Angiotensin - Vertebrates

Besides the stimulation of the adrenal cortex by ACTH and glomerulotrophic hormone to release aldosterone, kidneys themselves monitor the levels of sodium by renin-angiotensin system. When the sodium level falls, juxtaglomerular cells of the glomerulus release an enzyme renin into the blood.

  Figure: Hormonal mechanism involved in osmoregulation

Renin acts on a precursor plasma protein angiotensin, hydrolysing it to the active hormone angiotensin. Angiotensin acts on the adrenal cortex and promotes aldosterone secretion. Aldosterone in turn promotes uptake of sodium by the renal tubules. Aldosterone also acts on the kidney arterioles ensuring a regular blood flow in the organ. In figure you can see the complex interactions of all the hormones in the maintenance of water and salt balance.