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Biomedical subjects

M R Johnson

Publications and source records attributed to M R Johnson.

At least 217 records · Page 12Linked to original sources
PubMed1990

2-Fluoro-beta-alanine, a previously unrecognized substrate for bile acid coenzyme A:amino acid:N-acyltransferase from human liver.

Our laboratory has demonstrated recently that conjugates of 2-fluoro-beta-alanine (FBAL) and bile acids are the major biliary metabolites of 5-fluorouracil (FUra) in cancer patients. Bile acids are normally conjugated with glycine or taurine, and therefore the identification of the FBAL-bile acid conjugates suggested that FBAL may also be a substrate for the bile acid conjugating enzyme, bile acid CoA:amino acid:N-acyltransferase. Enzyme activity detected using glycine and taurine as substrates was purified 8-fold from human liver cytosol using a DEAE-cellulose column. This preparation when tested for its activity towards beta-alanine and FBAL using cholyl CoA as the bile acid substrate only catalyzed the formation of FBAL-cholate. beta-Alanine was not a substrate. Confirmation of FBAL-cholate as the enzymatic product was demonstrated by (1) coelution of the product of this reaction on HPLC with authentic FBAL-cholate, (2) specific hydrolysis of this product by cholylglycine hydrolase, and (3) molecular weight of the product (497) being identical to that of the authentic FBAL-cholate. Kinetic experiments demonstrated that the enzyme had an affinity for FBAL (Km 1.45 mM) comparable to taurine (Km 1.32 mM), but greater than glycine (Km 6.45 mM). Formation of FBAL-cholate was inhibited competitively by taurine (Ki 1.27 mM) and glycine (Ki 4.47 mM), suggesting that a single enzyme is responsible for conjugation of glycine, taurine and FBAL with bile acids. These data indicate that the formation of the FBAL-bile acid conjugates in patients receiving FUra results from high affinity of the bile acid conjugating enzyme for FBAL.

Acyltransferases↗
PubMed1990

The cannabinoid receptor: biochemical, anatomical and behavioral characterization.

The actions of the active principle of marihuana, delta 9-tetrahydrocannabinol, are mimicked by synthetic cannabinoid agonists showing high potency and enantio-selectivity in behavioral assays. These drugs have been used to characterize cannabinoid receptor binding, biochemistry and pharmacology, leading to a better understanding of the effects of cannabinoids in the CNS of humans and experimental animals.

Animals↗
PubMed1990

Cannabinoid receptor localization in brain.

[3H]CP 55,940, a radiolabeled synthetic cannabinoid, which is 10-100 times more potent in vivo than delta 9-tetrahydrocannabinol, was used to characterize and localize a specific cannabinoid receptor in brain sections. The potencies of a series of natural and synthetic cannabinoids as competitors of [3H]CP 55,940 binding correlated closely with their relative potencies in several biological assays, suggesting that the receptor characterized in our in vitro assay is the same receptor that mediates behavioral and pharmacological effects of cannabinoids, including human subjective experience. Autoradiography of cannabinoid receptors in brain sections from several mammalian species, including human, reveals a unique and conserved distribution; binding is most dense in outflow nuclei of the basal ganglia--the substantia nigra pars reticulata and globus pallidus--and in the hippocampus and cerebellum. Generally high densities in forebrain and cerebellum implicate roles for cannabinoids in cognition and movement. Sparse densities in lower brainstem areas controlling cardiovascular and respiratory functions may explain why high doses of delta 9-tetrahydrocannabinol are not lethal.

Animals↗
PubMed1990

Effect of naloxone on neurohypophyseal peptide responses to breast feeding and breast stimulation in man.

We have investigated the role of endogenous opioid peptides in the release of oxytocin (OT) in response to breast feeding and breast stimulation in humans. Five breast feeding women were studied on two separate occasions within 4 weeks of delivery. Saline or naloxone, 4 mg bolus and 6 mg/h, was administered intravenously, in random order. Blood samples were taken at regular intervals. In the saline-infused group OT rose from a baseline of 1.1 +/- 0.1 pmol/l (mean +/- SEM) to a peak of 7.0 +/- 0.9 after 6 min, and in the naloxone-infused group from 1.0 +/- 0.1 pmol/l to 5.8 +/- 1.3 (P less than 0.05). There were no significant differences between the two groups at any time point. Plasma vasopressin (AVP) did not change. In the second study six women in the luteal phase of the menstrual cycle were investigated on two occasions at least 48 h apart. They were similarly infused with either naloxone or saline in random sequence. A mechanical breast pump provided breast stimulation. In saline-infused women OT levels rose from a baseline of 1.0 +/- 0.1 pmol/l (mean +/- SEM) to a peak of 3.0 +/- 1.1 (P less than 0.05) after 6 min, and in naloxone infused women from 1.1 +/- 0.1 pmol/l to 3.0 +/- 1.4 (NS). There were no differences in OT between the groups. AVP did not change. We conclude that endogenous opioid peptides do not modulate OT release during breast feeding or breast stimulation in women.

