Diurnal rhythm of water intake and plasma angiotensin II in the Japanese quail (Coturnix coturnix japonica).

A diurnal rhythm was noted in the hourly water intake of the Japanese quail exposed to a 12L:12D photoperiod. Two peaks for the water intake were observed: from 07:00 to 08:00, 1 hr after turning on the light source, and from 18:00 to 19:00, 1 hr before termination of the light source. The plasma angiotensin II (AII) concentration also showed two peaks: one at 06:00, 1 hr before the light source was turned on, and another at 18:00, 1 hr before the light was turned off. The two plasma AII peaks each occurred 1 hr before those for the water intake, respectively. The drinking rate was reduced by Captopril (SQ14225) administered at 07:05 and 18:14, when the plasma AII concentration and drinking rate were highest. The hematocrit was significantly higher during the dark period than the light period.