The vasomotor responses to neuropeptides of the angular oculi and facial veins of reindeer were examined in vitro and correlated with the neuropeptide distribution in the perivascular nerves, as demonstrated by immunohistochemistry. 2. Nerves displaying calcitonin gene related peptide (CGRP)- or neuropeptide Y (NPY)-like immunoreactivity (-LI) were observed in the media of both veins, while very few fibers were immunoreactive to vasoactive intestinal polypeptide (VIP) or substance P (SP) in either vein. 3. The staining pattern for NPY-LI was largely identical to that of dopamine-beta-hydroxylase, a marker for noradrenaline (NA) producing fibers, indicating coexistence of NPY and NA. 4. Administration of NPY in vitro elicited contractions in both veins in the presence of propranolol, though more conspicuously in the angular oculi vein. 5. The peptide was without any modulating effect on NA-stimulated contractions in the angular oculi vein, whereas a small enhancement of the NA-induced tone was seen in the facial vein. 6. CGRP caused partial relaxation of both veins, whereas atrial natriuretic polypeptide caused relaxation only in the facial vein. VIP and SP had no effect on either vein. 7. The results suggest that in reindeer the sympathetic nerve fibres to both facial and angular oculi veins contain the vasoconstrictor neuropeptide NPY besides NA, even though these fibres exert a vasodilator action on the myogenically active facial vein. 8. The vasodilator neuropeptide CGRP, which is present in other more sparse perivascular nerve fibres mainly in angular oculi vein, is perhaps of afferent nature in which case CGRP might subserve axon reflex functions. 9. If, however, also the CGRP fibres are truly efferent in nature, chances for a central reciprocal control of flow through angular oculi vein might be at hand.
