Relationship between vasopressin and opioids in hypoxia induced
pial artery vasodilation.
Rossberg, M. I., and W. M. Armstead.
Departments of Anesthesia and Pharmacology, The University of
Pennsylvania and The Children's Hospital of Philadelphia,
Philadelphia, PA 19104-4399
APStracts 3:0018H, 1996.
It has been observed that a vasopressin receptor antagonist attenuates
hypoxic hyperemia in fetal sheep, while methionine enkephalin (Met)
and leucine enkephalin (Leu) contribute to hypoxia-induced pial
artery dilation in newborn pigs. This study was designed to
investigate the relationship between vasopressin and opioids in
hypoxia-induced pial artery dilation in the newborn pig using the
closed cranial window technique. Hypoxia-induced pial artery dilation
was attenuated during moderate (Pao2 nearly equal to 35mmHg) and
severe hypoxia (Pao2 nearly equal to 25mmHg) by the vasopressin
receptor antagonist [1-([beta]-mercapto-bb-cyclopentamethylene
propionic acid) 2 (0-methyl)-Tyr-AVP] (MEAVP; 5[mu]g/kg i.v.) (29+1
vs 14+2 and 37+2 vs 18+2% for moderate and severe hypoxia in the
absence vs presence of MEAVP, respectively, n=7). Hypoxia- induced
dilation was accompanied by increased CSF vasopressin concentration
(26+1 vs 67+4 and 26+1 vs 99+4 pg/ml for control vs moderate and
control vs severe hypoxia, n=5). Vasopressin increased CSF Met
(895+28, 1147+63, 1327+48, and 1600+75 pg/ml for control, 40, 400,
4000 pg/ml vasopressin, respectively, n=7). CSF Leu concentration was
similarly increased by vasopressin. Furthermore, MEAVP attenuated the
release of Met during moderate hypoxia (910+38 and 2682+49 vs 911+38
and 2110+84 pg/ml for control and moderate hypoxia in the absence and
presence of MEAVP, respectively, n=5). MEAVP had similar effects on
hypoxia-induced Leu release. These data show that vasopressin
contributes to hypoxia-induced pial artery dilation and that
vasopressin increases CSF Met and Leu concentrations. These data also
suggest that elevated CSF vasopressin concentrations that occur
during hypoxemia result in opioid release which subsequently
contributes to hypoxic pial artery dilation.
Received 11 October 1995; accepted in final form 15 December
1995.
APS Manuscript Number H953-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 22 January 96