Factors that affect the uptake of ammonia by the brain: the blood-brain pH gradient.

The brain uptake index (BUI) for [13N]ammonia was measured in 7 areas of the rat brain at 8 different pH values ranging from 6.58 to 7.73. When the regional BUI was plotted as a function of the pH of the test bolus, a significant linear correlation was found for each region (P less than 0.001). The highest slope was observed in the thalamus-basal ganglia complex (0.392 +/- 0.018) (S.D.), and the lowest in the ventral pons (0.143 +/- 0.011). These studies indicate that the brain-blood pH gradient plays a major role in determining the forward flux of ammonia from the blood into the brain in the physiological pH range. Regional differences in the slope may be due to metabolic factors. This pH effect may be important in clinical conditions characterized by hyperammonemia such as hepatic encephalopathy, and in the interpretation of [13N]ammonia emission tomographic images of the brain.

Amebiasis and trypanosomiasis.

Parasitic diseases, once limited to developing countries, may be seen in the United States with increasing frequency as air travel links continents. When cutaneous manifestations of these diseases are a part of the clinical picture, dermatologists are often called upon to contribute to the diagnosis. Amebiasis may result in painful anogenital ulcers; African trypanosomiasis (sleeping sickness) often begins with the trypanosomal chancre at the site of parasitic entry, and American trypanosomiasis (Chagas' disease) most commonly presents as Romaña's sign. Epidemiology, pathophysiology, immunology, clinical presentation, and treatment are reviewed for each of these diseases.