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Biomedical subjects

S David

Publications and source records attributed to S David.

At least 145 records · Page 8Linked to original sources
PubMed1986

Biosynthesis of thiamine: origin of the methyl carbon atom of the pyrimidine moiety in Salmonella typhimurium.

Two biosynthetic, unevenly labeled samples of 5-aminoimidazole riboside were prepared. The incorporation of radioactivity from these labeled samples was studied in a Salmonella typhimurium strain able to use this riboside as precursor of the pyrimidine moiety of thiamine. In one sample, the ribose part was labeled almost equally at C-1' and C-2' and threefold more at C-3' but unlabeled at C-4' and C-5'. The pyrimidine moiety of thiamine derived from it was found almost inactive at C-5, C-7; the specific activity of the methyl carbon atom was found close to that of C-1' or C-2' of ribose in the precursor. On the other hand, only a poor incorporation of radioactivity occurred from a sample in which the ribose part was labeled mainly at C-1'. We conclude that C-5, C-7 of the pyrimidine moiety of thiamine derive from C-4', C-5' and the methyl carbon atom of the pyrimidine derives from C-2' of the ribose part of 5-aminoimidazole ribotide.

Binding Sites↗
PubMed1986

Crown-rump length and serum human chorionic gonadotropin as predictors of gestational age.

The accuracy of fetal crown-rump length measurement and maternal serum human chorionic gonadotropin (hCG) concentration in the prediction of obstetric gestational age was analyzed in a study population of 77 patients for whom time of ovulation was reliably determined. Published nomograms relating maternal serum hCG concentration to gestational age were not found to be valid predictors of gestational age for the study population. Fetal crown-rump length measurement using the uncorrected regression equation of Robinson was found to give the most accurate prediction of gestational age.

Chorionic Gonadotropin↗
PubMed1986

Effect of adrenalectomy on gamma-aminobutyric acid concentrations in the central nervous system.

Pyridoxal-5'-phosphate (PLP) plays a crucial role in regulating the steady-state levels of gamma-aminobutyric acid (GABA) in CNS. Adrenalectomy resulted in decreased conversion of dietary vitamin B6 to PLP. As a consequence of this, GABA levels in cerebral cortex decrease, since synthesis of GABA is determined by glutamate decarboxylase, a PLP-dependent enzyme. Feeding diet supplemented with vitamin B6 elevated the GABA levels in adrenalectomized animals, because of increased availability of the coenzyme for apodecarboxylase. The data suggest a role for corticosteroids in maintaining GABA levels, through their effects on PLP formation.

Adrenalectomy↗
PubMed1986

Danger of an unnecessarily prolonged dialysis session: carpal tunnel syndrome.

Ten patients of a population of 319 on chronic intermittent treatment with Cuprophan dialyzers have undergone surgery for carpal tunnel syndrome (CTS). Since 1971 the dialysis schedule for all patients has been 4 m2/h three times per week. All patients were anuric. The operated patients represent 16% of the total population. In comparison with a dialysis population in other units described in the literature (12), 8 m2/h performed three times per week, with similar dialysis aging and a CTS incidence of 47%, it appears that the duration of the dialysis session per se increases the frequency of CTS and leads to the problem of the consequences of blood membrane interaction.

Adult↗
PubMed1986

Arrhythmias associated with intermittent outpatient dobutamine infusion.

The use of intermittent outpatient dobutamine infusion has recently been studied as an alternative therapy modality for patients with refractory congestive heart failure. We studied the arrhythmogenic effects of intermittent outpatient dobutamine infusion in two patients with NYHA class IV heart failure. The patients received dobutamine at 5mcg./kg./min. for four hours per day for an eight week period. Ambulatory Holter monitoring was obtained during the infusion periods and compared to infusion-free periods. A significant increase of complex ventricular arrhythmias, including multifocal PVC's and ventricular tachycardias, was observed during the infusion period. The incidence of complex ventricular ectopy was dose related and could be suppressed to baseline levels with appropriate antiarrhythmic therapy. We concluded that dobutamine is extremely arrhythmogenic when used in patients with heart failure and that this effect was controllable with antiarrhythmics. Extreme caution and careful monitoring is required for this new therapeutic modality in the treatment of refractory heart failure.

Ambulatory Care↗
PubMed1986

Is reactive gliosis a property of a distinct subpopulation of astrocytes?

