Calcitonin-mediated changes in plasma tryptophan and brain 5-hydroxytryptamine and acetylcholinesterase activity in rats

Abstract

After a single injection of calcitonin (20 M.R.C. units/kg body wt.) marked decreases in both Ca2+ and free tryptophan in plasma were observed, during the initial period of the treatment (up to 1 h). However, 5-hydrotryptamine contents of the whole brain and the cerebral acetylcholinesterase activity were greatly enhanced. The cerebellar acetylcholinesterase activity was not influenced by calcitonin.

Stimulation of Cerebral Acetylcholinesterase Activity by Calcitonin: a Possible Mediation by 5-Hydroxytryptamine

“…The results of the present experiments show that a single injection of CT to normal rats causes an increase in the activity of AChE in the cerebral hemisphere with a concomitant decrease in the concentration of TP in the plasma, an observation which was reported earlier (9). When the animals were pretreated with PCPA no significant changes in the enzyme activity and plasma TP were induced by the hormone treatment ( fig.…”

“…It has been found that the enhanced concentration of brain 5-HT after CT treatment was accompanied by a decrease in plasma TP (9). On the other hand, PCPA does not block TP uptake into the brain (5).…”

“…Therefore the enhanced activity of AChE following TP administration could be a result of the increased concentration of either TP or 5-HT in the brain. When CT was found to augment the enzyme activity simultaneously with tine concentration of 5-HT in the brain, it was postulated that the stimulated enzyme activity is due to the increased 5-HT concentration in the brain (9). In the present work, the synthesis of 5-HT was blocked by treating rats with PCPA, an inhibitor of the hydroxylation of TP to 5-hydroxytryptophan which rep resents the rate-limiting step in 5-HT synthesis (8).…”

“…The stimulated enzyme activity was accom panied by an increase in 5-hydroxytryptamine (5-HT; serotonin) content in the brain and a decrease in tryptophan (TP) concentration in plasma. It was postulated that the enhanced activity of AChE is due to the increased synthesis of 5-HT in the brain (9). The present work was designed to investigate this possibility by blocking 5-HT synthesis with p-chlorophenylalanine (PCPA).…”

Effect of calcitonin on acetylcholinesterase activity in the gastrointestinal tract and pancreas

“…1). The dose of CT applied in this study was chosen from previous work, where it produced a maximal response for AChE activity in the brain (Nakhla and Majumdar, 1978). Thirty minutes after injection CT causes its maximal effect on pancreatic and intestinal 5-hydroxytryptamine (Nakhla and Latif, 1978).…”