Apoptosis of circulating lymphocyte in unilateral ureteral obstructive rat : role of angiotensin system

Abstract

This research studied apoptosis of circulating lymphocyte in unilateral ureteral obstructive (UUO) rats as well as the role of angiotensin system. The experiments were conducted in two main studies. In study I, male Wistar rats weighted 220-250 g. were induced to be UUO at different periods (1 day to 7 days). The levels of circulating lymphocyte were measured and the percentage of cell death was examined by trypan blue dye exclusion assay. In study II, the animals were divided into two main groups: sham operation (S) and UUO. Each group of these, then was further divided into three subgroups of treatment: 1) only water, 2) water + angiotensin II receptor antagonist (ARA, losartan: 10 mg/kg/d), and 3) water + angiotensin converting enzyme inhibitor (ACEI, enalapril: 5 mg/kg/d). The treatment was performed for either 1 day or 7 days. Besides the measurement of number of circulating lymphocyte and percentage of cell death, the apoptosis of the cell was detected as well by in situ terminal deoxynucleotidyl transferase (TdT assay). The apoptotic markers were counted under fluorescence microscope. The results, from study I, showed that the levels of serum creatinine in rats with UUO was significant increased only on day 1, 4 and 7 as compared with the control group (p<0.05). The number of circulating lymphocyte significantly decreased especially on day 4 (p<0.05) and then restored back, whereas the percentage of cell death reached a significant rise on day 1 and 4 (p<0.05) as compared with control. In study II, the data demonstrated that all 1-day UUO animals had significant increases in serum creatinine while the 7-day UUO rats showed a higher level only in ACEI treated group (p<0.05) as compared to their respective ร groups. The ARA treatment in 1-day UUO rats caused a decrease in circulating lymphocyte level when compared with S (p<0.05) as well as with UUO + water group (p<0.001). This circulating level did not alter in 7-day UUO group. The ACEI, but not ARA, could attenuate the percentage of cell death in both 1-day and 7-day UUO animals (p<0.05). When compared with the respective S groups, UUO at both 1 day and 7 days markedly induced increases in lymphocyte apoptosis expressed as apoptotic index (p<0.001). ACEI as well as ARA could reduce the heightened apoptotic index at 7-day period of UUO (p<0.001 and p< 0.01, respectively), but had no effects in 1-day UUO animals. Thus, the present data are the first evidence that, during UUO, the angiotensin system plays a pivotal role in circulating lymphocyte apoptosis. The longer blockage of this system could abolish the induction of apoptotic lymphocyte cell. This may result in improvement of immune defense mechanism during unilateral ureteral obstruction.