Inhibition of Acetyl Cholinesterase Extracted from Five Parts of the Brain by 5,6 Dihydroxytryptamine

Abstract

5,6 dihydroxytryptamine (DHT) is a neurogenic analogue of serotonin and physostigmine (eserine), both containing tertiary nitrogen group which is lipid soluble. The addition of 5,6 DHT to cholinesterase (ChE) extracted from whole and five different parts of rat brain namely: basal ganglia, cerebellum, frontal cortex, medulla oblongata, and pons in vitro was studied. The inhibition of ChE in the different parts of the brain was of the competitive type. The highest values of the enzyme‐inhibitor dissociation constant (Ki) were obtained with the extracts of medulla oblongata and pons. Those are the parts responsible for the vital centres. The inhibition of the extracts by DHT was reversible and the enzymes restored their whole activities by dialysis. The difference in the inhibition between the extracts of the parts was due to the difference in the gray and white matter content in these parts which was proved experimentally in this work. The inhibition was higher in the extracts obtained from the parts containing white matter than those containing gray matter. Erythrocyte and plasma ChEs were also inhibited by DHT. The inhibition of erythrocyte ChE was higher than plasma ChE and lower than the inhibition of the extracts of the brain parts. The inhibition of ChE by 5,6 DHT saves acetylcholine which helps in certain diseases like myasthenia gravis, Alzheimer's disease and Parkinsonism.Support or Funding InformationDepartment of Biochemistry, Medical Research Institute, Alexandria University,165 Horria Avenue Elhadarah, Alexandria, EGYPT