Yuji Okawara

Water intake induced by water deprivation in the quail, Coturnix coturnix japonica.

SummaryMechanisms inducing drinking after water deprivation, and mechanisms terminating drinking after rehydration, were investigated in the quail,Coturnix coturnix japonica.1.Water intake was induced after 4 h of water deprivation, and the amount of water drunk increased in proportion to the period of water deprivation. Drinking occurred immediately after deprived birds were given access to water, and continued for periods proportional to the period of water deprivation.2.Plasma angiotensin II concentration increased, as did plasma osmolality and Na+ concentration, and blood volume decreased after water deprivation. The increase in plasma angiotensin II concentration and decrease in blood volume occurred soon after the start of water deprivation, whereas plasma osmolality and Na+ concentration did not increase until at least 4 h after the start of water deprivation.3.These results indicate that extracellular dehydration and angiotensin II are responsible for the significant drinking that follows 4 h of water deprivation, and that cellular dehydration is also involved in the stimulation of drinking that occurs after longer periods of water deprivation.4.Plasma osmolality and Na+ concentration in birds deprived of water for 48 h quickly returned to normal levels after the birds were allowed access to water. Plasma angiotensin II levels and blood volume also approached the values measured prior to water deprivation. However, the rate and degree of restoration of normal values were reduced, and normal values were not restored even after 1.5 h of rehydration when drinking terminated.5.The amount of water drunk over the course of 1.5 h by birds deprived of water for 48 h was much greater than the amount required to restore the changes in plasma osmolality and blood volume to normal, but neither excessive dilution of plasma nor abnormally high blood volumes were observed during drinking or 0.5 h after drinking terminated.

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.

Effects of Leu5-enkephalin on natural and angiotensin II-induced drinking in the Japanese quail (Coturnix coturnix japonica)

Natural drinking behavior was inhibited by intracranial (ic) injections of Leu5-enkephalin (LEN) (30 and 60 micrograms/100 g) for 60 min, but not by iv injections (30 and 100 micrograms/100 g) in the Japanese quail. Drinking induced by angiotensin II (AII) (30 and 50 micrograms/bird, ip) was also inhibited for 60 min by LEN (40, 60, and 100 micrograms/100 g, ic), given 5 min after the AII injections. Naloxone (3 mg/bird, ip) attenuated the inhibition of LEN (60 micrograms/100 g, ic) and when administered alone (3 mg/bird, ip) induced copious drinking. These results indicated that LEN binds with central opiate receptors to inhibit natural and AII-induced drinking and that endogenous enkephalins physiologically inhibit drinking.

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.