RESUMO
We investigated the effects of i.v. and intracerebroventricular (i.c.v) administration of increasing doses of recombinant human IL-1 beta, TNF alpha and IL-6 on plasma corticosterone (B) levels in rats. Rats were equipped with a jugular cannula for repeated blood sampling anda subgroup of rats also received an i.c.v implanted cannula. I.v. administration of IL-1 beta, TNF alpha or IL-6 and i.c.v administration of IL-1 beta and IL-6 induced a significant dose-dependent increase in plasma B levels, whereas i.c.v injection of TNF alpha in doses up to 1000 ng/rat was not effective. I.v. pretreatment of rats with anti-CRH antiserum had no significant overall effect on the plasma B response to i.v. administered IL-1 beta (500 and 3000 ng/rat), whereas the plasma B response to i.v. TNF alpha or IL-6 administration (3000 ng/rat) were significantly reduced. I.v. pretreatment of the animals with recombinant human IL-1 receptor antagonist (IL-1ra) significantly blocked the plasma B response to i.v. treatment with IL-1 beta, whereas the TNF alpha- and IL-6-induced increases in plasma B levels were not affected. Our data show that 1) i.v. administration of IL-beta, TNF alpha or IL-6 and i.c.v administration of IL-1 beta or IL-6 dose-dependently stimulate the HPA axis; 2) when given i.v. or i.c.v, IL-1 beta is more powerful than TNF alpha and IL-6 in activating the HPA axis; 3) endogenous CRH is involved in the activation of the HPA axis by acute i.v. administration of TNF alpha and IL-6. It is most likely that in case of i.v. treatment with IL-1 beta a CRH-independent mechanism is involved. This study provides no arguments for the involvement of endogenous IL-1 in TNF alpha- or IL-6-induced activation of the HPA axis.
