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Biomedical subjects

M D Johnson

Publications and source records attributed to M D Johnson.

At least 253 records · Page 14Linked to original sources
PubMed1986

Vitamin D3 derivatives inhibit the differentiation of Friend erythroleukemia cells.

A number of vitamin D3 metabolites inhibit benzodiazepine- and dimethyl sulfoxide-induced differentiation of Friend erythroleukemia cells. The inhibition is dose dependent and occurs at nM concentrations. The order of potency of these compounds is 1,25-dihydroxycholecalciferol greater than 1,25,26-trihydroxycholecalciferol greater than 1,24R,25-trihydroxycholecalciferol greater than 1 alpha-hydroxycholecalciferol greater than 24R,25-dihydroxycholecalciferol greater than 25S,26-dihydroxycholecalciferol. The inhibition is maximal when the vitamin D3 analogs are added together with the inducer, and becomes progressively decreased with delayed addition. These results suggest that the vitamin D3 metabolites may play a regulatory role in erythropoiesis.

Animals↗
PubMed1986

Studies on the mechanism of action of protein kinase C and the isolation of molecular clones encoding the enzyme.

Protein kinase C (PKC) plays an important role in signal transduction and the action of phorbol ester tumor promoters, and it is of interest to isolate the coding sequence of this enzyme. Using a 53-base pair synthetic oligonucleotide probe that corresponds to an 18-amino acid peptide obtained from rat brain PKC, we have isolated rat brain cDNA clones corresponding to PKC. We have also isolated several closely related clones. Partial nucleotide sequence analysis of one of the PKC clones (RP41) identifies a 224-amino acid region with approximately 40% homology to the carboxy terminal and catalytic domains of both the cAMP-dependent and cGMP-dependent protein kinases. The levels of mRNA homologous to RP41 are very high in brain; very low but detectable levels are present in heart and liver. A second cDNA (RP16) was only partially sequenced, and based on its predicted amino acid sequence, it shares 65% homology with the corresponding region of the PKC clone RP41. The levels of mRNA corresponding to RP16 are also highest in rat brain, but they are of a different size than those detected with RP41. These and additional results indicate that the gene for the enzyme PKC shares considerable homology with other protein kinases and that PKC itself may belong to a new multigene family. The availability of these cDNA clones should greatly facilitate further studies on the role of PKC in growth control, differentiation, and multistage carcinogenesis.

Amino Acid Sequence↗
PubMed1985

Effect of intravenous epinephrine infusion on plasma renin activity in adrenalectomized dogs.

Previous experiments have shown that circulating epinephrine stimulates renin secretin and increases plasma renin activity (PRA) when it is infused intravenously, but not when it is infused directly into the renal artery at similar infusion rates. The present experiments were designed to test the hypothesis that the adrenal glands mediate the PRA response to intravenous epinephrine infusion. Accordingly, anesthetized dogs were prepared with either an acute bilateral adrenalectomy or a sham-adrenalectomy procedure. Epinephrine was then infused intravenously into each animal for 45 minutes at a rate of 25 ng X kg-1 X min-1. Time control experiments in which epinephrine was not infused were also conducted. In sham-adrenalectomized dogs, PRA (in nanograms per ml h-1) rose from 4.1 +/- 1.4 in the control period to 13.0 +/- 3.0 during intravenous epinephrine infusion (means +/- SE; p less than 0.01). In adrenalectomized dogs, PRA rose from 2.1 +/- 0.4 during the control period to 5.5 +/- 0.9 during intravenous epinephrine infusion (p less than 0.01). Neither the absolute increments in PRA nor the percent increases in PRA were significantly different between the two groups receiving epinephrine. PRA remained unchanged in time control experiments. These data demonstrate that the adrenal glands need not be present in order for intravenous epinephrine infusion to elicit an increase in PRA. The data do not support the hypothesis, therefore, that epinephrine-induced increases in PRA are initiated by receptors located within the adrenal glands.

Adrenalectomy↗
PubMed1985

Quinolinic acid stimulates luteinizing hormone secretion in female rats: evidence for involvement of N-methyl-D-aspartate-preferring receptors.

