RBC‐cholinesterase (RBC‐ACHE) activity is not a reliable marker for low‐dose long‐term organophosphate exposure (OPE) in rats

OPE is monitored via cholinesterase (ChE) activity. No consensus exists as to which ChE to be measured: plasma or RBC. Purpose of the study was to determine the suitability of RBC‐AChE determinations for OPE. Material & Methods The number of rats per group (G) was 6. Substances were applied i.p.daily for 5 days, followed by a 2‐day break. The cycle was repeated x10. After 8 week recovery the rats were sacrificed. Blood was collected at base line (t 0 ), at the end of each cycle (t 1 to t 10 ) and after the recovery period (t 11 ) and RBC‐AChE activities determined. G 1 received 10 nM paraoxon, G 2 10 nM malathion & G 3 saline. Statistics: Mann‐Whitney test (α ≤ 0.05). Results‐ G 1 vs G 3 : At t 1–2 enzyme activity in G 1 is significantly higher. From t 3‐6 no difference exists, while at t 7 activities are higher in G 3 . At t 8‐11 no difference between groups exists. (See Table I) RESULTS‐ G 2 vs G 3 : At t 1–2 enzyme activity in G 1 is higher; thereafter no differences exist. (See Table II) Conclusions After an initial drop in RBC‐AChE activity, there is probably enzyme induction with a maximum arround week 7. RBC‐AChE activity is not a reliable marker for OPE in rats. Clinical Pharmacology & Therapeutics (2004) 75 , P43–P43; doi: 10.1016/j.clpt.2003.11.162 Table It 10 11G 1 100 85±4 97±4 107±14 126±11 125±13 130±7 123±22 113±2 112±11 G 3 100 107±9 115±7 100±10 114±5 108±3 116±9 115±6 125±11 115±13 112±11 100±6 P NA 0.004 0.004 NS 0.03 NS 0.008 NS NS NSTable IIt 10 11G 2 100 96±7 103±6 101±4 117±17 120±12 113±10 114±7 111±10 124±15 G 3 100 107±9 115±7 100±10 114±5 108±3 116±9 115±6 125±11 115±13 112±11 100±6 P NA 0.05 0.03 NS NS NS NS NS NS NS