Immunoneutralization of lipocortin 1 reverses the acute inhibitory effects of dexamethasone on the hypothalamo-pituitary-adrenocortical responses to cytokines in the rat in vitro and in vivo.

Abstract

Our recent studies suggest that lipocortin 1 (LC1), a potential mediator of the anti-inflammatory, antiproliferative and anti-fever actions of glucocorticoids in peripheral tissues, may also contribute to the powerful negative feedback actions of the steroids on the hypothalamo-pituitary-adrenal (HPA) axis. In the present study we have used (1) an in vitro model to examine the influence of a specific neutralizing monoclonal anti-LC1 antibody (anti-LC1 mAb) on the capacity of dexamethasone to suppress the cytokine-induced release of the 41-amino acid corticotropin-releasing factor (CRF-41) and arginine vasopressin (AVP) from the rat hypothalamus and (2) a passive immunization protocol to assess the contribution of LC1 to the inhibitory actions of dexamethasone on the HPA responses to immunological (i.p. injection of interleukin 1 beta, IL-1 beta) and surgical (laparotomy under ether anaesthesia) stress. In vitro, Il-1 alpha (0.2 ng/ml), IL-1 beta (0.5 ng/ml), IL-6 (10 ng/ml) and IL-8 (1 ng/ml) each caused significant increases in the release of immunoreactive (ir)-CRF-41 and ir-AVP from hypothalami removed from rats adrenalectomized 10-12 days before autopsy; these responses were readily inhibited by preincubation of the tissue with dexamethasone (10(-7) M). The inhibitory actions of the steroid were attenuated and, in many instances, abolished by inclusion in the medium of a monoclonal anti-LC1 antibody (LC1 mAb, diluted 1:15,000); an isotype-matched control antibody (antispectrin alpha+beta, diluted 1:15,000) was ineffective in this regard. IL-1 alpha (0.2 ng/ml), IL-1 beta (0.5 ng/ml) and IL-6 (10 ng/ml) also initiated similar increases in the release of CRF-41 and AVP from hypothalami from intact rats which were effectively blocked by dexamethasone (10(-7) M). However, although the inhibitory actions of the steroid on the pharmacologically evoked release of CRF-41 were specifically overcome by anti-LC1 mAb (diluted 1:15,000), the steroid blockade of AVP release was not. In vivo, rats pretreated with either a polyclonal anti-LC1 antibody (anti-LC1 pAb, 1 ml/day s.c. for 2 days) or a corresponding volume of a nonimmune sheep serum (NSS) responded to immunological (IL-1 beta, 3 micrograms/kg i.p.) or surgical (laparotomy under ether anaesthesia) trauma with significant increases in the serum ACTH and corticosterone concentrations. In the NSS-treated groups, dexamethasone (100 micrograms/kg), which had no effect on the prestress concentrations of ACTH and corticosterone in the blood, completely prevented the HPA responses to both IL-1 beta and laparotomy.(ABSTRACT TRUNCATED AT 400 WORDS)