AJP - Regulatory, Integrative and Comparative Physiology, Vol 255, Issue 4 575-R582, Copyright © 1988 by American Physiological Society
Vasoactive intestinal peptide stimulates blood flow and secretion of avian salt glands
R. Gerstberger, H. Sann and E. Simon
Max-Planck-Institut fur Physiologische und Klinische Forschung, William G. Kerckhoff-Institut, Bad Nauheim, Federal Republic of Germany.
The neuromodulatory role of vasoactive intestinal peptide (VIP) in avian
salt gland secretion and blood flow was investigated in conscious
saltwater-acclimated Pekin ducks. Glandular blood flow was measured by
laser-Doppler flowmetry or the radioactive microspheres technique. Osmolal
excretion was closely related to salt gland blood flow during salt loading.
At threshold conditions of salt gland secretion, VIP infused
intracarotidally induced both osmolal excretion and arteriolar vasodilation
dose dependently (30-240 pmol.min-1.kg body wt-1). The VIPergic effect on
the secretory process for NaCl was enhanced by simultaneous intracarotid
application of acetylcholine (5 nmol.min-1.kg body wt-1), whereas the
intrinsic vasodilatory potency of acetylcholine appeared to be nonadditive
in coinfusion experiments. Ongoing secretion induced by systemic infusion
of hypertonic saline could be suppressed by muscarinic antagonists, with
salt gland blood flow being sustained at the reduced level of
atropine-resistant vasodilation. Subsequent intracarotid infusion of VIP
stimulated glandular blood perfusion and also, to a minor extent, osmolal
excretion, suggesting an independent, functional VIP system in efferent
salt gland control.
