The neuropeptide arginine vasopressin (AVP) can replace the cytokine interleukin 2 (IL-2) as a T-cell mitogen for the induction of interferon gamma (IFN gamma) expression in splenic cultures. IL-2-like and IL-2 receptor immunoreactivity have been reported in different brain regions, under normal and pathophysiological conditions. Regulatory functions for IL-2 in the CNS have been suggested. In addition to the spleen, AVP might also mediate some IL-2 effects centrally. In the present study, we evaluated the effect of IL-2 on the in vitro release of AVP from the hypothalamus and amygdala. In addition, we used these release systems to study the possible involvement of NO-mediated signaling in AVP release, based on the reported detection of nitric oxide synthase (NOS) in the hypothalamus and amygdala. IL-2 rapidly stimulates AVP release in both regions, in a calcium- and dose-dependent manner. In addition, nitroprusside also induces AVP release. Norepinephrine also induces AVP release from both the hypothalamus, as well as the amygdala. The norepinephrine-induced AVP release is antagonized by phentolamine, but not by propranolol, suggesting an alpha-adrenergic receptor-mediated AVP response in both brain regions. The IL-2- and acetylcholine-induced AVP release is antagonized by Ng-methyl-L-arginine, indicating a role for NO in this AVP release. Ng-methyl-L-arginine does not affect the norepinephrine- induced AVP release. A stimulatory effect of IL-2 on hypothalamic CRF release and plasma ACTH has already been reported. Our results suggest that in addition to CRF, AVP may also mediate the IL-2 stimulation of ACTH secretion. These data further suggest that in addition to the hypothalamus, the amygdala may also play a role in the bidirectional communication between neuroendocrine and immune systems. Understanding the mode of interaction between IL-2 with AVP could clarify the pathophysiologic or toxic effects of high brain levels of IL-2.