A new spectrophotometric assay for enzymes of purine metabolism. II. Determination of guanase activity.

A new method for the determination of guanase is described. Xanthine, the product of the guanase reaction, is oxidized by xanthine oxidase, forming uric acid and hydrogen peroxide. Hydrogen peroxide is further reduced to water by catalase in the presence of ethanol. The acetaldehyde formed in this reaction step is dehydrogenated NAD or NADP dependent by aldehyde dehydrogenase. The NADH or NADPH production is measured and utilized for the calculation of the guanase activity. The sensitivity of the method can be doubled by the addition of uricase, which oxidizes uric acid to permit the formation of another mole of hydrogen peroxide.     

Ultrastructural alteration of cytolytic T lymphocytes following their interaction with target cells. II. Morphogenesis of secretory granules and intracellular vacuoles.

“Secretory” granules, crystal-like structures, lysosema-like granules, ergastoplasmatic lamellae, electron-opaque ribosomes, and lipid vacuoles were detected in the cytoplasm of cytolytic T lymphocytes. After 30 to 60 min interaction with a target cell the fusion of “secretory” granules and crystal-like structures with lipids, mitochondrion degeneration, hypertrophy and reorientation of the Golgi apparatus toward the contact zone with a target cell were observed.     

Overnight dexamethasone suppression test: normal responses and the diagnosis of Cushing's syndrome

Serum cortisol levels were measured the morning after the administration of 1 mg of dexamethasone. Only 5 of 190 subjects had serum cortisol levels greater than 2 micrograms/dL. Thus, the normal value after dexamethasone suppression is less than 2 micrograms/dL rather than less than 5 micrograms/dL as has generally been accepted. The distinction is important because some individuals with Cushing's syndrome partially suppress their cortisol levels to less than 5 but more than 2 micrograms/dL during the test procedure. Thus, the use of 5 micrograms/dL as the normal value may lead to an unnecessary delay in diagnosis.     

Computerized topographical analysis of functionally homogeneous neuronal sets.

A computer-assisted analysis of the spatial distribution of neurons having homogeneous characteristics is described in this paper. The camera lucida drawings of sections of a brain nucleus and the points representing the neurons labeled on the basis of a specific behavior of discharge rates were digitized on a personal computer Amiga 2000 or IBM compatible. Our software provided: a) the computerized, stereotaxically oriented reconstruction of the stored sections and of the plotted neurons; b) the identification within each section of the mass center (MC) of the units sharing a given behavior and of the area where the density of such neurons was maximal (MDA). The routine was tested on the spatial distribution of neuronal responses to serotonin in the lateral vestibular nucleus.     

Magnesium movement in hypothyroid sheep.

We described magnesium transport in hypothyroid and normal sheep with an eight-compartment biomodel fitted by a least-squares technique to data from multiple compartments and routes of entry of 28-Mg. Isotopic equilibrium was not attained during this period of observation in hypothyroid or control sheep. Hypothyroidism reduced transfer coefficients for absorption (P less than 0.01) of 28-Mg from the GI tract but did not change the rate coefficient for endogenous 28-Mg losses to feces (P less than 0.05). Nutritional balance data indicated higher absorption and retention of Mg in hypothyroid sheep, and the observed decrease in rate of passage of digestive residues suggested that mean retention time of GI tract contents had a definite effect on the availability of Mg.