Adolescent↗
PubMed1990

In vitro and in vivo analysis of the processing and fate of the peptide products of the short proopiomelanocortin mRNA.

Many peripheral tissues express the proopiomelanocortin (POMC) gene as an 800-base mRNA that lacks the 5' end of the 1200-base pituitary transcript. The missing region encodes the peptide signal sequence, and thus, it is unlikely that any translation product would be secreted. We have found that a RNA transcript equivalent to this short message, generated by transcription in vitro from a T7 polymerase promoter, is translatable in a rabbit reticulocyte lysate, generating peptides of 27.5, 22.5, and 15.5 kD. None of these peptides appears to be processed or protected from proteinase-K digestion by a microsomal membrane fraction. In vivo studies were undertaken by transfecting into GH3 cells one of two expression vectors containing sequences that would produce either a full-length mRNA or a short (800-base) mRNA. The neomycin resistance gene was cotransfected with these plasmids, and 30 permanent cell lines were produced after selection in G418. Cell lines containing the full-length RNA secreted large quantities of ACTH and beta-endorphin immunoreactivity, whereas those expressing the short transcript secreted neither of these peptides. However extractable peptide was present in this latter type of cell line, thereby suggesting that the 800-base mRNA was translated, and that no peptide reached the secretory vesicle. These findings raise important questions about the role of peripheral POMC gene expression.

Adrenocorticotropic Hormone↗
PubMed1990

Neurohypophysial secretion to insulin-induced hypoglycemia and its regulation by endogenous opioids in women.

In animals, there is sexual dimorphism of both neurohypophysial peptide secretion in response to stressful stimuli and to the inhibitory effects of opioids. In men, endogenous opioids inhibit the release of oxytocin when AVP secretion is stimulated by insulin-induced hypoglycemia. We have now investigated the role of endogenous opioids in the AVP and oxytocin response to insulin-induced hypoglycemia in women. Twelve subjects, 6 in the follicular and 6 in the luteal phase of the menstrual cycle, were infused on 2 occasions with naloxone (4 mg bolus and 6 mg/h) or saline. Soluble insulin (Human Actrapid, 0.15 mu/kg, iv) was given and serial blood samples taken. Blood sugar fell significantly (p less than 0.05) and similarly in all groups. In the follicular phase hypoglycemia led to a rise in plasma AVP from 1.3 +/- 0.2 to 1.8 +/- 0.2 pmol/l in the saline-infused subjects (NS), and from 1.0 +/- 0.1 to 2.0 +/- 0.2 pmol/l in the naloxone-infused (p less than 0.05). AVP rose similarly from 0.6 +/- 0.1 to 1.6 +/- 0.5 pmol/l (p less than 0.05) in the luteal phase controls and from 0.8 +/- 0.1 to 1.5 +/- 0.3 pmol/l (p less than 0.05) in naloxone-infused subjects in the luteal phase. There were no significant differences between any of these groups. There were no significant changes in plasma oxytocin in any group. We therefore conclude that in women, unlike men, endogenous opioids do not modulate oxytocin or vasopressin release during insulin-induced hypoglycemia.

Arginine Vasopressin↗
PubMed1989

Radioassay of bile acid coenzyme A:glycine/taurine: N-acyltransferase using an n-butanol solvent extraction procedure.

A rapid, specific, and sensitive radioassay for measuring bile acid CoA:glycine/taurine: N-acyltransferase (EC 2.3.1) has been developed. In this assay, 3H-labeled amino acids (glycine or taurine) are conjugated with unlabeled bile acid CoA derivatives to form 3H-labeled bile acid amidates. Following incubation, the 3H-labeled bile acid amidate is separated from the unreacted amino acid by an n-butanol extraction method. The extraction procedure was developed by evaluating the effects of buffer concentration and pH on the recovery of radiolabeled bile acid amidate standards in the presence of human hepatic cytosol. Highest recovery (greater than 90%) of bile acid amidate standards occurred under acidic conditions (pH 2) in the presence of 1% (w/v) SDS. When the radioassay and accompanying n-butanol extraction procedure were utilized to study the amidation of glycine or taurine with cholic acid in human hepatic cytosol, a single peak of radioactivity corresponding with either authentic glycocholate or taurocholate was detected in the n-butanol phase by high-performance liquid chromatography. This assay for bile acid CoA:glycine/taurine: N-acyltransferase activity was linear with incubation time and protein concentration. This assay should be useful in the biochemical studies of this enzyme, as well as in the examination of bile acid amidation in clinical liver specimens.

