AJP - Heart and Circulatory Physiology, Vol 247, Issue 1 17-H24, Copyright © 1984 by American Physiological Society
Autonomic mechanisms in the ductus venosus of the lamb
F. Coceani, A. S. Adeagbo, E. Cutz and P. M. Olley
Morphological and pharmacological studies were performed in the ductus
venosus from near-term fetal and neonatal (1 day of age) lambs. Light and
electron microscopic analysis demonstrated a concentration of circularly
oriented muscle fibers at the junction of the ductus with the portal sinus
(the sphincter region). With the use of histochemical methods, adrenergic
and cholinergic fibers were visualized in both the sphincter and
extrasphincter regions of the ductus. At either site, nerve fibers were
confined to the adventitial layer and never formed a plexus. Norepinephrine
and transmural electrical stimulation contracted the ductus sphincter in
vitro, and their action was abolished by dibenzyline. In contrast, atropine
had no effect on the transmural response. Moreover, acetylcholine
contracted the vessel inconsistently. In the fetus, both the
norepinephrine-induced and the electrically induced contractions increased
on raising the O2 tension of the bathing fluid from 17-31 to 520-705 mmHg.
In addition, the transmural response increased with advancing gestation.
Norepinephrine and transmural stimulation relaxed dibenzyline-treated
preparations in which the tone had been raised with indomethacin.
Norepinephrine relaxation was antagonized by propranolol. We conclude that
the ductus venosus sphincter contains functional adrenergic nerves, causing
contraction and relaxation via, respectively, alpha- and
beta-adrenoceptors. The alpha-adrenoceptor-mediated contraction may have a
role in postnatal closure of the vessel.
