH) to testosterone enanthate (TE; 2.5 mumol/kg/day for 9 days) was sex-dependent in adult rats, the enzyme being very resistant to TE in normal adult or ovariectomized females. Administration of testosterone propionate or diethylstilbestrol (1.45 mumol) to neonatal female rats at 1 and 3 days of age did not increase the responsivity to TE in adulthood. However, exposure of female rats to TE (5.0 mumol/kg/day) during the peripubertal period (35-50 days old) resulted in increased sensitivity to TE (+55.2%) when tested in adulthood. The responsivity was further potentiated (+109.3%) if the animals were ovariectomized at 28 days of age. Prepubescent ovariectomized females which received corn oil or estradiol benzoate (1.5 mumol/kg on alternate days) during puberty were not able to respond to TE significantly. These results suggest that the refractoriness of the hepatic AHH to testosterone in adult female rats is determined by the absence of testosterone, as well as the presence of estrogens, during puberty.

Animals↗
PubMed1982

Dopamine turnover estimated by simultaneous LCEC assay of dopamine and dopamine metabolites.

The estimation of changes in tissue levels of dopamine (DA) and its metabolites has been employed to approximate the turnover rate or release of DA. We have developed an assay using high pressure liquid chromatography with electrochemical detection to quantify DA, dihydroxyphenylacetic acid (DOPAC), 3-methoxytyramine (3-MT), and homovanillic acid (HVA) simultaneously in brain homogenates. The assay is simple, inexpensive, rapid and accurate; the sensitivity of the assay for DA and DOPAC was 10 pg, for HVA 50 pg, and 200 pg for 3-MT. Apomorphine treatment resulted in a reduction in tissue levels of DOPAC and HVA, while haloperidol administration increased tissue levels of DOPAC and HVA. Neither drug treatment caused changes in DA levels. Administration of d-amphetamine 2.5 mg/kg S.C. resulted 1 hour later in increases in the striatal concentration of DA (57%) and 3-MT (44%) and decreases in DOPAC (40%) and HVA (39%). These data are consistent with the agonistic effect of apomorphine and antagonistic effect of haloperidol on DA autoreceptors and post-synaptic receptors. In the case of amphetamine, the increases in the levels of DA and 3-MT probably reflect the ability of d-amphetamine to induce DA release and block re-uptake. The reduction of DOPAC and HVA levels are consistent with the ability of d-amphetamine to competitively inhibit monoamine oxidase activity as well as the neuronal reuptake of DA. The simultaneous estimation of DA, DOPAC, 3-MT, and HVA should facilitate the understanding of dopaminergic drugs with complicated mechanisms of action.

Animals↗
PubMed1982

Radiation control through licensing and intensive training.

Various types of intensive training courses to suit radiation workers in different fields were sponsored by both the Atomic Energy Council of Executive Yuan and the National Health Administration of Executive Yuan, Republic of China during the past seven years. During the years 1974-79, the number of radiation workers attending each training course, their age, sex and educational background are presented in detail. The typical course contents for both medical and non-medical radiation workers are given. A summary of the percentage of passes and failures of the final examination given at the end of each training course is also given. The present status of licensing for radiation facilities and workers is described, and its results are indicated. The successful control of ionizing radiation through this kind of intensive training and licensing is evidenced in the film badge records given by a centralized service laboratory located at the National Tsing Hua University.

Adult↗
PubMed1982

Melanotropins: aldosterone- and corticosterone-stimulating activity in isolated rat adrenal cells.

Stimulation of corticosterone and aldosterone production in rat adrenal decapsular and capsular cells respectively by alpha- and beta-melanotropins (alpha- and beta-MSH) have been investigated. Although they are considerably less potent than corticotropin (ACTH), the dose-response curves are parallel to those for ACTH except in the case of aldosterone stimulation by beta-MSH where the dose-response curve is biphasic. The steroidogenic actions of ACTH, beta-MSH and alpha-MSH are antagonized by corticotropin-inhibiting peptide in both capsular and decapsular cells. A synthetic analog of beta-MSH ([Gly10]-betac1-MSH) inhibits both beta-MSH and ACTH in aldosterone output in capsular cells, but it does not inhibit their corticosteroidogenic actions in decapsular cells.

Adrenal Glands↗
PubMed1981

Two contiguous thrombin fragments of human somatotropin form a functionally active recombinant, but the two homologous fragments from sheep hormone do not.

Two thrombin fragments of reduced-carbamidomethylated human somatotropin representing the full primary structure of the native hormone (residues 1-134 and 135-191) have been found to form a recombinant molecule with properties similar to those of reduced-carbamidomethylated human somatotropin as shown by circular dichroism spectroscopy, two receptor-binding assays, and radioimmunoassay. In contrast, the homologous thrombin fragments of reduced-carbamidomethylated sheep hormone (residues 1-133 and 134-191) do not undergo recombination. Furthermore, neither the reduced-alkylated nor the reduced and nonalkylated C-terminal thrombin fragment of sheep hormone is able to interact with the reduced-carbamidomethylated N-terminal thrombin fragment of human hormone, under conditions which favor the recombination of the two human somatotropin fragments.

Amino Acid Sequence↗
PubMed1981

Simultaneous radioenzymatic assay of dopamine and dihydroxyphenylacetic acid: an index of in vivo dopamine release.

