Reduced EDHF responses and connexin activity in mesenteric arteries from the insulin-resistant obese Zucker rat.
OBJECTIVE
The objective of this study was to examine the effect of insulin resistance on endothelium-derived hyperpolarising factor (EDHF) and small mesenteric artery endothelial function using 25-week-old insulin-resistant obese Zucker rats (OZRs) and lean littermate control rats (LZRs). The involvement of gap junctions and their connexin subunits in the EDHF relaxation response was also assessed.


METHODS
Mesenteric arteries were evaluated using the following assays: (1) endothelial function by pressure myography, with internal diameter recorded using video microscopy; (2) connexin protein levels by western blotting; and (3) Cx mRNA expression by real-time PCR.


RESULTS
Relaxations in response to acetylcholine were significantly smaller in mesenteric arteries from the OZRs than the LZRs, whereas there was no difference in relaxations in response to levcromakalim. Responses to acetylcholine were not altered by nitric oxide inhibitors, but were abolished by charybdotoxin in combination with apamin, which blocked the EDHF component of the response. 40Gap27 significantly attenuated the response to acetylcholine in the LZRs, but had no effect in the OZRs. Connexin 40 protein and Cx40 mRNA levels in mesenteric vascular homogenates were significantly smaller in the OZRs than in the LZRs, with no difference in connexin 43 or Cx43 mRNA levels.


CONCLUSIONS
These findings demonstrate that endothelial dysfunction in mesenteric arteries from the insulin-resistant OZRs can be attributed to a defect in EDHF. The results also suggest that the defective EDHF is at least partly related to an impairment of connexin 40-associated gap junctions, through a decrease in connexin 40 protein and Cx40 mRNA expression in the OZRs.
Young
E J
EJ
School of Medical Sciences, RMIT University, Melbourne, Victoria, Australia. elisa.young@leica-microsystems.com
Hill
M A
MA
Wiehler
W B
WB
Triggle
C R
CR
Reid
J J
JJ
D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D001685:Biological Factors / Q000502:physiology*; D001786:Blood Glucose / Q000378:metabolism; D001835:Body Weight; D005260:Female; D007333:Insulin Resistance; D009765:Obesity / Q000235:genetics / Q000503:physiopathology*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011924:Rats, Zucker; D014664:Vasodilation / Q000187:drug effects / Q000502:physiology
D001685:Biological Factors; D001786:Blood Glucose; D012333:RNA, Messenger; C067410:endothelium-dependent hyperpolarization factor; D000109:Acetylcholine