Abstract
Using the colorimetric micromethod of Mattenheimer and deBruin for the assay of carbonic anhydrase activity, a considerable loss of substrate (CO2 gas) from the incubation medium was measured during spontaneous hydration. Adding gaseous CO2 and coating the surface of the incubation medium with oil were employed in order to prevent this loss, which otherwise led to serious errors in the measurement of the enzyme activity. A mixture of 80% paraffin and 20% hexadecane as surface coating was satisfactory for reducing the CO2 exchange to negligible proportions. With this modified method, the carbonic anhydrase activity of frozen-dried samples of rat neurohypophysis was studied as a possible "marker" for pituicyte activity following osmotic stress. The enzyme activity increased about 130% after 6 days of water deprivation. Experiments with perfused tissue, however, indicated that this increase in enzyme activity was caused by an increase in the blood content of the neural lobe.