Effects of melatonin on carbonic anhydrase from human erythrocytes in vitro and from rat erythrocytes in vivo.

The in vitro effects of melatonin (N-acetyl-5-methoxy-tryptamine) on human carbonic anhydrase isozymes (HCA-I and HCA-II) from human erythrocytes and in vivo effects on rat erythrocytes carbonic anhydrase (CA) were determined. Human erythrocyte carbonic anhydrase isozymes were purified by haemolysate preparation and Sepharose-4B-L tyrosine-sulfanilamide affinity gel chromatography. The HCA-I enzyme, having a specific activity of 7337.5 EU/mg protein, was purified 843-fold with a yield of 60% and the HCA-II enzyme, having a specific activity of 17067EU/mg protein, was purified 1962-fold with a yield of 22.7%. For in vitro experiments, the enzyme activity was minimal at 2 x 10(-4) M melatonin concentration and increased above this concentration. Ten mgkg(-1) melatonin was administered intraperitoneally and showed a stimulatory effect on the enzyme. Time-dependent in vivo studies were conducted for melatonin in Sprague-Dawley type rats. It was found that CA activity in the rat erythrocytes was decreased by the melatonin after 1 and 3 hours to 2500 +/- 500.0 and 1875 +/- 239.4 respectively which were statistically significant (p < 0.05) differences to the control (2660 +/- 235.8). However, CA activity was restored to its normal level after 6h (2666 +/- 235.7) (p > 0.05) probably due to metabolism of the melatonin. The findings indicate that melatonin may be pharmacologically useful in some diseases.