Histamine and serotonin released from the rat perfused heart by compound 48/80 or by allergen challenge influence noradrenaline or acetylcholine exocytotic release.

Terminal nerve fibres of the autonomic nervous system closely approach mast cells in peripheral organs, and mutual influences between release of neurotransmitters or mast cell mediators may cause neuro-immunological interactions. We have studied the influence of mast cell degranulation on the release of endogenous noradrenaline and newly incorporated acetylcholine (such as 14C-choline/acetylcholine overflow) evoked by stimulation of extrinsic postganglionic sympathetic or preganglionic vagal nerves in the rat Langendorff heart perfused with Tyrode solution. Compound 48/80 perfused in normal hearts, or ovalbumin infused into hearts from rats sensitized to ovalbumin, enhanced the overflow of endogenous histamine and serotonin. Both stimuli increased the release of mediators to a similar extent and with fast kinetics. Maximum average concentrations in the perfusate of histamine were about 800 nmol/l, and of serotonin 40 nmol/l, in a sample collected within 4 min after mast cell degranulation. Stimulation of autonomic nerves did not affect basal histamine or serotonin overflow. Whereas basal overflows were unaffected, the stimulation-evoked releases of both noradrenaline and acetylcholine, were facilitated when compound 48/80 was perfused before and during nerve stimulation. The facilitation of noradrenaline overflow was more pronounced (by 60%) when compound 48/80-induced mediator overflow started 4 min before nerve stimulation as compared to 30 s (15%), and was reduced by cocaine (by 50%), and, in the presence of cocaine, abolished by cimetidine (but was unaffected by mepyramine and thioperamide) and NG-nitro-(L)-(-)-arginine. In the presence of cimetidine and cocaine, when the facilitatory components were abolished, the evoked noradrenaline overflow observed 30 s after the start of infusion of compound 48/80 was inhibited, and the inhibition was partly reduced by methiotepin and ketanserin. Ovalbumin infusion in hearts from sensitized animals caused an inhibition of evoked noradrenaline overflow sensitive to methiotepin and also partly to ketanserin, and no facilitation was observed. The facilitation (> 100%) of evoked overflow of acetylcholine observed at 4 min after the start of perfusion with compound 48/80 was partly reduced by thioperamide (but not mepyramine or cimetidine) and to a comparable extent either by tropisetron (3 mumol/l) alone or by tropisetron plus methiotepin. In conclusion, degranulation of immunological cells is followed by histamine and serotonin release in the rat heart and may affect the release of autonomic neurotransmitters in rather unusual ways, by i) an uptake1-dependent and ii) an H2-mediated facilitation which probably involves nitric oxide as a permissive mediator, and iii) a serotonergic inhibition, of noradrenaline release, and iv) an H3- and serotonergic facilitation of acetylcholine release.