Prejunctional effects of 5-hydroxytryptamine on noradrenergic nerves in the cardiovascular system.

Recent studies indicate that some peripheral noradrenergic nerves have specific 5-hydroxytryptamine (5-HT) receptors on their terminals that can mediate inhibition of release of transmitter after neuronal stimulation. It is now also known that 5-HT will cause norepinephrine release from noradrenergic nerve terminals in the isolated rabbit heart by a receptor mechanism. The evidence for the existence of these two types of prejunctional 5-HT receptor is discussed together with findings to date on their distribution and possible functional importance in the whole animal. In addition 5-HT has weak sympathomimetic actions, which result from its ability to interact with noradrenergic removal processes. The displaced transmitter can then interact with adrenoceptors situated pre- or postjunctionally.