Effect of (D-Met2, Pro5)enkephalinamide, a highly potent opiate agonist, on the drinking behaviour of rats

The highly potent opiate agonist, (D-Met2, Pro5)enkephalinamide, markedly influenced drinking behaviour of the rat. It inhibited the drinking caused by water deprivation, the drinking response to intracerebroventricular application of angiotensin-II, as well as the drinking evoked by systemic administration of isoprenaline. The compound investigated was effective not only upon intracerebroventricular injection but also upon systemic application. The LD50 values were low; 0.42 mg/kg after intraperitoneal administration and about 1.1 micrograms after intracerebroventricular injection. The findings not only support the view that opioid receptors are involved in one way or other in the regulation of fluid intake of the rat, but indicate also an interesting peptide-peptide interaction within the brain.