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Biomedical subjects

A R Johnson

Publications and source records attributed to A R Johnson.

173 records · Page 10Linked to original sources
PubMedDate not supplied

Enzymes in placental microvilli: angiotensin I converting enzyme, angiotensinase A, carboxypeptidase, and neutral endopeptidase ("enkephalinase").

Microvilli from human placental syncytiotrophoblast are rich in angiotensin I converting enzyme (ACE), aminopeptidase A, a carboxypeptidase N-like enzyme, and a neutral endopeptidase (NEP). The specific activities of these enzymes were enhanced in microvillus-enriched fractions obtained by differential centrifugation: Purified microvilli were isolated in a discontinuous sucrose gradient. The placental microvilli hydrolyzed angiotensin II, vasopressin and oxytocin as shown by high pressure liquid chromatography. The inhibitors, bestatin, phosphoramidon, and o-phenanthroline, established the specificity of the enzymes. Aminopeptidase A (angiotensinase A) cleaved angiotensin II to angiotensin III and Asp1. NEP from placenta and from human kidney hydrolyzed oxytocin at the Pro7-Leu8 bond to yield oxytocin 1-7 and leucyl-glycine amide, but did not hydrolyze vasopressin. Vasopressin was cleaved by aminopeptidases in the placental membranes. On electroblotting placental NEP appeared as a double band with a molecular weight slightly higher than the 90,000 of the purified kidney enzyme. Neuraminidase treatment reduced the molecular weight of the placental enzyme to approximately 90,000, indicating that it contains a large amount of sialic acid. The microvilli of human placenta are thus rich in enzymes that may regulate passage of peptides at the maternal-fetal interface.

Aminopeptidases↗
PubMedDate not supplied

Anti-platelet activity of beta-adrenergic antagonists: inhibition of thromboxane synthesis and platelet aggregation in patients receiving long-term propranolol treatment.

Treatment of hypertensive patients with dl-propranolol (640 mg/day) significantly inhibited thromboxane synthesis by their platelets and platelet aggregation induced by thrombin or arachidonic acid. The effects were dose-related and were also caused by the stereoisomer, d-propranolol (640 mg/day), which has very little beta-blocking activity. These findings suggest that the cardioprotective effects of propranolol may be due partly to this anti-platelet activity, to a reduction in thromboxane-induced coronary-artery vasoconstriction, or to both. d-Propranolol treatment may be particularly useful, since this isomer provides similar benefits without causing pronounced beta-adrenergic blockade.

Adrenergic beta-Antagonists↗
PubMedDate not supplied

Distinction between adrenal adenomas and metastases using MR imaging.

Magnetic resonance imaging was performed on 12 patients with known neoplastic disease and adrenal masses shown by CT. Three patients with metastases had high signal intensity in the adrenals on T2 weighted spin echo scans (SE 2,500/80) and nine patients with nonfunctioning adenomas had low signal intensity on T2 weighted images. The ability to distinguish metastases from nonhyperfunctioning adrenal adenomas may be of use in the pre-operative evaluation in patients with known carcinoma and incidental adrenal masses.

Adenocarcinoma↗
PubMedDate not supplied

Observations on calcium-induced stability of salivary proteins in a lipid-extraction system.

The system described for investigating the effects of small ions on macromolecules of saliva may be applied to other solutions and is amenable to manipulation in order to obtain more specific information. Studies using aqueous solutions of saliva fractions previously separated by gel filtration are being conducted with C/M solutions containing various bivalent cation chloride salts. Preliminary results from these current studies have demonstrated that when the proteins are stabilized they vary as a function of the cation used.

Adult↗
PubMedDate not supplied

Neurotoxicity in single photon emission computed tomography brain scans of patients reporting chemical sensitivities.

The subset of patients reporting chemical sensitivity with neurocognitive complaints usually exhibits specific abnormalities of brain metabolism consistent with neurotoxicity, on imaging with single photon emission computed tomography (SPECT). These recurrent neurotoxic patterns are characterized by a mismatch in tracer uptake between early- and late-phase imaging, multiple hot and cold foci throughout the cortex, temporal asymmetry and increased tracer uptake into the soft tissues and, sometimes, the basal ganglia. Previous studies confirm these neurotoxic findings in patients with neurotoxic chemical exposures and breast implants. Affective processes such as depression do not, alone, show this pattern. These abnormalities in SPECT images correlate with documented neurocognitive impairment. Controlled challenges to ambient chemicals can induce profound neurotoxic changes seen on SPECT imaging in chemically sensitive patients. Detoxification treatment techniques frequently produce significant improvement on brain SPECT brain imaging in these patients. Neurotoxicity appears to be characteristic in many cases of chemical sensitivity.

Brain↗
PubMedDate not supplied

Single photon emission computed tomography of the brain in patients with chemical sensitivities.

Chemical sensitivities display a recurrent pattern on scintigraphic examinations of the brain. The pattern can include mismatching between early and late imaging, multiple hot and cold foci distributed throughout the cortex without regard to lobar distribution (salt and pepper pattern), temporal asymmetries, and sometimes increased activity in the basal ganglia. This study used Desert Shield/Desert Storm veterans who present with abnormal neurological and psychological symptoms as a model to exhibit abnormalities by brain scintigraphy. These are typical of those seen in patients with documented exposure to neurotoxic compounds who develop a clinical syndrome that has been termed "chemical sensitivity." Exposure to cocaine, alcohol, and other substances of abuse can result in abnormal scintigrams of the brain using tracers such as [technetium-99m]hexamethylpropyleneoxime. This study used techniques combining regional cerebral blood flow data with delayed distributional data after the intracellular conversion of the tracer into a hydrophilic molecule. In addition to delayed image abnormalities, a mismatch occurs in the regional activity between the two image sets of the veterans. This degree of mismatch was not seen in control subjects who were screened for avoidance of neurotoxic agents. Patterns identified from examinations performed on patients with known exposure to petroleum distillates, pesticides and other materials linked with neurotoxicity were identified in some veterans of the Desert Shield/Desert Storm operation. A single case of repeated examinations on a veteran showed a reversion of these patterns toward normal after therapy. This reversion followed independent assessments of clinical improvement.

Adult↗