Morphine inhibits erythrocyte carbonic anhydrase in vitro and in vivo

Morphine is implicated in diverse functions, from development to immune modulation in the central and peripheral nervous systems. At the present time, morphine is one of the most effective antinociceptive agents used to manage pain. It has been used extensively in the clinical management of pain due to its potent analgesic effect. In this study, the in vitro and in vivo inhibitory effects of morphine on erythrocyte carbonic anhydrase (CA) were investigated. Human erythrocyte isoenzymes, HCA-I and HCA-II, were purified by Sepharose-4B affinity chromatography column with a yield of 66.95 and 62.82%, a specific activity of 3892.3 and 11663.2 EU/mg proteins with 745.1 and 2232.6-fold purification of each isoenzyme, respectively. To determine enzyme purity, sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was performed. In vitro inhibition of erythrocyte HCA-I and HCA-II by morphine using the CO2-hydratase enzyme gave IC50 values 4.50×10 -5M (r2: 0.954) and 9.23×10-5M (r 2: 0.996), respectively. CA activity was significantly attenuated in vivo in Spraque-Dawley rats for up to 3 h (p<0.001) following intraperitoneal administration of morphine. In conclusion, morphine inhibited CA activity both in vitro and in vivo. © 2007 Pharmaceutical Society of Japan.