Osmoregulation
Secretin modulates water and electrolyte transport in pancreatic duct cells, liver cholangiocytes, and epididymis epithelial cells. It has been recently been found to play a role in the vasopressin-independent regulation of renal water reabsorption.
Secretin is found in the hypothalamus and neurohypophysis. During increased osmolality, it is released from the posterior pituitary. In the hypothalamus, it activates vasopressin release.
It has been suggested that abnormalities in such secretin release could explain the abnormalities underlying type D syndrome of inappropriate antidiuretic hormone hypersecretion (SIADH). In these individuals, vasopressin release and response are normal, although abnormal renal expression, translocation of aquaporin 2, or both are found. It has been suggested that "Secretin as a neurosecretory hormone from the posterior pituitary, therefore, could be the long-sought vasopressin independent mechanism to solve the riddle that has puzzled clinicians and physiologists for decades."
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