ADP-induced pial arteriolar dilation in ovariectomized rats involves gap junctional communication.
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(omega)-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.
Department of Anesthesiology, University of Illinois at Chicago, Chicago, Illinois 60607, USA.
H L
HL
Xu
R A
RA
Santizo
V L
VL
Baughman
D A
DA
Pelligrino
D000244:Adenosine Diphosphate / Q000494:pharmacology*; D000818:Animals; D001160:Arterioles / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D001685:Biological Factors / Q000378:metabolism; D002450:Cell Communication / Q000502:physiology; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism; D017630:Connexins / Q000494:pharmacology; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004967:Estrogens / Q000378:metabolism; D005260:Female; D017629:Gap Junctions / Q000502:physiology*; D007213:Indomethacin / Q000494:pharmacology; D019335:Nitroarginine / Q000494:pharmacology; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D009842:Oligopeptides; D010052:Ovariectomy; D010841:Pia Mater / Q000098:blood supply*; D058919:Purinergic P2 Receptor Antagonists; D051381:Rats; D017207:Rats, Sprague-Dawley; D058472:Receptors, Purinergic P2Y1; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology*
D001685:Biological Factors; D018031:Connexin 43; D017630:Connexins; D016861:Cyclooxygenase Inhibitors; D004791:Enzyme Inhibitors; D004967:Estrogens; D016376:Oligonucleotides, Antisense; D009842:Oligopeptides; D058919:Purinergic P2 Receptor Antagonists; D058472:Receptors, Purinergic P2Y1; C067410:endothelium-dependent hyperpolarization factor; C455880:gap 27 peptide; D019335:Nitroarginine; D000244:Adenosine Diphosphate; D007213:Indomethacin