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Biomedical subjects

J G Carter

Publications and source records attributed to J G Carter.

13 recordsLinked to original sources
PubMed1992

Glucose metabolism assessed with 2-deoxyglucose and the effect of glutamate in subdivisions of rat hippocampal slices.

A new approach to the study of glucose phosphorylation in brain slices is described. It is based on timed incubation with nonradioactive 2-deoxyglucose (DG), after which the tissue levels of DG and 2-deoxyglucose-6-phosphate (DG6P) are measured separately with sensitive enzymatic methods applied to specific small subregions. The smallest samples had dry weights of approximately 0.5 microgram. Direct measurements in different regions of hippocampal slices showed that within 6 min after exposure to DG, the ratios of DG to glucose in the tissue were almost the same as in the incubation medium, which simplifies the calculation of glucose phosphorylation rates and increases their reliability. Data are given for ATP, phosphocreatine, sucrose space, and K+ in specific subregions of the slices. DG6P accumulation proceeded at a constant rate for at least 10 min, even when stimulated by 10 mM glutamate in the medium. The calculated control rate of glucose phosphorylation was 2 mmol/kg (dry weight)/min. In the presence of 10 mM glutamate it was twice as great. The response to 10 mM glutamate of different regions of the slice was not uniform, ranging from 164% of control values in the molecular layer of CA1 to 256% in the stratum radiatum of CA1. There was a profound fall in phosphocreatine levels (75%) in response to 10 mM glutamate despite a 2.4-fold increase in glucose phosphorylation. Even in the presence of 1 mM glutamate, the increase in glucose phosphorylation (50%) was not great enough to prevent a significant drop in phosphocreatine content.

Adenosine Triphosphate↗
PubMed1991

Distribution in brain and retina of four enzymes of acetyl CoA synthesis in relation to choline acetyl transferase and acetylcholine esterase.

Eleven regions of mouse brain and twelve layers of monkey retina were assayed for choline acetyl transferase (ChAT), acetylcholine esterase (AChE), and 4 enzymes that synthesize acetyl CoA. The purpose was to seek evidence concerning the source of acetyl CoA for acetylcholine generation. In brain ATP citrate lyase was strongly correlated with ChAT as well as AChE (r = 0.914 in both cases). Weak, but statistically significant correlation, was observed between ChAT and both cytoplasmic and mitochondrial thiolase, whereas there was a significant negative correlation between ChAT and acetyl thiokinase. In retina ChAT was essentially limited to the inner plexiform and ganglion cell layers, whereas substantial AChE activity extended as well into inner nuclear, outer plexiform and fiber layers, but no further. ATP citrate lyase activity was also highest in the inner four retinal layers, but was not strongly correlated with either ChAT or AChE (r = 0.724 and 0.761, respectively). Correlation between ChAT and acetyl thiokinase was at least as strong (r = 0.757), and in the six inner layers of retina, the correlation between ChAT and acetylthiokinase was very strong (r = 0.932).

Acetate-CoA Ligase↗
PubMed1991

Enzyme levels in cultured astrocytes, oligodendrocytes and Schwann cells, and neurons from the cerebral cortex and superior cervical ganglia of the rat.

Data are presented for 16 enzymes from 8 metabolic systems in cell cultures consisting of approximately 95% astrocytes and 5% oligodendrocytes. Nine of these enzymes were also measured in cultures of oligodendrocytes, Schwann cells, and neurons prepared from both cerebral cortex and superior cervical ganglia. Activities, in mature astrocyte cultures, expressed as percentage of their activity in brain, ranged from 9% for glycerol-3-phosphate dehydrogenase to over 300% for glucose-6-phosphate dehydrogenase. Creatine phosphokinase activity in astrocytes was about the same as in brain, half as high in oligodendrocytes, but 7% or less of the brain level in Schwann cells and superior cervical ganglion neurons and only 16% of brain in cortical neurons. Three enzymes which generate NADPH, the dehydrogenases for glucose-6-phosphate and 6-phosphogluconate, and the NADP-requiring isocitrate dehydrogenase, were present in astrocytes at levels at least twice that of brain. Oligodendrocytes had enzyme levels only 30% to 70% of those of astrocytes. Schwann cells had much higher lactate dehydrogenase and 6-phosphogluconate dehydrogenase activities than oligodendrocytes, but showed a remarkable similarity in enzyme pattern to those of cortical and superior cervical ganglion neurons.

Animals↗
PubMed1991

Increased carbamazepine plasma concentrations after fluoxetine coadministration.

The interaction between fluoxetine and carbamazepine was investigated in six normal, healthy male volunteers (aged 23 to 40 years). Subjects were given carbamazepine, 400 mg every morning, for 3 weeks. Venous carbamazepine blood samples were obtained at baseline and 1, 2, 4, 6, 8, 10, 12, and 24 hours after the morning dose. Fluoxetine, 20 mg every morning, was then coadministered with carbamazepine for 7 days. Venous carbamazepine blood samples were again obtained as described. Carbamazepine and carbamazepine-10,11-epoxide (CBZE) were assayed by HPLC. Addition of fluoxetine resulted in a significant increase in the area under the concentration-time curve of carbamazepine (105.93 +/- 18.05 micrograms/ml.hr versus 134.97 +/- 12.15 micrograms/ml.hr; t = 3.284; df = 5; p = 0.022) and CBZE (11.6 +/- 1.93 micrograms/ml.hr versus 15.2 +/- 2.4 micrograms/ml.hr; t = 2.805; df = 5; p = 0.038). Both oral and intrinsic clearance of carbamazepine was decreased significantly on fluoxetine addition (3.87 +/- 0.68 L/hr versus 2.98 +/- 0.26 L/hr; t = 3.025; df = 5; p = 0.029 and 17.90 +/- 4.9 L/hr versus 11.92 +/- 1.4 L/hr; t = 3.037; df = 5; p = 0.029, respectively). No significant changes were determined for fraction of absorbed dose, volume of distribution, absorption rate constant, and elimination rate constant. These findings suggest that fluoxetine can inhibit the metabolism of carbamazepine. Careful monitoring of patients is recommended when these two drugs are coadministered.

Administration, Oral↗
PubMed1979

Cardio-circulatory effects of enflurane anesthesia in health and disease.

The circulatory effects of enflurane (Ethrane) were studied in 10 unmedicated volunteers during anesthesia over a period of 90 min or more. Cardiac output did not change significantly at a mean alveolar concentration of 2.3 vol.%. Heart rate was increased in all cases. Enflurane causes negative inotropic activity in the heart muscle but has little influence on the pump performance of the heart.

Anesthesia, Inhalation↗
PubMed1979

Malignant hyperthermia.

A short review of the history, incidence, and present-day concept of the etiology of malignant hyperthermia is presented. Protocols for diagnosis, treatment of the unexpected occurrence, and management of known malignant hyperthermic patients is presented. The exact etiology of the syndrome is still unknown.

Anesthesia, Inhalation↗
PubMed1975

Intrarenal redistribution of blood flow in the early postburn period.

We interpret the findings of the present study and other studies reported here to indicate that alterations of renal outer to inner cortical blood flow distribution develop in the early postburn period. These alterations are similar to those observed by other investigators in animals subjected to various other traumatic events. Such flow redistributions were observed in both untreated animals and those receiving intravenous fluid resuscitation. Sharp reductions in urinary chloride and sodium concentrations observed in conjunction with these blood flow shifts may be a reflection of the relatively greater perfusion of juxtamedullary nephrons, which are alleged to have greater salt-retaining characteristics than their outer cortical counterparts.

Analysis of Variance↗