Brain amino acid abnormalities in kidney disease and diabetes mellitus.

The present postmortem study examines whether specific amino acid abnormalities associated with renal diseases or diabetes mellitus in animal experiments and on clinical examination may also be found in human brain samples obtained at clinical autopsies. The material includes 12 deceased with renal insufficiency, 23 deceased with diabetes mellitus and 26 control cases with lethal cardiovascular diseases (without a history of hepatic, renal or metabolic disturbances). The autopsy and clinical records were retrospectively analyzed for age, sex, postmortem delay, cause of death, substantial preexisting diseases and histological findings. The analysis of free amino acid concentrations in human brain specimens was performed applying a Beckman amino acid analyzer. The results were evaluated using the U-test according to Mann, Willcox and Whitney. A P-value less than 0.05 was considered to be significantly different. Differences of amino acid concentrations attributable to sex, age and postmortem delay were not significant. The comparison of postmortem amino acid concentrations in the brains of patients with diabetes mellitus and controls did not reveal relevant changes. However, the patients with renal diseases, as compared to controls, showed a significant cerebral increase of urea, phenylethanolamine and gamma-aminobutyric acid. Thus, the postmortem amino acid analysis may contribute to the understanding of pathophysiological mechanisms of uremic encephalopathy and may supplement the conventional postmortem morphological diagnosis in kidney diseases by indication of functional impairment.

Glare-correction in DNA image cytometry.

We tested the reproducibility of a simple method for glare correction in a modern video-based optical densitometer (CYDOK) by performing repeated measurements of the DNA content on identical sets of different rat hepatocyte DNA-classes and lymphocytes. Using a computer-controlled scanning stage of the microscope we were able to re-localize each nucleus of air-dried Feulgen-stained preparations with different microscope settings. The proposed microscope-adjusted glare-correction algorithm is based on the measurement of the transmittance of opaque bars a standard micrometric glass. The procedure gives local glare errors and allows calculation of the mean glare error which is applicable for the entire view field. Subtraction of this mean glare transmittance from each object and normalization of the background allows the user to eliminate errors due to different nuclear Feulgen-staining intensities. The method eliminates the need to use cell-type-dependent constants to correct the known DNA disproportionalities in air-dried, Feulgen-stained preparations. An additional advantage of the glare correction algorithm is the low coefficients of variation (CV, < 3%) within each nuclear DNA-class which reflect the highly reproducible DNA measurements.