1-Butanol↗
PubMed1989

Differentiation of Sarcocystis species in European sheep by isoelectric focusing.

Isoelectric focusing was carried out on total proteins derived from cystozoites of Sarcocystis tenella, S. arieticanis and S. gigantea. The overall protein profile of each species was distinct and reproducible and enabled the unequivocal differentiation of the three Sarcocystis species. In total, approximately 60 bands could be counted for S. tenella and S. arieticanis and approximately 45 bands for S. gigantea cystozoites in the pH range of 3-9. Isoelectric points (pIs) were determined for dominant peaks of densitometric scans of gels in the pH range of 3-9 (cathodal and anodal sample application) and arbitrary identification numbers were assigned to 25 (5 and 20) peaks of S. tenella, 25 (8 and 17) peaks of S. arieticanis and 21 (7 and 14) peaks of S. gigantea; similar assignments were also used for 11 peaks of S. tenella, 18 peaks of S. arieticanis and 12 peaks of S. gigantea observed on densitometric scans of gels in the pH range of 4-6.5.

Animals↗
PubMed1989

Vasopressin and oxytocin responses to hypertonic saline infusion: effect of the opioid antagonist naloxone.

Endogenous opioids inhibit the release of oxytocin (OT) when vasopressin (AVP) is secreted in response to acute pharmacological stimuli in man and to a variety of physiological and pharmacological stimuli to animals. We have investigated the effect of naloxone on the AVP and OT responses to hypertonic saline in man. In two separate studies, six male subjects were infused with hypertonic saline (675 mmol/l, 0.05 ml/kg/min for 2 h) and either naloxone (4 mg bolus and 6 mg/h) or normal saline in random order. Hypertonic saline resulted in similar significant rises of plasma osmolality and AVP in both groups and a small but significant decrease in OT. Thirst sensation was not altered by naloxone. Endogenous opioids do not play an important role in the suppression of OT release when AVP is secreted in response to an osmotic stimulus in man.

Adult↗
PubMed1989

Selective defect in gonadotrophin secretion in patients with autonomic failure.

We studied the neuroendocrine effects of a condition associated with abnormal hypothalamic amines. Hypothalamo-anterior pituitary function was assessed in five male subjects with autonomic failure (AF) and in five age and sex-matched controls. All subjects showed normal gonadotrophin and TSH responses to GnRH and TRH, respectively. In control subjects, intravenous infusion of naloxone caused a significant rise in overall LH concentrations as well as increased frequency and amplitude of LH pulses. In contrast, in AF subjects naloxone did not alter LH concentrations or increase LH pulse frequency. Naloxone also caused an increase in neurosecretory GH pulses not only in AF subjects but also in the controls. These results suggest that in man, ascending catecholamine pathways are important in the control of gonadotrophin secretion. The markedly different response of GH to an opioid antagonist in elderly subjects should be further investigated.

Aged↗
PubMed1989

A comparison of chiropractic, medical and osteopathic care for work-related sprains and strains.

The cost of care and the number of days lost because of work injury were analyzed from information gathered in a postal card survey sent to all Iowa back or neck injury claimants (sprain/strain) on record for 1984. Descriptive findings for the flow of care of the respondents were evaluated and a comparison made of the benefits and costs of care received by patients treated by chiropractic doctors (DCs), medical doctors (MDs) or osteopathic doctors (DOs). The analysis focused on those workers who lost enough time from work to qualify for compensation (4 days or more), whose cases were closed and who received all their care from one health professional. For those who received care from DCs (n = 266), the mean number of compensated days lost from work was at least 2.3 days less than for those who were treated by MDs (n = 494; p less than 0.025) and at least 3.8 days less than for those who were treated by DOs (n = 102; p less than 0.025). Consequently, much less money in employment compensation was paid, on the average, to those who saw DCs. Findings on provider care costs are less clear-cut because care-cost data on only a portion of the cases was recorded on the State records used. For the data available, the median provider cost was highest for patients who saw DCs, but the mean was highest for those who saw MDs. The study showed that 38% of claimants did change doctors. When change of provider occurred, days lost from work and cost of care varied widely across the care options, but generally, fewer workdays were lost and lower amounts of disability compensation and provider cost paid when chiropractic was included in the care pattern.

Absenteeism↗
PubMed1989

Clinical reference values for serum protein electrophoresis for the llama (Lama glama).

Serum protein electrophoresis was performed on 71 clinically healthy juvenile and adult llamas (6 juvenile males, 7 juvenile females, 25 adult males, 13 adult females, and 20 pregnant females) to determine normal serum protein concentrations. Values were reported for each of the 5 groups because the groups were not homogeneous in all 8 peaks. Although the values reported here may serve as reference values for adults, they represent only a guideline for the juveniles because of the limited number of animals in each of these groups.

Animals↗