Anaphylactoid reactions activate hypothalamo-pituitary-adrenocortical axis: Comparison with endotoxic reactions

Infectious and allergic diseases represent distinct aspects of immune respo nse that can be experimentally modeled as endotoxic reactions following bac terial lipopolysaccharide (LPS) administration and anaphylactoid reactions following systemic injection of foreign proteins, respectively. Although it is well established that LPS stimulates the activity of the hypothalamo-pi tuitary-adrenocortical (HPA) axis, such effects of anaphylactoid reactions are completely unknown. To evaluate the impact of anaphylactoid reactions o n HPA regulation, secretion of adrenocorticotropin hormone (ACTH) was follo wed and the pattern of c-Fos induction in the hypothalamic paraventricular nucleus (PVN) was revealed in rats that were challenged with egg white or c ompound 48/80. Male rats were intravenously injected with 0.1 ml/100g b.wt. 1:1 diluted egg white or 50 mu g/100 g b.wt. compound 48/80, blood samples were taken before and various time intervals between 15-240 min after chal lenge for plasma ACTH measurement. Anaphylactoid reactions resulted in a ra pid, significant activation of ACTH secretion and induced c-Fos immunoreact ivity in the corticotropin-releasing hormone (CRH)-secreting subset of the parvocellular neurosecretory neurons. In addition, magnocellular neurosecre tory neurons and autonomic-related projection neurons in the PVN became als o c-Fos positive upon challenge. Changes in these parameters are compared t o those seen in rats challenged with bacterial endotoxin, LPS. (C) 2000 Els evier Science Inc.