Anaphylactoid reactions activate hypothalamo-pituitary-adrenocortical axis: comparison with endotoxic reactions.

Infectious and allergic diseases represent distinct aspects of immune response that can be experimentally modeled as endotoxic reactions following bacterial 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-pituitary-adrenocortical (HPA) axis, such effects of anaphylactoid reactions are completely unknown. To evaluate the impact of anaphylactoid reactions on HPA regulation, secretion of adrenocorticotropin hormone (ACTH) was followed and the pattern of c-Fos induction in the hypothalamic paraventricular nucleus (PVN) was revealed in rats that were challenged with egg white or compound 48/80. Male rats were intravenously injected with 0.1 ml/100g b.wt. 1:1 diluted egg white or 50 microg/100 g b.wt. compound 48/80, blood samples were taken before and various time intervals between 15-240 min after challenge for plasma ACTH measurement. Anaphylactoid reactions resulted in a rapid, significant activation of ACTH secretion and induced c-Fos immunoreactivity in the corticotropin-releasing hormone (CRH)-secreting subset of the parvocellular neurosecretory neurons. In addition, magnocellular neurosecretory neurons and autonomic-related projection neurons in the PVN became also c-Fos positive upon challenge. Changes in these parameters are compared to those seen in rats challenged with bacterial endotoxin, LPS.