Abstract

Chlorothiazide and mersalyl (mersalyl sodium and theophylline) administered intravenously to trained unanesthetized dogs under the conditions described in this study demonstrated the following:

Chlorothiazide has a more rapid onset of action than mersalyl.

Chlorothiazide is an effective diuretic even in the presence of a significant decrease in glomerular filtration rate, indicating a direct tubular response.

In moderately hydrated dogs, chlorothiazide produced no change in "free" water clearance and a moderate increase in osmolar clearance. Mersalvl increased "free" water clearance and greatly increased osmolar clearance.

In dogs undergoing maximal water diuresis both diuretics produced a significant increase in osmolar clearance and no significant change in "free" water clearance.

The possible reasons for the difference observed between moderately and maximally hydrated dogs are discussed.