Changes in the vasopressin content of discrete brain regions in response to stimuli for vasopressin secretion

In order to better understand the function of vasopressin-containing axons which project to areas outside the hypothalamus, we measured vasopressin content in hypothalamic and extrahypothalamic brain regions following various periods of oral hypertonic saline or 1 week after pituitary stalk section. The supraoptic and paraventricular nuclei and nearly all of the brain regions examined which are known to receive vasopressin-containing axons from these nuclei showed parallel changes in vasopressin levels in response to both stimuli. In response to hypertonic saline there was an initial rise followed by a fall in vasopressin content. The suprachiasmatic and lateral septal nuclei, as well as the nucleus of the solitary tract, were unaffected by either stimulus. These results indicate that there are at least two functionally different vasopressin systems within the central nervous system, one of which is responsive to osmotic stimulation.