Age dependence of cerebrovascular response mechanisms in the
domestic pig.
Zuckerman, S. L., W. M. Armstead, P. Hsu, M. Shibata, and C. W.
Leffler.
The Laboratory for Research in Neonatal Physiology, Departments of
Physiology and Biophysics and Pediatrics, University of Tennessee,
Memphis, TN 38163, Division of Critical Care and Pulmonary Medicine,
St. Jude Children's Research Hospital, Memphis, TN 38101
APStracts 2:0565H, 1995.
Hypercapnia-induced cerebral vasodilation in the newborn pig is a
prostanoid-associated response. In some adult models, hypercapnic
cerebral vasodilation is associated with the generation of nitric
oxide. Acetylcholine produces a nitric oxide dependent cerebral
vasodilation in many adult models, but topical acetylcholine is a
prostanoid associated cerebral vasoconstrictor in the newborn pig. We
hypothesized that mediators influencing cerebral response can be age
-dependent. Juvenile domestic pigs were compared to newborn pigs, and
pial arteriolar diameters were measured using a closed cranial window
during hypercapnia and topical acetylcholine (Ach) (10-5 M). 4
different conditions were explored : control, topical N_-nitro-L
-arginine (LNA) (10-3 M), indomethacin (5mg/kg i.v.), and both LNA and
indomethacin. All animals were anesthetized with [alpha]-chloralose.
As opposed to the complete block in the newborn, indomethacin only
partially attenuated the hypercapnic cerebral vasodilation in the
juvenile pig. LNA which had no effect on the response of the newborn
produced a partial attenuation of the hypercapnic response of the
juvenile. The combination of indomethacin and LNA blocked the
response in both age groups. Topical Ach in both age groups initially
produced cerebral vasoconstriction; but, in the juvenile, this was
followed by a sustained cerebral vasodilation. Indomethacin blocked
the early vasoconstriction in both age groups. LNA, which had no
effect in the response of the newborn to Ach, blocked the
vasodilation seen in the juvenile. The combination of both inhibitors
blocked all response to Ach in the juvenile. These data indicate that
while the cerebral vascular responses to Ach and hypercapnia are
prostanoid associated and nitric oxide independent in the newborn
pig, nitric oxide assumes an increasing role in dilatory responses
with development.
Received 24 May 1995; accepted in final form 8 December 1995.
APS Manuscript Number H484-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 23 December 95