We analyzed the effect of tumor necrosis factor α (TNF-α) on β-endorphin concentrations and proopiomelanocortin mRNA in the rat anterior and neurointermediate pituitaries. The intraperitoneal injection of 5 (µg/kg TNF-α decreases β-endorphin in neurointermediate pituicytes 4, 8 and 24 h after the treatment without affecting proopiomelanocortin (POMC) RNA. In contrast, in the anterior pituitary 4 h after the injection of the cytokine, POMC RNA was decreased while the peptide content was increased. These effects can be relevant to the modulation of the pituitary-adrenal axis and immune responses in conditions, such as infections, in which TNF levels are incr