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.