Effect of endotoxin on pituitary hormone secretion in sheep

Endotoxin, a potent stimulator of the immune system and an important mediator in the pathophysiology of septic shock, has been shown to alter the release of certain hormones following its systemic administration. The purpose of this study was to determine the effects of endotoxin on pituitary hormone secretion both in vivo and in vitro in sheep, with emphasis placed on its effects on growth hormone (GH) release. Endotoxin (400 ng/kg i.v.) increased plasma GH, adrenocorticotropic hormone (ACTH), cortisol and prolactin, while it decreased luteinizing hormone (LH) pulse frequency (p < 0.05). Plasma levels of tumor necrosis factor, 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 endotoxin to alter GH secretion from dispersed sheep anterior pituitary cells at dosages of 1, 10 and 50 micrograms/ml, with samples collected at 4, 8 and 24 h. Endotoxin increased pituitary GH secretion at 24 h for 1 microgram/ml (p < 0.05) and at all time periods for 10 and 50 micrograms/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 pituitary hormone secretion both in vivo and in vitro in sheep, suggesting a direct effect of endotoxin on the pituitary gland.