We have shown previously that the A2B5 monoclonal antibody distinguishes two types of glial fibrillary acidic protein-containing astrocytes in semithin frozen sections of adult rat optic nerve: A2B5- (type-1) astrocytes are found mainly at the periphery of the nerve, where they form the glial limiting membrane, while A2B5+ (type-2) astrocytes are found mainly in the interior of the nerve and constitute more than 65% of the astrocytes in the adult optic nerve. In the present study we show that although most astrocytes in semithin frozen sections of adult rat corpus callosum and optic nerve are A2B5+, the great majority of reactive astrocytes in similar sections of corpus callosum examined 20 weeks after a stab lesion, and in optic nerve examined 20 weeks after adult transection, are A2B5-. Although both A2B5+ and A2B5- astrocytes are stimulated to synthesize DNA in the first week after transection, adult optic nerves examined 20 weeks after transection contain only half as many astrocytes as do normal optic nerves: While A2B5+ astrocytes are reduced almost 10-fold, A2B5- astrocytes are increased by about 25%. We consider the simplest interpretation of these findings to be that type-1 astrocytes are largely responsible for forming glial scars in adult white matter following either a stab lesion or Wallerian degeneration and that in transected optic nerves, most type-2 astrocytes eventually die, possibly because they depend on axons for their long-term survival.

Animals↗
PubMed1985

Axonal regeneration after crush injury of rat central nervous system fibres innervating peripheral nerve grafts.

Recent experimental studies in adult rodents indicate that neurons in many regions of the brain and spinal cord are capable of extensive axonal growth along peripheral nerve grafts inserted into the C.N.S. To explore further the capacity of damaged intrinsic C.N.S. neurons to initiate and sustain fibre growth we have studied the regenerative response of brain stem and spinal neurons to the crushing of their axons after such axons had already grown across peripheral nerve 'bridges' linking both these levels of the neuraxis. In adult rats, an autologous segment of sciatic nerve approximately 4 cm long was used to connect the medulla oblongata and the lower cervical spinal cord. After 6-42 weeks, when C.N.S. axons are known to have regenerated across these 'bridges', the nerve grafts were crushed near both their rostral and caudal insertions into the C.N.S. Axonal regeneration beyond the sites of injury was investigated 4-11 weeks after crush by retrogradely labelling C.N.S. neurons with horseradish peroxidase (HRP) applied 1 cm away from the injured site, along the assumed course of the C.N.S. fibres regrowing across the graft. The number and distribution of HRP-labelled neurons was found to be similar to that in rats with uncrushed grafts. To prove that such axonal regrowth from spinal and brain stem nerve cells did originate from injury of central nerve fibres innervating the graft and not by sprouting from undamaged C.N.S. neurons at both ends of the 'bridge', we first labelled with the fluorescent dye Fast Blue (FB) the cells whose axons were interrupted by the crush and, after two weeks, applied a second dye, Nuclear Yellow (NY) 1 cm beyond the site of injury. The presence of FB and NY double-labelled C.N.S. neurons in these animals, together with the results of the HRP-labelling experiments, suggest that central neurons whose axons innervate peripheral nerve grafts are capable of renewed growth after axonal injury. Under such experimental conditions these intrinsic C.N.S. neurons respond to axonal interruption in a manner that resembles the responses of cells that normally project along peripheral nerves. We believe this to be an additional indication of the powerful role in regeneration of interactions between neurons and the axonal environment.

Animals↗
PubMed1985

A quantitative immunohistochemical study of macroglial cell development in the rat optic nerve: in vivo evidence for two distinct astrocyte lineages.

We have shown previously that three antibodies--anti-galactocerebroside (GC), anti-glial fibrillary acidic protein (GFAP), and the A2B5 monoclonal antibody--can be used to help distinguish three classes of glial cells in the rat optic nerve: oligodendrocytes are GC+, GFAP-, almost all type-1 astrocytes are A2B5-, GFAP+, and almost all type-2 astrocytes are A2B5+, GFAP+. In the present study we have used these antibodies to examine the timing and sequence of the development of the three types of glial cells in vivo. We show that type-1 astrocytes first appear at embryonic Day 16 (E16), oligodendrocytes at birth (E21), and type-2 astrocytes between postnatal Days 7 and 10 (P7-10). Moreover, we demonstrate quantitatively that astrocytes in the optic nerve develop in two waves, with more than 95% of type-1 astrocytes developing before P15 and more than 95% of type-2 astrocytes developing after P15. Finally, we provide indirect evidence that type-2 astrocytes do not develop from type-1 astrocytes in vivo, supporting previous direct evidence that the two types of astrocytes develop from two serologically distinct precursor cells in vitro.

