Calcium control of glycogen synthase activities in mouse diaphragms, rat adipocytes and rat hepatocytes.

The following article provides evidence that cellular calcium controls the activity of glycogen synthase in all three major glycogen storage tissues; muscle, fat, and liver. Depletion of cellular calcium resulted in a moderate increase of glycogen synthase %I activities in intact mouse diaphragms, in isolated rat adipocytes, and in rat hepatocytes. The increase in %I activity of glycogen synthase was more pronounced when the uridine di-phosphoglucose concentration in the glycogen synthase assay was lowered from 4.4 mM to 0.2 mM. Calcium depletion resulted in an approximately two-fold decrease in the Ka values for glucose-6-phosphate in all three tissues. The activities of glycogen synthase also correlated well with the content of cell-associated calcium in rat hepatocytes. The glucose-6-phosphate independent activities of glycogen synthase in extracts of calcium-replete and calcium-depleted tissue approached the same value following the exposure to crude phosphoprotein phosphatase. The activities of glycogen phosphorylase decreased in calcium-depleted tissues and cells. Insulin stimulated the activity of glycogen synthase in muscle and fat in the absence of added sugar and in the absence of extracellular calcium. It is concluded that glycogen synthase is under the control of calcium in the three main glycogen storage tissues. The actions of calcium are probably mediated through the actions of calcium-sensitive protein kinase(s).

Magnetic resonance imaging relaxation times and gadolinium-DTPA relaxivity values in human cerebrospinal fluid.

RATIONALE AND OBJECTIVES: This study was conducted to prove the feasibility of using cerebrospinal fluid (CSF) T1 and T2 measurements to assess the blood-brain barrier integrity in disease states not noted for focal blood-brain barrier disruption, such as Alzheimer's disease. METHODS: T1 and T2 of human CSF samples were measured with and without gadolinium Gd-DTPA over a concentration range of 1.98 x 10(-3) to 6.32 mM, in a GE 1.5-T Signa scanner. RESULTS: T1 and T2 of human CSF without Gd-DTPA were measured as 2.39 and 0.23 s. K1 and K2 were calculated as 6.25 and 6.74 mM(-1) s(-1). The lowest Gd-DTPA concentration with measurable T1 and T2 was 1.98 x 10(-3) mM. There is no statistically significant difference in T2 and K2 at different repetition times. CONCLUSIONS: This work demonstrates that a single measurement of relaxation times after contrast-enhanced magnetic resonance imaging could be used to determine the Gd-DTPA concentration in CSF. It may thus be feasible, using this technique, to measure intersubject and intraregional variability in the quantity of Gd-DTPA transferred across the blood-brain barrier after intravenous injection of contrast agent.

The impact of requisition design on laboratory utilization.

Laboratory utilization by clinician specialty groups serving outpatients was monitored before and after requisition redesign. Requisition changes were designed to address compliance and utilization issues and included implementation of test groupings and cascades or ordering algorithms. Data collected included the number of selected tests and test sets ordered during both time intervals and the number of patient office visits. Selected tests for monitoring included CBC counts, metabolic panels, thyroid function tests, hepatic function tests, urine analysis, and send-out testing. Statistical significance was measured using Poisson rates for test ordering. The composite effect was a significant decrease in the overall number of tests ordered per outpatient visit for most specialties, with a shift in ordering practices from panels to individual tests. Utilization rates by specialty groups were characterized by average number of laboratory tests ordered per patient visit.

Cortical CSF volume fluctuations by MRI in brain aging, dementia and hydrocephalus.

Dynamic MR imaging has revealed dramatic fluctuations in the appearance of CSF in the cortical sulci and cortical subarachnoid spaces in aging individuals and patients with hydrocephalus, dementia and Down syndrome in contrast to young healthy volunteers. The changes have been interpreted as volume fluctuations that represent undamped CSF hydrodynamics and have implications with respect to the origin of CSF in the cortical regions and with respect to the similarity between aging and dementia and edematous states of the brain.

Magnetic resonance imaging of the aging brain in Down syndrome.

MRI studies to date have confirmed and expanded upon findings of morphologic differences between the brains of subjects with DS and those of the general population found by CT and post-mortem examination. [table; see text] Hippocam pal and neocortical structures are smaller in DS while unexpectedly the parahippocampal gyrus was found to be larger. MRI has demonstrated that subjects with DS develop signs associated with [table; see text] brain aging at an earlier age. These findings include increased rate of dilatation of ventricles, increased peripheral atrophy, and increased deep white matter lesions. In addition, changes that are associated with AD occur earlier in the DS population. Functional studies reveal decreasing cerebral perfusion with age in adults with DS, a pattern similar to non-DS subjects with clinically progressive dementia, and provide evidence for altered blood-brain barrier permeability. Dynamic MRI studies have also shown adults with DS to have fluctuating cortical CSF volumes, similar to some elderly non-DS subjects and subjects with shunted hydrocephalus. This is a new finding in brain aging that suggests a relationship between aging in DS and edematous states of the brain.

Data analysis for dynamic contrast-enhanced MRI-based cerebral perfusion measurements: correcting for changing cortical CSF volumes.

The time evolution of the histogram (number of pixels versus signal intensity) is used to calculate delta R2 parameters from dynamic contrast-enhanced magnetic resonance (MR) imaging of the brain. This method partially corrects for partial volume effects and is an improvement over the approach using the signal intensity as a function of time when confounding factors such as changing cortical cerebrospinal fluid volumes are involved. The maximum value for delta R2 is found to correlate with relative cerebral blood flow as assessed by xenon inhalation and can be used to discriminate between vascular dementia and healthy volunteers. With this method, the normal range for delta R2 values is found to be the same for both young (19-40 years old) and elderly (65-85 years old) healthy volunteers.