AJP - Heart and Circulatory Physiology, Vol 246, Issue 4 640-H643, Copyright © 1984 by American Physiological Society
Cytochrome P 450-linked monooxygenase: involvement in the lamb ductus arteriosus
F. Coceani, N. C. Hamilton, J. Labuc and P. M. Olley
CO and metyrapone were tested on isolated ductus arteriosus preparations
from mature fetal lambs equilibrated at low (4-12 Torr) and high (511-712
Torr) O2 partial pressure (PO2). CO completely reversed the contractile
tension of the ductus at either PO2 value and was equally effective in the
absence and presence of indomethacin. CO relaxation still occurred when the
tissue was exposed to a gas mixture having a CO-to-O2 ratio of 0.27. The
inhibitory effect of CO on the O2-contracted ductus was variably reversed
by light. Metyrapone was also a relaxant agent, and its action was greater
at low than at high PO2. Unlike the lamb ductus, the O2-constricted guinea
pig ductus did not respond to CO (maximum CO-to-O2 ratio around 1), whereas
it was relaxed by metyrapone. These findings implicate a cytochrome
P450-catalyzed enzymic process in the maintenance of muscle tone of the
lamb ductus arteriosus and in the contractile response of the vessel to O2.
