TACHYKININ-LIKE IMMUNOREACTIVITY IN THE SINUS VENOSUS OF THE DOGFISH (SCYLIORHINUS-CANICULA)

The sinus venosus of the elasmobranch heart is characterized by the pr esence of large bundles of unmyelinated nerve fibres that bulge into t he cardiac lumen, below the endocardium. In the dogfish (Scyliorhinns canicula), these fibres contain numerous dense-core membrane-bounded g ranules of about 200 nm in diameter. Most intramural ganglion cells of the sinus venosus also show densely packed granules similar to those found in the subendocardial fibres. We have observed strong substance- P-like immunoreactivity in the large fibre bundles and in the perikary a of the ganglion cells. Preabsorption of the antisera with fragment 7 -11 of substance P has shown that the antisera recognize the tachykini n canonic sequence. Our findings suggest that an undetermined tachykin in is secreted in the elasmobranch heart, and that it is probably rele ased into the blood stream in the context of a little-known neuroendoc rine system.