Increased Secretion of Vasopressin and Adenosine 3',5'-Monophosphate from Hypothalamic-Posterior Pituitary Units of Spontaneously Hypertensive Rats

To determine if the increased vasopressin (AVP) levels observed in the blood and urine ospontaneously hypertensive rats (SHR) are a response to peripheral factors that may influence AVP release or are a consequence of altered hypothalamic- neurohypophysial activity, AVP release from hypothalamic- neurohypophysial units was studied using an in vitro perifusion system. Spontaneous and 30 mM K⁺-stimulated AVP release was significantly greater from tissue of SHR rats than from those of WKYN. Adenosine (10⁻⁵ M) added to the perifusion medium increased AVP release into the perifusate in both strains, even though AVP release into the perifusate was greater in tissue of SHR rats. Measurement of AVP content revealed that hypothalamic AVP was lower in SHR rats, whereas the neural lobes of the SHR contained a significantly higher concentration of AVP compared to the tissue of WKYN rats. In addition, exposing tissue from SHR rats to 30 mM K⁺ stimulated an increase in cAMP release into the perifusate, whereas tissue from WKYN rats did not increase cAMP release above basal level. These data suggest that central nervous system-mediated hyperresponsiveness is the basis for the increased AVP secretion that occurs in the SHR rat and are consistent with reports of a hypersensitive hypothalamic-anterior pituitary axis in these animals.