Cytokines stimulate the CRH but not the vasopressin neuronal system: evidence for a median eminence site of interleukin-6 action.

Antigen-activated immune cells acutely release cytokines which, besides their effects on the immune system, increase hypothalamopituitary-adrenocortical (HPA) function to counteract the inflammatory process. The present study was designed to test, using in vitro paradigms, whether there exists a hypothalamic and/or a median eminence site of action, whereby different substances derived from the immune system could stimulate the CRH and/or the arginine-vasopressin (AVP) neuronal pathway. For this purpose, whole medial basal hypothalamus (containing the median eminence) were dissected from female rats and incubated in vitro with several concentrations of interleukin-1 (IL-1)beta, interleukin-6 (IL-6), tumor necrosis factor (TNF)-alpha, thymosin fraction 5 (TF5) or bacterial lipopolysaccharide (LPS). After a 40-min incubation period, the amounts of CRH and AVP released into the incubation medium were measured by specific radioimmunoassays (RIAs). Additional experiments were carried out by superfusing isolated rat median eminence fragments with the different test substances; CRH and AVP released into the medium were also measured by RIAs. The results indicated that IL-1 beta (10(-11) to 10(-7) M), IL-6 (0.06 x 10(-10) to 0.4 x 10(-10) M), TNF-alpha (6 x 10(-9) to 6 x 10(-7) M) and TF5 (5-500 micrograms/ml) but not LPS (1-100 ng/ml) significantly enhanced hypothalamic CRH secretion above baseline in a concentration-related fashion. Additionally, superfusion experiments demonstrated that, among all test substances, only IL-6 possesses a direct and dose-dependent CRH-releasing activity at the median eminence level. Conversely, no preparation enhanced basal AVP release in either in vitro design.(ABSTRACT TRUNCATED AT 250 WORDS)