Stimulatory effect of trans-cinnamaldehyde on noradrenaline secretion in guinea-pig ileum myenteric nerve terminals

The effect of trans-cinnamaldehyde (CNMA) on the release of noradrenaline ( NA)from nerve terminal was investigated using isolated ileal synaptosomes o f guineapig. Release was determined as the amount of NA, quantified by h.p. l.c.-electrochemical detection, from samples incubated with CNMA minus that in parallel blanks treated with same volume of vehicle. CNMA stimulated th e secretion of NA in a concentration-dependent manner from 5 mu M to 50 mu M, while the value of lactate dehydrogenase in the incubated medium was not influenced by CNMA. However, trans-cinnamic acid, cinnamoyl chloride and c innamamide failed to produce similar effect. Specific action of CNMA can th us be considered. Guanethidine inhibited the release of NA by CNMA in a con centration dependent manner. Saxitoxin attenuated the action of CNMA at con centrations sufficient to block sodium channels. The depolarizing effect of CNMA on the membrane potential was also illustrated by a concentration-dep endent increase in the fluorescence of bisoxonol, a potential sensitive dye . The NA releasing action of CNMA was deleted by removal of calcium chlorid e from the bathing medium. This action of CNMA was also attenuated by Rp-cA MP at concentrations sufficient to inhibit the action of cyclic AMP. These findings suggest that CNMA can depolarize the membrane to result in a calci um-dependent and cyclic AMP-related release of NA from noradrenergic termin als.