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Neuroanesthesia Research Laboratory, 1 Department of Anesthesiology, and 2 Department of Pharmacology, University of Illinois at Chicago, Chicago, Illinois 60607
It was previously shown that,
despite the loss of nitric oxide (NO) dependence, ADP-induced pial
arteriolar dilation was not attenuated in estrogen-depleted [i.e.,
ovariectomized (Ovx)] rats. Additional evidence suggested that the NO
was replaced by an endothelium-dependent hyperpolarizing factor
(EDHF)-like mechanism. To further characterize the nascent EDHF role in
Ovx females, the current study was undertaken to test whether, in Ovx
rats, ADP-induced pial arteriolar dilation retained its endothelial
dependence and whether gap junctions are involved in that response. A
closed cranial window and intravital microscopy system was used to
monitor pial arteriolar diameter changes in anesthetized rats. The
endothelial portion of the ADP-induced dilation was evaluated using
light dye endothelial injury (L/D). The study was organized around
three experimental approaches. First, the responses of pial arterioles
to ADP before and after L/D exposure in intact and Ovx female rats were
tested. L/D reduced the ADP response by 50-70% in both groups,
thereby indicating that the endothelium dependence of ADP-induced
vasodilation is not altered by chronic estrogen depletion. Second, the
NO synthase inhibitor
N
-nitro-L-arginine
(L-NNA) and the prostanoid synthesis inhibitor indomethacin
(Indo) were coapplied. In intact females, L-NNA-Indo attenuated the response to ADP by 50%, with no further changes upon
the addition of L/D. On the other hand, L-NNA-Indo did not affect ADP reactivity in Ovx rats, but subsequent L/D exposure reduced
the ADP response by >50%. The NO-prostanoid-independent, but
endothelium-dependent, nature of the response in Ovx females is a
hallmark of EDHF participation. Third, gap junctional inhibition strategies were applied. A selective inhibitor of gap junctional function, Gap 27, did not affect ADP reactivity in intact females but
reduced the the ADP response by 50% in Ovx females. A similar result
was obtained following application of a connexin43 antisense oligonucleotide. These findings suggest that the nascent EDHF dependency of ADP-induced pial arteriolar dilation in Ovx females involves connexin43-related gap junctional communication.
endothelium-derived hyperpolarizing factor; connexin43; gap junction; adenosine diphosphate; estrogen
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