Evidence That the Hypothalamus Mediates Endotoxin Stimulation of Adrenocorticotropic Hormone Secretion*

The site of action of Escherichia coli endotoxin in inducing ACTH secretion was studied in vivo and in vitro. Hypophysectomized rats, bearing two to three transplanted pituitaries under the kidney capsule and "primed" with exogenous ACTH, responded to 2.0-7.5 microgram/100 g BW ip or iv endotoxin with a several-fold increase of plasma corticosterone. This response was markedly reduced by hypothalamic lesions and completely abolished by removing the entire forebrain. Endotoxin added directly to cultured rat adenohypophyseal cells in a concentration up to 10 microgram/ml did not induce significant ACTH secretion. We conclude that endotoxin-induced ACTH secretion from heterotopically transplanted pituitaries is mediated primarily by the hypothalamus, presumably through hypothalamic CRF that reaches the transplanted pituitaries via the systemic circulation.