<Table> <Tr> <Td_colspan="2"> View / Edit Human </Td> <Td_colspan="2"> View / Edit Mouse </Td> </Tr> </Table> <Tr> <Td_colspan="2"> View / Edit Human </Td> <Td_colspan="2"> View / Edit Mouse </Td> </Tr> <P> Vasopressin, also named antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP . It then travels down the axon of that cell, which terminates in the posterior pituitary, and is released from vesicles into the circulation in response to extracellular fluid hypertonicity (hyperosmolality). AVP has two primary functions . First, it increases the amount of solute - free water reabsorbed back into the circulation from the filtrate in the kidney tubules of the nephrons . Second, AVP constricts arterioles, which increases peripheral vascular resistance and raises arterial blood pressure . </P> <P> A third function is possible . Some AVP may be released directly into the brain from the hypothalamus, and may play an important role in social behavior, sexual motivation and pair bonding, and maternal responses to stress . </P>

Which part of the nephron does antidiuretic hormone act upon