Enhancement of water intake by captopril (SQ14225), an angiotensin I-converting enzyme inhibitor, in the goldfish, Carassius auratus.

Single intraperitoneal (ip) injections of angiotension II (ANG II) stimulated water intake for 60 min in a dose-related manner in the goldfish, Carassius auratus. Single ip injections of captopril (SQ14225), an angiotension I-converting enzyme (ACE) inhibitor, at lower doses (0.4 and 4.0 micrograms/fish), stimulated water intake for 60 min. This stimulation cannot be ascribed to an increase in levels of plasma ANG I, since ANG I (2.2 micrograms/fish) did not stimulate drinking in the presence of SQ14225 (two injections of 9.9 micrograms/fish). It is suggested that the elevated plasma ANG I concentration achieved after blockade of ACE was converted into ANG II approximately 50 min after SQ14225 injections (4.0 g/fish), when the injected SQ14225 was effectively metabolized. Thus, the newly elevated level of ANG II may have been responsible for the vigorous drinking. Higher doses of SQ14225 (40 and 200 microgram/fish) did not affect the water intake for 60 min, indicating that the rate of basal water intake is independent of the renin-angiotensin system in the goldfish.