Local Venous Responses to Endotoxin in Humans

Abstract

Background Septic shock is characterized by arterial and venous dilatation and decreased responsiveness to vasoconstrictors. We have developed a method to explore the effects and mechanisms of action of administration of endotoxin into a blood vessel in vivo. Methods and Results Endotoxin was instilled into a dorsal hand vein for 1 hour and then removed. A dose-response curve to norepinephrine was constructed before and 1, 2, 3, and 4 hours after endotoxin. In a separate study, dose-response curves to norepinephrine were constructed in two separate veins on the same hand, only one of which received endotoxin. Sympathetic-mediated venoconstrictor responses were also studied. Cyclooxygenase inhibitors, nitric oxide synthase inhibitors, and hydrocortisone were used to explore the mechanisms of the effects seen. Endotoxin caused a rightward shift in the dose-response curve to norepinephrine. The effect was greatest at 1 hour (maximal constriction: before endotoxin, 87±4%; after endotoxin, 52±8%; n=4; P <.05) and returned to normal by 4 hours. In addition, deep-breath venoconstrictor responses were abolished in the endotoxin-treated vein. Instillation of endotoxin daily for 3 days resulted in the development of tolerance (maximal constriction to norepinephrine after endotoxin: day 1, 39±6%; day 2, 67±7%; day 3, 85±7%). Cyclooxygenase and/or nitric oxide synthase inhibitors did not alter the response to endotoxin, whereas prior administration of hydrocortisone abolished the effects. Conclusions Instillation of endotoxin caused a glucocorticoid-inhibitable hyporesponsiveness to the constrictor effects of norepinephrine and abolished sympathetically induced and drug-induced venoconstriction. This acute response does not appear to be mediated by nitric oxide or prostanoids. Direct vascular tolerance to endotoxin occurs on repeated administration.