Pharmacological evidence suggests that endogenous excitatory amino acid neurotransmitters stimulate luteinizing hormone (LH) secretion in neonatal and adult rats. Recent studies have identified quinolinic acid (QUIN), an endogenous brain and peripheral metabolite of tryptophan, as a potent agonist at N-methyl-D-aspartate (NMDA)-preferring excitatory amino acid receptors. The present studies examined whether QUIN alters LH secretion in ovariectomized, estradiol-primed rats and whether such effects are mediated by specific amino acid receptor subtypes. In one experiment, animals received intracisternal injections of either quinolinic acid, N-methyl-DL-aspartate (NMA), aspartate (ASP), quisqualic acid (QA), or monosodium glutamate (GLU) five minutes prior to decapitation. In a second study, animals receiving central QUIN or NMA were treated simultaneously with either 2-amino-7-phosphonoheptanoic acid (APH) or kynurenic acid (KYA), both antagonists of NMDA-preferring receptors, or the quisqualate antagonist, glutamate diethyl ester (GDEE). Serum LH concentrations were measured by radioimmunoassay. Intracisternal administration of either QUIN or NMA resulted in an acute, dose-dependent increase of serum LH concentrations. Coadministration of APH blocked the effects of QUIN and NMA. QUIN stimulation of LH was also blocked by KYA, but not GDEE. Neither GLU nor ASP increased LH release, but QA did produce a small, significant elevation of LH. Light microscopic evaluation of brains showed no morphologic disturbance resulting from administration of these agents. The present results suggest that QUIN, or other endogenous ligands of NMDA-preferring receptors, may participate in the regulation of LH secretion in the adult female rat.

Animals↗
PubMed1985

Quinolinic acid stimulates luteinizing hormone secretion through a serotonin-dependent mechanism.

Previous results from this laboratory suggest that the tryptophan metabolite, quinolinic acid (QUIN), stimulates luteinizing hormone (LH) secretion in female rats, most likely through actions on NMDA-preferring excitatory amino acid receptors. The present experiments examined whether QUIN alters LH secretion through actions requiring intact catecholaminergic or serotonergic mechanisms. Each study examined the effects of intracisternal (i.c.) injections of 25 microliter acidic saline or saline containing QUIN (500 nmol) or the synthetic analogue, N-methyl-DL-aspartate (NMA, 500 nmol), into ovariectomized, estradiol benzoate-primed rats after pharmacologic disruption of monoaminergic neurotransmission. In each experiment, animals were decapitated 5 min after QUIN or NMA administration. Experiment 1 examined whether reduction in brain serotonin (5-HT) or of norepinephrine (NE) and epinephrine (E) alters the QUIN- or NMA-induced stimulation of LH secretion. Rats were pretreated with the dopamine-beta-hydroxylase inhibitor, FLA-63 (40 mg/kg 2 h prior). A second experiment examined the effects of the 5-HT antagonist, methysergide, on QUIN or NMA stimulation of LH secretion. Methysergide (15 mg/kg) was administered 30 min prior to experimentation. Experiment 3 examined whether selective destruction of raphe serotonergic neurons with the indoleamine neurotoxin, 5,7 dihydroxytryptamine (5,7 DHT), alters QUIN's stimulatory effects. In each study, serum LH concentrations were determined by radioimmunoassay. Hypothalamic catecholamine and 5-HT concentrations were measured by radioenzymatic assay and liquid chromatography with electrochemical detection, respectively. Depletion of brain 5-HT with PCPA significantly reduced the stimulation of LH secretion by QUIN, but not by NMA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Serial cultivation of normal rat bladder epithelial cells in vitro.

Recent advances in culture techniques for human urothelial cells have led to the development of an improved method for growing primary rat bladder epithelial cells. We report here the conditions developed for large-scale in vitro growth and serial cultivation of normal diploid rat bladder epithelial cells. Primary cultures were initiated by attachment of bladder mucosal explants to type I collagen gels. A rapid outgrowth of epithelial cells from the explants occurred when cultured in a hormone-supplemented medium with epidermal growth factor. These primary outgrowths were passaged by nonenzymatic dispersion with 0.1 per cent ethylenediaminetetracetic acid and replating onto new gels. The capacity for routine serial passaging and maintenance of rat bladder epithelial cells required the presence of epidermal growth factor, a requirement not observed with human urothelial cells. The characteristics of the cultured rat bladder epithelial cells were similar to human urothelial cells in: ultrastructural and phase-contrast morphologic properties, showing junctional complexes, desmosomes, stratification and an apical glycocalyx; the absence of stromal cell contamination; and the ability to be serially passaged. Spontaneous cell-line formation was observed with the rat bladder epithelial cells, but has not been found with the human urothelial cells. With the method that we have developed, the number of rat bladder epithelial cells generated from a single bladder of a 4 to 6 week old rat was increased 100-fold from about 7 X 10(5) cells to 7 X 10(7) viable cells within 3 weeks of culture. The capability of culturing normal, primary rat bladder epithelial cells on this scale has not been reported previously and will facilitate comparative studies of the biological and molecular characteristics of the mammalian urothelium. Furthermore, this culture system will be useful for carcinogenesis studies, including metabolic activation of carcinogens and cellular transformation in vitro.

