EFFECT OF ENDOTOXIN ON PITUITARY-HORMONE SECRETION IN SHEEP

Endotoxin, a potent stimulator of the immune system and an important m ediator in the pathophysiology of septic shock, has been shown to alte r the release of certain hormones following its systemic administratio n. The purpose of this study was to determine the effects of endotoxin on pituitary hormone secretion both in vivo and in vitro in sheep, wi th emphasis placed on its effects on growth hormone (GH) release. Endo toxin (400 ng/kg i.v.) increased plasma GH, adrenocorticotropic hormon e (ACTH), cortisol and prolactin, while it decreased luteinizing hormo ne (LH) pulse frequency (p < 0.05). Plasma levels of tumor necrosis fa ctor, a major mediator of endotoxin effects, also increased following endotoxin administration. Endotoxin did not affect the GH response to human GH-releasing hormone. In vitro studies evaluated the effect of e ndotoxin to alter GH secretion from dispersed sheep anterior pituitary cells at dosages of 1, 10 and 50 mug/ml, with samples collected at 4, 8 and 24 h. Endotoxin increased pituitary GH secretion at 24 h for 1 mug/ml ( p < 0.05) and at all time periods for 10 and 50 mug/ml (p < 0 .05). It also led to an increased release of ACTH and LH in vitro. The results of this study demonstrate the ability of endotoxin to alter p ituitary hormone secretion both in vivo and in vitro in sheep, suggest ing a direct effect of endotoxin on the pituitary gland.