Actions of endotoxin and morphine

Abstract

In summary, our current studies show that treatment with a bacterial endotoxin, lipopolysaccharide (LPS), induces the expression of mu opioid receptors in the rat mesentery. This induction may be mediated through IL-1's actions on mu opioid receptors. Morphine stimulates the expression of adhesion molecules in human brain microvascular endothelial cells (HBMEC) isolated from pathological tissues. Under pathological conditions, mu opioid receptor-dependent pathways may be modulated through the induction of mu opioid receptors, especially in endothelial cells. Treatment with morphine increases [14C]-inulin permeability of an in vitro microvascular endothelial cell barrier, and decreases endothelial cell viability. Morphine pre-treatment potentiates the effects of LPS on endothelial cell viability, and on LPS induction of IL-1β secretion from 1α, 25-dihydroxy-vitamin D3-treated HL-60 human leukemia cells. Previously, it was suggested that an opioid-dependent pathway may be involved in the recovery from endotoxin shock (D'Amato and Holaday, 1984). Induction of mu opioid receptors by treatment with high doses of endotoxin suggests that mu opioid receptor-dependent pathways may be involved in mediating the response to endotoxins. Taken together, these data provide valid evidence for an association between endotoxins and opioid actions. These studies suggest that opioid-dependent pathways in disease or in endotoxin exposure may be modified by cytokine-induced expression of opioid receptors in endothelial cells. In a pathological condition, an alteration of the opioid-dependent pathway may be expected. When morphine is used for its therapeutic values, it may, indeed, potentiate LPS' effects in an adverse manner. From a clinical perspective, these data indicate that morphine and an endotoxin, such as LPS, may interact in a positive feedback type of reaction, and thereby modulate the body's immune responses with unexpected and detrimental results.