ABSTRACT
The renin-angiotensin system (RAS) plays an important role in the control of salt and water balance of most vertebrates. In this chapter, the authors review their knowledge of the RASs of fish, and their understanding of the roles of angiotensin (Ang) in their osmoregulatory processes, discussing both the circulating RAS and the recent evidence of tissue-specific paracrine systems. The classical mammalian picture of renin-producing cells within the wall of the afferent glomerular arteriole has led to their description as juxtaglomerular cells, but in fish these cells often occur well away from the glomerulus. Identification of the cells producing renin in fish has often proved more difficult than in mammals. Initial studies relied on complex histological staining of the tiny renin granules. Gills play an important role in salt balance in teleost fish and autoradiographic studies suggests the existence of Ang II binding sites that may have a significant role in osmoregulation.
