Vasopressin release from rat medial basal hypothalamus in vitro after adrenalectomy or lesions of the paraventricular nuclei

Rat medial basal hypothalami (MBH) or neurointermediate lobes of the hypophysis (NIL) were superfused in vitro and stimulated electrically. The evoked release of vasopressin from the MBH was enhanced to 700% of controls when the tissue was taken from adrenalectomized rats. By contrast, the evoked release of vasopressin from the NIL was not changed after adrenalectomy. After bilateral lesions of the paraventricular nuclei, the evoked release of vasopressin from the MBH was reduced in subsequent in vitro experiments. The marked changes in vasopressin release occurred in spite of no or only small changes in the total tissue content of vasopressin. These data support the view that vasopressin may be released from the external layer of the median eminence into the hypophysial portal blood after activation of the hypothalamo-pituitary-adrenal axis.