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Biomedical subjects

R Jansen

Publications and source records attributed to R Jansen.

At least 127 records · Page 7Linked to original sources
PubMed1985

The corallopyronins, new inhibitors of bacterial RNA synthesis from Myxobacteria.

From the culture broth of the myxobacterium, Corallococcus (Myxococcus) coralloides, three new antibiotics have been isolated: corallopyronin A, B and C. The compounds, which are chemically related to the recently discovered myxopyronins, act mainly on Gram-positive bacteria, with MIC values between 0.1 and 10 micrograms/ml, and only exceptionally or at much higher concentrations (MIC values; 100 and more micrograms/ml) on Gram-negatives. They do not inhibit eukaryotic organisms and show no toxicity for mice (sc). The corallopyronins appear to block specifically eubacterial RNA polymerase.

Animals↗
PubMed1984

The role of glucose, pyruvate and lactate in ATP production by rat spermatocytes and spermatids.

The ATP content of pachytene spermatocytes and round spermatids, isolated from rat testes, was not maintained during incubation of the germ cells in the presence of glucose. Glucose was metabolized via glycolysis at a considerable rate, but the rate of oxidation of the resulting endogenous pyruvate in the mitochondria was too low to support fully ATP production. Exogenous pyruvate (0.25 mM) or exogenous L-lactate (3-6 mM), however, were effective energy substrates. The lactate dehydrogenase reaction in isolated germ cells favoured the rapid conversion of pyruvate to lactate, at the expense of reducing equivalents from mitochondrial NADH. Hence, to support ATP production by the germ cells via mitochondrial metabolism of endogenous pyruvate, a relatively high concentration of exogenous lactate may be essential. In the spermatogenic microenvironment in vivo, such high concentrations of lactate could result from the net production of lactate by Sertoli cells. The mitochondria of the isolated germ cells produced ATP probably at a close to maximal rate, and spermatogenesis therefore may be extremely sensitive to compounds which interfere with mitochondrial energy metabolism and respiratory control.

Adenosine Triphosphate↗
PubMed1984

Effect of 8-methoxypsoralen on rat lens cations, membrane potential and protein levels.

Systemic application of 8-methoxypsoralen to rats, followed by u.v.-irradiation, induces a minor change in the lens membrane potential after one week, and by this time marked histological changes have already occurred. Alterations in lens sodium and potassium concentrations followed these early changes and coincided with the appearance of small light-scattering vacuoles when the lenses were examined in vivo with a slit lamp. Dramatic changes in the dry weight, soluble protein and calcium content of the lenses were apparent only after eight weeks from the start of treatment, and these changes coincided with the appearance of very large vacuoles in slit-lamp examinations of the eye.

Animals↗
PubMed1984

Neurosonographic identification of ventricular asymmetry in premature infants.

Routine head ultrasound scans have been performed on 185 consecutive infants weighing under 1500 g at birth. In 40 of these infants a significant difference in the size of the lateral ventricles was observed on one or more occasions. In 38 of these infants the left ventricle was larger than the right. The aetiology of this ventricular asymmetry is unknown. It is not believed to be due to germinal matrix or ventricular haemorrhage, hydrocephalus or the position of the infant at the time of scanning.

Cerebral Hemorrhage↗
PubMed1984

Evaluation of the gasless abdomen in the newborn and young infant with metrizamide.

The finding of a gasless abdomen on the abdominal radiograph of an infant over 12 hr old is usually abnormal and may reflect a serious pathologic disorder. Accurate diagnosis is important to plan appropriate therapy. A careful review of the clinical history and the plain chest and abdominal radiographs will often permit an accurate diagnosis to be made. In cases where the diagnosis remains in doubt, contrast studies of the bowel with metrizamide have proved helpful. This report presents six infants with gasless abdomens of unknown cause. In each case, a metrizamide contrast study of the bowel was helpful in providing an accurate diagnosis.

Child, Preschool↗
PubMed1983

A new look at the neonatal bowel-contrast studies with metrizamide (Amipaque).

Metrizamide is the first water-soluble radiographic contrast agent which, because it is nonionic, can be used in isotonic solution and gives good visualization of the desired body structure. Its only major disadvantage is that it is very expensive. Metrizamide can be used to study the neonatal bowel in clinical situations where all the other existing contrast agents are contraindicated. The results of 55 metrizamide studies of the bowel in infants are reviewed. In necrotizing enterocolitis metrizamide aids in confirming or rejecting the diagnosis, identifying patients for surgery, and in evaluating the response to surgery. Metrizamide can identify the etiology in unusual cases of bowel obstruction. Metrizamide correctly identified a thoracic origin of free peritoneal air in four cases and a bowel origin in two cases. It identified bowel perforation in two patients in the absence of pneumoperitoneum. In six patients, the metrizamide study identified the cause for a gasless abdomen. It is concluded that metrizamide has a valuable role to play in evaluating a variety of neonatal bowel disorders.

