Ethacrynic acid effect on the composition of cochlear fluids.

Ethacrynic acid, when administered to six dogs, caused a fall in the concentration of potassium in endolymph from 145 to 21 milliequivalents per liter and a rise in the concentration of sodium from 5.9 to 146 milliequivalents per liter. The composition of perilymph is unaffected. Perilymph and endolymph are slightly hypertonic as compared to plasma.

The mutual independence of the endolymphatic potential and the concentrations of sodium and potassium in endolymph.

The relationship between the endolymphatic potential (EP) and the sodium and potassium concentration gradients between endolymph and interstitial fluid was studied both by measuring the EP at varying concentrations of sodium and potassium in endolymph and by measuring the effect of a depressed EP on the concentrations of these cations. Ethacrynic acid was used in dogs to change the concentration of sodium and potassium (meq/liter) in endolymph from 5.8 and 148 to 134 and 24.3, respectively. No change in the EP accompanied these alterations. In a second series of experiments the EP was reduced from + 72 mV to + 31 mV for a mean duration of 20 min. No change in the concentration of sodium and potassium in endolymph was found during the period of reduced EP. These data suggest that there is little relationship between the EP and the sodium and potassium concentrations in endolymph.

Cystic fibrosis. Problems encountered with sweat testing.

The sweat test is the only practical and reliable laboratory test for confirmation of the diagnosis of cystic fibrosis. Among 234 patients referred to The Johns Hopkins Hospital for sweat testing, 62 had had a previous test; 29 tests had been reported as negative, and 33 tests had been reported as positive. Results of quantitative pilocarpine-iontophoresis sweat tests at this center led to a change in diagnosis in 27 (43.5%) of these 62 patients. Most of the errors were false-positive.