12.1 Endocrine Control of Electrolyte and Fluid Balance
Regulatory mechanisms involve several hormones which include aldosterone, arginine vasopressin, atrial natriuretic factor and the rennin-angiotensin axis. These hormones have differing sites of synthesis and actions (Laragh, 1985).
12.1.1 Arginine Vasopressin (AVP)
Also called antidiuretic hormone (ADH), this nonapeptide is synthesized in the hypothalamus and secreted via the posterior pituitary gland. The hormone is released in response to change of osmolality and plasma sodium, which is a major determinant of plasma osmolality (Robertson,1987; see later). In the renal collecting tubules, AVP acts on adenylate cyclase generating adenosine monophosphate and protein kinases, which in turn alter the permeability of the renal collecting ducts and distal tubules to water. The threshold for AW release varies with plasma osmolality values in the different species. AVP release is also stimulated by a depletion of the body’s effective circulating fluid volume, and AVP acts as an arterial vasoconstrictor thus altering blood pressure (Mohr and Richter, 1994). AVP is not detectable in the plasma of Brattleboro rats