Role of monokines in control of anterior pituitary hormone release

It has long been known that endogenous pyrogen, released as a result of injection of typhoid vaccine or in response to infection, produces fever and increases ACTH secretion. Recent studies have indicated that endogenous pyrogen is, at least in part, IL-1. This monokine has now been shown to activate the release of ACTH by a hypothalamic mechanism with release of CRF and possibly vasopressin, which stimulates the corticotrophs. There may also be a pituitary action to stimulate the release of ACTH directly. In our experiments we showed that IL-1 at low but not higher doses appears to act intrahypothalamically to stimulate GH and PRL release and to inhibit TSH release. In the meantime, another monokine, cachectin, was isolated and its structure determined. We have found that this monokine can act following its third ventricular injection to stimulate ACTH, PRL, and GH release and to inhibit TSH release, at least in part, by release of prostaglandins since indomethacin, an inhibitor of prostaglandin synthesis, produced a blockade of the responses except for those of ACTH. This peptide also has highly potent effects to alter pituitary hormone release by direct action on the pituitary to stimulate ACTH, GH, and TSH and to a slight extent PRL release. These actions appear to involve prostaglandins since indomethacin blocks all of the effects except for the effect on ACTH secretion. This monokine also produces a dose-related lowering of anterior pituitary cyclic AMP levels. When the monokine was incubated along with somatostatin, the lowering of cyclic AMP was reversed, and a potent PRL-releasing effect of the monokine was visible. We have begun studies with a third monokine, gamma interferon, which indicate that it stimulates ACTH release but suppresses plasma GH and TSH levels by a hypothalamic action. It is apparent that these various monokines have powerful effects to alter hypothalamic-pituitary function and that they probably mediate most of the effects of infections on the release of anterior pituitary hormones.