Drug Evaluation↗
PubMed1983

The myxalamids, new antibiotics from Myxococcus xanthus (Myxobacterales). I. Production, physico-chemical and biological properties, and mechanism of action.

From the cell mass and culture supernatant of Myxococcus xanthus strain Mx X12 an antibiotic activity against yeasts, molds and some Gram-positive bacteria could be extracted. It consisted of 4 biologically active compounds which were named myxalamid A, B, C and D. The main component, myxalamid B, was shown to block in beef heart submitochondrial particles the respiratory chain at the site of complex I, i.e. NADH: ubiquinone oxidoreductase. The myxalamids are new antibiotics.

Animals↗
PubMed1982

Ca2+-induced fusion of cardiolipin/phosphatidylcholine vesicles monitored by mixing of aqueous contents.

The kinetics of Ca2+-induced fusion of large (0.1 micrometer) unilamellar cardiolipin/phosphatidylcholine (1:1) vesicles have been investigated by continuous monitoring of the mixing of the aqueous vesicle contents. In parallel, release of vesicle contents to the external medium has been followed. Initial fusion of the vesicles is non-leaky, release of vesicle contents to the external medium have been followed. Initial fusion of the vesicles is non-leaky, release of vesicle contents being largely a secondary phenomenon. The minimal Ca2+ concentration required for fusion in this system is approx. 9 mM. At higher Ca2+ concentrations fusion is extremely fast, occurring on the time scale of seconds.

Animals↗
PubMed1982

Regulation of survival of rat pachytene spermatocytes by lactate supply from Sertoli cells.

During incubation of fragments of seminiferous tubules in the absence of glucose, pachytene spermatocytes and round spermatids died within 24 h, while Sertoli cells were still viable. The germ cells survived for at least 72 h in seminiferous tubule fragments which were incubated in the presence of glucose. Lactate rather than glucose is essential for [3H]uridine incorporation and survival of isolated pachytene spermatocytes. However, if the spermatocytes were incubated in the presence of Sertoli cells, glucose maintained the incorporation of [3H]uridine into the germ cells. Sertoli cells secreted lactate in the presence of glucose and the lactate secretion was stimulated 2--4-fold by FSH. It is concluded that the activity and survival of pachytene spermatocytes in vitro can be regulated by the supply of lactate from Sertoli cells.

Animals↗
PubMed1981

Hypotyrosinemia, hypocystinemia, and failure to retain nitrogen during total parenteral nutrition of cirrhotic patients.

Six patients with gastrointestinal malabsorption and 12 with alcoholic cirrhosis received total parenteral nutrition for 4 wk. Freamine II, the source of the amino acids, is nearly devoid of cystine and tyrosine. We monitored daily nitrogen balance and other nutritional parameters and 22 plasma amino acids. Malabsorbers had a strongly positive nitrogen balance and improvements in nutritional parameters. Plasma amino acids were maintained within or above their normal fasting ranges. Eight of 12 cirrhotics resembled malabsorbing patients in terms of positive nitrogen balance, improved nutritional parameters, and plasma amino acids. In 4 cirrhotics, nitrogen balance remained negative and nutritional repletion failed to occur. Plasma cystine and tyrosine fell to below 30% of their normal fasting means. In 2 of these patients, oral supplements of cystine and tyrosine were given during the fifth week of parenteral nutrition. Plasma cystine and tyrosine were normalized, nitrogen balance became positive, and other repletion indicators demonstrated recovery. We conclude that in 4 cirrhotics, repletion was blocked by deficiencies of cystine and tyrosine, resulting from hepatic inability to synthesize cystine from methionine and tyrosine from phenylalanine.

Amino Acids↗
PubMed1981

Charcoal hemoperfusion for treatment of carbamazepine poisoning.

We report a case of carbamazepine (Tegretol) poisoning that was treated with charcoal hemoperfusion. When admitted, the patient was comatose and required ventilatory support. Hemoperfusion with coated activated charcoal successfully decreased her serum carbamazepine concentration from 60 mg/L to 36 mg/L within 2 h, with subsequent clinical improvement. Approximately 39 h would have been required to obtain this decrease via the patient's inherent elimination rate. Activated charcoal hemoperfusion may be useful as an adjunctive therapy for patients in advanced comatose states with associated respiratory depression and potentially fatal outcome.

Carbamazepine↗
PubMed1980

Application of low-cost extrusion cooking to weaning foods in feeding programmes. Part 1.

Supplementary foods can be used as a direct means for providing malnourished population groups with the additional food they require. These foods may supply not only much needed food energy, but also substantial amounts of high quality protein, vitamins and minerals. One of the objections to supplementary feeding programmes in the past has been that they have often distributed imported foods and have done little to stimulate local food production. The low-cost extrusion cooker (LEC) programme to be described in this article has as its primary objective the low cost manufacture in developing countries of highly nutritious supplementary foods from locally-grown food crops.

Cooking↗