The Effects of Sub Lethal Levels of Lead on Acetylcholinesterase Activity in the Rock Pigeon, (Columba Livia)

Abstract

Lead is one of the most abundant heavy metals that has become widely distributed and mobilised in the environment. It exists in various forms which are bioavailable to many organisms including birds, causing physiological changes upon exposure. The aim of this study was to investigate the effects of sub lethal levels of lead on acetylcholinesterase activity in the Rock pigeon (Columba livia). Twelve free range and two pen reared (control) pigeons were collected from breeders around the city of Bulawayo and placed in separate cages. Six free range and one pen reared birds were exposed to 1.25 ppm lead acetate spiked feed and water for 72 hrs, whilst the remaining birds served as the unexposed control. Spiked feed and water were changed daily. Both the exposed and unexposed birds were sacrificed and the muscle, heart and liver tissues isolated and assayed for acetylcholinesterase activity. There was significant inhibition of enzyme activity in all tissue samples obtained from lead exposed free range birds when compared to their unexposed counterparts. In the lead exposed free range birds, muscle and liver acetylcholinesterase activity was below 0.005 µg/min/mg protein while that of the heart was in the 0.02-0.07 µg/min/mg protein range. Enzyme activity was greater than 0.1 µg/min/mg protein in the unexposed free range birds. Comparing the acetylcholinesterase activity of the lead exposed pen reared control, with that of the lead exposed free range birds, the latter demonstrated significant inhibition (p<0.05). The results therefore highlight the inhibitory effect of sub lethal levels of lead on acetylcholinesterase activity which could also be possibly enhanced by prior exposure to other environmental contaminants.>