Animals↗
PubMed1985

Valorphin: a novel chemical structure with opioid activity.

Valorphin is a semisynthetic derivative of dihydrovaltrate with opioid analgesic activity. In vitro binding studies using brain homogenates from rat and guinea-pig indicate a preference for the mu-receptor site. Bath application to cultured cerebellar Purkinje cells inhibited the spontaneous firing, similar to the effect seen with morphine. Analgesic activity has been demonstrated in the hot plate and the tail flick test in the mouse and the Randall-Selitto test in the rat. In the rhesus monkey valorphin was self-administered, but naloxone challenge induced only mild withdrawal signs. Valorphin is a novel chemical entity, structurally not related to known opioids, which interacts preferentially with opiate mu-receptors.

Adamantane↗
PubMed1985

Human pancreatic polypeptide and somatostatin in chronic renal failure.

Human pancreatic polypeptide is the only hormone so far reported which clearly suppresses somatostatin release, suggesting that this peptide may have a role in controlling somatostatin secretion from the gut and pancreas. In this study endogenous high circulating human pancreatic polypeptide concentrations in patients with chronic renal failure do not decrease somatostatin circulating levels. The reduced clearance rate of somatostatin in chronic renal failure may partially account for the normal circulating levels of somatostatin observed in our patients with respect to controls. Renal insufficiency may, itself, induce an increase in some gastrointestinal peptides capable of stimulating somatostatin secretion.

Humans↗
PubMed1985

[Seroepidemiology of infection by hepatitis B virus in student nurses: some implications for vaccination policy].

To estimate the risk of hepatitis B virus (HBV) infection among student nurses, we measured the prevalence of HBV infection in 218 student nurses (192 female and 26 male nurses) and the annual attack rate in a subgroup of 117 subjects. In both studies sera were tested with an enzyme immunoassay for the presence of HBsAg, anti-HBc and anti-HBs. In the prevalence study 24 student nurses (11.1%) had a marker of prior HBV infection; the presence of both anti-HBc and anti-HBs was the most prevalent serologic pattern. 2 student nurses were HBsAg positive (0.9%). Prevalence of infection was strongly related to increasing age, while the occupation of the head of the family showed no effect. In the incidence study 7 subjects seroconverted in a year (6.2%): 6 acquired only anti-HBc and 1 only anti-HBs. These data suggested the hypothesis that the presence of anti-HBc alone (a pattern usually associated with past infections in which anti-HBs is no more detectable) may represent false positive results. The implications of such hypothesis are discussed with particular reference to prevaccination screening policy.

Adult↗
PubMed1985

[Hemorheological changes induced by uremia. Effects of hemodialysis].

Fifteen patients affected by chronic uremia and treated with hemodialysis were studied. The main hemorheological parameters were evaluated in basal conditions and after hemodialytic therapy and were correlated with some hematochemical indices. Although some limitations to the purpose of this study derive from the heparinization of the blood during hemodialysis, the results of this study demonstrate that erythrocyte filtration does not significantly change during the hemodialytic therapy. The only hemorheological parameter altered in the uremic patient is represented by plasma viscosity; this is probably due to the increase of fibrinogenemia in these patients.

Adult↗
PubMed1985

Comparison of the effects of general and regional anesthesia for cesarean section on neonatal neurologic and adaptive capacity scores.

Fifty-two neonates delivered by elective cesarean section were evaluated using the Neonatal Neurologic and Adaptive Capacity Scores. Twenty of the mothers received general anesthesia, 14 received epidural, and 18 received spinal anesthesia. All mothers receiving regional anesthesia were prehydrated with 1000 ml of lactated Ringer's solution and were given oxygen via a transparent face mask. All mothers undergoing general anesthesia received thiopental for induction followed by N2O-O2 (4 L:4 L) and 0.5% enflurane until delivery of the baby. All mothers were healthy, not in labor, and were scheduled for elective cesarean section. All neonates weighed 2500 g or more, had Apgar scores of 7 or more at 1 and 5 min, and had normal acid base and blood gas data. Neonates delivered with general anesthesia scored significantly lower on some of the test items for adaptive capacity, passive tone, active tone, primary reflexes, and total scores at both 15 min and 2 hr of age (P less than 0.05) than those delivered with either epidural or spinal anesthesia. Neonates delivered with epidural anesthesia scored lower than those delivered with spinal anesthesia on supporting reaction and motor activity at 2 hr of age (P less than 0.05). All neonates had high scores at 24 hr, at which time there were no significant differences between the three groups.

Adaptation, Psychological↗