Occurrence of the renin-angiotensin system in the vertebrates

The presence and absence of renin activity and juxtaglomerular cells (JGC) in the kidney have been extensively studied among the vertebrates. Renin and JGC have been found in the kidneys of tetrapods and teleostean fishes. Therefore the renin-angiotensin system probably appeared first during early evolution of teleosts. However, the findings of various investigators need to be analyzed precisely to summarize and the subjects remained for further research need to be pointed out. There still remains a possiblity that a similar hormone is present in the cyclostomes and elasmobranchs. There are some discrepancies between the renal renin activity determined biochemically and the histological visualization of the granules in some primitive bony fishes. There are contradictory reports regarding the presence of macula densa in nonmammalian kidney. The fact that JGC are present extrarenally in sea-horses may suggest some function of this system. Renin-like activity has been reported extra-renally in various mammalian tissues and in the corpuscles of Stannius (CS) in teleosts. Physiological roles of these extrarenal renin have not been clarified. It has been demonstrated that CG contain 'hypocalcin' which lowers plasma Ca level. It is of interest in determining the possible relationship between the renin-angiotensin substances in CS and hypocalcin.