Pa. Steele et al., ENDOGENOUS OPIOID-PEPTIDES IN PARASYMPATHETIC, SYMPATHETIC AND SENSORY NERVES IN THE GUINEA-PIG HEART, Cell and tissue research, 284(2), 1996, pp. 331-339
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.