Animals↗
PubMed1985

Peripheral-type benzodiazepines influence ornithine decarboxylase levels and neurite outgrowth in PC12 cells.

A number of the benzodiazepines (BZDs) inhibit nerve growth factor (NGF)-induced neurite outgrowth in a dose-dependent manner in PC12 cell cultures. The rank order of potency of a series of BZDs for inhibition of neurite outgrowth does not correlate with the order of their affinity constants for the so-called peripheral BZD sites present on PC12 cells. Whereas the inhibition of neurite extension is stereospecific, the binding to the peripheral site is not. The inhibition of neurite outgrowth is not attributable to a blockade of NGF binding to either its fast or slow receptors. Additionally, several other characteristics of NGF stimulation of PC12 cells, such as autoadhesion and the induction of ornithine decarboxylase (OrnDCase), remain unaltered in the presence of BZDs. Many BZDs increase OrnDCase levels in PC12 cells in the absence of NGF. The OrnDCase response to BZDs is blocked by actinomycin D. Furthermore, the structural requirements of BZDs for induction of OrnDCase activity is not identical to that for the inhibition of NGF-induced neurite extension. Thus, unlike attenuation of neurite extension, BZD induction of OrnDCase is not stereospecific. Also, some BZDs block neurite growth but do not induce OrnDCase. We propose that there are at least three sites of action of BZDs on PC12 cells. The first is the well-characterized high-affinity peripheral site. The second distinct locus of action results in a blockade of NGF-induced neurite outgrowth. The structural requirements for the latter effect are essentially indistinguishable from those for BZD induction of hemoglobin synthesis in Friend erythroleukemia cells. The third site of action results in an induction of OrnDCase. Structural requirements for this activity are not identical to those for either the differentiation of Friend cells or the inhibition of neurite outgrowth.

Animals↗
PubMed1985

An improved bioassay method for determining natriuretic activity of atrial extracts.

Extracts of mammalian atrial tissue contain potent natriuretic substances known collectively as atrial natriuretic factor (ANF). The purposes of the present experiments were: 1) to improve on existing bioassay methodology for the detection of ANF activity in atrial extracts, and 2) to compare the ANF activity of atrial extracts prepared from Brattleboro-stain diabetes insipidus (DI) rats with that from normal and water-deprived Long-Evans (LE) rats. A pool of atrial tissue extract (AE) was prepared from normal Sprague-Dawley rats for use as a standard against which unknown AE samples could be compared. Five doses, ranging from 27 to 432 micrograms of AE protein, were assayed in the Sprague-Dawley bioassay rats. Phosphate-buffered saline (PBS) vehicle and ventricular tissue extracts were also assayed. Statistical analysis of several log dose-response relationships revealed that the bioassay response most appropriate in determining relative natriuretic activity of AE was the log of the experimental/control ratio for sodium excretion. The bioassay was used to demonstrate that PBS atrial extracts from both water-deprived LE rats and DI rats contain more natriuretic activity than do PBS atrial extracts from LE rats.

Animals↗
PubMed1985

Very large scale suspension cultures of mammalian cells.

Suspension cultures of mammalian cells can be used to produce virus vaccines, as a source of interferons, and as a host system for expressing inserted human genes. We will discuss the experience with this technology in our organisation over the past 18 years, during which we have progressively expanded our facilities for such work: we are now operating routinely with 8 000 litre fermenters. Information will be summarized in relation to the following topics: design of plant, medium and serum requirements, plant operation and product processing.

Cells, Cultured↗
PubMed1985

A highly sensitive immunoassay system involving antibody-coated tubes and liposome-entrapped dye.

In this colorimetric immunoassay for digoxin, large, unilamellar phospholipid vesicles approximately 0.2 micron in diameter are loaded with high concentrations of Sulforhodamine B. Digoxigenin coupled to phosphatidylethanolamine, incorporated into the lipid formulation, confers immunological specificity. The liposomes are then used as tracers in simple competitive-binding immunoassays with antibody-coated tubes. Results are amplified by 10(3) to 10(4) of what could be achieved with one label group attached to each hapten, so that the results can be read spectrophotometrically. The stability of the liposomes is excellent. The method should be applicable to measuring a wide variety of analytes.

Antibody Affinity↗
PubMed1984

Effects of the serotonin agonist, quipazine, on luteinizing hormone and prolactin release: evidence for serotonin-catecholamine interactions.

