ENDOGENOUS OPIOID-PEPTIDES IN PARASYMPATHETIC, SYMPATHETIC AND SENSORY NERVES IN THE GUINEA-PIG HEART

Research has suggested that exogenous opioid substances can have direc t effects on cardiac muscle or influence neurotransmitter release via presynaptic modulation of neuronal inputs to the heart, In the present study, multiple-labelling immunohistochemistry was employed to determ ine the distribution of endogenous opioid peptides within the guinea-p ig heart. Approximately 40% of cardiac ganglion cells contained immuno reactivity for dynorphin A (1-8), dynorphin A (1-17) and dynorphin B w hilst 20% displayed leu-enkephalin immunoreactivity. Different populat ions of opioid-containing ganglion cells were identified according to the co-existence of opioid immunoreactivity with immunoreactivity for somatostatin and neuropeptide Y. Immunoreactivity for prodynorphin-der ived peptides was observed in many sympathetic axons in the heart and was also observed, though to a lesser extent, in sensory axons. Leu-en kephalin immunoreactivity was observed in occasional sympathetic and s ensory axons. No immunoreactivity was observed for met-enkephalin-arg- gly-leu or for beta-endorphin. These results demonstrate that prodynor phin-derived peptides are present in parasympathetic, sympathetic and sensory nerves within the heart, but suggest that only the prodynorphi n gene is expressed in guinea-pig cardiac nerves. This study has shown that endogenous opioid peptides are well placed to regulate cardiac f unction via both autonomic and sensory pathways.