DELETION OF THE VENTRAL NORADRENERGIC BUNDLE OBLITERATES THE EARLY ACTH RESPONSE AFTER SYSTEMIC LPS, INDEPENDENTLY FROM THE PLASMA IL-1-BETA SURGE

We have recently shown that total lesion of the ventral noradrenergic bundle (VNAB-X), enhanced the short-lived (<120 min) triggering effect of intra-arterially (i.a.) given IL-1 beta on plasma ACTH levels. In the present study we used the same VNAB-X paradigm to explore the mech anisms of the long-lived (480 min) LPS stimulatory effect on plasma AC TH, corticosterone (CORT) and IL-1 beta levels. In control rats, 25 mu g kg(-1) LPS induced a 20-fold increase in ACTH and a 7-fold increase in CORT concentrations at 30 min, which continued to rise until 60 mi n, before receding tb baseline at 480 min. In contrast, the plasma IL- 1 beta concentration started to increase above undetectable levels onl y at 120 min. In VNAB-X animals, the early (30 min) ACTH/CORT response to LPS was completely blunted, and the ACTH surge was reduced by 75% at 60 min. However, the sustained hormonal response (120 to 480 min) w as unaltered. Both the temporal pattern and the amplitude of the plasm a IL-1 beta response were normal. We conclude that (1) the VNAB is inv olved in the early (first 60 min) ACTH/CORT response to systemic LPS, (2) plasma IL-1 beta does not appear to be associated with this early corticotropic activation and (3) the later stages of the ACTH/CORT res ponse to LPS (60 to 480 min) appear to be independent of the VNAB cont rol and may therefore involve different control mechanisms, in which t he IL-1 beta, by this stage massively released in the blood, may play a major role.