The present study tested whether administration of the serotonin agonist, quipazine maleate, affects the secretion of luteinizing hormone (LH) and prolactin (PRL) and concomitantly, the activity of central noradrenergic and dopaminergic systems. Quipazine (15 mg/kg, ip) significantly reduced LH and increased PRL when administered to ovariectomized rats. Associated with these changes, the depletion of dopamine seen after synthesis inhibition with alpha-methyl tyrosine was reduced by quipazine in the caudate nucleus and median eminence, suggesting a depression of dopaminergic activity. The depletion of norepinephrine in the median eminence was unaffected. In a second experiment, quipazine (1 microM) diminished the potassium-induced release of both norepinephrine and dopamine from fragments of medial basal hypothalamus, in vitro. Release from preoptic area was unaffected. These results suggest that central serotonergic systems may interact with noradrenergic and dopaminergic systems that regulate LH and PRL secretion, respectively.

Animals↗
PubMed1984

Risk of stomach cancer after gastric surgery for benign conditions. A case-control study.

Patients with previous gastric surgery for benign conditions are thought to be at increased risk for gastric cancer based on studies from Europe. Recommendations have been made to screen these patients repeatedly in order to detect early gastric cancers. We conducted a case-control study to estimate the risk in the United States where the rates of gastric cancer are lower. There were 521 gastric cancer cases who were matched by age, race, sex, and date of admission to an equal number of hospital controls. The odds ratio for cancer after gastric surgery was 0.7 (P = 0.4) which indicates no increased risk. The sample size was sufficient to detect risks in the range reported in previous studies. The odds ratios rose with longer postoperative intervals but were based on small numbers and were not statistically significant. This case-control study failed to demonstrate an overall increased risk for gastric cancer after surgery. Further study is needed before general screening can be endorsed in the United States.

Adenocarcinoma↗
PubMed1984

Circulating epinephrine stimulates renin secretion in anesthetized dogs by activation of extrarenal adrenoceptors.

The present experiments were designed to determine the location of the adrenoceptors responsible for initiating epinephrine-induced stimulation of renin secretion in vivo. Three hypotheses were tested: 1) the receptors are located intrarenally, 2) the receptors are located extrarenally , and 3) an interaction exists between intrarenal receptors and some event initiated by extrarenal receptors. All experiments were conducted in anesthetized dogs surgically prepared for renal clearance studies. Intravenous infusion of epinephrine at 250 ng X kg-1 X min-1 increased one-kidney renin secretion rate more than fivefold. In contrast, direct intrarenal infusion of epinephrine at 25 ng X kg-1 X min-1 only doubled renin secretion rate from the infused kidney. In six animals in which renin secretion rates were measured bilaterally during intrarenal epinephrine infusion, no differences in renin secretion rates were detected between the two kidneys. To examine the hypothesis that an interaction exists between intrarenal and extrarenal adrenoceptors, epinephrine was infused intravenously at 25 ng X kg-1 X min-1 and simultaneously into one renal artery at 10 ng X kg-1 X min-1. Renin secretion rates rose significantly (P less than 0.01) but equally from both kidneys. At lower epinephrine infusion rates (10 ng X kg-1 X min-1 intravenously plus 3 ng X kg-1 X min-1 intrarenally), renin secretion rates increased submaximally but still equally from both kidneys. It is concluded that epinephrine-induced stimulation of renin secretion in vivo is initiated by adrenoceptors located only extrarenally .

Anesthesia, General↗
PubMed1984

Effects of opiate antagonists on serotonin turnover and on luteinizing hormone and prolactin secretion in estrogen- or morphine-treated rats.

Previous findings indicate that estradiol benzoate (EB) acutely activates serotonergic projections in the medial preoptic area that are stimulatory to prolactin (PRL) secretion. Because opioid agonists also stimulate both PRL release and serotonin (5-HT) turnover, the present experiments tested whether endogenous opioid neurons may mediate estrogen feedback effects. In experiment 1, ovariectomized rats received either 50 micrograms EB or oil vehicle, and either saline or a long-acting opiate receptor blocker, nalmetrene (10 mg/kg), simultaneously, 3 h prior to decapitation. The pargyline method was used to determine 5-HT turnover; hence members of each treatment group received either saline or pargyline (75 mg/kg i.p.) 30 min prior to decapitation. Plasma PRL and luteinizing hormone (LH) concentrations were determined by radioimmunoassays, and 5-HT concentrations from microdissected, individual brain nuclei were measured by liquid chromatography with electrochemical detection. Nalmetrene blocked both the acute elevation of PRL and the increase in 5-HT turnover in the medial preoptic nucleus and ventromedial nucleus induced by EB. Nalmetrene alone also enhanced LH release and 5-HT turnover in the bed nucleus of the stria terminalis, and these effects were prevented by EB. A second study tested whether the opioid agonist, morphine, mimics estrogen effects on PRL and preoptic 5-HT turnover. Animals received saline, morphine (10 mg/kg i.p.) and/or naloxone (5 mg/kg i.p.) 30 min prior to decapitation. Simultaneously, half in each group received pargyline as above.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