Alteration in specific opioid-receptor labeling on peripheral blood leukocytes of bile duct-ligated rat

Cholestasis is associated with increased tonus and activity of opioidergic system. Opioid peptides have also immunomodulatory effects through stimulation of specific opioid receptors on the immune cells, or in an indirect fashion via the central nervous system. The combination of immunofluorescent technique and flow cytometry has proven to be sensitive method for the detection of leukocyte opioid receptors. This study was designed to examine the effect of cholestasis on the opioid-receptor labeling on the leukocytes from bile duct-ligated rats. Seven days after surgery, leukocytes were isolated from the peripheral blood of bile duct-ligated or sham-operated rats. The cells were incubated with naltrexone-fluorescein, in the absence or presence of unlabeled naltrexone, as a competitor and analysed by flow cytometry. Monocytes and granulocytes from bile duct-ligated rats showed an increase in the percentage of opioid-receptor labeling (29.6 ± 2.08 for cholestatic versus 23 ± 1.9 for sham, p < 0.001; 50.6 ± 3.18 for cholestatic versus 39.6 ± 1.7 for sham, p < 0.05; respectively). Furthermore, there was a decrease in the expression of opioid receptors on leukocytes due to cholestasis. In conclusion, changes in specific opioid-receptor labeling and percent of labeled leukocytes indicate that endogenous opioid-receptor interaction may be altered in peripheral blood leukocytes in acute cholestasis.