The relative brain tissue concentrations of dopamine (DA) and its deaminated metabolite, dihydroxyphenylacetic acid (DOPAC), appears to be a reliable index of the functional activity of dopaminergic neurons. In order to apply this approach to the assessment of dopaminergic neuronal activity in small regions of brain, we have developed a sensitive radioenzymatic assay for simultaneous measurement of DA and DOPAC. The sensitivity of the assay for DA is approximately 10 pg and for DOPAC 100 pg. In addition, the assay is highly specific, simple, and relatively inexpensive. The concurrent estimation of tissue DA and DOPAC concentrations seems to be a reliable means of evaluating the rate of DA turnover or release in behavioral, electrical stimulation, and certain drug paradigms. However, the release or turnover of DA as induced by D-amphetamine (and perhaps other indirectly-acting dopaminemimetic drugs) cannot be meaningfully assessed by measurement of DA and DOPAC alone.

3,4-Dihydroxyphenylacetic Acid↗
PubMed1981

Radioimmunoreactivity and receptor-binding activity of the recombined molecule obtained by complementation of two fibrinolysin fragments of ovine prolactin.

The recombined molecule obtained by complementation of two fibrinolysin fragments of ovine prolactin (oPRL) has been characterized by radioimmunoassay and radioreceptor assay. The recombinant alone exhibits very low radioimmunoreactivity and radioreceptor activity. However, in the presence of excess fragment oPRL-(1-53), which does not compete with oPRL in either assay, the recombinant has 101% of the radioimmunoreactivity and only 13% of the radioreceptor activity. The result shows that the low activity of the recombinant when assayed alone is due to dissociation of the molecule. When the molecule is completely in the recombined form in the presence of excess oPRL-(1-53), it retains full immunoreactivity but only part of the radioreceptor activity.

Animals↗
PubMed1981

Ovine prolactin. Isoelectricfocusing and characterization of the separated components.

Highly purified ovine prolactin was subjected to preparative isoelectricfocusing. Although complete separation of the isoelectrically different components was not achieved, four enriched fractions of these components were prepared by this method. Studies on the separated fractions revealed that these components of ovine prolactin, probably a result of deamidation processes, have rather different properties. The more acidic components appeared to be less active in both the radioreceptor assay on mammary gland membranes and the pigeon crop-sac assay. However, the more acidic forms appeared to be more immunoreactive as revealed by radioimmunoassay.

Amino Acids↗
PubMed1980

The inactivation of rat adipocyte Mg2+-dependent phosphatidate phosphohydrolase by noradrenaline.

The inactivation of rat adipocyte Mg2+-dependent phosphatidate phosphohydrolase by noradrenaline [Cheng & Saggerson (1978) FEBS Lett. 87, 65--68; Cheng & Saggerson (1978) FEBS Lett. 93, 120--124] persists for at least 40 min in crude defatted homogenates kept at 0 degrees C or 20 degrees C, but is diminished at 37 degrees C. The effect of noradrenaline persists through the isolation of post-105000 g supernatants and is then stable in these preparations at 0 degrees C and 37 degrees C. Inclusion of albumin (10--20 mg/ml) in homogenization buffers abolishes the effect of noradrenaline. The effect of noradrenaline is not removed by dialysis of extracts or by raising the concentrations of Mg2+ or phosphatidate in assays.

Adipose Tissue↗
PubMed1980

Subcellular distribution and some properties of N-ethylmaleimide-sensitive and-insensitive forms of glycerol phosphate acyltransferase in rat adipocytes.

1. Glycerol phosphate acyltransferase (GPAT) activities were measured in subcellular fractions obtained from rat epididymal adipocytes. These contained both N-ethylmaleimide-sensitive and N-ethylmaleimide-insensitive forms of the enzyme. 2. As shown by parallel measurements of marker enzymes, N-ethylmaleimide-insensitive GPAT is most probably a mitochondrial activity, whereas N-ethylmaleimide-sensitive GPAT is the microsomal enzyme. 3. Subcellular distributions are also reported for dihydroxyacetone phosphate acyltransferase (DHAPAT) (assayed with and without N-ethylmaleimide), monoacylglycerol phosphate acyltransferase (MGPAT) and Mg2+-dependent and Mg2+-independent forms of phosphatidate phosphohydrolase (PPH).

1-Acylglycerol-3-Phosphate O-Acyltransferase↗
PubMed1980

A highly sensitive radioenzymatic assay for simultaneous estimation of norepinephrine, dopamine, and epinephrine.

We have developed a radioenzymatic assay for simultaneous estimation of norepinephrine (NE), dopamine (DA), and epinephrine (E) that was the result of the integration of several unique features of previously described assay procedures. Catecholamines in sera or tissue homogenates were enzymatically O-methylated in the presence of partially purified catechol-O-methyltransferase with S-[methyl-3H] adenosyl methionine serving as the methyl donor. The O-methylated products were then separated by thin-layer chromatography, eluted from the gel, and their tritium content determined. The assay allows measurement of catecholamines with a sensitivity in the ranges of 15-20 pg. In addition, the assay is highly specific, reproducible, relatively rapid and simple, and inexpensive.

Adult↗