Ecological adaptation of angiotensin-induced thirst mechanism in tetrapods

Abstract

Dipsogenic action of angiotensin II (AII) was tested by intraperitoneal injection in 2 species of amphibians, 9 species of reptiles, 18 species of birds, and 8 species of mammals. The amphibians did not respond to AII by drinking. Most of the tetrapods other than the amphibians responded to AII (5–30 μg/100 g) by drinking. Among reptiles, birds, and mammals, however, the following species were relatively insensitive to AII: (1) the hibernating reptiles, Calotes versicolor and Natrix piscator, (2) the animals originated in arid areas, such as Testudo graeca, Melopsittacus undulatus, Lonchura malabarica, Meriones unguiculatus and Mus musculus, and (3) the carnivorous birds, Accipiter badius, Athene brama and Falco tinnunculus. Thus, it is likely that animals, which drink little water in nature, are relatively insensitive to AII in drinking. These observations suggest that AII has become adaptively involved in the physiological mechanisms inducing thirst during the evolutionary process. Evolution of receptive sites for AII in the brain is discussed in vertebrates.